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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
44e97401 | 3 | @c Copyright (C) 1990-1995, 1998-2012 Free Software Foundation, Inc. |
b8d4c8d0 | 4 | @c See the file elisp.texi for copying conditions. |
6336d8c3 | 5 | @setfilename ../../info/display |
b8d4c8d0 GM |
6 | @node Display, System Interface, Processes, Top |
7 | @chapter Emacs Display | |
8 | ||
9 | This chapter describes a number of features related to the display | |
10 | that Emacs presents to the user. | |
11 | ||
12 | @menu | |
13 | * Refresh Screen:: Clearing the screen and redrawing everything on it. | |
14 | * Forcing Redisplay:: Forcing redisplay. | |
15 | * Truncation:: Folding or wrapping long text lines. | |
16 | * The Echo Area:: Displaying messages at the bottom of the screen. | |
17 | * Warnings:: Displaying warning messages for the user. | |
18 | * Invisible Text:: Hiding part of the buffer text. | |
19 | * Selective Display:: Hiding part of the buffer text (the old way). | |
20 | * Temporary Displays:: Displays that go away automatically. | |
21 | * Overlays:: Use overlays to highlight parts of the buffer. | |
22 | * Width:: How wide a character or string is on the screen. | |
23 | * Line Height:: Controlling the height of lines. | |
24 | * Faces:: A face defines a graphics style for text characters: | |
25 | font, colors, etc. | |
26 | * Fringes:: Controlling window fringes. | |
27 | * Scroll Bars:: Controlling vertical scroll bars. | |
28 | * Display Property:: Enabling special display features. | |
29 | * Images:: Displaying images in Emacs buffers. | |
30 | * Buttons:: Adding clickable buttons to Emacs buffers. | |
44e97401 | 31 | * Abstract Display:: Emacs's Widget for Object Collections. |
b8d4c8d0 | 32 | * Blinking:: How Emacs shows the matching open parenthesis. |
9a69676a | 33 | * Character Display:: How Emacs displays individual characters. |
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34 | * Beeping:: Audible signal to the user. |
35 | * Window Systems:: Which window system is being used. | |
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36 | * Bidirectional Display:: Display of bidirectional scripts, such as |
37 | Arabic and Farsi. | |
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38 | @end menu |
39 | ||
40 | @node Refresh Screen | |
41 | @section Refreshing the Screen | |
42 | ||
43 | The function @code{redraw-frame} clears and redisplays the entire | |
44 | contents of a given frame (@pxref{Frames}). This is useful if the | |
45 | screen is corrupted. | |
46 | ||
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47 | @defun redraw-frame frame |
48 | This function clears and redisplays frame @var{frame}. | |
49 | @end defun | |
50 | ||
51 | Even more powerful is @code{redraw-display}: | |
52 | ||
53 | @deffn Command redraw-display | |
54 | This function clears and redisplays all visible frames. | |
55 | @end deffn | |
56 | ||
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57 | In Emacs, processing user input takes priority over redisplay. If |
58 | you call these functions when input is available, they don't redisplay | |
59 | immediately, but the requested redisplay does happen | |
60 | eventually---after all the input has been processed. | |
b8d4c8d0 | 61 | |
a08a07e3 | 62 | On text terminals, suspending and resuming Emacs normally also |
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63 | refreshes the screen. Some terminal emulators record separate |
64 | contents for display-oriented programs such as Emacs and for ordinary | |
65 | sequential display. If you are using such a terminal, you might want | |
66 | to inhibit the redisplay on resumption. | |
b8d4c8d0 | 67 | |
01f17ae2 | 68 | @defopt no-redraw-on-reenter |
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69 | @cindex suspend (cf. @code{no-redraw-on-reenter}) |
70 | @cindex resume (cf. @code{no-redraw-on-reenter}) | |
71 | This variable controls whether Emacs redraws the entire screen after it | |
72 | has been suspended and resumed. Non-@code{nil} means there is no need | |
73 | to redraw, @code{nil} means redrawing is needed. The default is @code{nil}. | |
01f17ae2 | 74 | @end defopt |
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75 | |
76 | @node Forcing Redisplay | |
77 | @section Forcing Redisplay | |
78 | @cindex forcing redisplay | |
79 | ||
20c63e44 | 80 | Emacs normally tries to redisplay the screen whenever it waits for |
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81 | input. With the following function, you can request an immediate |
82 | attempt to redisplay, in the middle of Lisp code, without actually | |
83 | waiting for input. | |
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84 | |
85 | @defun redisplay &optional force | |
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86 | This function tries immediately to redisplay. The optional argument |
87 | @var{force}, if non-@code{nil}, forces the redisplay to be performed, | |
88 | instead of being preempted, even if input is pending and the variable | |
89 | @code{redisplay-dont-pause} is @code{nil} (see below). If | |
90 | @code{redisplay-dont-pause} is non-@code{nil} (the default), this | |
91 | function redisplays in any case, i.e.@: @var{force} does nothing. | |
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92 | |
93 | The function returns @code{t} if it actually tried to redisplay, and | |
94 | @code{nil} otherwise. A value of @code{t} does not mean that | |
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95 | redisplay proceeded to completion; it could have been preempted by |
96 | newly arriving input. | |
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97 | @end defun |
98 | ||
20c63e44 | 99 | @defvar redisplay-dont-pause |
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100 | If this variable is @code{nil}, arriving input events preempt |
101 | redisplay; Emacs avoids starting a redisplay, and stops any redisplay | |
102 | that is in progress, until the input has been processed. In | |
103 | particular, @code{(redisplay)} returns @code{nil} without actually | |
104 | redisplaying, if there is pending input. | |
105 | ||
106 | The default value is @code{t}, which means that pending input does not | |
107 | preempt redisplay. | |
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108 | @end defvar |
109 | ||
b8d4c8d0 | 110 | @defvar redisplay-preemption-period |
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111 | If @code{redisplay-dont-pause} is @code{nil}, this variable specifies |
112 | how many seconds Emacs waits between checks for new input during | |
113 | redisplay; if input arrives during this interval, redisplay stops and | |
114 | the input is processed. The default value is 0.1; if the value is | |
115 | @code{nil}, Emacs does not check for input during redisplay. | |
116 | ||
117 | This variable has no effect when @code{redisplay-dont-pause} is | |
118 | non-@code{nil} (the default). | |
119 | @end defvar | |
b8d4c8d0 | 120 | |
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121 | Although @code{redisplay} tries immediately to redisplay, it does |
122 | not change how Emacs decides which parts of its frame(s) to redisplay. | |
123 | By contrast, the following function adds certain windows to the | |
124 | pending redisplay work (as if their contents had completely changed), | |
125 | but does not immediately try to perform redisplay. | |
b8d4c8d0 | 126 | |
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127 | @defun force-window-update &optional object |
128 | This function forces some or all windows to be updated the next time | |
129 | Emacs does a redisplay. If @var{object} is a window, that window is | |
130 | to be updated. If @var{object} is a buffer or buffer name, all | |
131 | windows displaying that buffer are to be updated. If @var{object} is | |
132 | @code{nil} (or omitted), all windows are to be updated. | |
133 | ||
134 | This function does not do a redisplay immediately; Emacs does that as | |
135 | it waits for input, or when the function @code{redisplay} is called. | |
136 | @end defun | |
b8d4c8d0 | 137 | |
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138 | @node Truncation |
139 | @section Truncation | |
140 | @cindex line wrapping | |
141 | @cindex line truncation | |
142 | @cindex continuation lines | |
143 | @cindex @samp{$} in display | |
144 | @cindex @samp{\} in display | |
145 | ||
146 | When a line of text extends beyond the right edge of a window, Emacs | |
147 | can @dfn{continue} the line (make it ``wrap'' to the next screen | |
148 | line), or @dfn{truncate} the line (limit it to one screen line). The | |
149 | additional screen lines used to display a long text line are called | |
150 | @dfn{continuation} lines. Continuation is not the same as filling; | |
151 | continuation happens on the screen only, not in the buffer contents, | |
152 | and it breaks a line precisely at the right margin, not at a word | |
153 | boundary. @xref{Filling}. | |
154 | ||
155 | On a graphical display, tiny arrow images in the window fringes | |
156 | indicate truncated and continued lines (@pxref{Fringes}). On a text | |
157 | terminal, a @samp{$} in the rightmost column of the window indicates | |
158 | truncation; a @samp{\} on the rightmost column indicates a line that | |
159 | ``wraps.'' (The display table can specify alternate characters to use | |
160 | for this; @pxref{Display Tables}). | |
161 | ||
162 | @defopt truncate-lines | |
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163 | If this buffer-local variable is non-@code{nil}, lines that extend |
164 | beyond the right edge of the window are truncated; otherwise, they are | |
165 | continued. As a special exception, the variable | |
166 | @code{truncate-partial-width-windows} takes precedence in | |
025de85b | 167 | @dfn{partial-width} windows (i.e.@: windows that do not occupy the |
c4adeee0 | 168 | entire frame width). |
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169 | @end defopt |
170 | ||
b8d4c8d0 | 171 | @defopt truncate-partial-width-windows |
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172 | This variable controls line truncation in @dfn{partial-width} windows. |
173 | A partial-width window is one that does not occupy the entire frame | |
174 | width (@pxref{Splitting Windows}). If the value is @code{nil}, line | |
175 | truncation is determined by the variable @code{truncate-lines} (see | |
176 | above). If the value is an integer @var{n}, lines are truncated if | |
177 | the partial-width window has fewer than @var{n} columns, regardless of | |
178 | the value of @code{truncate-lines}; if the partial-width window has | |
179 | @var{n} or more columns, line truncation is determined by | |
180 | @code{truncate-lines}. For any other non-@code{nil} value, lines are | |
181 | truncated in every partial-width window, regardless of the value of | |
182 | @code{truncate-lines}. | |
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183 | @end defopt |
184 | ||
185 | When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in | |
186 | a window, that forces truncation. | |
187 | ||
c4f4682b | 188 | @defvar wrap-prefix |
c4adeee0 | 189 | If this buffer-local variable is non-@code{nil}, it defines a |
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190 | @dfn{wrap prefix} which Emacs displays at the start of every |
191 | continuation line. (If lines are truncated, @code{wrap-prefix} is | |
192 | never used.) Its value may be a string or an image (@pxref{Other | |
193 | Display Specs}), or a stretch of whitespace such as specified by the | |
194 | @code{:width} or @code{:align-to} display properties (@pxref{Specified | |
195 | Space}). The value is interpreted in the same way as a @code{display} | |
196 | text property. @xref{Display Property}. | |
197 | ||
198 | A wrap prefix may also be specified for regions of text, using the | |
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199 | @code{wrap-prefix} text or overlay property. This takes precedence |
200 | over the @code{wrap-prefix} variable. @xref{Special Properties}. | |
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201 | @end defvar |
202 | ||
203 | @defvar line-prefix | |
c4adeee0 | 204 | If this buffer-local variable is non-@code{nil}, it defines a |
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205 | @dfn{line prefix} which Emacs displays at the start of every |
206 | non-continuation line. Its value may be a string or an image | |
207 | (@pxref{Other Display Specs}), or a stretch of whitespace such as | |
208 | specified by the @code{:width} or @code{:align-to} display properties | |
209 | (@pxref{Specified Space}). The value is interpreted in the same way | |
210 | as a @code{display} text property. @xref{Display Property}. | |
211 | ||
212 | A line prefix may also be specified for regions of text using the | |
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213 | @code{line-prefix} text or overlay property. This takes precedence |
214 | over the @code{line-prefix} variable. @xref{Special Properties}. | |
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215 | @end defvar |
216 | ||
b8d4c8d0 | 217 | If your buffer contains @emph{very} long lines, and you use |
c4adeee0 | 218 | continuation to display them, computing the continuation lines can |
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219 | make redisplay slow. The column computation and indentation functions |
220 | also become slow. Then you might find it advisable to set | |
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221 | @code{cache-long-line-scans} to @code{t}. |
222 | ||
223 | @defvar cache-long-line-scans | |
224 | If this variable is non-@code{nil}, various indentation and motion | |
225 | functions, and Emacs redisplay, cache the results of scanning the | |
226 | buffer, and consult the cache to avoid rescanning regions of the buffer | |
227 | unless they are modified. | |
228 | ||
229 | Turning on the cache slows down processing of short lines somewhat. | |
230 | ||
231 | This variable is automatically buffer-local in every buffer. | |
232 | @end defvar | |
233 | ||
234 | @node The Echo Area | |
235 | @section The Echo Area | |
236 | @cindex error display | |
237 | @cindex echo area | |
238 | ||
239 | The @dfn{echo area} is used for displaying error messages | |
240 | (@pxref{Errors}), for messages made with the @code{message} primitive, | |
241 | and for echoing keystrokes. It is not the same as the minibuffer, | |
242 | despite the fact that the minibuffer appears (when active) in the same | |
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243 | place on the screen as the echo area. @xref{Minibuffer,, The |
244 | Minibuffer, emacs, The GNU Emacs Manual}. | |
b8d4c8d0 | 245 | |
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246 | Apart from the functions documented in this section, you can print |
247 | Lisp objects to the echo area by specifying @code{t} as the output | |
248 | stream. @xref{Output Streams}. | |
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249 | |
250 | @menu | |
251 | * Displaying Messages:: Explicitly displaying text in the echo area. | |
252 | * Progress:: Informing user about progress of a long operation. | |
253 | * Logging Messages:: Echo area messages are logged for the user. | |
254 | * Echo Area Customization:: Controlling the echo area. | |
255 | @end menu | |
256 | ||
257 | @node Displaying Messages | |
258 | @subsection Displaying Messages in the Echo Area | |
259 | @cindex display message in echo area | |
260 | ||
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261 | This section describes the standard functions for displaying |
262 | messages in the echo area. | |
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263 | |
264 | @defun message format-string &rest arguments | |
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265 | This function displays a message in the echo area. |
266 | @var{format-string} is a format string, and @var{arguments} are the | |
267 | objects for its format specifications, like in the @code{format} | |
268 | function (@pxref{Formatting Strings}). The resulting formatted string | |
269 | is displayed in the echo area; if it contains @code{face} text | |
270 | properties, it is displayed with the specified faces (@pxref{Faces}). | |
271 | The string is also added to the @samp{*Messages*} buffer, but without | |
272 | text properties (@pxref{Logging Messages}). | |
273 | ||
274 | In batch mode, the message is printed to the standard error stream, | |
275 | followed by a newline. | |
b8d4c8d0 | 276 | |
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277 | If @var{format-string} is @code{nil} or the empty string, |
278 | @code{message} clears the echo area; if the echo area has been | |
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279 | expanded automatically, this brings it back to its normal size. If |
280 | the minibuffer is active, this brings the minibuffer contents back | |
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281 | onto the screen immediately. |
282 | ||
283 | @example | |
284 | @group | |
285 | (message "Minibuffer depth is %d." | |
286 | (minibuffer-depth)) | |
287 | @print{} Minibuffer depth is 0. | |
288 | @result{} "Minibuffer depth is 0." | |
289 | @end group | |
290 | ||
291 | @group | |
292 | ---------- Echo Area ---------- | |
293 | Minibuffer depth is 0. | |
294 | ---------- Echo Area ---------- | |
295 | @end group | |
296 | @end example | |
297 | ||
298 | To automatically display a message in the echo area or in a pop-buffer, | |
299 | depending on its size, use @code{display-message-or-buffer} (see below). | |
300 | @end defun | |
301 | ||
302 | @defmac with-temp-message message &rest body | |
303 | This construct displays a message in the echo area temporarily, during | |
304 | the execution of @var{body}. It displays @var{message}, executes | |
305 | @var{body}, then returns the value of the last body form while restoring | |
306 | the previous echo area contents. | |
307 | @end defmac | |
308 | ||
309 | @defun message-or-box format-string &rest arguments | |
310 | This function displays a message like @code{message}, but may display it | |
311 | in a dialog box instead of the echo area. If this function is called in | |
312 | a command that was invoked using the mouse---more precisely, if | |
313 | @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either | |
314 | @code{nil} or a list---then it uses a dialog box or pop-up menu to | |
315 | display the message. Otherwise, it uses the echo area. (This is the | |
316 | same criterion that @code{y-or-n-p} uses to make a similar decision; see | |
317 | @ref{Yes-or-No Queries}.) | |
318 | ||
319 | You can force use of the mouse or of the echo area by binding | |
320 | @code{last-nonmenu-event} to a suitable value around the call. | |
321 | @end defun | |
322 | ||
323 | @defun message-box format-string &rest arguments | |
324 | @anchor{message-box} | |
325 | This function displays a message like @code{message}, but uses a dialog | |
326 | box (or a pop-up menu) whenever that is possible. If it is impossible | |
327 | to use a dialog box or pop-up menu, because the terminal does not | |
328 | support them, then @code{message-box} uses the echo area, like | |
329 | @code{message}. | |
330 | @end defun | |
331 | ||
332 | @defun display-message-or-buffer message &optional buffer-name not-this-window frame | |
333 | This function displays the message @var{message}, which may be either a | |
334 | string or a buffer. If it is shorter than the maximum height of the | |
335 | echo area, as defined by @code{max-mini-window-height}, it is displayed | |
336 | in the echo area, using @code{message}. Otherwise, | |
337 | @code{display-buffer} is used to show it in a pop-up buffer. | |
338 | ||
339 | Returns either the string shown in the echo area, or when a pop-up | |
340 | buffer is used, the window used to display it. | |
341 | ||
342 | If @var{message} is a string, then the optional argument | |
343 | @var{buffer-name} is the name of the buffer used to display it when a | |
344 | pop-up buffer is used, defaulting to @samp{*Message*}. In the case | |
345 | where @var{message} is a string and displayed in the echo area, it is | |
346 | not specified whether the contents are inserted into the buffer anyway. | |
347 | ||
348 | The optional arguments @var{not-this-window} and @var{frame} are as for | |
349 | @code{display-buffer}, and only used if a buffer is displayed. | |
350 | @end defun | |
351 | ||
352 | @defun current-message | |
353 | This function returns the message currently being displayed in the | |
354 | echo area, or @code{nil} if there is none. | |
355 | @end defun | |
356 | ||
357 | @node Progress | |
358 | @subsection Reporting Operation Progress | |
359 | @cindex progress reporting | |
360 | ||
361 | When an operation can take a while to finish, you should inform the | |
362 | user about the progress it makes. This way the user can estimate | |
363 | remaining time and clearly see that Emacs is busy working, not hung. | |
ddb54206 | 364 | A convenient way to do this is to use a @dfn{progress reporter}. |
b8d4c8d0 | 365 | |
ddb54206 | 366 | Here is a working example that does nothing useful: |
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367 | |
368 | @smallexample | |
369 | (let ((progress-reporter | |
370 | (make-progress-reporter "Collecting mana for Emacs..." | |
371 | 0 500))) | |
372 | (dotimes (k 500) | |
373 | (sit-for 0.01) | |
374 | (progress-reporter-update progress-reporter k)) | |
375 | (progress-reporter-done progress-reporter)) | |
376 | @end smallexample | |
377 | ||
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378 | @defun make-progress-reporter message &optional min-value max-value current-value min-change min-time |
379 | This function creates and returns a progress reporter object, which | |
380 | you will use as an argument for the other functions listed below. The | |
381 | idea is to precompute as much data as possible to make progress | |
382 | reporting very fast. | |
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383 | |
384 | When this progress reporter is subsequently used, it will display | |
385 | @var{message} in the echo area, followed by progress percentage. | |
386 | @var{message} is treated as a simple string. If you need it to depend | |
387 | on a filename, for instance, use @code{format} before calling this | |
388 | function. | |
389 | ||
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390 | The arguments @var{min-value} and @var{max-value} should be numbers |
391 | standing for the starting and final states of the operation. For | |
392 | instance, an operation that ``scans'' a buffer should set these to the | |
393 | results of @code{point-min} and @code{point-max} correspondingly. | |
394 | @var{max-value} should be greater than @var{min-value}. | |
395 | ||
396 | Alternatively, you can set @var{min-value} and @var{max-value} to | |
397 | @code{nil}. In that case, the progress reporter does not report | |
398 | process percentages; it instead displays a ``spinner'' that rotates a | |
399 | notch each time you update the progress reporter. | |
400 | ||
401 | If @var{min-value} and @var{max-value} are numbers, you can give the | |
402 | argument @var{current-value} a numerical value specifying the initial | |
403 | progress; if omitted, this defaults to @var{min-value}. | |
404 | ||
405 | The remaining arguments control the rate of echo area updates. The | |
406 | progress reporter will wait for at least @var{min-change} more | |
407 | percents of the operation to be completed before printing next | |
408 | message; the default is one percent. @var{min-time} specifies the | |
409 | minimum time in seconds to pass between successive prints; the default | |
410 | is 0.2 seconds. (On some operating systems, the progress reporter may | |
411 | handle fractions of seconds with varying precision). | |
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412 | |
413 | This function calls @code{progress-reporter-update}, so the first | |
414 | message is printed immediately. | |
415 | @end defun | |
416 | ||
417 | @defun progress-reporter-update reporter value | |
418 | This function does the main work of reporting progress of your | |
419 | operation. It displays the message of @var{reporter}, followed by | |
420 | progress percentage determined by @var{value}. If percentage is zero, | |
421 | or close enough according to the @var{min-change} and @var{min-time} | |
422 | arguments, then it is omitted from the output. | |
423 | ||
424 | @var{reporter} must be the result of a call to | |
425 | @code{make-progress-reporter}. @var{value} specifies the current | |
426 | state of your operation and must be between @var{min-value} and | |
427 | @var{max-value} (inclusive) as passed to | |
428 | @code{make-progress-reporter}. For instance, if you scan a buffer, | |
429 | then @var{value} should be the result of a call to @code{point}. | |
430 | ||
431 | This function respects @var{min-change} and @var{min-time} as passed | |
432 | to @code{make-progress-reporter} and so does not output new messages | |
433 | on every invocation. It is thus very fast and normally you should not | |
434 | try to reduce the number of calls to it: resulting overhead will most | |
435 | likely negate your effort. | |
436 | @end defun | |
437 | ||
438 | @defun progress-reporter-force-update reporter value &optional new-message | |
439 | This function is similar to @code{progress-reporter-update} except | |
440 | that it prints a message in the echo area unconditionally. | |
441 | ||
442 | The first two arguments have the same meaning as for | |
443 | @code{progress-reporter-update}. Optional @var{new-message} allows | |
444 | you to change the message of the @var{reporter}. Since this functions | |
445 | always updates the echo area, such a change will be immediately | |
446 | presented to the user. | |
447 | @end defun | |
448 | ||
449 | @defun progress-reporter-done reporter | |
450 | This function should be called when the operation is finished. It | |
451 | prints the message of @var{reporter} followed by word ``done'' in the | |
452 | echo area. | |
453 | ||
454 | You should always call this function and not hope for | |
455 | @code{progress-reporter-update} to print ``100%.'' Firstly, it may | |
456 | never print it, there are many good reasons for this not to happen. | |
457 | Secondly, ``done'' is more explicit. | |
458 | @end defun | |
459 | ||
460 | @defmac dotimes-with-progress-reporter (var count [result]) message body@dots{} | |
461 | This is a convenience macro that works the same way as @code{dotimes} | |
462 | does, but also reports loop progress using the functions described | |
463 | above. It allows you to save some typing. | |
464 | ||
465 | You can rewrite the example in the beginning of this node using | |
466 | this macro this way: | |
467 | ||
468 | @example | |
469 | (dotimes-with-progress-reporter | |
470 | (k 500) | |
471 | "Collecting some mana for Emacs..." | |
472 | (sit-for 0.01)) | |
473 | @end example | |
474 | @end defmac | |
475 | ||
476 | @node Logging Messages | |
477 | @subsection Logging Messages in @samp{*Messages*} | |
478 | @cindex logging echo-area messages | |
479 | ||
480 | Almost all the messages displayed in the echo area are also recorded | |
481 | in the @samp{*Messages*} buffer so that the user can refer back to | |
482 | them. This includes all the messages that are output with | |
483 | @code{message}. | |
484 | ||
485 | @defopt message-log-max | |
486 | This variable specifies how many lines to keep in the @samp{*Messages*} | |
487 | buffer. The value @code{t} means there is no limit on how many lines to | |
488 | keep. The value @code{nil} disables message logging entirely. Here's | |
489 | how to display a message and prevent it from being logged: | |
490 | ||
491 | @example | |
492 | (let (message-log-max) | |
493 | (message @dots{})) | |
494 | @end example | |
495 | @end defopt | |
496 | ||
497 | To make @samp{*Messages*} more convenient for the user, the logging | |
498 | facility combines successive identical messages. It also combines | |
499 | successive related messages for the sake of two cases: question | |
500 | followed by answer, and a series of progress messages. | |
501 | ||
502 | A ``question followed by an answer'' means two messages like the | |
503 | ones produced by @code{y-or-n-p}: the first is @samp{@var{question}}, | |
504 | and the second is @samp{@var{question}...@var{answer}}. The first | |
505 | message conveys no additional information beyond what's in the second, | |
506 | so logging the second message discards the first from the log. | |
507 | ||
508 | A ``series of progress messages'' means successive messages like | |
509 | those produced by @code{make-progress-reporter}. They have the form | |
510 | @samp{@var{base}...@var{how-far}}, where @var{base} is the same each | |
511 | time, while @var{how-far} varies. Logging each message in the series | |
512 | discards the previous one, provided they are consecutive. | |
513 | ||
514 | The functions @code{make-progress-reporter} and @code{y-or-n-p} | |
515 | don't have to do anything special to activate the message log | |
516 | combination feature. It operates whenever two consecutive messages | |
517 | are logged that share a common prefix ending in @samp{...}. | |
518 | ||
519 | @node Echo Area Customization | |
520 | @subsection Echo Area Customization | |
521 | ||
522 | These variables control details of how the echo area works. | |
523 | ||
524 | @defvar cursor-in-echo-area | |
525 | This variable controls where the cursor appears when a message is | |
526 | displayed in the echo area. If it is non-@code{nil}, then the cursor | |
527 | appears at the end of the message. Otherwise, the cursor appears at | |
528 | point---not in the echo area at all. | |
529 | ||
530 | The value is normally @code{nil}; Lisp programs bind it to @code{t} | |
531 | for brief periods of time. | |
532 | @end defvar | |
533 | ||
534 | @defvar echo-area-clear-hook | |
535 | This normal hook is run whenever the echo area is cleared---either by | |
536 | @code{(message nil)} or for any other reason. | |
537 | @end defvar | |
538 | ||
01f17ae2 | 539 | @defopt echo-keystrokes |
b8d4c8d0 GM |
540 | This variable determines how much time should elapse before command |
541 | characters echo. Its value must be an integer or floating point number, | |
542 | which specifies the | |
543 | number of seconds to wait before echoing. If the user types a prefix | |
544 | key (such as @kbd{C-x}) and then delays this many seconds before | |
545 | continuing, the prefix key is echoed in the echo area. (Once echoing | |
546 | begins in a key sequence, all subsequent characters in the same key | |
547 | sequence are echoed immediately.) | |
548 | ||
549 | If the value is zero, then command input is not echoed. | |
01f17ae2 | 550 | @end defopt |
b8d4c8d0 GM |
551 | |
552 | @defvar message-truncate-lines | |
553 | Normally, displaying a long message resizes the echo area to display | |
554 | the entire message. But if the variable @code{message-truncate-lines} | |
555 | is non-@code{nil}, the echo area does not resize, and the message is | |
fb5b8aca | 556 | truncated to fit it. |
b8d4c8d0 GM |
557 | @end defvar |
558 | ||
559 | The variable @code{max-mini-window-height}, which specifies the | |
560 | maximum height for resizing minibuffer windows, also applies to the | |
fb5b8aca CY |
561 | echo area (which is really a special use of the minibuffer window; |
562 | @pxref{Minibuffer Misc}). | |
b8d4c8d0 GM |
563 | |
564 | @node Warnings | |
565 | @section Reporting Warnings | |
566 | @cindex warnings | |
567 | ||
568 | @dfn{Warnings} are a facility for a program to inform the user of a | |
569 | possible problem, but continue running. | |
570 | ||
571 | @menu | |
572 | * Warning Basics:: Warnings concepts and functions to report them. | |
573 | * Warning Variables:: Variables programs bind to customize their warnings. | |
574 | * Warning Options:: Variables users set to control display of warnings. | |
3d439cd1 | 575 | * Delayed Warnings:: Deferring a warning until the end of a command. |
b8d4c8d0 GM |
576 | @end menu |
577 | ||
578 | @node Warning Basics | |
579 | @subsection Warning Basics | |
580 | @cindex severity level | |
581 | ||
582 | Every warning has a textual message, which explains the problem for | |
583 | the user, and a @dfn{severity level} which is a symbol. Here are the | |
584 | possible severity levels, in order of decreasing severity, and their | |
585 | meanings: | |
586 | ||
587 | @table @code | |
588 | @item :emergency | |
589 | A problem that will seriously impair Emacs operation soon | |
590 | if you do not attend to it promptly. | |
591 | @item :error | |
592 | A report of data or circumstances that are inherently wrong. | |
593 | @item :warning | |
594 | A report of data or circumstances that are not inherently wrong, but | |
595 | raise suspicion of a possible problem. | |
596 | @item :debug | |
597 | A report of information that may be useful if you are debugging. | |
598 | @end table | |
599 | ||
600 | When your program encounters invalid input data, it can either | |
601 | signal a Lisp error by calling @code{error} or @code{signal} or report | |
602 | a warning with severity @code{:error}. Signaling a Lisp error is the | |
603 | easiest thing to do, but it means the program cannot continue | |
604 | processing. If you want to take the trouble to implement a way to | |
605 | continue processing despite the bad data, then reporting a warning of | |
606 | severity @code{:error} is the right way to inform the user of the | |
607 | problem. For instance, the Emacs Lisp byte compiler can report an | |
608 | error that way and continue compiling other functions. (If the | |
609 | program signals a Lisp error and then handles it with | |
610 | @code{condition-case}, the user won't see the error message; it could | |
611 | show the message to the user by reporting it as a warning.) | |
612 | ||
613 | @cindex warning type | |
614 | Each warning has a @dfn{warning type} to classify it. The type is a | |
615 | list of symbols. The first symbol should be the custom group that you | |
616 | use for the program's user options. For example, byte compiler | |
617 | warnings use the warning type @code{(bytecomp)}. You can also | |
618 | subcategorize the warnings, if you wish, by using more symbols in the | |
619 | list. | |
620 | ||
621 | @defun display-warning type message &optional level buffer-name | |
622 | This function reports a warning, using @var{message} as the message | |
623 | and @var{type} as the warning type. @var{level} should be the | |
624 | severity level, with @code{:warning} being the default. | |
625 | ||
626 | @var{buffer-name}, if non-@code{nil}, specifies the name of the buffer | |
627 | for logging the warning. By default, it is @samp{*Warnings*}. | |
628 | @end defun | |
629 | ||
630 | @defun lwarn type level message &rest args | |
631 | This function reports a warning using the value of @code{(format | |
632 | @var{message} @var{args}...)} as the message. In other respects it is | |
633 | equivalent to @code{display-warning}. | |
634 | @end defun | |
635 | ||
636 | @defun warn message &rest args | |
637 | This function reports a warning using the value of @code{(format | |
638 | @var{message} @var{args}...)} as the message, @code{(emacs)} as the | |
639 | type, and @code{:warning} as the severity level. It exists for | |
640 | compatibility only; we recommend not using it, because you should | |
641 | specify a specific warning type. | |
642 | @end defun | |
643 | ||
644 | @node Warning Variables | |
645 | @subsection Warning Variables | |
646 | ||
647 | Programs can customize how their warnings appear by binding | |
648 | the variables described in this section. | |
649 | ||
650 | @defvar warning-levels | |
651 | This list defines the meaning and severity order of the warning | |
652 | severity levels. Each element defines one severity level, | |
653 | and they are arranged in order of decreasing severity. | |
654 | ||
655 | Each element has the form @code{(@var{level} @var{string} | |
656 | @var{function})}, where @var{level} is the severity level it defines. | |
657 | @var{string} specifies the textual description of this level. | |
658 | @var{string} should use @samp{%s} to specify where to put the warning | |
659 | type information, or it can omit the @samp{%s} so as not to include | |
660 | that information. | |
661 | ||
662 | The optional @var{function}, if non-@code{nil}, is a function to call | |
663 | with no arguments, to get the user's attention. | |
664 | ||
665 | Normally you should not change the value of this variable. | |
666 | @end defvar | |
667 | ||
668 | @defvar warning-prefix-function | |
669 | If non-@code{nil}, the value is a function to generate prefix text for | |
670 | warnings. Programs can bind the variable to a suitable function. | |
671 | @code{display-warning} calls this function with the warnings buffer | |
672 | current, and the function can insert text in it. That text becomes | |
673 | the beginning of the warning message. | |
674 | ||
675 | The function is called with two arguments, the severity level and its | |
676 | entry in @code{warning-levels}. It should return a list to use as the | |
677 | entry (this value need not be an actual member of | |
678 | @code{warning-levels}). By constructing this value, the function can | |
679 | change the severity of the warning, or specify different handling for | |
680 | a given severity level. | |
681 | ||
682 | If the variable's value is @code{nil} then there is no function | |
683 | to call. | |
684 | @end defvar | |
685 | ||
686 | @defvar warning-series | |
687 | Programs can bind this variable to @code{t} to say that the next | |
688 | warning should begin a series. When several warnings form a series, | |
689 | that means to leave point on the first warning of the series, rather | |
690 | than keep moving it for each warning so that it appears on the last one. | |
691 | The series ends when the local binding is unbound and | |
692 | @code{warning-series} becomes @code{nil} again. | |
693 | ||
694 | The value can also be a symbol with a function definition. That is | |
695 | equivalent to @code{t}, except that the next warning will also call | |
696 | the function with no arguments with the warnings buffer current. The | |
697 | function can insert text which will serve as a header for the series | |
698 | of warnings. | |
699 | ||
700 | Once a series has begun, the value is a marker which points to the | |
701 | buffer position in the warnings buffer of the start of the series. | |
702 | ||
703 | The variable's normal value is @code{nil}, which means to handle | |
704 | each warning separately. | |
705 | @end defvar | |
706 | ||
707 | @defvar warning-fill-prefix | |
708 | When this variable is non-@code{nil}, it specifies a fill prefix to | |
709 | use for filling each warning's text. | |
710 | @end defvar | |
711 | ||
712 | @defvar warning-type-format | |
713 | This variable specifies the format for displaying the warning type | |
714 | in the warning message. The result of formatting the type this way | |
715 | gets included in the message under the control of the string in the | |
716 | entry in @code{warning-levels}. The default value is @code{" (%s)"}. | |
717 | If you bind it to @code{""} then the warning type won't appear at | |
718 | all. | |
719 | @end defvar | |
720 | ||
721 | @node Warning Options | |
722 | @subsection Warning Options | |
723 | ||
724 | These variables are used by users to control what happens | |
725 | when a Lisp program reports a warning. | |
726 | ||
727 | @defopt warning-minimum-level | |
728 | This user option specifies the minimum severity level that should be | |
729 | shown immediately to the user. The default is @code{:warning}, which | |
730 | means to immediately display all warnings except @code{:debug} | |
731 | warnings. | |
732 | @end defopt | |
733 | ||
734 | @defopt warning-minimum-log-level | |
735 | This user option specifies the minimum severity level that should be | |
736 | logged in the warnings buffer. The default is @code{:warning}, which | |
737 | means to log all warnings except @code{:debug} warnings. | |
738 | @end defopt | |
739 | ||
740 | @defopt warning-suppress-types | |
741 | This list specifies which warning types should not be displayed | |
742 | immediately for the user. Each element of the list should be a list | |
743 | of symbols. If its elements match the first elements in a warning | |
744 | type, then that warning is not displayed immediately. | |
745 | @end defopt | |
746 | ||
747 | @defopt warning-suppress-log-types | |
748 | This list specifies which warning types should not be logged in the | |
749 | warnings buffer. Each element of the list should be a list of | |
750 | symbols. If it matches the first few elements in a warning type, then | |
751 | that warning is not logged. | |
752 | @end defopt | |
753 | ||
3d439cd1 CY |
754 | @node Delayed Warnings |
755 | @subsection Delayed Warnings | |
756 | ||
757 | Sometimes, you may wish to avoid showing a warning while a command is | |
758 | running, and only show it only after the end of the command. You can | |
759 | use the variable @code{delayed-warnings-list} for this. | |
760 | ||
761 | @defvar delayed-warnings-list | |
762 | The value of this variable is a list of warnings to be displayed after | |
763 | the current command has finished. Each element must be a list | |
764 | ||
765 | @smallexample | |
766 | (@var{type} @var{message} [@var{level} [@var{buffer-name}]]) | |
767 | @end smallexample | |
768 | ||
769 | @noindent | |
770 | with the same form, and the same meanings, as the argument list of | |
771 | @code{display-warning} (@pxref{Warning Basics}). Immediately after | |
772 | running @code{post-command-hook} (@pxref{Command Overview}), the Emacs | |
773 | command loop displays all the warnings specified by this variable, | |
774 | then resets it to @code{nil}. | |
775 | @end defvar | |
776 | ||
777 | Programs which need to further customize the delayed warnings | |
778 | mechanism can change the variable @code{delayed-warnings-hook}: | |
779 | ||
780 | @defvar delayed-warnings-hook | |
781 | This is a normal hook which is run by the Emacs command loop, after | |
782 | @code{post-command-hook}, in order to to process and display delayed | |
783 | warnings. | |
784 | ||
785 | Its default value is a list of two functions: | |
786 | ||
787 | @smallexample | |
788 | (collapse-delayed-warnings display-delayed-warnings) | |
789 | @end smallexample | |
790 | ||
791 | @findex collapse-delayed-warnings | |
792 | @findex display-delayed-warnings | |
793 | @noindent | |
794 | The function @code{collapse-delayed-warnings} iterates through | |
795 | @code{delayed-warnings-list}, removing repeated entries. The function | |
796 | @code{display-delayed-warnings} calls @code{display-warning} on each | |
797 | of the entries in @code{delayed-warnings-list}, in turn, and then sets | |
798 | @code{delayed-warnings-list} to @code{nil}. | |
799 | @end defvar | |
800 | ||
b8d4c8d0 GM |
801 | @node Invisible Text |
802 | @section Invisible Text | |
803 | ||
804 | @cindex invisible text | |
805 | You can make characters @dfn{invisible}, so that they do not appear on | |
806 | the screen, with the @code{invisible} property. This can be either a | |
fb5b8aca | 807 | text property (@pxref{Text Properties}) or an overlay property |
b8d4c8d0 | 808 | (@pxref{Overlays}). Cursor motion also partly ignores these |
fb5b8aca CY |
809 | characters; if the command loop finds that point is inside a range of |
810 | invisible text after a command, it relocates point to the other side | |
811 | of the text. | |
b8d4c8d0 GM |
812 | |
813 | In the simplest case, any non-@code{nil} @code{invisible} property makes | |
814 | a character invisible. This is the default case---if you don't alter | |
815 | the default value of @code{buffer-invisibility-spec}, this is how the | |
816 | @code{invisible} property works. You should normally use @code{t} | |
817 | as the value of the @code{invisible} property if you don't plan | |
818 | to set @code{buffer-invisibility-spec} yourself. | |
819 | ||
820 | More generally, you can use the variable @code{buffer-invisibility-spec} | |
821 | to control which values of the @code{invisible} property make text | |
822 | invisible. This permits you to classify the text into different subsets | |
823 | in advance, by giving them different @code{invisible} values, and | |
824 | subsequently make various subsets visible or invisible by changing the | |
825 | value of @code{buffer-invisibility-spec}. | |
826 | ||
827 | Controlling visibility with @code{buffer-invisibility-spec} is | |
828 | especially useful in a program to display the list of entries in a | |
829 | database. It permits the implementation of convenient filtering | |
830 | commands to view just a part of the entries in the database. Setting | |
831 | this variable is very fast, much faster than scanning all the text in | |
832 | the buffer looking for properties to change. | |
833 | ||
834 | @defvar buffer-invisibility-spec | |
835 | This variable specifies which kinds of @code{invisible} properties | |
836 | actually make a character invisible. Setting this variable makes it | |
837 | buffer-local. | |
838 | ||
839 | @table @asis | |
840 | @item @code{t} | |
841 | A character is invisible if its @code{invisible} property is | |
842 | non-@code{nil}. This is the default. | |
843 | ||
844 | @item a list | |
845 | Each element of the list specifies a criterion for invisibility; if a | |
846 | character's @code{invisible} property fits any one of these criteria, | |
847 | the character is invisible. The list can have two kinds of elements: | |
848 | ||
849 | @table @code | |
850 | @item @var{atom} | |
fb5b8aca CY |
851 | A character is invisible if its @code{invisible} property value is |
852 | @var{atom} or if it is a list with @var{atom} as a member; comparison | |
853 | is done with @code{eq}. | |
b8d4c8d0 GM |
854 | |
855 | @item (@var{atom} . t) | |
856 | A character is invisible if its @code{invisible} property value is | |
fb5b8aca CY |
857 | @var{atom} or if it is a list with @var{atom} as a member; comparison |
858 | is done with @code{eq}. Moreover, a sequence of such characters | |
859 | displays as an ellipsis. | |
b8d4c8d0 GM |
860 | @end table |
861 | @end table | |
862 | @end defvar | |
863 | ||
864 | Two functions are specifically provided for adding elements to | |
865 | @code{buffer-invisibility-spec} and removing elements from it. | |
866 | ||
867 | @defun add-to-invisibility-spec element | |
868 | This function adds the element @var{element} to | |
869 | @code{buffer-invisibility-spec}. If @code{buffer-invisibility-spec} | |
870 | was @code{t}, it changes to a list, @code{(t)}, so that text whose | |
871 | @code{invisible} property is @code{t} remains invisible. | |
872 | @end defun | |
873 | ||
874 | @defun remove-from-invisibility-spec element | |
875 | This removes the element @var{element} from | |
876 | @code{buffer-invisibility-spec}. This does nothing if @var{element} | |
877 | is not in the list. | |
878 | @end defun | |
879 | ||
880 | A convention for use of @code{buffer-invisibility-spec} is that a | |
881 | major mode should use the mode's own name as an element of | |
882 | @code{buffer-invisibility-spec} and as the value of the | |
883 | @code{invisible} property: | |
884 | ||
885 | @example | |
886 | ;; @r{If you want to display an ellipsis:} | |
887 | (add-to-invisibility-spec '(my-symbol . t)) | |
888 | ;; @r{If you don't want ellipsis:} | |
889 | (add-to-invisibility-spec 'my-symbol) | |
890 | ||
891 | (overlay-put (make-overlay beginning end) | |
892 | 'invisible 'my-symbol) | |
893 | ||
fb5b8aca | 894 | ;; @r{When done with the invisibility:} |
b8d4c8d0 GM |
895 | (remove-from-invisibility-spec '(my-symbol . t)) |
896 | ;; @r{Or respectively:} | |
897 | (remove-from-invisibility-spec 'my-symbol) | |
898 | @end example | |
899 | ||
c4adeee0 CY |
900 | You can check for invisibility using the following function: |
901 | ||
902 | @defun invisible-p pos-or-prop | |
903 | If @var{pos-or-prop} is a marker or number, this function returns a | |
904 | non-@code{nil} value if the text at that position is invisible. | |
905 | ||
906 | If @var{pos-or-prop} is any other kind of Lisp object, that is taken | |
907 | to mean a possible value of the @code{invisible} text or overlay | |
908 | property. In that case, this function returns a non-@code{nil} value | |
909 | if that value would cause text to become invisible, based on the | |
910 | current value of @code{buffer-invisibility-spec}. | |
911 | @end defun | |
912 | ||
b8d4c8d0 GM |
913 | @vindex line-move-ignore-invisible |
914 | Ordinarily, functions that operate on text or move point do not care | |
915 | whether the text is invisible. The user-level line motion commands | |
c4adeee0 CY |
916 | ignore invisible newlines if @code{line-move-ignore-invisible} is |
917 | non-@code{nil} (the default), but only because they are explicitly | |
918 | programmed to do so. | |
b8d4c8d0 | 919 | |
fb5b8aca CY |
920 | However, if a command ends with point inside or at the boundary of |
921 | invisible text, the main editing loop relocates point to one of the | |
922 | two ends of the invisible text. Emacs chooses the direction of | |
923 | relocation so that it is the same as the overall movement direction of | |
924 | the command; if in doubt, it prefers a position where an inserted char | |
925 | would not inherit the @code{invisible} property. Additionally, if the | |
926 | text is not replaced by an ellipsis and the command only moved within | |
927 | the invisible text, then point is moved one extra character so as to | |
928 | try and reflect the command's movement by a visible movement of the | |
929 | cursor. | |
f4e90db0 SM |
930 | |
931 | Thus, if the command moved point back to an invisible range (with the usual | |
932 | stickiness), Emacs moves point back to the beginning of that range. If the | |
933 | command moved point forward into an invisible range, Emacs moves point forward | |
934 | to the first visible character that follows the invisible text and then forward | |
935 | one more character. | |
b8d4c8d0 GM |
936 | |
937 | Incremental search can make invisible overlays visible temporarily | |
938 | and/or permanently when a match includes invisible text. To enable | |
939 | this, the overlay should have a non-@code{nil} | |
940 | @code{isearch-open-invisible} property. The property value should be a | |
941 | function to be called with the overlay as an argument. This function | |
942 | should make the overlay visible permanently; it is used when the match | |
943 | overlaps the overlay on exit from the search. | |
944 | ||
945 | During the search, such overlays are made temporarily visible by | |
946 | temporarily modifying their invisible and intangible properties. If you | |
947 | want this to be done differently for a certain overlay, give it an | |
948 | @code{isearch-open-invisible-temporary} property which is a function. | |
949 | The function is called with two arguments: the first is the overlay, and | |
950 | the second is @code{nil} to make the overlay visible, or @code{t} to | |
951 | make it invisible again. | |
952 | ||
953 | @node Selective Display | |
954 | @section Selective Display | |
955 | @c @cindex selective display Duplicates selective-display | |
956 | ||
957 | @dfn{Selective display} refers to a pair of related features for | |
958 | hiding certain lines on the screen. | |
959 | ||
960 | The first variant, explicit selective display, is designed for use | |
961 | in a Lisp program: it controls which lines are hidden by altering the | |
962 | text. This kind of hiding in some ways resembles the effect of the | |
963 | @code{invisible} property (@pxref{Invisible Text}), but the two | |
964 | features are different and do not work the same way. | |
965 | ||
966 | In the second variant, the choice of lines to hide is made | |
967 | automatically based on indentation. This variant is designed to be a | |
968 | user-level feature. | |
969 | ||
970 | The way you control explicit selective display is by replacing a | |
971 | newline (control-j) with a carriage return (control-m). The text that | |
972 | was formerly a line following that newline is now hidden. Strictly | |
973 | speaking, it is temporarily no longer a line at all, since only | |
974 | newlines can separate lines; it is now part of the previous line. | |
975 | ||
976 | Selective display does not directly affect editing commands. For | |
977 | example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly | |
978 | into hidden text. However, the replacement of newline characters with | |
979 | carriage return characters affects some editing commands. For | |
980 | example, @code{next-line} skips hidden lines, since it searches only | |
981 | for newlines. Modes that use selective display can also define | |
982 | commands that take account of the newlines, or that control which | |
983 | parts of the text are hidden. | |
984 | ||
985 | When you write a selectively displayed buffer into a file, all the | |
986 | control-m's are output as newlines. This means that when you next read | |
987 | in the file, it looks OK, with nothing hidden. The selective display | |
988 | effect is seen only within Emacs. | |
989 | ||
990 | @defvar selective-display | |
991 | This buffer-local variable enables selective display. This means that | |
992 | lines, or portions of lines, may be made hidden. | |
993 | ||
994 | @itemize @bullet | |
995 | @item | |
996 | If the value of @code{selective-display} is @code{t}, then the character | |
997 | control-m marks the start of hidden text; the control-m, and the rest | |
998 | of the line following it, are not displayed. This is explicit selective | |
999 | display. | |
1000 | ||
1001 | @item | |
1002 | If the value of @code{selective-display} is a positive integer, then | |
1003 | lines that start with more than that many columns of indentation are not | |
1004 | displayed. | |
1005 | @end itemize | |
1006 | ||
1007 | When some portion of a buffer is hidden, the vertical movement | |
1008 | commands operate as if that portion did not exist, allowing a single | |
1009 | @code{next-line} command to skip any number of hidden lines. | |
1010 | However, character movement commands (such as @code{forward-char}) do | |
1011 | not skip the hidden portion, and it is possible (if tricky) to insert | |
1012 | or delete text in an hidden portion. | |
1013 | ||
1014 | In the examples below, we show the @emph{display appearance} of the | |
1015 | buffer @code{foo}, which changes with the value of | |
1016 | @code{selective-display}. The @emph{contents} of the buffer do not | |
1017 | change. | |
1018 | ||
1019 | @example | |
1020 | @group | |
1021 | (setq selective-display nil) | |
1022 | @result{} nil | |
1023 | ||
1024 | ---------- Buffer: foo ---------- | |
1025 | 1 on this column | |
1026 | 2on this column | |
1027 | 3n this column | |
1028 | 3n this column | |
1029 | 2on this column | |
1030 | 1 on this column | |
1031 | ---------- Buffer: foo ---------- | |
1032 | @end group | |
1033 | ||
1034 | @group | |
1035 | (setq selective-display 2) | |
1036 | @result{} 2 | |
1037 | ||
1038 | ---------- Buffer: foo ---------- | |
1039 | 1 on this column | |
1040 | 2on this column | |
1041 | 2on this column | |
1042 | 1 on this column | |
1043 | ---------- Buffer: foo ---------- | |
1044 | @end group | |
1045 | @end example | |
1046 | @end defvar | |
1047 | ||
01f17ae2 | 1048 | @defopt selective-display-ellipses |
b8d4c8d0 GM |
1049 | If this buffer-local variable is non-@code{nil}, then Emacs displays |
1050 | @samp{@dots{}} at the end of a line that is followed by hidden text. | |
1051 | This example is a continuation of the previous one. | |
1052 | ||
1053 | @example | |
1054 | @group | |
1055 | (setq selective-display-ellipses t) | |
1056 | @result{} t | |
1057 | ||
1058 | ---------- Buffer: foo ---------- | |
1059 | 1 on this column | |
1060 | 2on this column ... | |
1061 | 2on this column | |
1062 | 1 on this column | |
1063 | ---------- Buffer: foo ---------- | |
1064 | @end group | |
1065 | @end example | |
1066 | ||
1067 | You can use a display table to substitute other text for the ellipsis | |
1068 | (@samp{@dots{}}). @xref{Display Tables}. | |
01f17ae2 | 1069 | @end defopt |
b8d4c8d0 GM |
1070 | |
1071 | @node Temporary Displays | |
1072 | @section Temporary Displays | |
1073 | ||
1074 | Temporary displays are used by Lisp programs to put output into a | |
1075 | buffer and then present it to the user for perusal rather than for | |
1076 | editing. Many help commands use this feature. | |
1077 | ||
2cc775f9 | 1078 | @defmac with-output-to-temp-buffer buffer-name forms@dots{} |
b8d4c8d0 GM |
1079 | This function executes @var{forms} while arranging to insert any output |
1080 | they print into the buffer named @var{buffer-name}, which is first | |
1081 | created if necessary, and put into Help mode. Finally, the buffer is | |
1082 | displayed in some window, but not selected. | |
1083 | ||
1084 | If the @var{forms} do not change the major mode in the output buffer, | |
1085 | so that it is still Help mode at the end of their execution, then | |
1086 | @code{with-output-to-temp-buffer} makes this buffer read-only at the | |
1087 | end, and also scans it for function and variable names to make them | |
1088 | into clickable cross-references. @xref{Docstring hyperlinks, , Tips | |
1089 | for Documentation Strings}, in particular the item on hyperlinks in | |
1090 | documentation strings, for more details. | |
1091 | ||
1092 | The string @var{buffer-name} specifies the temporary buffer, which | |
1093 | need not already exist. The argument must be a string, not a buffer. | |
1094 | The buffer is erased initially (with no questions asked), and it is | |
1095 | marked as unmodified after @code{with-output-to-temp-buffer} exits. | |
1096 | ||
1097 | @code{with-output-to-temp-buffer} binds @code{standard-output} to the | |
1098 | temporary buffer, then it evaluates the forms in @var{forms}. Output | |
1099 | using the Lisp output functions within @var{forms} goes by default to | |
1100 | that buffer (but screen display and messages in the echo area, although | |
1101 | they are ``output'' in the general sense of the word, are not affected). | |
1102 | @xref{Output Functions}. | |
1103 | ||
1104 | Several hooks are available for customizing the behavior | |
1105 | of this construct; they are listed below. | |
1106 | ||
1107 | The value of the last form in @var{forms} is returned. | |
1108 | ||
1109 | @example | |
1110 | @group | |
1111 | ---------- Buffer: foo ---------- | |
1112 | This is the contents of foo. | |
1113 | ---------- Buffer: foo ---------- | |
1114 | @end group | |
1115 | ||
1116 | @group | |
1117 | (with-output-to-temp-buffer "foo" | |
1118 | (print 20) | |
1119 | (print standard-output)) | |
1120 | @result{} #<buffer foo> | |
1121 | ||
1122 | ---------- Buffer: foo ---------- | |
1123 | 20 | |
1124 | ||
1125 | #<buffer foo> | |
1126 | ||
1127 | ---------- Buffer: foo ---------- | |
1128 | @end group | |
1129 | @end example | |
2cc775f9 | 1130 | @end defmac |
b8d4c8d0 | 1131 | |
01f17ae2 | 1132 | @defopt temp-buffer-show-function |
b8d4c8d0 GM |
1133 | If this variable is non-@code{nil}, @code{with-output-to-temp-buffer} |
1134 | calls it as a function to do the job of displaying a help buffer. The | |
1135 | function gets one argument, which is the buffer it should display. | |
1136 | ||
1137 | It is a good idea for this function to run @code{temp-buffer-show-hook} | |
1138 | just as @code{with-output-to-temp-buffer} normally would, inside of | |
1139 | @code{save-selected-window} and with the chosen window and buffer | |
1140 | selected. | |
01f17ae2 | 1141 | @end defopt |
b8d4c8d0 GM |
1142 | |
1143 | @defvar temp-buffer-setup-hook | |
1144 | This normal hook is run by @code{with-output-to-temp-buffer} before | |
1145 | evaluating @var{body}. When the hook runs, the temporary buffer is | |
1146 | current. This hook is normally set up with a function to put the | |
1147 | buffer in Help mode. | |
1148 | @end defvar | |
1149 | ||
1150 | @defvar temp-buffer-show-hook | |
1151 | This normal hook is run by @code{with-output-to-temp-buffer} after | |
1152 | displaying the temporary buffer. When the hook runs, the temporary buffer | |
6733e827 | 1153 | is current, and the window it was displayed in is selected. |
b8d4c8d0 GM |
1154 | @end defvar |
1155 | ||
1156 | @defun momentary-string-display string position &optional char message | |
1157 | This function momentarily displays @var{string} in the current buffer at | |
1158 | @var{position}. It has no effect on the undo list or on the buffer's | |
1159 | modification status. | |
1160 | ||
1161 | The momentary display remains until the next input event. If the next | |
1162 | input event is @var{char}, @code{momentary-string-display} ignores it | |
1163 | and returns. Otherwise, that event remains buffered for subsequent use | |
1164 | as input. Thus, typing @var{char} will simply remove the string from | |
1165 | the display, while typing (say) @kbd{C-f} will remove the string from | |
1166 | the display and later (presumably) move point forward. The argument | |
1167 | @var{char} is a space by default. | |
1168 | ||
1169 | The return value of @code{momentary-string-display} is not meaningful. | |
1170 | ||
1171 | If the string @var{string} does not contain control characters, you can | |
1172 | do the same job in a more general way by creating (and then subsequently | |
1173 | deleting) an overlay with a @code{before-string} property. | |
1174 | @xref{Overlay Properties}. | |
1175 | ||
1176 | If @var{message} is non-@code{nil}, it is displayed in the echo area | |
1177 | while @var{string} is displayed in the buffer. If it is @code{nil}, a | |
1178 | default message says to type @var{char} to continue. | |
1179 | ||
1180 | In this example, point is initially located at the beginning of the | |
1181 | second line: | |
1182 | ||
1183 | @example | |
1184 | @group | |
1185 | ---------- Buffer: foo ---------- | |
1186 | This is the contents of foo. | |
1187 | @point{}Second line. | |
1188 | ---------- Buffer: foo ---------- | |
1189 | @end group | |
1190 | ||
1191 | @group | |
1192 | (momentary-string-display | |
1193 | "**** Important Message! ****" | |
1194 | (point) ?\r | |
1195 | "Type RET when done reading") | |
1196 | @result{} t | |
1197 | @end group | |
1198 | ||
1199 | @group | |
1200 | ---------- Buffer: foo ---------- | |
1201 | This is the contents of foo. | |
1202 | **** Important Message! ****Second line. | |
1203 | ---------- Buffer: foo ---------- | |
1204 | ||
1205 | ---------- Echo Area ---------- | |
1206 | Type RET when done reading | |
1207 | ---------- Echo Area ---------- | |
1208 | @end group | |
1209 | @end example | |
1210 | @end defun | |
1211 | ||
1212 | @node Overlays | |
1213 | @section Overlays | |
1214 | @cindex overlays | |
1215 | ||
1216 | You can use @dfn{overlays} to alter the appearance of a buffer's text on | |
1217 | the screen, for the sake of presentation features. An overlay is an | |
1218 | object that belongs to a particular buffer, and has a specified | |
1219 | beginning and end. It also has properties that you can examine and set; | |
1220 | these affect the display of the text within the overlay. | |
1221 | ||
b20ecfa1 EZ |
1222 | @cindex scalability of overlays |
1223 | The visual effect of an overlay is the same as of the corresponding | |
1224 | text property (@pxref{Text Properties}). However, due to a different | |
1225 | implementation, overlays generally don't scale well (many operations | |
1226 | take a time that is proportional to the number of overlays in the | |
1227 | buffer). If you need to affect the visual appearance of many portions | |
0c1cfe01 | 1228 | in the buffer, we recommend using text properties. |
b20ecfa1 | 1229 | |
b8d4c8d0 GM |
1230 | An overlay uses markers to record its beginning and end; thus, |
1231 | editing the text of the buffer adjusts the beginning and end of each | |
1232 | overlay so that it stays with the text. When you create the overlay, | |
1233 | you can specify whether text inserted at the beginning should be | |
1234 | inside the overlay or outside, and likewise for the end of the overlay. | |
1235 | ||
1236 | @menu | |
1237 | * Managing Overlays:: Creating and moving overlays. | |
1238 | * Overlay Properties:: How to read and set properties. | |
d24880de | 1239 | What properties do to the screen display. |
b8d4c8d0 GM |
1240 | * Finding Overlays:: Searching for overlays. |
1241 | @end menu | |
1242 | ||
1243 | @node Managing Overlays | |
1244 | @subsection Managing Overlays | |
1245 | ||
1246 | This section describes the functions to create, delete and move | |
1247 | overlays, and to examine their contents. Overlay changes are not | |
1248 | recorded in the buffer's undo list, since the overlays are not | |
1249 | part of the buffer's contents. | |
1250 | ||
1251 | @defun overlayp object | |
1252 | This function returns @code{t} if @var{object} is an overlay. | |
1253 | @end defun | |
1254 | ||
1255 | @defun make-overlay start end &optional buffer front-advance rear-advance | |
1256 | This function creates and returns an overlay that belongs to | |
1257 | @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start} | |
1258 | and @var{end} must specify buffer positions; they may be integers or | |
1259 | markers. If @var{buffer} is omitted, the overlay is created in the | |
1260 | current buffer. | |
1261 | ||
1262 | The arguments @var{front-advance} and @var{rear-advance} specify the | |
1263 | marker insertion type for the start of the overlay and for the end of | |
1264 | the overlay, respectively. @xref{Marker Insertion Types}. If they | |
1265 | are both @code{nil}, the default, then the overlay extends to include | |
1266 | any text inserted at the beginning, but not text inserted at the end. | |
1267 | If @var{front-advance} is non-@code{nil}, text inserted at the | |
1268 | beginning of the overlay is excluded from the overlay. If | |
1269 | @var{rear-advance} is non-@code{nil}, text inserted at the end of the | |
1270 | overlay is included in the overlay. | |
1271 | @end defun | |
1272 | ||
1273 | @defun overlay-start overlay | |
1274 | This function returns the position at which @var{overlay} starts, | |
1275 | as an integer. | |
1276 | @end defun | |
1277 | ||
1278 | @defun overlay-end overlay | |
1279 | This function returns the position at which @var{overlay} ends, | |
1280 | as an integer. | |
1281 | @end defun | |
1282 | ||
1283 | @defun overlay-buffer overlay | |
1284 | This function returns the buffer that @var{overlay} belongs to. It | |
1285 | returns @code{nil} if @var{overlay} has been deleted. | |
1286 | @end defun | |
1287 | ||
1288 | @defun delete-overlay overlay | |
1289 | This function deletes @var{overlay}. The overlay continues to exist as | |
1290 | a Lisp object, and its property list is unchanged, but it ceases to be | |
1291 | attached to the buffer it belonged to, and ceases to have any effect on | |
1292 | display. | |
1293 | ||
1294 | A deleted overlay is not permanently disconnected. You can give it a | |
1295 | position in a buffer again by calling @code{move-overlay}. | |
1296 | @end defun | |
1297 | ||
1298 | @defun move-overlay overlay start end &optional buffer | |
1299 | This function moves @var{overlay} to @var{buffer}, and places its bounds | |
1300 | at @var{start} and @var{end}. Both arguments @var{start} and @var{end} | |
1301 | must specify buffer positions; they may be integers or markers. | |
1302 | ||
1303 | If @var{buffer} is omitted, @var{overlay} stays in the same buffer it | |
1304 | was already associated with; if @var{overlay} was deleted, it goes into | |
1305 | the current buffer. | |
1306 | ||
1307 | The return value is @var{overlay}. | |
1308 | ||
1309 | This is the only valid way to change the endpoints of an overlay. Do | |
1310 | not try modifying the markers in the overlay by hand, as that fails to | |
1311 | update other vital data structures and can cause some overlays to be | |
1312 | ``lost.'' | |
1313 | @end defun | |
1314 | ||
1315 | @defun remove-overlays &optional start end name value | |
1316 | This function removes all the overlays between @var{start} and | |
1317 | @var{end} whose property @var{name} has the value @var{value}. It can | |
1318 | move the endpoints of the overlays in the region, or split them. | |
1319 | ||
1320 | If @var{name} is omitted or @code{nil}, it means to delete all overlays in | |
1321 | the specified region. If @var{start} and/or @var{end} are omitted or | |
1322 | @code{nil}, that means the beginning and end of the buffer respectively. | |
1323 | Therefore, @code{(remove-overlays)} removes all the overlays in the | |
1324 | current buffer. | |
78427304 CY |
1325 | @end defun |
1326 | ||
1327 | @defun copy-overlay overlay | |
1328 | This function returns a copy of @var{overlay}. The copy has the same | |
1329 | endpoints and properties as @var{overlay}. However, the marker | |
1330 | insertion type for the start of the overlay and for the end of the | |
1331 | overlay are set to their default values (@pxref{Marker Insertion | |
1332 | Types}). | |
b8d4c8d0 GM |
1333 | @end defun |
1334 | ||
1335 | Here are some examples: | |
1336 | ||
1337 | @example | |
1338 | ;; @r{Create an overlay.} | |
1339 | (setq foo (make-overlay 1 10)) | |
1340 | @result{} #<overlay from 1 to 10 in display.texi> | |
1341 | (overlay-start foo) | |
1342 | @result{} 1 | |
1343 | (overlay-end foo) | |
1344 | @result{} 10 | |
1345 | (overlay-buffer foo) | |
1346 | @result{} #<buffer display.texi> | |
1347 | ;; @r{Give it a property we can check later.} | |
1348 | (overlay-put foo 'happy t) | |
1349 | @result{} t | |
1350 | ;; @r{Verify the property is present.} | |
1351 | (overlay-get foo 'happy) | |
1352 | @result{} t | |
1353 | ;; @r{Move the overlay.} | |
1354 | (move-overlay foo 5 20) | |
1355 | @result{} #<overlay from 5 to 20 in display.texi> | |
1356 | (overlay-start foo) | |
1357 | @result{} 5 | |
1358 | (overlay-end foo) | |
1359 | @result{} 20 | |
1360 | ;; @r{Delete the overlay.} | |
1361 | (delete-overlay foo) | |
1362 | @result{} nil | |
1363 | ;; @r{Verify it is deleted.} | |
1364 | foo | |
1365 | @result{} #<overlay in no buffer> | |
1366 | ;; @r{A deleted overlay has no position.} | |
1367 | (overlay-start foo) | |
1368 | @result{} nil | |
1369 | (overlay-end foo) | |
1370 | @result{} nil | |
1371 | (overlay-buffer foo) | |
1372 | @result{} nil | |
1373 | ;; @r{Undelete the overlay.} | |
1374 | (move-overlay foo 1 20) | |
1375 | @result{} #<overlay from 1 to 20 in display.texi> | |
1376 | ;; @r{Verify the results.} | |
1377 | (overlay-start foo) | |
1378 | @result{} 1 | |
1379 | (overlay-end foo) | |
1380 | @result{} 20 | |
1381 | (overlay-buffer foo) | |
1382 | @result{} #<buffer display.texi> | |
1383 | ;; @r{Moving and deleting the overlay does not change its properties.} | |
1384 | (overlay-get foo 'happy) | |
1385 | @result{} t | |
1386 | @end example | |
1387 | ||
1388 | Emacs stores the overlays of each buffer in two lists, divided | |
1389 | around an arbitrary ``center position.'' One list extends backwards | |
1390 | through the buffer from that center position, and the other extends | |
1391 | forwards from that center position. The center position can be anywhere | |
1392 | in the buffer. | |
1393 | ||
1394 | @defun overlay-recenter pos | |
1395 | This function recenters the overlays of the current buffer around | |
1396 | position @var{pos}. That makes overlay lookup faster for positions | |
1397 | near @var{pos}, but slower for positions far away from @var{pos}. | |
1398 | @end defun | |
1399 | ||
1400 | A loop that scans the buffer forwards, creating overlays, can run | |
1401 | faster if you do @code{(overlay-recenter (point-max))} first. | |
1402 | ||
1403 | @node Overlay Properties | |
1404 | @subsection Overlay Properties | |
1405 | ||
1406 | Overlay properties are like text properties in that the properties that | |
1407 | alter how a character is displayed can come from either source. But in | |
1408 | most respects they are different. @xref{Text Properties}, for comparison. | |
1409 | ||
1410 | Text properties are considered a part of the text; overlays and | |
1411 | their properties are specifically considered not to be part of the | |
1412 | text. Thus, copying text between various buffers and strings | |
1413 | preserves text properties, but does not try to preserve overlays. | |
1414 | Changing a buffer's text properties marks the buffer as modified, | |
1415 | while moving an overlay or changing its properties does not. Unlike | |
1416 | text property changes, overlay property changes are not recorded in | |
1417 | the buffer's undo list. | |
1418 | ||
f7a7f4eb RS |
1419 | Since more than one overlay can specify a property value for the |
1420 | same character, Emacs lets you specify a priority value of each | |
1421 | overlay. You should not make assumptions about which overlay will | |
1422 | prevail when there is a conflict and they have the same priority. | |
1423 | ||
b8d4c8d0 GM |
1424 | These functions read and set the properties of an overlay: |
1425 | ||
1426 | @defun overlay-get overlay prop | |
1427 | This function returns the value of property @var{prop} recorded in | |
1428 | @var{overlay}, if any. If @var{overlay} does not record any value for | |
1429 | that property, but it does have a @code{category} property which is a | |
1430 | symbol, that symbol's @var{prop} property is used. Otherwise, the value | |
1431 | is @code{nil}. | |
1432 | @end defun | |
1433 | ||
1434 | @defun overlay-put overlay prop value | |
1435 | This function sets the value of property @var{prop} recorded in | |
1436 | @var{overlay} to @var{value}. It returns @var{value}. | |
1437 | @end defun | |
1438 | ||
1439 | @defun overlay-properties overlay | |
1440 | This returns a copy of the property list of @var{overlay}. | |
1441 | @end defun | |
1442 | ||
1443 | See also the function @code{get-char-property} which checks both | |
1444 | overlay properties and text properties for a given character. | |
1445 | @xref{Examining Properties}. | |
1446 | ||
1447 | Many overlay properties have special meanings; here is a table | |
1448 | of them: | |
1449 | ||
1450 | @table @code | |
1451 | @item priority | |
1452 | @kindex priority @r{(overlay property)} | |
5319014e | 1453 | This property's value (which should be a non-negative integer number) |
f7a7f4eb RS |
1454 | determines the priority of the overlay. No priority, or @code{nil}, |
1455 | means zero. | |
1456 | ||
1457 | The priority matters when two or more overlays cover the same | |
1458 | character and both specify the same property; the one whose | |
1459 | @code{priority} value is larger overrides the other. For the | |
1460 | @code{face} property, the higher priority overlay's value does not | |
1461 | completely override the other value; instead, its face attributes | |
1462 | override the face attributes of the lower priority @code{face} | |
1463 | property. | |
b8d4c8d0 GM |
1464 | |
1465 | Currently, all overlays take priority over text properties. Please | |
1466 | avoid using negative priority values, as we have not yet decided just | |
1467 | what they should mean. | |
1468 | ||
1469 | @item window | |
1470 | @kindex window @r{(overlay property)} | |
1471 | If the @code{window} property is non-@code{nil}, then the overlay | |
1472 | applies only on that window. | |
1473 | ||
1474 | @item category | |
1475 | @kindex category @r{(overlay property)} | |
1476 | If an overlay has a @code{category} property, we call it the | |
1477 | @dfn{category} of the overlay. It should be a symbol. The properties | |
1478 | of the symbol serve as defaults for the properties of the overlay. | |
1479 | ||
1480 | @item face | |
1481 | @kindex face @r{(overlay property)} | |
1482 | This property controls the way text is displayed---for example, which | |
1483 | font and which colors. @xref{Faces}, for more information. | |
1484 | ||
1485 | In the simplest case, the value is a face name. It can also be a list; | |
1486 | then each element can be any of these possibilities: | |
1487 | ||
1488 | @itemize @bullet | |
1489 | @item | |
1490 | A face name (a symbol or string). | |
1491 | ||
1492 | @item | |
1493 | A property list of face attributes. This has the form (@var{keyword} | |
1494 | @var{value} @dots{}), where each @var{keyword} is a face attribute | |
1495 | name and @var{value} is a meaningful value for that attribute. With | |
1496 | this feature, you do not need to create a face each time you want to | |
1497 | specify a particular attribute for certain text. @xref{Face | |
1498 | Attributes}. | |
1499 | ||
1500 | @item | |
dfc47e35 CY |
1501 | A cons cell, of the form @code{(foreground-color . @var{color-name})} |
1502 | or @code{(background-color . @var{color-name})}. These elements | |
1503 | specify just the foreground color or just the background color. | |
b8d4c8d0 GM |
1504 | |
1505 | @code{(foreground-color . @var{color-name})} has the same effect as | |
1506 | @code{(:foreground @var{color-name})}; likewise for the background. | |
1507 | @end itemize | |
1508 | ||
1509 | @item mouse-face | |
1510 | @kindex mouse-face @r{(overlay property)} | |
1511 | This property is used instead of @code{face} when the mouse is within | |
ebb552ed CY |
1512 | the range of the overlay. However, Emacs ignores all face attributes |
1513 | from this property that alter the text size (e.g. @code{:height}, | |
1514 | @code{:weight}, and @code{:slant}). Those attributes are always the | |
1515 | same as in the unhighlighted text. | |
b8d4c8d0 GM |
1516 | |
1517 | @item display | |
1518 | @kindex display @r{(overlay property)} | |
1519 | This property activates various features that change the | |
1520 | way text is displayed. For example, it can make text appear taller | |
1521 | or shorter, higher or lower, wider or narrower, or replaced with an image. | |
1522 | @xref{Display Property}. | |
1523 | ||
1524 | @item help-echo | |
1525 | @kindex help-echo @r{(overlay property)} | |
1526 | If an overlay has a @code{help-echo} property, then when you move the | |
1527 | mouse onto the text in the overlay, Emacs displays a help string in the | |
1528 | echo area, or in the tooltip window. For details see @ref{Text | |
1529 | help-echo}. | |
1530 | ||
1531 | @item modification-hooks | |
1532 | @kindex modification-hooks @r{(overlay property)} | |
1533 | This property's value is a list of functions to be called if any | |
1534 | character within the overlay is changed or if text is inserted strictly | |
1535 | within the overlay. | |
1536 | ||
1537 | The hook functions are called both before and after each change. | |
1538 | If the functions save the information they receive, and compare notes | |
1539 | between calls, they can determine exactly what change has been made | |
1540 | in the buffer text. | |
1541 | ||
1542 | When called before a change, each function receives four arguments: the | |
1543 | overlay, @code{nil}, and the beginning and end of the text range to be | |
1544 | modified. | |
1545 | ||
1546 | When called after a change, each function receives five arguments: the | |
1547 | overlay, @code{t}, the beginning and end of the text range just | |
1548 | modified, and the length of the pre-change text replaced by that range. | |
1549 | (For an insertion, the pre-change length is zero; for a deletion, that | |
1550 | length is the number of characters deleted, and the post-change | |
1551 | beginning and end are equal.) | |
1552 | ||
1553 | If these functions modify the buffer, they should bind | |
1554 | @code{inhibit-modification-hooks} to @code{t} around doing so, to | |
1555 | avoid confusing the internal mechanism that calls these hooks. | |
1556 | ||
1557 | Text properties also support the @code{modification-hooks} property, | |
1558 | but the details are somewhat different (@pxref{Special Properties}). | |
1559 | ||
1560 | @item insert-in-front-hooks | |
1561 | @kindex insert-in-front-hooks @r{(overlay property)} | |
1562 | This property's value is a list of functions to be called before and | |
1563 | after inserting text right at the beginning of the overlay. The calling | |
1564 | conventions are the same as for the @code{modification-hooks} functions. | |
1565 | ||
1566 | @item insert-behind-hooks | |
1567 | @kindex insert-behind-hooks @r{(overlay property)} | |
1568 | This property's value is a list of functions to be called before and | |
1569 | after inserting text right at the end of the overlay. The calling | |
1570 | conventions are the same as for the @code{modification-hooks} functions. | |
1571 | ||
1572 | @item invisible | |
1573 | @kindex invisible @r{(overlay property)} | |
1574 | The @code{invisible} property can make the text in the overlay | |
1575 | invisible, which means that it does not appear on the screen. | |
1576 | @xref{Invisible Text}, for details. | |
1577 | ||
1578 | @item intangible | |
1579 | @kindex intangible @r{(overlay property)} | |
1580 | The @code{intangible} property on an overlay works just like the | |
1581 | @code{intangible} text property. @xref{Special Properties}, for details. | |
1582 | ||
1583 | @item isearch-open-invisible | |
1584 | This property tells incremental search how to make an invisible overlay | |
1585 | visible, permanently, if the final match overlaps it. @xref{Invisible | |
1586 | Text}. | |
1587 | ||
1588 | @item isearch-open-invisible-temporary | |
1589 | This property tells incremental search how to make an invisible overlay | |
1590 | visible, temporarily, during the search. @xref{Invisible Text}. | |
1591 | ||
1592 | @item before-string | |
1593 | @kindex before-string @r{(overlay property)} | |
1594 | This property's value is a string to add to the display at the beginning | |
1595 | of the overlay. The string does not appear in the buffer in any | |
1596 | sense---only on the screen. | |
1597 | ||
1598 | @item after-string | |
1599 | @kindex after-string @r{(overlay property)} | |
1600 | This property's value is a string to add to the display at the end of | |
1601 | the overlay. The string does not appear in the buffer in any | |
1602 | sense---only on the screen. | |
1603 | ||
0c1cfe01 CY |
1604 | @item line-prefix |
1605 | This property specifies a display spec to prepend to each | |
1606 | non-continuation line at display-time. @xref{Truncation}. | |
1607 | ||
5319014e | 1608 | @item wrap-prefix |
0c1cfe01 CY |
1609 | This property specifies a display spec to prepend to each continuation |
1610 | line at display-time. @xref{Truncation}. | |
1611 | ||
b8d4c8d0 GM |
1612 | @item evaporate |
1613 | @kindex evaporate @r{(overlay property)} | |
1614 | If this property is non-@code{nil}, the overlay is deleted automatically | |
1615 | if it becomes empty (i.e., if its length becomes zero). If you give | |
1616 | an empty overlay a non-@code{nil} @code{evaporate} property, that deletes | |
1617 | it immediately. | |
1618 | ||
1619 | @item local-map | |
1620 | @cindex keymap of character (and overlays) | |
1621 | @kindex local-map @r{(overlay property)} | |
1622 | If this property is non-@code{nil}, it specifies a keymap for a portion | |
1623 | of the text. The property's value replaces the buffer's local map, when | |
1624 | the character after point is within the overlay. @xref{Active Keymaps}. | |
1625 | ||
1626 | @item keymap | |
1627 | @kindex keymap @r{(overlay property)} | |
1628 | The @code{keymap} property is similar to @code{local-map} but overrides the | |
1629 | buffer's local map (and the map specified by the @code{local-map} | |
1630 | property) rather than replacing it. | |
1631 | @end table | |
1632 | ||
32c94598 CY |
1633 | The @code{local-map} and @code{keymap} properties do not affect a |
1634 | string displayed by the @code{before-string}, @code{after-string}, or | |
1635 | @code{display} properties. This is only relevant for mouse clicks and | |
1636 | other mouse events that fall on the string, since point is never on | |
1637 | the string. To bind special mouse events for the string, assign it a | |
1638 | @code{local-map} or @code{keymap} text property. @xref{Special | |
1639 | Properties}. | |
1640 | ||
b8d4c8d0 GM |
1641 | @node Finding Overlays |
1642 | @subsection Searching for Overlays | |
1643 | ||
1644 | @defun overlays-at pos | |
1645 | This function returns a list of all the overlays that cover the | |
1646 | character at position @var{pos} in the current buffer. The list is in | |
1647 | no particular order. An overlay contains position @var{pos} if it | |
1648 | begins at or before @var{pos}, and ends after @var{pos}. | |
1649 | ||
1650 | To illustrate usage, here is a Lisp function that returns a list of the | |
1651 | overlays that specify property @var{prop} for the character at point: | |
1652 | ||
1653 | @smallexample | |
1654 | (defun find-overlays-specifying (prop) | |
1655 | (let ((overlays (overlays-at (point))) | |
1656 | found) | |
1657 | (while overlays | |
1658 | (let ((overlay (car overlays))) | |
1659 | (if (overlay-get overlay prop) | |
1660 | (setq found (cons overlay found)))) | |
1661 | (setq overlays (cdr overlays))) | |
1662 | found)) | |
1663 | @end smallexample | |
1664 | @end defun | |
1665 | ||
1666 | @defun overlays-in beg end | |
1667 | This function returns a list of the overlays that overlap the region | |
1668 | @var{beg} through @var{end}. ``Overlap'' means that at least one | |
1669 | character is contained within the overlay and also contained within the | |
1670 | specified region; however, empty overlays are included in the result if | |
c70a68db MR |
1671 | they are located at @var{beg}, strictly between @var{beg} and @var{end}, |
1672 | or at @var{end} when @var{end} denotes the position at the end of the | |
1673 | buffer. | |
b8d4c8d0 GM |
1674 | @end defun |
1675 | ||
1676 | @defun next-overlay-change pos | |
1677 | This function returns the buffer position of the next beginning or end | |
1678 | of an overlay, after @var{pos}. If there is none, it returns | |
1679 | @code{(point-max)}. | |
1680 | @end defun | |
1681 | ||
1682 | @defun previous-overlay-change pos | |
1683 | This function returns the buffer position of the previous beginning or | |
1684 | end of an overlay, before @var{pos}. If there is none, it returns | |
1685 | @code{(point-min)}. | |
1686 | @end defun | |
1687 | ||
1688 | As an example, here's a simplified (and inefficient) version of the | |
1689 | primitive function @code{next-single-char-property-change} | |
1690 | (@pxref{Property Search}). It searches forward from position | |
1691 | @var{pos} for the next position where the value of a given property | |
1692 | @code{prop}, as obtained from either overlays or text properties, | |
1693 | changes. | |
1694 | ||
1695 | @smallexample | |
1696 | (defun next-single-char-property-change (position prop) | |
1697 | (save-excursion | |
1698 | (goto-char position) | |
1699 | (let ((propval (get-char-property (point) prop))) | |
1700 | (while (and (not (eobp)) | |
1701 | (eq (get-char-property (point) prop) propval)) | |
1702 | (goto-char (min (next-overlay-change (point)) | |
1703 | (next-single-property-change (point) prop))))) | |
1704 | (point))) | |
1705 | @end smallexample | |
1706 | ||
1707 | @node Width | |
1708 | @section Width | |
1709 | ||
1710 | Since not all characters have the same width, these functions let you | |
1711 | check the width of a character. @xref{Primitive Indent}, and | |
1712 | @ref{Screen Lines}, for related functions. | |
1713 | ||
1714 | @defun char-width char | |
fb5b8aca CY |
1715 | This function returns the width in columns of the character |
1716 | @var{char}, if it were displayed in the current buffer (i.e.@: taking | |
1717 | into account the buffer's display table, if any; @pxref{Display | |
1718 | Tables}). The width of a tab character is usually @code{tab-width} | |
1719 | (@pxref{Usual Display}). | |
b8d4c8d0 GM |
1720 | @end defun |
1721 | ||
1722 | @defun string-width string | |
1723 | This function returns the width in columns of the string @var{string}, | |
1724 | if it were displayed in the current buffer and the selected window. | |
1725 | @end defun | |
1726 | ||
1727 | @defun truncate-string-to-width string width &optional start-column padding ellipsis | |
1728 | This function returns the part of @var{string} that fits within | |
1729 | @var{width} columns, as a new string. | |
1730 | ||
1731 | If @var{string} does not reach @var{width}, then the result ends where | |
1732 | @var{string} ends. If one multi-column character in @var{string} | |
1733 | extends across the column @var{width}, that character is not included in | |
1734 | the result. Thus, the result can fall short of @var{width} but cannot | |
1735 | go beyond it. | |
1736 | ||
1737 | The optional argument @var{start-column} specifies the starting column. | |
1738 | If this is non-@code{nil}, then the first @var{start-column} columns of | |
1739 | the string are omitted from the value. If one multi-column character in | |
1740 | @var{string} extends across the column @var{start-column}, that | |
1741 | character is not included. | |
1742 | ||
1743 | The optional argument @var{padding}, if non-@code{nil}, is a padding | |
1744 | character added at the beginning and end of the result string, to extend | |
1745 | it to exactly @var{width} columns. The padding character is used at the | |
1746 | end of the result if it falls short of @var{width}. It is also used at | |
1747 | the beginning of the result if one multi-column character in | |
1748 | @var{string} extends across the column @var{start-column}. | |
1749 | ||
1750 | If @var{ellipsis} is non-@code{nil}, it should be a string which will | |
1751 | replace the end of @var{str} (including any padding) if it extends | |
1752 | beyond @var{end-column}, unless the display width of @var{str} is | |
1753 | equal to or less than the display width of @var{ellipsis}. If | |
1754 | @var{ellipsis} is non-@code{nil} and not a string, it stands for | |
1755 | @code{"..."}. | |
1756 | ||
1757 | @example | |
1758 | (truncate-string-to-width "\tab\t" 12 4) | |
1759 | @result{} "ab" | |
1760 | (truncate-string-to-width "\tab\t" 12 4 ?\s) | |
1761 | @result{} " ab " | |
1762 | @end example | |
1763 | @end defun | |
1764 | ||
1765 | @node Line Height | |
1766 | @section Line Height | |
1767 | @cindex line height | |
1768 | ||
1769 | The total height of each display line consists of the height of the | |
1770 | contents of the line, plus optional additional vertical line spacing | |
1771 | above or below the display line. | |
1772 | ||
1773 | The height of the line contents is the maximum height of any | |
1774 | character or image on that display line, including the final newline | |
1775 | if there is one. (A display line that is continued doesn't include a | |
1776 | final newline.) That is the default line height, if you do nothing to | |
1777 | specify a greater height. (In the most common case, this equals the | |
1778 | height of the default frame font.) | |
1779 | ||
1780 | There are several ways to explicitly specify a larger line height, | |
1781 | either by specifying an absolute height for the display line, or by | |
1782 | specifying vertical space. However, no matter what you specify, the | |
1783 | actual line height can never be less than the default. | |
1784 | ||
1785 | @kindex line-height @r{(text property)} | |
1786 | A newline can have a @code{line-height} text or overlay property | |
1787 | that controls the total height of the display line ending in that | |
1788 | newline. | |
1789 | ||
1790 | If the property value is @code{t}, the newline character has no | |
1791 | effect on the displayed height of the line---the visible contents | |
1792 | alone determine the height. This is useful for tiling small images | |
1793 | (or image slices) without adding blank areas between the images. | |
1794 | ||
1795 | If the property value is a list of the form @code{(@var{height} | |
1796 | @var{total})}, that adds extra space @emph{below} the display line. | |
1797 | First Emacs uses @var{height} as a height spec to control extra space | |
1798 | @emph{above} the line; then it adds enough space @emph{below} the line | |
1799 | to bring the total line height up to @var{total}. In this case, the | |
1800 | other ways to specify the line spacing are ignored. | |
1801 | ||
1802 | Any other kind of property value is a height spec, which translates | |
1803 | into a number---the specified line height. There are several ways to | |
1804 | write a height spec; here's how each of them translates into a number: | |
1805 | ||
1806 | @table @code | |
1807 | @item @var{integer} | |
1808 | If the height spec is a positive integer, the height value is that integer. | |
1809 | @item @var{float} | |
1810 | If the height spec is a float, @var{float}, the numeric height value | |
1811 | is @var{float} times the frame's default line height. | |
1812 | @item (@var{face} . @var{ratio}) | |
1813 | If the height spec is a cons of the format shown, the numeric height | |
1814 | is @var{ratio} times the height of face @var{face}. @var{ratio} can | |
1815 | be any type of number, or @code{nil} which means a ratio of 1. | |
1816 | If @var{face} is @code{t}, it refers to the current face. | |
1817 | @item (nil . @var{ratio}) | |
1818 | If the height spec is a cons of the format shown, the numeric height | |
1819 | is @var{ratio} times the height of the contents of the line. | |
1820 | @end table | |
1821 | ||
1822 | Thus, any valid height spec determines the height in pixels, one way | |
1823 | or another. If the line contents' height is less than that, Emacs | |
1824 | adds extra vertical space above the line to achieve the specified | |
1825 | total height. | |
1826 | ||
1827 | If you don't specify the @code{line-height} property, the line's | |
1828 | height consists of the contents' height plus the line spacing. | |
1829 | There are several ways to specify the line spacing for different | |
1830 | parts of Emacs text. | |
1831 | ||
ed8ab760 CY |
1832 | On graphical terminals, you can specify the line spacing for all |
1833 | lines in a frame, using the @code{line-spacing} frame parameter | |
4e3b4528 SM |
1834 | (@pxref{Layout Parameters}). However, if the default value of |
1835 | @code{line-spacing} is non-@code{nil}, it overrides the | |
ed8ab760 CY |
1836 | frame's @code{line-spacing} parameter. An integer value specifies the |
1837 | number of pixels put below lines. A floating point number specifies | |
1838 | the spacing relative to the frame's default line height. | |
b8d4c8d0 GM |
1839 | |
1840 | @vindex line-spacing | |
1841 | You can specify the line spacing for all lines in a buffer via the | |
1842 | buffer-local @code{line-spacing} variable. An integer value specifies | |
ed8ab760 CY |
1843 | the number of pixels put below lines. A floating point number |
1844 | specifies the spacing relative to the default frame line height. This | |
1845 | overrides line spacings specified for the frame. | |
b8d4c8d0 GM |
1846 | |
1847 | @kindex line-spacing @r{(text property)} | |
1848 | Finally, a newline can have a @code{line-spacing} text or overlay | |
1849 | property that overrides the default frame line spacing and the buffer | |
1850 | local @code{line-spacing} variable, for the display line ending in | |
1851 | that newline. | |
1852 | ||
1853 | One way or another, these mechanisms specify a Lisp value for the | |
1854 | spacing of each line. The value is a height spec, and it translates | |
1855 | into a Lisp value as described above. However, in this case the | |
1856 | numeric height value specifies the line spacing, rather than the line | |
1857 | height. | |
1858 | ||
a08a07e3 | 1859 | On text terminals, the line spacing cannot be altered. |
ed8ab760 | 1860 | |
b8d4c8d0 GM |
1861 | @node Faces |
1862 | @section Faces | |
1863 | @cindex faces | |
1864 | ||
fb5b8aca CY |
1865 | A @dfn{face} is a collection of graphical @dfn{attributes} for |
1866 | displaying text: font, foreground color, background color, optional | |
1867 | underlining, and so on. Faces control how Emacs displays text in | |
1868 | buffers, as well as other parts of the frame such as the mode line. | |
42a2a154 CY |
1869 | @xref{Standard Faces,,, emacs, The GNU Emacs Manual}, for the list of |
1870 | faces Emacs normally comes with. | |
b8d4c8d0 GM |
1871 | |
1872 | @cindex face id | |
42a2a154 | 1873 | For most purposes, you refer to a face in Lisp programs using its |
fb5b8aca CY |
1874 | @dfn{face name}, which is usually a Lisp symbol. For backward |
1875 | compatibility, a face name can also be a string, which is equivalent | |
1876 | to a Lisp symbol of the same name. | |
b8d4c8d0 GM |
1877 | |
1878 | @defun facep object | |
42a2a154 CY |
1879 | This function returns a non-@code{nil} value if @var{object} is a Lisp |
1880 | symbol or string that names a face. Otherwise, it returns @code{nil}. | |
b8d4c8d0 GM |
1881 | @end defun |
1882 | ||
fb5b8aca CY |
1883 | By default, each face name corresponds to the same set of attributes |
1884 | in all frames. But you can also assign a face name a special set of | |
1885 | attributes in one frame (@pxref{Attribute Functions}). | |
b8d4c8d0 GM |
1886 | |
1887 | @menu | |
1888 | * Defining Faces:: How to define a face with @code{defface}. | |
1889 | * Face Attributes:: What is in a face? | |
1890 | * Attribute Functions:: Functions to examine and set face attributes. | |
1891 | * Displaying Faces:: How Emacs combines the faces specified for a character. | |
35137ed3 | 1892 | * Face Remapping:: Remapping faces to alternative definitions. |
b8d4c8d0 GM |
1893 | * Face Functions:: How to define and examine faces. |
1894 | * Auto Faces:: Hook for automatic face assignment. | |
35137ed3 | 1895 | * Basic Faces:: Faces that are defined by default. |
9185bf49 | 1896 | * Font Selection:: Finding the best available font for a face. |
b8d4c8d0 GM |
1897 | * Font Lookup:: Looking up the names of available fonts |
1898 | and information about them. | |
1899 | * Fontsets:: A fontset is a collection of fonts | |
1900 | that handle a range of character sets. | |
c2aa555a | 1901 | * Low-Level Font:: Lisp representation for character display fonts. |
b8d4c8d0 GM |
1902 | @end menu |
1903 | ||
1904 | @node Defining Faces | |
1905 | @subsection Defining Faces | |
1906 | ||
1907 | The way to define a new face is with @code{defface}. This creates a | |
fb5b8aca CY |
1908 | kind of customization item which the user can customize using the |
1909 | Customization buffer (@pxref{Customization}). | |
b8d4c8d0 | 1910 | |
15688fce GM |
1911 | People are sometimes tempted to create variables whose values specify |
1912 | which faces to use (for example, Font-Lock does this). In the vast | |
1913 | majority of cases, this is not necessary, and simply using faces | |
1914 | directly is preferable. | |
1915 | ||
b8d4c8d0 | 1916 | @defmac defface face spec doc [keyword value]@dots{} |
42a2a154 CY |
1917 | This declares @var{face} as a customizable face whose default |
1918 | attributes are given by @var{spec}. You should not quote the symbol | |
1919 | @var{face}, and it should not end in @samp{-face} (that would be | |
1920 | redundant). The argument @var{doc} specifies the face documentation. | |
1921 | The keywords you can use in @code{defface} are the same as in | |
1922 | @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}). | |
b8d4c8d0 GM |
1923 | |
1924 | When @code{defface} executes, it defines the face according to | |
1925 | @var{spec}, then uses any customizations that were read from the | |
1926 | init file (@pxref{Init File}) to override that specification. | |
1927 | ||
1928 | When you evaluate a @code{defface} form with @kbd{C-M-x} in Emacs | |
1929 | Lisp mode (@code{eval-defun}), a special feature of @code{eval-defun} | |
1930 | overrides any customizations of the face. This way, the face reflects | |
1931 | exactly what the @code{defface} says. | |
1932 | ||
1933 | The purpose of @var{spec} is to specify how the face should appear on | |
1934 | different kinds of terminals. It should be an alist whose elements | |
fb5b8aca CY |
1935 | have the form @code{(@var{display} @var{atts})}. @var{display} |
1936 | specifies a class of terminals (see below), while @var{atts} is a | |
1937 | property list of face attributes and their values, specifying the | |
1938 | appearance of the face on matching terminals | |
1939 | @iftex | |
1940 | (see the next section for details about face attributes). | |
1941 | @end iftex | |
1942 | @ifnottex | |
1943 | (@pxref{Face Attributes}, for details about face attributes). | |
1944 | @end ifnottex | |
b8d4c8d0 GM |
1945 | |
1946 | The @var{display} part of an element of @var{spec} determines which | |
1947 | frames the element matches. If more than one element of @var{spec} | |
1948 | matches a given frame, the first element that matches is the one used | |
1949 | for that frame. There are three possibilities for @var{display}: | |
1950 | ||
1951 | @table @asis | |
1952 | @item @code{default} | |
1953 | This element of @var{spec} doesn't match any frames; instead, it | |
1954 | specifies defaults that apply to all frames. This kind of element, if | |
1955 | used, must be the first element of @var{spec}. Each of the following | |
1956 | elements can override any or all of these defaults. | |
1957 | ||
1958 | @item @code{t} | |
1959 | This element of @var{spec} matches all frames. Therefore, any | |
1960 | subsequent elements of @var{spec} are never used. Normally | |
1961 | @code{t} is used in the last (or only) element of @var{spec}. | |
1962 | ||
1963 | @item a list | |
1964 | If @var{display} is a list, each element should have the form | |
1965 | @code{(@var{characteristic} @var{value}@dots{})}. Here | |
1966 | @var{characteristic} specifies a way of classifying frames, and the | |
1967 | @var{value}s are possible classifications which @var{display} should | |
1968 | apply to. Here are the possible values of @var{characteristic}: | |
1969 | ||
1970 | @table @code | |
1971 | @item type | |
1972 | The kind of window system the frame uses---either @code{graphic} (any | |
1973 | graphics-capable display), @code{x}, @code{pc} (for the MS-DOS console), | |
9e2a2647 DN |
1974 | @code{w32} (for MS Windows 9X/NT/2K/XP), or @code{tty} |
1975 | (a non-graphics-capable display). | |
b8d4c8d0 GM |
1976 | @xref{Window Systems, window-system}. |
1977 | ||
1978 | @item class | |
1979 | What kinds of colors the frame supports---either @code{color}, | |
1980 | @code{grayscale}, or @code{mono}. | |
1981 | ||
1982 | @item background | |
1983 | The kind of background---either @code{light} or @code{dark}. | |
1984 | ||
1985 | @item min-colors | |
1986 | An integer that represents the minimum number of colors the frame | |
1987 | should support. This matches a frame if its | |
1988 | @code{display-color-cells} value is at least the specified integer. | |
1989 | ||
1990 | @item supports | |
1991 | Whether or not the frame can display the face attributes given in | |
42a2a154 CY |
1992 | @var{value}@dots{} (@pxref{Face Attributes}). @xref{Display Face |
1993 | Attribute Testing}, for more information on exactly how this testing | |
1994 | is done. | |
b8d4c8d0 GM |
1995 | @end table |
1996 | ||
1997 | If an element of @var{display} specifies more than one @var{value} for a | |
1998 | given @var{characteristic}, any of those values is acceptable. If | |
1999 | @var{display} has more than one element, each element should specify a | |
2000 | different @var{characteristic}; then @emph{each} characteristic of the | |
2001 | frame must match one of the @var{value}s specified for it in | |
2002 | @var{display}. | |
2003 | @end table | |
2004 | @end defmac | |
2005 | ||
fb5b8aca | 2006 | Here's how the standard face @code{highlight} is defined: |
b8d4c8d0 GM |
2007 | |
2008 | @example | |
fb5b8aca CY |
2009 | (defface highlight |
2010 | '((((class color) (min-colors 88) (background light)) | |
2011 | :background "darkseagreen2") | |
2012 | (((class color) (min-colors 88) (background dark)) | |
2013 | :background "darkolivegreen") | |
b8d4c8d0 | 2014 | (((class color) (min-colors 16) (background light)) |
fb5b8aca CY |
2015 | :background "darkseagreen2") |
2016 | (((class color) (min-colors 16) (background dark)) | |
2017 | :background "darkolivegreen") | |
b8d4c8d0 | 2018 | (((class color) (min-colors 8)) |
fb5b8aca CY |
2019 | :background "green" :foreground "black") |
2020 | (t :inverse-video t)) | |
2021 | "Basic face for highlighting." | |
b8d4c8d0 | 2022 | :group 'basic-faces) |
b8d4c8d0 GM |
2023 | @end example |
2024 | ||
2025 | Internally, @code{defface} uses the symbol property | |
42a2a154 CY |
2026 | @code{face-defface-spec} to record the specified face attributes. The |
2027 | attributes saved by the user with the customization buffer are | |
2028 | recorded in the symbol property @code{saved-face}; the attributes | |
2029 | customized by the user for the current session, but not saved, are | |
2030 | recorded in the symbol property @code{customized-face}. The | |
2031 | documentation string is recorded in the symbol property | |
2032 | @code{face-documentation}. | |
b8d4c8d0 GM |
2033 | |
2034 | @defopt frame-background-mode | |
2035 | This option, if non-@code{nil}, specifies the background type to use for | |
2036 | interpreting face definitions. If it is @code{dark}, then Emacs treats | |
2037 | all frames as if they had a dark background, regardless of their actual | |
2038 | background colors. If it is @code{light}, then Emacs treats all frames | |
2039 | as if they had a light background. | |
2040 | @end defopt | |
2041 | ||
2042 | @node Face Attributes | |
2043 | @subsection Face Attributes | |
2044 | @cindex face attributes | |
2045 | ||
2046 | The effect of using a face is determined by a fixed set of @dfn{face | |
42a2a154 CY |
2047 | attributes}. This table lists all the face attributes, their possible |
2048 | values, and their effects. You can specify more than one face for a | |
2049 | given piece of text; Emacs merges the attributes of all the faces to | |
2050 | determine how to display the text. @xref{Displaying Faces}. | |
2051 | ||
2052 | In addition to the values given below, each face attribute can also | |
2053 | have the value @code{unspecified}. This special value means the face | |
2054 | doesn't specify that attribute. In face merging, when the first face | |
2055 | fails to specify a particular attribute, the next face gets a chance. | |
2056 | However, the @code{default} face must specify all attributes. | |
2057 | ||
fb5b8aca CY |
2058 | Some of these attributes are meaningful only on certain kinds of |
2059 | displays. If your display cannot handle a certain attribute, the | |
42a2a154 | 2060 | attribute is ignored. |
b8d4c8d0 GM |
2061 | |
2062 | @table @code | |
2063 | @item :family | |
b7527639 CY |
2064 | Font family or fontset (a string). @xref{Fonts,,, emacs, The GNU |
2065 | Emacs Manual}. If you specify a font family name, the wild-card | |
2066 | characters @samp{*} and @samp{?} are allowed. The function | |
2067 | @code{font-family-list}, described below, returns a list of available | |
2068 | family names. @xref{Fontsets}, for information about fontsets. | |
42a2a154 CY |
2069 | |
2070 | @item :foundry | |
b7527639 CY |
2071 | The name of the @dfn{font foundry} for the font family specified by |
2072 | the @code{:family} attribute (a string). The wild-card characters | |
2073 | @samp{*} and @samp{?} are allowed. @xref{Fonts,,, emacs, The GNU | |
2074 | Emacs Manual}. | |
b8d4c8d0 GM |
2075 | |
2076 | @item :width | |
42a2a154 | 2077 | Relative proportionate character width, also known as the character |
b8d4c8d0 GM |
2078 | set width. This should be one of the symbols @code{ultra-condensed}, |
2079 | @code{extra-condensed}, @code{condensed}, @code{semi-condensed}, | |
2080 | @code{normal}, @code{semi-expanded}, @code{expanded}, | |
2081 | @code{extra-expanded}, or @code{ultra-expanded}. | |
2082 | ||
2083 | @item :height | |
23696fd7 CY |
2084 | The height of the font. In the simplest case, this is an integer in |
2085 | units of 1/10 point. | |
2086 | ||
2087 | The value can also be a floating point number or a function, which | |
2088 | specifies the height relative to an @dfn{underlying face} (i.e., a | |
2089 | face that has a lower priority in the list described in | |
2090 | @ref{Displaying Faces}). If the value is a floating point number, | |
2091 | that specifies the amount by which to scale the height of the | |
2092 | underlying face. If the value is a function, that function is called | |
2093 | with one argument, the height of the underlying face, and returns the | |
2094 | height of the new face. If the function is passed an integer | |
2095 | argument, it must return an integer. | |
42a2a154 CY |
2096 | |
2097 | The height of the default face must be specified using an integer; | |
2098 | floating point and function values are not allowed. | |
b8d4c8d0 GM |
2099 | |
2100 | @item :weight | |
42a2a154 | 2101 | Font weight---one of the symbols (from densest to faintest) |
b8d4c8d0 | 2102 | @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold}, |
42a2a154 | 2103 | @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, or |
a08a07e3 | 2104 | @code{ultra-light}. On text terminals which support |
42a2a154 CY |
2105 | variable-brightness text, any weight greater than normal is displayed |
2106 | as extra bright, and any weight less than normal is displayed as | |
2107 | half-bright. | |
b8d4c8d0 GM |
2108 | |
2109 | @item :slant | |
42a2a154 CY |
2110 | Font slant---one of the symbols @code{italic}, @code{oblique}, |
2111 | @code{normal}, @code{reverse-italic}, or @code{reverse-oblique}. On | |
a08a07e3 CY |
2112 | text terminals that support variable-brightness text, slanted text is |
2113 | displayed as half-bright. | |
b8d4c8d0 GM |
2114 | |
2115 | @item :foreground | |
2116 | Foreground color, a string. The value can be a system-defined color | |
42a2a154 CY |
2117 | name, or a hexadecimal color specification. @xref{Color Names}. On |
2118 | black-and-white displays, certain shades of gray are implemented by | |
2119 | stipple patterns. | |
b8d4c8d0 GM |
2120 | |
2121 | @item :background | |
42a2a154 CY |
2122 | Background color, a string. The value can be a system-defined color |
2123 | name, or a hexadecimal color specification. @xref{Color Names}. | |
b8d4c8d0 GM |
2124 | |
2125 | @item :underline | |
2126 | Whether or not characters should be underlined, and in what color. If | |
2127 | the value is @code{t}, underlining uses the foreground color of the | |
2128 | face. If the value is a string, underlining uses that color. The | |
2129 | value @code{nil} means do not underline. | |
2130 | ||
2131 | @item :overline | |
2132 | Whether or not characters should be overlined, and in what color. | |
2133 | The value is used like that of @code{:underline}. | |
2134 | ||
2135 | @item :strike-through | |
2136 | Whether or not characters should be strike-through, and in what | |
2137 | color. The value is used like that of @code{:underline}. | |
2138 | ||
b8d4c8d0 GM |
2139 | @item :box |
2140 | Whether or not a box should be drawn around characters, its color, the | |
42a2a154 CY |
2141 | width of the box lines, and 3D appearance. Here are the possible |
2142 | values of the @code{:box} attribute, and what they mean: | |
b8d4c8d0 GM |
2143 | |
2144 | @table @asis | |
2145 | @item @code{nil} | |
2146 | Don't draw a box. | |
2147 | ||
2148 | @item @code{t} | |
2149 | Draw a box with lines of width 1, in the foreground color. | |
2150 | ||
2151 | @item @var{color} | |
2152 | Draw a box with lines of width 1, in color @var{color}. | |
2153 | ||
2154 | @item @code{(:line-width @var{width} :color @var{color} :style @var{style})} | |
2155 | This way you can explicitly specify all aspects of the box. The value | |
b00d8c1a CY |
2156 | @var{width} specifies the width of the lines to draw; it defaults to |
2157 | 1. A negative width @var{-n} means to draw a line of width @var{n} | |
2158 | that occupies the space of the underlying text, thus avoiding any | |
2159 | increase in the character height or width. | |
b8d4c8d0 GM |
2160 | |
2161 | The value @var{color} specifies the color to draw with. The default is | |
2162 | the foreground color of the face for simple boxes, and the background | |
2163 | color of the face for 3D boxes. | |
2164 | ||
2165 | The value @var{style} specifies whether to draw a 3D box. If it is | |
2166 | @code{released-button}, the box looks like a 3D button that is not being | |
2167 | pressed. If it is @code{pressed-button}, the box looks like a 3D button | |
2168 | that is being pressed. If it is @code{nil} or omitted, a plain 2D box | |
2169 | is used. | |
2170 | @end table | |
2171 | ||
42a2a154 CY |
2172 | @item :inverse-video |
2173 | Whether or not characters should be displayed in inverse video. The | |
2174 | value should be @code{t} (yes) or @code{nil} (no). | |
b8d4c8d0 | 2175 | |
42a2a154 CY |
2176 | @item :stipple |
2177 | The background stipple, a bitmap. | |
b8d4c8d0 | 2178 | |
42a2a154 CY |
2179 | The value can be a string; that should be the name of a file containing |
2180 | external-format X bitmap data. The file is found in the directories | |
2181 | listed in the variable @code{x-bitmap-file-path}. | |
b8d4c8d0 | 2182 | |
42a2a154 CY |
2183 | Alternatively, the value can specify the bitmap directly, with a list |
2184 | of the form @code{(@var{width} @var{height} @var{data})}. Here, | |
2185 | @var{width} and @var{height} specify the size in pixels, and | |
2186 | @var{data} is a string containing the raw bits of the bitmap, row by | |
2187 | row. Each row occupies @math{(@var{width} + 7) / 8} consecutive bytes | |
2188 | in the string (which should be a unibyte string for best results). | |
2189 | This means that each row always occupies at least one whole byte. | |
b8d4c8d0 | 2190 | |
42a2a154 | 2191 | If the value is @code{nil}, that means use no stipple pattern. |
b8d4c8d0 | 2192 | |
42a2a154 CY |
2193 | Normally you do not need to set the stipple attribute, because it is |
2194 | used automatically to handle certain shades of gray. | |
b8d4c8d0 | 2195 | |
42a2a154 | 2196 | @item :font |
9185bf49 CY |
2197 | The font used to display the face. Its value should be a font object. |
2198 | @xref{Font Selection}, for information about font objects. | |
42a2a154 CY |
2199 | |
2200 | When specifying this attribute using @code{set-face-attribute} | |
9185bf49 | 2201 | (@pxref{Attribute Functions}), you may also supply a font spec, a font |
42a2a154 | 2202 | entity, or a string. Emacs converts such values to an appropriate |
9185bf49 CY |
2203 | font object, and stores that font object as the actual attribute |
2204 | value. If you specify a string, the contents of the string should be | |
969aa734 CY |
2205 | a font name (@pxref{Fonts,,, emacs, The GNU Emacs Manual}); if the |
2206 | font name is an XLFD containing wildcards, Emacs chooses the first | |
2207 | font matching those wildcards. Specifying this attribute also changes | |
2208 | the values of the @code{:family}, @code{:foundry}, @code{:width}, | |
2209 | @code{:height}, @code{:weight}, and @code{:slant} attributes. | |
b8d4c8d0 | 2210 | |
42a2a154 CY |
2211 | @item :inherit |
2212 | The name of a face from which to inherit attributes, or a list of face | |
2213 | names. Attributes from inherited faces are merged into the face like | |
2214 | an underlying face would be, with higher priority than underlying | |
23696fd7 CY |
2215 | faces (@pxref{Displaying Faces}). If a list of faces is used, |
2216 | attributes from faces earlier in the list override those from later | |
2217 | faces. | |
b8d4c8d0 GM |
2218 | @end table |
2219 | ||
42a2a154 CY |
2220 | For compatibility with Emacs 20, you can also specify values for two |
2221 | ``fake'' face attributes: @code{:bold} and @code{:italic}. Their | |
2222 | values must be either @code{t} or @code{nil}; a value of | |
2223 | @code{unspecified} is not allowed. Setting @code{:bold} to @code{t} | |
2224 | is equivalent to setting the @code{:weight} attribute to @code{bold}, | |
2225 | and setting it to @code{nil} is equivalent to setting @code{:weight} | |
2226 | to @code{normal}. Setting @code{:italic} to @code{t} is equivalent to | |
2227 | setting the @code{:slant} attribute to @code{italic}, and setting it | |
2228 | to @code{nil} is equivalent to setting @code{:slant} to @code{normal}. | |
2229 | ||
9185bf49 CY |
2230 | @defun font-family-list &optional frame |
2231 | This function returns a list of available font family names. The | |
2232 | optional argument @var{frame} specifies the frame on which the text is | |
2233 | to be displayed; if it is @code{nil}, the selected frame is used. | |
2234 | @end defun | |
2235 | ||
01f17ae2 | 2236 | @defopt underline-minimum-offset |
0c1cfe01 CY |
2237 | This variable specifies the minimum distance between the baseline and |
2238 | the underline, in pixels, when displaying underlined text. | |
01f17ae2 | 2239 | @end defopt |
0c1cfe01 | 2240 | |
01f17ae2 | 2241 | @defopt x-bitmap-file-path |
b8d4c8d0 GM |
2242 | This variable specifies a list of directories for searching |
2243 | for bitmap files, for the @code{:stipple} attribute. | |
01f17ae2 | 2244 | @end defopt |
b8d4c8d0 GM |
2245 | |
2246 | @defun bitmap-spec-p object | |
2247 | This returns @code{t} if @var{object} is a valid bitmap specification, | |
2248 | suitable for use with @code{:stipple} (see above). It returns | |
2249 | @code{nil} otherwise. | |
2250 | @end defun | |
2251 | ||
2252 | @node Attribute Functions | |
2253 | @subsection Face Attribute Functions | |
2254 | ||
2255 | This section describes the functions for accessing and modifying the | |
2256 | attributes of an existing face. | |
2257 | ||
2258 | @defun set-face-attribute face frame &rest arguments | |
42a2a154 | 2259 | This function sets one or more attributes of @var{face} for |
b8d4c8d0 GM |
2260 | @var{frame}. The attributes you specify this way override whatever |
2261 | the @code{defface} says. | |
2262 | ||
2263 | The extra arguments @var{arguments} specify the attributes to set, and | |
fb5b8aca CY |
2264 | the values for them. They should consist of alternating attribute |
2265 | names (such as @code{:family} or @code{:underline}) and values. Thus, | |
b8d4c8d0 GM |
2266 | |
2267 | @example | |
2268 | (set-face-attribute 'foo nil | |
2269 | :width 'extended | |
fb5b8aca | 2270 | :weight 'bold) |
b8d4c8d0 GM |
2271 | @end example |
2272 | ||
2273 | @noindent | |
fb5b8aca CY |
2274 | sets the attribute @code{:width} to @code{extended} and the attribute |
2275 | @code{:weight} to @code{bold}. | |
b8d4c8d0 GM |
2276 | |
2277 | If @var{frame} is @code{t}, this function sets the default attributes | |
2278 | for new frames. Default attribute values specified this way override | |
2279 | the @code{defface} for newly created frames. | |
2280 | ||
2281 | If @var{frame} is @code{nil}, this function sets the attributes for | |
2282 | all existing frames, and the default for new frames. | |
2283 | @end defun | |
2284 | ||
2285 | @defun face-attribute face attribute &optional frame inherit | |
42a2a154 CY |
2286 | This returns the value of the @var{attribute} attribute of @var{face} |
2287 | on @var{frame}. If @var{frame} is @code{nil}, that means the selected | |
2288 | frame (@pxref{Input Focus}). | |
b8d4c8d0 GM |
2289 | |
2290 | If @var{frame} is @code{t}, this returns whatever new-frames default | |
2291 | value you previously specified with @code{set-face-attribute} for the | |
2292 | @var{attribute} attribute of @var{face}. If you have not specified | |
2293 | one, it returns @code{nil}. | |
2294 | ||
2295 | If @var{inherit} is @code{nil}, only attributes directly defined by | |
2296 | @var{face} are considered, so the return value may be | |
2297 | @code{unspecified}, or a relative value. If @var{inherit} is | |
2298 | non-@code{nil}, @var{face}'s definition of @var{attribute} is merged | |
2299 | with the faces specified by its @code{:inherit} attribute; however the | |
2300 | return value may still be @code{unspecified} or relative. If | |
2301 | @var{inherit} is a face or a list of faces, then the result is further | |
2302 | merged with that face (or faces), until it becomes specified and | |
2303 | absolute. | |
2304 | ||
2305 | To ensure that the return value is always specified and absolute, use | |
2306 | a value of @code{default} for @var{inherit}; this will resolve any | |
2307 | unspecified or relative values by merging with the @code{default} face | |
2308 | (which is always completely specified). | |
2309 | ||
2310 | For example, | |
2311 | ||
2312 | @example | |
2313 | (face-attribute 'bold :weight) | |
2314 | @result{} bold | |
2315 | @end example | |
2316 | @end defun | |
2317 | ||
2318 | @defun face-attribute-relative-p attribute value | |
2319 | This function returns non-@code{nil} if @var{value}, when used as the | |
2320 | value of the face attribute @var{attribute}, is relative. This means | |
2321 | it would modify, rather than completely override, any value that comes | |
2322 | from a subsequent face in the face list or that is inherited from | |
2323 | another face. | |
2324 | ||
d466a866 CY |
2325 | @code{unspecified} is a relative value for all attributes. For |
2326 | @code{:height}, floating point and function values are also relative. | |
b8d4c8d0 GM |
2327 | |
2328 | For example: | |
2329 | ||
2330 | @example | |
2331 | (face-attribute-relative-p :height 2.0) | |
2332 | @result{} t | |
2333 | @end example | |
2334 | @end defun | |
2335 | ||
b3d50cff EZ |
2336 | @defun face-all-attributes face &optional frame |
2337 | This function returns an alist of attributes of @var{face}. The | |
2338 | elements of the result are name-value pairs of the form | |
2339 | @w{@code{(@var{attr-name} . @var{attr-value})}}. Optional argument | |
2340 | @var{frame} specifies the frame whose definition of @var{face} to | |
2341 | return; if omitted or @code{nil}, the returned value describes the | |
2342 | default attributes of @var{face} for newly created frames. | |
2343 | @end defun | |
2344 | ||
b8d4c8d0 GM |
2345 | @defun merge-face-attribute attribute value1 value2 |
2346 | If @var{value1} is a relative value for the face attribute | |
2347 | @var{attribute}, returns it merged with the underlying value | |
2348 | @var{value2}; otherwise, if @var{value1} is an absolute value for the | |
2349 | face attribute @var{attribute}, returns @var{value1} unchanged. | |
2350 | @end defun | |
2351 | ||
fb5b8aca CY |
2352 | The following commands and functions mostly provide compatibility |
2353 | with old versions of Emacs. They work by calling | |
2354 | @code{set-face-attribute}. Values of @code{t} and @code{nil} for | |
2355 | their @var{frame} argument are handled just like | |
2356 | @code{set-face-attribute} and @code{face-attribute}. The commands | |
2357 | read their arguments using the minibuffer, if called interactively. | |
b8d4c8d0 | 2358 | |
fb5b8aca CY |
2359 | @deffn Command set-face-foreground face color &optional frame |
2360 | @deffnx Command set-face-background face color &optional frame | |
2361 | These set the @code{:foreground} attribute (or @code{:background} | |
2362 | attribute, respectively) of @var{face} to @var{color}. | |
2363 | @end deffn | |
b8d4c8d0 | 2364 | |
fb5b8aca CY |
2365 | @deffn Command set-face-stipple face pattern &optional frame |
2366 | This sets the @code{:stipple} attribute of @var{face} to | |
d466a866 | 2367 | @var{pattern}. |
fb5b8aca | 2368 | @end deffn |
b8d4c8d0 | 2369 | |
fb5b8aca CY |
2370 | @deffn Command set-face-font face font &optional frame |
2371 | This sets the @code{:font} attribute of @var{face} to @var{font}. | |
2372 | @end deffn | |
b8d4c8d0 GM |
2373 | |
2374 | @defun set-face-bold-p face bold-p &optional frame | |
fb5b8aca CY |
2375 | This sets the @code{:weight} attribute of @var{face} to @var{normal} |
2376 | if @var{bold-p} is @code{nil}, and to @var{bold} otherwise. | |
b8d4c8d0 GM |
2377 | @end defun |
2378 | ||
2379 | @defun set-face-italic-p face italic-p &optional frame | |
fb5b8aca CY |
2380 | This sets the @code{:slant} attribute of @var{face} to @var{normal} if |
2381 | @var{italic-p} is @code{nil}, and to @var{italic} otherwise. | |
b8d4c8d0 GM |
2382 | @end defun |
2383 | ||
2384 | @defun set-face-underline-p face underline &optional frame | |
fb5b8aca | 2385 | This sets the @code{:underline} attribute of @var{face} to |
d466a866 | 2386 | @var{underline}. |
b8d4c8d0 GM |
2387 | @end defun |
2388 | ||
2389 | @defun set-face-inverse-video-p face inverse-video-p &optional frame | |
fb5b8aca CY |
2390 | This sets the @code{:inverse-video} attribute of @var{face} to |
2391 | @var{inverse-video-p}. | |
b8d4c8d0 GM |
2392 | @end defun |
2393 | ||
fb5b8aca CY |
2394 | @deffn Command invert-face face &optional frame |
2395 | This swaps the foreground and background colors of face @var{face}. | |
2396 | @end deffn | |
b8d4c8d0 | 2397 | |
d466a866 CY |
2398 | The following functions examine the attributes of a face. If you |
2399 | don't specify @var{frame}, they refer to the selected frame; @code{t} | |
2400 | refers to the default data for new frames. They return the symbol | |
b8d4c8d0 GM |
2401 | @code{unspecified} if the face doesn't define any value for that |
2402 | attribute. | |
2403 | ||
2404 | @defun face-foreground face &optional frame inherit | |
2405 | @defunx face-background face &optional frame inherit | |
2406 | These functions return the foreground color (or background color, | |
2407 | respectively) of face @var{face}, as a string. | |
2408 | ||
2409 | If @var{inherit} is @code{nil}, only a color directly defined by the face is | |
2410 | returned. If @var{inherit} is non-@code{nil}, any faces specified by its | |
2411 | @code{:inherit} attribute are considered as well, and if @var{inherit} | |
2412 | is a face or a list of faces, then they are also considered, until a | |
2413 | specified color is found. To ensure that the return value is always | |
2414 | specified, use a value of @code{default} for @var{inherit}. | |
2415 | @end defun | |
2416 | ||
2417 | @defun face-stipple face &optional frame inherit | |
2418 | This function returns the name of the background stipple pattern of face | |
2419 | @var{face}, or @code{nil} if it doesn't have one. | |
2420 | ||
2421 | If @var{inherit} is @code{nil}, only a stipple directly defined by the | |
2422 | face is returned. If @var{inherit} is non-@code{nil}, any faces | |
2423 | specified by its @code{:inherit} attribute are considered as well, and | |
2424 | if @var{inherit} is a face or a list of faces, then they are also | |
2425 | considered, until a specified stipple is found. To ensure that the | |
2426 | return value is always specified, use a value of @code{default} for | |
2427 | @var{inherit}. | |
2428 | @end defun | |
2429 | ||
2430 | @defun face-font face &optional frame | |
2431 | This function returns the name of the font of face @var{face}. | |
2432 | @end defun | |
2433 | ||
2434 | @defun face-bold-p face &optional frame | |
d466a866 CY |
2435 | This function returns a non-@code{nil} value if the @code{:weight} |
2436 | attribute of @var{face} is bolder than normal (i.e., one of | |
2437 | @code{semi-bold}, @code{bold}, @code{extra-bold}, or | |
2438 | @code{ultra-bold}). Otherwise, it returns @code{nil}. | |
b8d4c8d0 GM |
2439 | @end defun |
2440 | ||
2441 | @defun face-italic-p face &optional frame | |
d466a866 CY |
2442 | This function returns a non-@code{nil} value if the @code{:slant} |
2443 | attribute of @var{face} is @code{italic} or @code{oblique}, and | |
b8d4c8d0 GM |
2444 | @code{nil} otherwise. |
2445 | @end defun | |
2446 | ||
2447 | @defun face-underline-p face &optional frame | |
2448 | This function returns the @code{:underline} attribute of face @var{face}. | |
2449 | @end defun | |
2450 | ||
2451 | @defun face-inverse-video-p face &optional frame | |
2452 | This function returns the @code{:inverse-video} attribute of face @var{face}. | |
2453 | @end defun | |
2454 | ||
2455 | @node Displaying Faces | |
2456 | @subsection Displaying Faces | |
2457 | ||
d466a866 CY |
2458 | Here is how Emacs determines the face to use for displaying any |
2459 | given piece of text: | |
b8d4c8d0 GM |
2460 | |
2461 | @itemize @bullet | |
2462 | @item | |
d466a866 CY |
2463 | If the text consists of a special glyph, the glyph can specify a |
2464 | particular face. @xref{Glyphs}. | |
b8d4c8d0 GM |
2465 | |
2466 | @item | |
d466a866 CY |
2467 | If the text lies within an active region, Emacs highlights it using |
2468 | the @code{region} face. @xref{Standard Faces,,, emacs, The GNU Emacs | |
2469 | Manual}. | |
b8d4c8d0 GM |
2470 | |
2471 | @item | |
d466a866 CY |
2472 | If the text lies within an overlay with a non-@code{nil} @code{face} |
2473 | property, Emacs applies the face or face attributes specified by that | |
2474 | property. If the overlay has a @code{mouse-face} property and the | |
2475 | mouse is ``near enough'' to the overlay, Emacs applies the face or | |
2476 | face attributes specified by the @code{mouse-face} property instead. | |
2477 | @xref{Overlay Properties}. | |
b8d4c8d0 | 2478 | |
d466a866 CY |
2479 | When multiple overlays cover one character, an overlay with higher |
2480 | priority overrides those with lower priority. @xref{Overlays}. | |
b8d4c8d0 GM |
2481 | |
2482 | @item | |
d466a866 CY |
2483 | If the text contains a @code{face} or @code{mouse-face} property, |
2484 | Emacs applies the specified faces and face attributes. @xref{Special | |
2485 | Properties}. (This is how Font Lock mode faces are applied. | |
2486 | @xref{Font Lock Mode}.) | |
b8d4c8d0 GM |
2487 | |
2488 | @item | |
d466a866 CY |
2489 | If the text lies within the mode line of the selected window, Emacs |
2490 | applies the @code{mode-line} face. For the mode line of a | |
2491 | non-selected window, Emacs applies the @code{mode-line-inactive} face. | |
2492 | For a header line, Emacs applies the @code{header-line} face. | |
b8d4c8d0 GM |
2493 | |
2494 | @item | |
d466a866 CY |
2495 | If any given attribute has not been specified during the preceding |
2496 | steps, Emacs applies the attribute of the @code{default} face. | |
b8d4c8d0 GM |
2497 | @end itemize |
2498 | ||
2499 | If these various sources together specify more than one face for a | |
2500 | particular character, Emacs merges the attributes of the various faces | |
d466a866 | 2501 | specified. For each attribute, Emacs tries using the above order |
fb5b8aca CY |
2502 | (i.e.@: first the face of any special glyph; then the face for region |
2503 | highlighting, if appropriate; and so on). | |
b8d4c8d0 | 2504 | |
d466a866 CY |
2505 | @node Face Remapping |
2506 | @subsection Face Remapping | |
f2cec7a9 | 2507 | |
d466a866 | 2508 | The variable @code{face-remapping-alist} is used for buffer-local or |
fb5b8aca CY |
2509 | global changes in the appearance of a face. For instance, it is used |
2510 | to implement the @code{text-scale-adjust} command (@pxref{Text | |
2511 | Scale,,, emacs, The GNU Emacs Manual}). | |
f2cec7a9 | 2512 | |
d466a866 | 2513 | @defvar face-remapping-alist |
fb5b8aca CY |
2514 | The value of this variable is an alist whose elements have the form |
2515 | @code{(@var{face} . @var{remapping})}. This causes Emacs to display | |
2516 | any text having the face @var{face} with @var{remapping}, rather than | |
2517 | the ordinary definition of @var{face}. @var{remapping} may be any | |
2518 | face specification suitable for a @code{face} text property: either a | |
2519 | face name, or a property list of attribute/value pairs, or a list in | |
2520 | which each element is either a face name or a property list | |
2521 | (@pxref{Special Properties}). | |
d466a866 CY |
2522 | |
2523 | If @code{face-remapping-alist} is buffer-local, its local value takes | |
2524 | effect only within that buffer. | |
f2cec7a9 MB |
2525 | |
2526 | Two points bear emphasizing: | |
2527 | ||
2528 | @enumerate | |
2529 | @item | |
fb5b8aca CY |
2530 | @var{remapping} serves as the complete specification for the remapped |
2531 | face---it replaces the normal definition of @var{face}, instead of | |
2532 | modifying it. | |
f2cec7a9 MB |
2533 | |
2534 | @item | |
fb5b8aca CY |
2535 | If @var{remapping} references the same face name @var{face}, either |
2536 | directly or via the @code{:inherit} attribute of some other face in | |
2537 | @var{remapping}, that reference uses the normal definition of | |
2538 | @var{face}. In other words, the remapping cannot be recursive. | |
f2cec7a9 MB |
2539 | |
2540 | For instance, if the @code{mode-line} face is remapped using this | |
2541 | entry in @code{face-remapping-alist}: | |
2542 | @example | |
2543 | (mode-line italic mode-line) | |
2544 | @end example | |
2545 | @noindent | |
2546 | then the new definition of the @code{mode-line} face inherits from the | |
2547 | @code{italic} face, and the @emph{normal} (non-remapped) definition of | |
2548 | @code{mode-line} face. | |
2549 | @end enumerate | |
d466a866 | 2550 | @end defvar |
f2cec7a9 | 2551 | |
d466a866 | 2552 | The following functions implement a higher-level interface to |
fb5b8aca CY |
2553 | @code{face-remapping-alist}. Most Lisp code should use these |
2554 | functions instead of setting @code{face-remapping-alist} directly, to | |
2555 | avoid trampling on remappings applied elsewhere. These functions are | |
2556 | intended for buffer-local remappings, so they all make | |
2557 | @code{face-remapping-alist} buffer-local as a side-effect. They manage | |
2558 | @code{face-remapping-alist} entries of the form | |
9d3d42fb MB |
2559 | |
2560 | @example | |
fb5b8aca | 2561 | (@var{face} @var{relative-spec-1} @var{relative-spec-2} @var{...} @var{base-spec}) |
9d3d42fb MB |
2562 | @end example |
2563 | ||
fb5b8aca CY |
2564 | @noindent |
2565 | where, as explained above, each of the @var{relative-spec-N} and | |
2566 | @var{base-spec} is either a face name, or a property list of | |
2567 | attribute/value pairs. Each of the @dfn{relative remapping} entries, | |
2568 | @var{relative-spec-N}, is managed by the | |
2569 | @code{face-remap-add-relative} and @code{face-remap-remove-relative} | |
2570 | functions; these are intended for simple modifications like changing | |
2571 | the text size. The @dfn{base remapping} entry, @var{base-spec}, has | |
2572 | the lowest priority and is managed by the @code{face-remap-set-base} | |
2573 | and @code{face-remap-reset-base} functions; it is intended for major | |
2574 | modes to remap faces in the buffers they control. | |
9d3d42fb | 2575 | |
e40a85cd | 2576 | @defun face-remap-add-relative face &rest specs |
fb5b8aca CY |
2577 | This functions adds the face specifications in @var{specs} as relative |
2578 | remappings for face @var{face} in the current buffer. The remaining | |
2579 | arguments, @var{specs}, should form either a list of face names, or a | |
2580 | property list of attribute/value pairs. | |
9d3d42fb | 2581 | |
fb5b8aca CY |
2582 | The return value is a Lisp object that serves as a ``cookie''; you can |
2583 | pass this object as an argument to @code{face-remap-remove-relative} | |
2584 | if you need to remove the remapping later. | |
9d3d42fb | 2585 | |
fb5b8aca CY |
2586 | @example |
2587 | ;; Remap the `escape-glyph' face into a combination | |
2588 | ;; of the `highlight' and `italic' faces: | |
2589 | (face-remap-add-relative 'escape-glyph 'highlight 'italic) | |
2590 | ||
2591 | ;; Increase the size of the `default' face by 50%: | |
2592 | (face-remap-add-relative 'default :height 1.5) | |
2593 | @end example | |
9d3d42fb MB |
2594 | @end defun |
2595 | ||
e40a85cd | 2596 | @defun face-remap-remove-relative cookie |
fb5b8aca CY |
2597 | This function removes a relative remapping previously added by |
2598 | @code{face-remap-add-relative}. @var{cookie} should be the Lisp | |
2599 | object returned by @code{face-remap-add-relative} when the remapping | |
2600 | was added. | |
9d3d42fb MB |
2601 | @end defun |
2602 | ||
e40a85cd | 2603 | @defun face-remap-set-base face &rest specs |
fb5b8aca | 2604 | This function sets the base remapping of @var{face} in the current |
9d3d42fb | 2605 | buffer to @var{specs}. If @var{specs} is empty, the default base |
fb5b8aca CY |
2606 | remapping is restored, similar to calling @code{face-remap-reset-base} |
2607 | (see below); note that this is different from @var{specs} containing a | |
9d3d42fb MB |
2608 | single value @code{nil}, which has the opposite result (the global |
2609 | definition of @var{face} is ignored). | |
fb5b8aca CY |
2610 | |
2611 | This overwrites the default @var{base-spec}, which inherits the global | |
2612 | face definition, so it is up to the caller to add such inheritance if | |
2613 | so desired. | |
9d3d42fb MB |
2614 | @end defun |
2615 | ||
e40a85cd | 2616 | @defun face-remap-reset-base face |
fb5b8aca | 2617 | This function sets the base remapping of @var{face} to its default |
9d3d42fb MB |
2618 | value, which inherits from @var{face}'s global definition. |
2619 | @end defun | |
2620 | ||
9185bf49 CY |
2621 | @node Face Functions |
2622 | @subsection Functions for Working with Faces | |
2623 | ||
2624 | Here are additional functions for creating and working with faces. | |
2625 | ||
9185bf49 | 2626 | @defun face-list |
fb5b8aca | 2627 | This function returns a list of all defined face names. |
9185bf49 CY |
2628 | @end defun |
2629 | ||
2630 | @defun face-id face | |
2631 | This function returns the @dfn{face number} of face @var{face}. This | |
2632 | is a number that uniquely identifies a face at low levels within | |
2633 | Emacs. It is seldom necessary to refer to a face by its face number. | |
2634 | @end defun | |
2635 | ||
2636 | @defun face-documentation face | |
2637 | This function returns the documentation string of face @var{face}, or | |
2638 | @code{nil} if none was specified for it. | |
2639 | @end defun | |
2640 | ||
2641 | @defun face-equal face1 face2 &optional frame | |
2642 | This returns @code{t} if the faces @var{face1} and @var{face2} have the | |
2643 | same attributes for display. | |
2644 | @end defun | |
2645 | ||
2646 | @defun face-differs-from-default-p face &optional frame | |
2647 | This returns non-@code{nil} if the face @var{face} displays | |
2648 | differently from the default face. | |
2649 | @end defun | |
2650 | ||
2651 | @cindex face alias | |
2652 | A @dfn{face alias} provides an equivalent name for a face. You can | |
2653 | define a face alias by giving the alias symbol the @code{face-alias} | |
2654 | property, with a value of the target face name. The following example | |
2655 | makes @code{modeline} an alias for the @code{mode-line} face. | |
2656 | ||
2657 | @example | |
2658 | (put 'modeline 'face-alias 'mode-line) | |
2659 | @end example | |
2660 | ||
e7e2f529 GM |
2661 | @defun define-obsolete-face-alias obsolete-face current-face &optional when |
2662 | This function defines a face alias and marks it as obsolete, indicating | |
2663 | that it may be removed in future. The optional string @var{when} | |
2664 | indicates when the face was made obsolete (for example, a release number). | |
2665 | @end defun | |
2666 | ||
9185bf49 CY |
2667 | @node Auto Faces |
2668 | @subsection Automatic Face Assignment | |
2669 | @cindex automatic face assignment | |
2670 | @cindex faces, automatic choice | |
2671 | ||
2672 | This hook is used for automatically assigning faces to text in the | |
2673 | buffer. It is part of the implementation of Jit-Lock mode, used by | |
2674 | Font-Lock. | |
2675 | ||
2676 | @defvar fontification-functions | |
2677 | This variable holds a list of functions that are called by Emacs | |
c02f8fe2 AM |
2678 | redisplay as needed, just before doing redisplay. They are called even |
2679 | when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this | |
2680 | variable usually holds just one function, @code{jit-lock-function}. | |
9185bf49 CY |
2681 | |
2682 | The functions are called in the order listed, with one argument, a | |
c02f8fe2 AM |
2683 | buffer position @var{pos}. Collectively they should attempt to assign |
2684 | faces to the text in the current buffer starting at @var{pos}. | |
9185bf49 | 2685 | |
c02f8fe2 AM |
2686 | The functions should record the faces they assign by setting the |
2687 | @code{face} property. They should also add a non-@code{nil} | |
2688 | @code{fontified} property to all the text they have assigned faces to. | |
9185bf49 CY |
2689 | That property tells redisplay that faces have been assigned to that text |
2690 | already. | |
2691 | ||
c02f8fe2 | 2692 | It is probably a good idea for the functions to do nothing if the |
9185bf49 CY |
2693 | character after @var{pos} already has a non-@code{nil} @code{fontified} |
2694 | property, but this is not required. If one function overrides the | |
c02f8fe2 AM |
2695 | assignments made by a previous one, the properties after the last |
2696 | function finishes are the ones that really matter. | |
9185bf49 CY |
2697 | |
2698 | For efficiency, we recommend writing these functions so that they | |
2699 | usually assign faces to around 400 to 600 characters at each call. | |
2700 | @end defvar | |
2701 | ||
35137ed3 CY |
2702 | @node Basic Faces |
2703 | @subsection Basic Faces | |
2704 | ||
2705 | If your Emacs Lisp program needs to assign some faces to text, it is | |
2706 | often a good idea to use certain existing faces or inherit from them, | |
2707 | rather than defining entirely new faces. This way, if other users | |
2708 | have customized the basic faces to give Emacs a certain look, your | |
2709 | program will ``fit in'' without additional customization. | |
2710 | ||
2711 | Some of the basic faces defined in Emacs are listed below. In | |
2712 | addition to these, you might want to make use of the Font Lock faces | |
2713 | for syntactic highlighting, if highlighting is not already handled by | |
2714 | Font Lock mode, or if some Font Lock faces are not in use. | |
2715 | @xref{Faces for Font Lock}. | |
2716 | ||
2717 | @table @code | |
2718 | @item default | |
2719 | The default face, whose attributes are all specified. All other faces | |
2720 | implicitly inherit from it: any unspecified attribute defaults to the | |
2721 | attribute on this face (@pxref{Face Attributes}). | |
2722 | ||
2723 | @item bold | |
2724 | @itemx italic | |
2725 | @itemx bold-italic | |
2726 | @itemx underline | |
2727 | @itemx fixed-pitch | |
2728 | @itemx variable-pitch | |
2729 | These have the attributes indicated by their names (e.g. @code{bold} | |
2730 | has a bold @code{:weight} attribute), with all other attributes | |
2731 | unspecified (and so given by @code{default}). | |
2732 | ||
2733 | @item shadow | |
2734 | For ``dimmed out'' text. For example, it is used for the ignored | |
2735 | part of a filename in the minibuffer (@pxref{Minibuffer File,, | |
2736 | Minibuffers for File Names, emacs, The GNU Emacs Manual}). | |
2737 | ||
2738 | @item link | |
2739 | @itemx link-visited | |
2740 | For clickable text buttons that send the user to a different | |
2741 | buffer or ``location''. | |
2742 | ||
2743 | @item highlight | |
2744 | For stretches of text that should temporarily stand out. For example, | |
2745 | it is commonly assigned to the @code{mouse-face} property for cursor | |
2746 | highlighting (@pxref{Special Properties}). | |
2747 | ||
2748 | @item match | |
2749 | For text matching a search command. | |
2750 | ||
2751 | @item error | |
2752 | @itemx warning | |
2753 | @itemx success | |
2754 | For text concerning errors, warnings, or successes. For example, | |
2755 | these are used for messages in @samp{*Compilation*} buffers. | |
2756 | @end table | |
2757 | ||
c2aa555a CY |
2758 | @node Font Selection |
2759 | @subsection Font Selection | |
9185bf49 | 2760 | |
fb5b8aca | 2761 | Before Emacs can draw a character on a graphical display, it must |
9185bf49 CY |
2762 | select a @dfn{font} for that character@footnote{In this context, the |
2763 | term @dfn{font} has nothing to do with Font Lock (@pxref{Font Lock | |
b7527639 CY |
2764 | Mode}).}. @xref{Fonts,,, emacs, The GNU Emacs Manual}. Normally, |
2765 | Emacs automatically chooses a font based on the faces assigned to that | |
2766 | character---specifically, the face attributes @code{:family}, | |
2767 | @code{:weight}, @code{:slant}, and @code{:width} (@pxref{Face | |
2768 | Attributes}). The choice of font also depends on the character to be | |
2769 | displayed; some fonts can only display a limited set of characters. | |
2770 | If no available font exactly fits the requirements, Emacs looks for | |
2771 | the @dfn{closest matching font}. The variables in this section | |
2772 | control how Emacs makes this selection. | |
9185bf49 | 2773 | |
01f17ae2 | 2774 | @defopt face-font-family-alternatives |
c2aa555a CY |
2775 | If a given family is specified but does not exist, this variable |
2776 | specifies alternative font families to try. Each element should have | |
2777 | this form: | |
9185bf49 | 2778 | |
c2aa555a CY |
2779 | @example |
2780 | (@var{family} @var{alternate-families}@dots{}) | |
2781 | @end example | |
b8d4c8d0 | 2782 | |
c2aa555a CY |
2783 | If @var{family} is specified but not available, Emacs will try the other |
2784 | families given in @var{alternate-families}, one by one, until it finds a | |
2785 | family that does exist. | |
01f17ae2 | 2786 | @end defopt |
b8d4c8d0 | 2787 | |
01f17ae2 | 2788 | @defopt face-font-selection-order |
c2aa555a CY |
2789 | If there is no font that exactly matches all desired face attributes |
2790 | (@code{:width}, @code{:height}, @code{:weight}, and @code{:slant}), | |
2791 | this variable specifies the order in which these attributes should be | |
2792 | considered when selecting the closest matching font. The value should | |
2793 | be a list containing those four attribute symbols, in order of | |
2794 | decreasing importance. The default is @code{(:width :height :weight | |
2795 | :slant)}. | |
b8d4c8d0 GM |
2796 | |
2797 | Font selection first finds the best available matches for the first | |
c2aa555a CY |
2798 | attribute in the list; then, among the fonts which are best in that |
2799 | way, it searches for the best matches in the second attribute, and so | |
2800 | on. | |
b8d4c8d0 GM |
2801 | |
2802 | The attributes @code{:weight} and @code{:width} have symbolic values in | |
2803 | a range centered around @code{normal}. Matches that are more extreme | |
2804 | (farther from @code{normal}) are somewhat preferred to matches that are | |
2805 | less extreme (closer to @code{normal}); this is designed to ensure that | |
2806 | non-normal faces contrast with normal ones, whenever possible. | |
2807 | ||
b8d4c8d0 GM |
2808 | One example of a case where this variable makes a difference is when the |
2809 | default font has no italic equivalent. With the default ordering, the | |
2810 | @code{italic} face will use a non-italic font that is similar to the | |
2811 | default one. But if you put @code{:slant} before @code{:height}, the | |
2812 | @code{italic} face will use an italic font, even if its height is not | |
2813 | quite right. | |
01f17ae2 | 2814 | @end defopt |
b8d4c8d0 | 2815 | |
01f17ae2 | 2816 | @defopt face-font-registry-alternatives |
b8d4c8d0 GM |
2817 | This variable lets you specify alternative font registries to try, if a |
2818 | given registry is specified and doesn't exist. Each element should have | |
2819 | this form: | |
2820 | ||
2821 | @example | |
2822 | (@var{registry} @var{alternate-registries}@dots{}) | |
2823 | @end example | |
2824 | ||
2825 | If @var{registry} is specified but not available, Emacs will try the | |
2826 | other registries given in @var{alternate-registries}, one by one, | |
2827 | until it finds a registry that does exist. | |
01f17ae2 | 2828 | @end defopt |
b8d4c8d0 GM |
2829 | |
2830 | Emacs can make use of scalable fonts, but by default it does not use | |
c2aa555a | 2831 | them. |
b8d4c8d0 | 2832 | |
01f17ae2 | 2833 | @defopt scalable-fonts-allowed |
b8d4c8d0 GM |
2834 | This variable controls which scalable fonts to use. A value of |
2835 | @code{nil}, the default, means do not use scalable fonts. @code{t} | |
2836 | means to use any scalable font that seems appropriate for the text. | |
2837 | ||
2838 | Otherwise, the value must be a list of regular expressions. Then a | |
2839 | scalable font is enabled for use if its name matches any regular | |
2840 | expression in the list. For example, | |
2841 | ||
2842 | @example | |
2843 | (setq scalable-fonts-allowed '("muleindian-2$")) | |
2844 | @end example | |
2845 | ||
2846 | @noindent | |
2847 | allows the use of scalable fonts with registry @code{muleindian-2}. | |
01f17ae2 | 2848 | @end defopt |
b8d4c8d0 GM |
2849 | |
2850 | @defvar face-font-rescale-alist | |
2851 | This variable specifies scaling for certain faces. Its value should | |
2852 | be a list of elements of the form | |
2853 | ||
2854 | @example | |
2855 | (@var{fontname-regexp} . @var{scale-factor}) | |
2856 | @end example | |
2857 | ||
2858 | If @var{fontname-regexp} matches the font name that is about to be | |
2859 | used, this says to choose a larger similar font according to the | |
2860 | factor @var{scale-factor}. You would use this feature to normalize | |
2861 | the font size if certain fonts are bigger or smaller than their | |
2862 | nominal heights and widths would suggest. | |
2863 | @end defvar | |
2864 | ||
b8d4c8d0 GM |
2865 | @node Font Lookup |
2866 | @subsection Looking Up Fonts | |
2867 | ||
803ee7b9 | 2868 | @defun x-list-fonts name &optional reference-face frame maximum width |
b8d4c8d0 | 2869 | This function returns a list of available font names that match |
c2aa555a | 2870 | @var{name}. @var{name} should be a string containing a font name in |
969aa734 CY |
2871 | either the Fontconfig, GTK, or XLFD format (@pxref{Fonts,,, emacs, The |
2872 | GNU Emacs Manual}). Within an XLFD string, wildcard characters may be | |
2873 | used: the @samp{*} character matches any substring, and the @samp{?} | |
2874 | character matches any single character. Case is ignored when matching | |
2875 | font names. | |
c2aa555a CY |
2876 | |
2877 | If the optional arguments @var{reference-face} and @var{frame} are | |
2878 | specified, the returned list includes only fonts that are the same | |
2879 | size as @var{reference-face} (a face name) currently is on the frame | |
2880 | @var{frame}. | |
b8d4c8d0 GM |
2881 | |
2882 | The optional argument @var{maximum} sets a limit on how many fonts to | |
c2aa555a CY |
2883 | return. If it is non-@code{nil}, then the return value is truncated |
2884 | after the first @var{maximum} matching fonts. Specifying a small | |
2885 | value for @var{maximum} can make this function much faster, in cases | |
2886 | where many fonts match the pattern. | |
803ee7b9 CY |
2887 | |
2888 | The optional argument @var{width} specifies a desired font width. If | |
2889 | it is non-@code{nil}, the function only returns those fonts whose | |
2890 | characters are (on average) @var{width} times as wide as | |
2891 | @var{reference-face}. | |
b8d4c8d0 GM |
2892 | @end defun |
2893 | ||
2894 | @defun x-family-fonts &optional family frame | |
2895 | This function returns a list describing the available fonts for family | |
2896 | @var{family} on @var{frame}. If @var{family} is omitted or @code{nil}, | |
2897 | this list applies to all families, and therefore, it contains all | |
2898 | available fonts. Otherwise, @var{family} must be a string; it may | |
2899 | contain the wildcards @samp{?} and @samp{*}. | |
2900 | ||
2901 | The list describes the display that @var{frame} is on; if @var{frame} is | |
2902 | omitted or @code{nil}, it applies to the selected frame's display | |
2903 | (@pxref{Input Focus}). | |
2904 | ||
c2aa555a | 2905 | Each element in the list is a vector of the following form: |
b8d4c8d0 GM |
2906 | |
2907 | @example | |
2908 | [@var{family} @var{width} @var{point-size} @var{weight} @var{slant} | |
2909 | @var{fixed-p} @var{full} @var{registry-and-encoding}] | |
2910 | @end example | |
2911 | ||
2912 | The first five elements correspond to face attributes; if you | |
2913 | specify these attributes for a face, it will use this font. | |
2914 | ||
2915 | The last three elements give additional information about the font. | |
2916 | @var{fixed-p} is non-@code{nil} if the font is fixed-pitch. | |
2917 | @var{full} is the full name of the font, and | |
2918 | @var{registry-and-encoding} is a string giving the registry and | |
2919 | encoding of the font. | |
b8d4c8d0 GM |
2920 | @end defun |
2921 | ||
2922 | @defvar font-list-limit | |
2923 | This variable specifies maximum number of fonts to consider in font | |
2924 | matching. The function @code{x-family-fonts} will not return more than | |
2925 | that many fonts, and font selection will consider only that many fonts | |
2926 | when searching a matching font for face attributes. The default is | |
2927 | currently 100. | |
2928 | @end defvar | |
2929 | ||
2930 | @node Fontsets | |
2931 | @subsection Fontsets | |
2932 | ||
2933 | A @dfn{fontset} is a list of fonts, each assigned to a range of | |
2934 | character codes. An individual font cannot display the whole range of | |
2935 | characters that Emacs supports, but a fontset can. Fontsets have names, | |
2936 | just as fonts do, and you can use a fontset name in place of a font name | |
2937 | when you specify the ``font'' for a frame or a face. Here is | |
2938 | information about defining a fontset under Lisp program control. | |
2939 | ||
2940 | @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror | |
2941 | This function defines a new fontset according to the specification | |
2942 | string @var{fontset-spec}. The string should have this format: | |
2943 | ||
2944 | @smallexample | |
7b753744 | 2945 | @var{fontpattern}, @r{[}@var{charset}:@var{font}@r{]@dots{}} |
b8d4c8d0 GM |
2946 | @end smallexample |
2947 | ||
2948 | @noindent | |
2949 | Whitespace characters before and after the commas are ignored. | |
2950 | ||
2951 | The first part of the string, @var{fontpattern}, should have the form of | |
2952 | a standard X font name, except that the last two fields should be | |
2953 | @samp{fontset-@var{alias}}. | |
2954 | ||
2955 | The new fontset has two names, one long and one short. The long name is | |
2956 | @var{fontpattern} in its entirety. The short name is | |
2957 | @samp{fontset-@var{alias}}. You can refer to the fontset by either | |
2958 | name. If a fontset with the same name already exists, an error is | |
2959 | signaled, unless @var{noerror} is non-@code{nil}, in which case this | |
2960 | function does nothing. | |
2961 | ||
2962 | If optional argument @var{style-variant-p} is non-@code{nil}, that says | |
2963 | to create bold, italic and bold-italic variants of the fontset as well. | |
2964 | These variant fontsets do not have a short name, only a long one, which | |
2965 | is made by altering @var{fontpattern} to indicate the bold or italic | |
2966 | status. | |
2967 | ||
2968 | The specification string also says which fonts to use in the fontset. | |
2969 | See below for the details. | |
2970 | @end defun | |
2971 | ||
2972 | The construct @samp{@var{charset}:@var{font}} specifies which font to | |
2973 | use (in this fontset) for one particular character set. Here, | |
2974 | @var{charset} is the name of a character set, and @var{font} is the font | |
2975 | to use for that character set. You can use this construct any number of | |
2976 | times in the specification string. | |
2977 | ||
2978 | For the remaining character sets, those that you don't specify | |
2979 | explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces | |
2980 | @samp{fontset-@var{alias}} with a value that names one character set. | |
2981 | For the @acronym{ASCII} character set, @samp{fontset-@var{alias}} is replaced | |
2982 | with @samp{ISO8859-1}. | |
2983 | ||
2984 | In addition, when several consecutive fields are wildcards, Emacs | |
2985 | collapses them into a single wildcard. This is to prevent use of | |
2986 | auto-scaled fonts. Fonts made by scaling larger fonts are not usable | |
2987 | for editing, and scaling a smaller font is not useful because it is | |
2988 | better to use the smaller font in its own size, which Emacs does. | |
2989 | ||
2990 | Thus if @var{fontpattern} is this, | |
2991 | ||
2992 | @example | |
2993 | -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24 | |
2994 | @end example | |
2995 | ||
2996 | @noindent | |
2997 | the font specification for @acronym{ASCII} characters would be this: | |
2998 | ||
2999 | @example | |
3000 | -*-fixed-medium-r-normal-*-24-*-ISO8859-1 | |
3001 | @end example | |
3002 | ||
3003 | @noindent | |
3004 | and the font specification for Chinese GB2312 characters would be this: | |
3005 | ||
3006 | @example | |
3007 | -*-fixed-medium-r-normal-*-24-*-gb2312*-* | |
3008 | @end example | |
3009 | ||
3010 | You may not have any Chinese font matching the above font | |
3011 | specification. Most X distributions include only Chinese fonts that | |
3012 | have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In | |
3013 | such a case, @samp{Fontset-@var{n}} can be specified as below: | |
3014 | ||
3015 | @smallexample | |
3016 | Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\ | |
3017 | chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-* | |
3018 | @end smallexample | |
3019 | ||
3020 | @noindent | |
3021 | Then, the font specifications for all but Chinese GB2312 characters have | |
3022 | @samp{fixed} in the @var{family} field, and the font specification for | |
3023 | Chinese GB2312 characters has a wild card @samp{*} in the @var{family} | |
3024 | field. | |
3025 | ||
d6eb4e25 KH |
3026 | @defun set-fontset-font name character font-spec &optional frame add |
3027 | This function modifies the existing fontset @var{name} to use the font | |
3028 | matching with @var{font-spec} for the character @var{character}. | |
b8d4c8d0 | 3029 | |
d6eb4e25 KH |
3030 | If @var{name} is @code{nil}, this function modifies the fontset of the |
3031 | selected frame or that of @var{frame} if @var{frame} is not | |
3032 | @code{nil}. | |
3033 | ||
3034 | If @var{name} is @code{t}, this function modifies the default | |
b8d4c8d0 GM |
3035 | fontset, whose short name is @samp{fontset-default}. |
3036 | ||
3037 | @var{character} may be a cons; @code{(@var{from} . @var{to})}, where | |
d15c8cce | 3038 | @var{from} and @var{to} are character codepoints. In that case, use |
d6eb4e25 | 3039 | @var{font-spec} for all characters in the range @var{from} and @var{to} |
b8d4c8d0 GM |
3040 | (inclusive). |
3041 | ||
3042 | @var{character} may be a charset. In that case, use | |
d6eb4e25 KH |
3043 | @var{font-spec} for all character in the charsets. |
3044 | ||
664d56b8 | 3045 | @var{character} may be a script name. In that case, use |
d6eb4e25 | 3046 | @var{font-spec} for all character in the charsets. |
b8d4c8d0 | 3047 | |
d6eb4e25 | 3048 | @var{font-spec} may be a cons; @code{(@var{family} . @var{registry})}, |
b8d4c8d0 GM |
3049 | where @var{family} is a family name of a font (possibly including a |
3050 | foundry name at the head), @var{registry} is a registry name of a font | |
3051 | (possibly including an encoding name at the tail). | |
3052 | ||
d6eb4e25 KH |
3053 | @var{font-spec} may be a font name string. |
3054 | ||
3055 | The optional argument @var{add}, if non-@code{nil}, specifies how to | |
3056 | add @var{font-spec} to the font specifications previously set. If it | |
3057 | is @code{prepend}, @var{font-spec} is prepended. If it is | |
3058 | @code{append}, @var{font-spec} is appended. By default, | |
3059 | @var{font-spec} overrides the previous settings. | |
3060 | ||
b8d4c8d0 | 3061 | For instance, this changes the default fontset to use a font of which |
d6eb4e25 | 3062 | family name is @samp{Kochi Gothic} for all characters belonging to |
b8d4c8d0 GM |
3063 | the charset @code{japanese-jisx0208}. |
3064 | ||
3065 | @smallexample | |
d6eb4e25 KH |
3066 | (set-fontset-font t 'japanese-jisx0208 |
3067 | (font-spec :family "Kochi Gothic")) | |
b8d4c8d0 GM |
3068 | @end smallexample |
3069 | @end defun | |
3070 | ||
3071 | @defun char-displayable-p char | |
3072 | This function returns @code{t} if Emacs ought to be able to display | |
3073 | @var{char}. More precisely, if the selected frame's fontset has a | |
3074 | font to display the character set that @var{char} belongs to. | |
3075 | ||
3076 | Fontsets can specify a font on a per-character basis; when the fontset | |
3077 | does that, this function's value may not be accurate. | |
3078 | @end defun | |
3079 | ||
c2aa555a CY |
3080 | @node Low-Level Font |
3081 | @subsection Low-Level Font Representation | |
3082 | ||
3083 | Normally, it is not necessary to manipulate fonts directly. In case | |
3084 | you need to do so, this section explains how. | |
3085 | ||
3086 | In Emacs Lisp, fonts are represented using three different Lisp | |
f19fea97 | 3087 | object types: @dfn{font objects}, @dfn{font specs}, and @dfn{font |
c2aa555a CY |
3088 | entities}. |
3089 | ||
3090 | @defun fontp object &optional type | |
3091 | Return @code{t} if @var{object} is a font object, font spec, or font | |
3092 | entity. Otherwise, return @code{nil}. | |
3093 | ||
3094 | The optional argument @var{type}, if non-@code{nil}, determines the | |
3095 | exact type of Lisp object to check for. In that case, @var{type} | |
3096 | should be one of @code{font-object}, @code{font-spec}, or | |
3097 | @code{font-entity}. | |
3098 | @end defun | |
3099 | ||
3100 | A font object is a Lisp object that represents a font that Emacs has | |
3101 | @dfn{opened}. Font objects cannot be modified in Lisp, but they can | |
0c1cfe01 | 3102 | be inspected. |
c2aa555a CY |
3103 | |
3104 | @defun font-at position &optional window string | |
3105 | Return the font object that is being used to display the character at | |
3106 | position @var{position} in the window @var{window}. If @var{window} | |
3107 | is @code{nil}, it defaults to the selected window. If @var{string} is | |
3108 | @code{nil}, @var{position} specifies a position in the current buffer; | |
3109 | otherwise, @var{string} should be a string, and @var{position} | |
3110 | specifies a position in that string. | |
3111 | @end defun | |
3112 | ||
3113 | A font spec is a Lisp object that contains a set of specifications | |
3114 | that can be used to find a font. More than one font may match the | |
3115 | specifications in a font spec. | |
3116 | ||
3117 | @defun font-spec &rest arguments | |
3118 | Return a new font spec using the specifications in @var{arguments}, | |
3119 | which should come in @code{property}-@code{value} pairs. The possible | |
3120 | specifications are as follows: | |
3121 | ||
3122 | @table @code | |
3123 | @item :name | |
3124 | The font name (a string), in either XLFD, Fontconfig, or GTK format. | |
969aa734 | 3125 | @xref{Fonts,,, emacs, The GNU Emacs Manual}. |
c2aa555a CY |
3126 | |
3127 | @item :family | |
3128 | @itemx :foundry | |
3129 | @itemx :weight | |
3130 | @itemx :slant | |
3131 | @itemx :width | |
3132 | These have the same meanings as the face attributes of the same name. | |
3133 | @xref{Face Attributes}. | |
3134 | ||
3135 | @item :size | |
3136 | The font size---either a non-negative integer that specifies the pixel | |
3137 | size, or a floating point number that specifies the point size. | |
3138 | ||
3139 | @item :adstyle | |
3140 | Additional typographic style information for the font, such as | |
3141 | @samp{sans}. The value should be a string or a symbol. | |
3142 | ||
3143 | @item :registry | |
3144 | The charset registry and encoding of the font, such as | |
3145 | @samp{iso8859-1}. The value should be a string or a symbol. | |
3146 | ||
3147 | @item :script | |
3148 | The script that the font must support (a symbol). | |
a908c79a CY |
3149 | |
3150 | @item :otf | |
3151 | The font must be an OpenType font that supports these OpenType | |
3152 | features, provided Emacs is compiled with support for @samp{libotf} (a | |
3153 | library for performing complex text layout in certain scripts). The | |
3154 | value must be a list of the form | |
3155 | ||
3156 | @smallexample | |
3157 | @code{(@var{script-tag} @var{langsys-tag} @var{gsub} @var{gpos})} | |
3158 | @end smallexample | |
3159 | ||
3160 | where @var{script-tag} is the OpenType script tag symbol; | |
3161 | @var{langsys-tag} is the OpenType language system tag symbol, or | |
3162 | @code{nil} to use the default language system; @code{gsub} is a list | |
3163 | of OpenType GSUB feature tag symbols, or @code{nil} if none is | |
3164 | required; and @code{gpos} is a list of OpenType GPOS feature tag | |
3165 | symbols, or @code{nil} if none is required. If @code{gsub} or | |
3166 | @code{gpos} is a list, a @code{nil} element in that list means that | |
3167 | the font must not match any of the remaining tag symbols. The | |
3168 | @code{gpos} element may be omitted. | |
c2aa555a CY |
3169 | @end table |
3170 | @end defun | |
3171 | ||
3172 | @defun font-put font-spec property value | |
3173 | Set the font property @var{property} in the font-spec @var{font-spec} | |
3174 | to @var{value}. | |
3175 | @end defun | |
3176 | ||
3177 | A font entity is a reference to a font that need not be open. Its | |
3178 | properties are intermediate between a font object and a font spec: | |
3179 | like a font object, and unlike a font spec, it refers to a single, | |
3180 | specific font. Unlike a font object, creating a font entity does not | |
3181 | load the contents of that font into computer memory. | |
3182 | ||
3183 | @defun find-font font-spec &optional frame | |
3184 | This function returns a font entity that best matches the font spec | |
3185 | @var{font-spec} on frame @var{frame}. If @var{frame} is @code{nil}, | |
3186 | it defaults to the selected frame. | |
3187 | @end defun | |
3188 | ||
3189 | @defun list-fonts font-spec &optional frame num prefer | |
3190 | This function returns a list of all font entities that match the font | |
3191 | spec @var{font-spec}. | |
3192 | ||
3193 | The optional argument @var{frame}, if non-@code{nil}, specifies the | |
3194 | frame on which the fonts are to be displayed. The optional argument | |
3195 | @var{num}, if non-@code{nil}, should be an integer that specifies the | |
3196 | maximum length of the returned list. The optional argument | |
3197 | @var{prefer}, if non-@code{nil}, should be another font spec, which is | |
3198 | used to control the order of the returned list; the returned font | |
3199 | entities are sorted in order of decreasing ``closeness'' to that font | |
3200 | spec. | |
3201 | @end defun | |
3202 | ||
0c1cfe01 CY |
3203 | If you call @code{set-face-attribute} and pass a font spec, font |
3204 | entity, or font name string as the value of the @code{:font} | |
3205 | attribute, Emacs opens the best ``matching'' font that is available | |
3206 | for display. It then stores the corresponding font object as the | |
3207 | actual value of the @code{:font} attribute for that face. | |
3208 | ||
c2aa555a CY |
3209 | The following functions can be used to obtain information about a |
3210 | font. For these functions, the @var{font} argument can be a font | |
3211 | object, a font entity, or a font spec. | |
3212 | ||
3213 | @defun font-get font property | |
3214 | This function returns the value of the font property @var{property} | |
3215 | for @var{font}. | |
3216 | ||
3217 | If @var{font} is a font spec and the font spec does not specify | |
3218 | @var{property}, the return value is @code{nil}. If @var{font} is a | |
3219 | font object or font entity, the value for the @var{:script} property | |
3220 | may be a list of scripts supported by the font. | |
3221 | @end defun | |
3222 | ||
3223 | @defun font-face-attributes font &optional frame | |
3224 | This function returns a list of face attributes corresponding to | |
3225 | @var{font}. The optional argument @var{frame} specifies the frame on | |
3226 | which the font is to be displayed. If it is @code{nil}, the selected | |
3227 | frame is used. The return value has the form | |
3228 | ||
3229 | @smallexample | |
3230 | (:family @var{family} :height @var{height} :weight @var{weight} | |
3231 | :slant @var{slant} :width @var{width}) | |
3232 | @end smallexample | |
3233 | ||
3234 | where the values of @var{family}, @var{height}, @var{weight}, | |
3235 | @var{slant}, and @var{width} are face attribute values. Some of these | |
3236 | key-attribute pairs may be omitted from the list if they are not | |
3237 | specified by @var{font}. | |
3238 | @end defun | |
3239 | ||
3240 | @defun font-xlfd-name font &optional fold-wildcards | |
3241 | This function returns the XLFD (X Logical Font Descriptor), a string, | |
969aa734 CY |
3242 | matching @var{font}. @xref{Fonts,,, emacs, The GNU Emacs Manual}, for |
3243 | information about XLFDs. If the name is too long for an XLFD (which | |
3244 | can contain at most 255 characters), the function returns @code{nil}. | |
c2aa555a CY |
3245 | |
3246 | If the optional argument @var{fold-wildcards} is non-@code{nil}, | |
3247 | consecutive wildcards in the XLFD are folded into one. | |
3248 | @end defun | |
3249 | ||
b8d4c8d0 GM |
3250 | @node Fringes |
3251 | @section Fringes | |
3252 | @cindex fringes | |
3253 | ||
9a69676a CY |
3254 | On graphical displays, Emacs draws @dfn{fringes} next to each |
3255 | window: thin vertical strips down the sides which can display bitmaps | |
3256 | indicating truncation, continuation, horizontal scrolling, and so on. | |
b8d4c8d0 GM |
3257 | |
3258 | @menu | |
3259 | * Fringe Size/Pos:: Specifying where to put the window fringes. | |
3260 | * Fringe Indicators:: Displaying indicator icons in the window fringes. | |
3261 | * Fringe Cursors:: Displaying cursors in the right fringe. | |
3262 | * Fringe Bitmaps:: Specifying bitmaps for fringe indicators. | |
3263 | * Customizing Bitmaps:: Specifying your own bitmaps to use in the fringes. | |
3264 | * Overlay Arrow:: Display of an arrow to indicate position. | |
3265 | @end menu | |
3266 | ||
3267 | @node Fringe Size/Pos | |
3268 | @subsection Fringe Size and Position | |
3269 | ||
3270 | The following buffer-local variables control the position and width | |
9a69676a | 3271 | of fringes in windows showing that buffer. |
b8d4c8d0 GM |
3272 | |
3273 | @defvar fringes-outside-margins | |
3274 | The fringes normally appear between the display margins and the window | |
3275 | text. If the value is non-@code{nil}, they appear outside the display | |
3276 | margins. @xref{Display Margins}. | |
3277 | @end defvar | |
3278 | ||
3279 | @defvar left-fringe-width | |
3280 | This variable, if non-@code{nil}, specifies the width of the left | |
3281 | fringe in pixels. A value of @code{nil} means to use the left fringe | |
3282 | width from the window's frame. | |
3283 | @end defvar | |
3284 | ||
3285 | @defvar right-fringe-width | |
3286 | This variable, if non-@code{nil}, specifies the width of the right | |
3287 | fringe in pixels. A value of @code{nil} means to use the right fringe | |
3288 | width from the window's frame. | |
3289 | @end defvar | |
3290 | ||
9a69676a CY |
3291 | Any buffer which does not specify values for these variables uses |
3292 | the values specified by the @code{left-fringe} and @code{right-fringe} | |
3293 | frame parameters (@pxref{Layout Parameters}). | |
3294 | ||
3295 | The above variables actually take effect via the function | |
3296 | @code{set-window-buffer} (@pxref{Buffers and Windows}), which calls | |
3297 | @code{set-window-fringes} as a subroutine. If you change one of these | |
3298 | variables, the fringe display is not updated in existing windows | |
3299 | showing the buffer, unless you call @code{set-window-buffer} again in | |
3300 | each affected window. You can also use @code{set-window-fringes} to | |
3301 | control the fringe display in individual windows. | |
b8d4c8d0 GM |
3302 | |
3303 | @defun set-window-fringes window left &optional right outside-margins | |
3304 | This function sets the fringe widths of window @var{window}. | |
3305 | If @var{window} is @code{nil}, the selected window is used. | |
3306 | ||
3307 | The argument @var{left} specifies the width in pixels of the left | |
3308 | fringe, and likewise @var{right} for the right fringe. A value of | |
3309 | @code{nil} for either one stands for the default width. If | |
3310 | @var{outside-margins} is non-@code{nil}, that specifies that fringes | |
3311 | should appear outside of the display margins. | |
3312 | @end defun | |
3313 | ||
3314 | @defun window-fringes &optional window | |
3315 | This function returns information about the fringes of a window | |
3316 | @var{window}. If @var{window} is omitted or @code{nil}, the selected | |
3317 | window is used. The value has the form @code{(@var{left-width} | |
3318 | @var{right-width} @var{outside-margins})}. | |
3319 | @end defun | |
3320 | ||
3321 | ||
3322 | @node Fringe Indicators | |
3323 | @subsection Fringe Indicators | |
3324 | @cindex fringe indicators | |
3325 | @cindex indicators, fringe | |
3326 | ||
9a69676a CY |
3327 | @dfn{Fringe indicators} are tiny icons displayed in the window |
3328 | fringe to indicate truncated or continued lines, buffer boundaries, | |
3329 | etc. | |
b8d4c8d0 GM |
3330 | |
3331 | @defopt indicate-empty-lines | |
3332 | @cindex fringes, and empty line indication | |
3333 | When this is non-@code{nil}, Emacs displays a special glyph in the | |
3334 | fringe of each empty line at the end of the buffer, on graphical | |
3335 | displays. @xref{Fringes}. This variable is automatically | |
3336 | buffer-local in every buffer. | |
3337 | @end defopt | |
3338 | ||
01f17ae2 | 3339 | @defopt indicate-buffer-boundaries |
b8d4c8d0 GM |
3340 | This buffer-local variable controls how the buffer boundaries and |
3341 | window scrolling are indicated in the window fringes. | |
3342 | ||
3343 | Emacs can indicate the buffer boundaries---that is, the first and last | |
3344 | line in the buffer---with angle icons when they appear on the screen. | |
3345 | In addition, Emacs can display an up-arrow in the fringe to show | |
3346 | that there is text above the screen, and a down-arrow to show | |
3347 | there is text below the screen. | |
3348 | ||
3349 | There are three kinds of basic values: | |
3350 | ||
3351 | @table @asis | |
3352 | @item @code{nil} | |
3353 | Don't display any of these fringe icons. | |
3354 | @item @code{left} | |
3355 | Display the angle icons and arrows in the left fringe. | |
3356 | @item @code{right} | |
3357 | Display the angle icons and arrows in the right fringe. | |
3358 | @item any non-alist | |
3359 | Display the angle icons in the left fringe | |
3360 | and don't display the arrows. | |
3361 | @end table | |
3362 | ||
3363 | Otherwise the value should be an alist that specifies which fringe | |
3364 | indicators to display and where. Each element of the alist should | |
3365 | have the form @code{(@var{indicator} . @var{position})}. Here, | |
3366 | @var{indicator} is one of @code{top}, @code{bottom}, @code{up}, | |
3367 | @code{down}, and @code{t} (which covers all the icons not yet | |
3368 | specified), while @var{position} is one of @code{left}, @code{right} | |
3369 | and @code{nil}. | |
3370 | ||
3371 | For example, @code{((top . left) (t . right))} places the top angle | |
3372 | bitmap in left fringe, and the bottom angle bitmap as well as both | |
3373 | arrow bitmaps in right fringe. To show the angle bitmaps in the left | |
3374 | fringe, and no arrow bitmaps, use @code{((top . left) (bottom . left))}. | |
01f17ae2 | 3375 | @end defopt |
b8d4c8d0 | 3376 | |
b8d4c8d0 GM |
3377 | @defvar fringe-indicator-alist |
3378 | This buffer-local variable specifies the mapping from logical fringe | |
8c6e1920 CY |
3379 | indicators to the actual bitmaps displayed in the window fringes. The |
3380 | value is an alist of elements @code{(@var{indicator} | |
3381 | . @var{bitmaps})}, where @var{indicator} specifies a logical indicator | |
3382 | type and @var{bitmaps} specifies the fringe bitmaps to use for that | |
3383 | indicator. | |
b8d4c8d0 | 3384 | |
8c6e1920 | 3385 | Each @var{indicator} should be one of the following symbols: |
b8d4c8d0 GM |
3386 | |
3387 | @table @asis | |
8c6e1920 CY |
3388 | @item @code{truncation}, @code{continuation}. |
3389 | Used for truncation and continuation lines. | |
3390 | ||
3391 | @item @code{up}, @code{down}, @code{top}, @code{bottom}, @code{top-bottom} | |
d860baa0 CY |
3392 | Used when @code{indicate-buffer-boundaries} is non-@code{nil}: |
3393 | @code{up} and @code{down} indicate a buffer boundary lying above or | |
3394 | below the window edge; @code{top} and @code{bottom} indicate the | |
3395 | topmost and bottommost buffer text line; and @code{top-bottom} | |
3396 | indicates where there is just one line of text in the buffer. | |
8c6e1920 CY |
3397 | |
3398 | @item @code{empty-line} | |
3399 | Used to indicate empty lines when @code{indicate-empty-lines} is | |
3400 | non-@code{nil}. | |
3401 | ||
3402 | @item @code{overlay-arrow} | |
3403 | Used for overlay arrows (@pxref{Overlay Arrow}). | |
3404 | @c Is this used anywhere? | |
3405 | @c @item Unknown bitmap indicator: | |
3406 | @c @code{unknown}. | |
b8d4c8d0 GM |
3407 | @end table |
3408 | ||
8c6e1920 CY |
3409 | Each @var{bitmaps} value may be a list of symbols @code{(@var{left} |
3410 | @var{right} [@var{left1} @var{right1}])}. The @var{left} and | |
3411 | @var{right} symbols specify the bitmaps shown in the left and/or right | |
3412 | fringe, for the specific indicator. @var{left1} and @var{right1} are | |
3413 | specific to the @code{bottom} and @code{top-bottom} indicators, and | |
3414 | are used to indicate that the last text line has no final newline. | |
3415 | Alternatively, @var{bitmaps} may be a single symbol which is used in | |
3416 | both left and right fringes. | |
b8d4c8d0 | 3417 | |
d860baa0 CY |
3418 | @xref{Fringe Bitmaps}, for a list of standard bitmap symbols and how |
3419 | to define your own. In addition, @code{nil} represents the empty | |
3420 | bitmap (i.e.@: an indicator that is not shown). | |
8c6e1920 CY |
3421 | |
3422 | When @code{fringe-indicator-alist} has a buffer-local value, and | |
3423 | there is no bitmap defined for a logical indicator, or the bitmap is | |
3424 | @code{t}, the corresponding value from the default value of | |
3425 | @code{fringe-indicator-alist} is used. | |
3426 | @end defvar | |
3427 | ||
b8d4c8d0 GM |
3428 | @node Fringe Cursors |
3429 | @subsection Fringe Cursors | |
3430 | @cindex fringe cursors | |
3431 | @cindex cursor, fringe | |
3432 | ||
3433 | When a line is exactly as wide as the window, Emacs displays the | |
3434 | cursor in the right fringe instead of using two lines. Different | |
3435 | bitmaps are used to represent the cursor in the fringe depending on | |
3436 | the current buffer's cursor type. | |
3437 | ||
01f17ae2 | 3438 | @defopt overflow-newline-into-fringe |
b8d4c8d0 GM |
3439 | If this is non-@code{nil}, lines exactly as wide as the window (not |
3440 | counting the final newline character) are not continued. Instead, | |
3441 | when point is at the end of the line, the cursor appears in the right | |
3442 | fringe. | |
01f17ae2 | 3443 | @end defopt |
b8d4c8d0 GM |
3444 | |
3445 | @defvar fringe-cursor-alist | |
3446 | This variable specifies the mapping from logical cursor type to the | |
3447 | actual fringe bitmaps displayed in the right fringe. The value is an | |
d860baa0 CY |
3448 | alist where each element has the form @code{(@var{cursor-type} |
3449 | . @var{bitmap})}, which means to use the fringe bitmap @var{bitmap} to | |
3450 | display cursors of type @var{cursor-type}. | |
3451 | ||
3452 | Each @var{cursor-type} should be one of @code{box}, @code{hollow}, | |
3453 | @code{bar}, @code{hbar}, or @code{hollow-small}. The first four have | |
3454 | the same meanings as in the @code{cursor-type} frame parameter | |
3455 | (@pxref{Cursor Parameters}). The @code{hollow-small} type is used | |
3456 | instead of @code{hollow} when the normal @code{hollow-rectangle} | |
3457 | bitmap is too tall to fit on a specific display line. | |
3458 | ||
3459 | Each @var{bitmap} should be a symbol specifying the fringe bitmap to | |
3460 | be displayed for that logical cursor type. | |
3461 | @iftex | |
3462 | See the next subsection for details. | |
3463 | @end iftex | |
3464 | @ifnottex | |
3465 | @xref{Fringe Bitmaps}. | |
3466 | @end ifnottex | |
b8d4c8d0 GM |
3467 | |
3468 | When @code{fringe-cursor-alist} has a buffer-local value, and there is | |
3469 | no bitmap defined for a cursor type, the corresponding value from the | |
4e3b4528 | 3470 | default value of @code{fringes-indicator-alist} is used. |
b8d4c8d0 GM |
3471 | @end defvar |
3472 | ||
b8d4c8d0 GM |
3473 | @node Fringe Bitmaps |
3474 | @subsection Fringe Bitmaps | |
3475 | @cindex fringe bitmaps | |
3476 | @cindex bitmaps, fringe | |
3477 | ||
3478 | The @dfn{fringe bitmaps} are the actual bitmaps which represent the | |
3479 | logical fringe indicators for truncated or continued lines, buffer | |
d860baa0 CY |
3480 | boundaries, overlay arrows, etc. Each bitmap is represented by a |
3481 | symbol. | |
3482 | @iftex | |
3483 | These symbols are referred to by the variables | |
3484 | @code{fringe-indicator-alist} and @code{fringe-cursor-alist}, | |
3485 | described in the previous subsections. | |
3486 | @end iftex | |
3487 | @ifnottex | |
3488 | These symbols are referred to by the variable | |
3489 | @code{fringe-indicator-alist}, which maps fringe indicators to bitmaps | |
3490 | (@pxref{Fringe Indicators}), and the variable | |
3491 | @code{fringe-cursor-alist}, which maps fringe cursors to bitmaps | |
3492 | (@pxref{Fringe Cursors}). | |
3493 | @end ifnottex | |
3494 | ||
3495 | Lisp programs can also directly display a bitmap in the left or | |
3496 | right fringe, by using a @code{display} property for one of the | |
3497 | characters appearing in the line (@pxref{Other Display Specs}). Such | |
3498 | a display specification has the form | |
3499 | ||
3500 | @example | |
9a69676a | 3501 | (@var{fringe} @var{bitmap} [@var{face}]) |
d860baa0 CY |
3502 | @end example |
3503 | ||
3504 | @noindent | |
9a69676a CY |
3505 | @var{fringe} is either the symbol @code{left-fringe} or |
3506 | @code{right-fringe}. @var{bitmap} is a symbol identifying the bitmap | |
3507 | to display. The optional @var{face} names a face whose foreground | |
3508 | color is used to display the bitmap; this face is automatically merged | |
3509 | with the @code{fringe} face. | |
d860baa0 CY |
3510 | |
3511 | Here is a list of the standard fringe bitmaps defined in Emacs, and | |
3512 | how they are currently used in Emacs (via | |
3513 | @code{fringe-indicator-alist} and @code{fringe-cursor-alist}): | |
3514 | ||
3515 | @table @asis | |
3516 | @item @code{left-arrow}, @code{right-arrow} | |
3517 | Used to indicate truncated lines. | |
3518 | ||
3519 | @item @code{left-curly-arrow}, @code{right-curly-arrow} | |
3520 | Used to indicate continued lines. | |
3521 | ||
3522 | @item @code{right-triangle}, @code{left-triangle} | |
3523 | The former is used by overlay arrows. The latter is unused. | |
3524 | ||
3525 | @item @code{up-arrow}, @code{down-arrow}, @code{top-left-angle} @code{top-right-angle} | |
3526 | @itemx @code{bottom-left-angle}, @code{bottom-right-angle} | |
3527 | @itemx @code{top-right-angle}, @code{top-left-angle} | |
3528 | @itemx @code{left-bracket}, @code{right-bracket}, @code{top-right-angle}, @code{top-left-angle} | |
3529 | Used to indicate buffer boundaries. | |
3530 | ||
3531 | @item @code{filled-rectangle}, @code{hollow-rectangle} | |
3532 | @itemx @code{filled-square}, @code{hollow-square} | |
3533 | @itemx @code{vertical-bar}, @code{horizontal-bar} | |
3534 | Used for different types of fringe cursors. | |
3535 | ||
3536 | @item @code{empty-line}, @code{question-mark} | |
3537 | Unused. | |
3538 | @end table | |
3539 | ||
3540 | @noindent | |
3541 | The next subsection describes how to define your own fringe bitmaps. | |
b8d4c8d0 GM |
3542 | |
3543 | @defun fringe-bitmaps-at-pos &optional pos window | |
3544 | This function returns the fringe bitmaps of the display line | |
3545 | containing position @var{pos} in window @var{window}. The return | |
3546 | value has the form @code{(@var{left} @var{right} @var{ov})}, where @var{left} | |
3547 | is the symbol for the fringe bitmap in the left fringe (or @code{nil} | |
3548 | if no bitmap), @var{right} is similar for the right fringe, and @var{ov} | |
3549 | is non-@code{nil} if there is an overlay arrow in the left fringe. | |
3550 | ||
3551 | The value is @code{nil} if @var{pos} is not visible in @var{window}. | |
3552 | If @var{window} is @code{nil}, that stands for the selected window. | |
3553 | If @var{pos} is @code{nil}, that stands for the value of point in | |
3554 | @var{window}. | |
3555 | @end defun | |
3556 | ||
3557 | @node Customizing Bitmaps | |
3558 | @subsection Customizing Fringe Bitmaps | |
3559 | ||
3560 | @defun define-fringe-bitmap bitmap bits &optional height width align | |
3561 | This function defines the symbol @var{bitmap} as a new fringe bitmap, | |
3562 | or replaces an existing bitmap with that name. | |
3563 | ||
3564 | The argument @var{bits} specifies the image to use. It should be | |
3565 | either a string or a vector of integers, where each element (an | |
3566 | integer) corresponds to one row of the bitmap. Each bit of an integer | |
3567 | corresponds to one pixel of the bitmap, where the low bit corresponds | |
3568 | to the rightmost pixel of the bitmap. | |
3569 | ||
3570 | The height is normally the length of @var{bits}. However, you | |
3571 | can specify a different height with non-@code{nil} @var{height}. The width | |
3572 | is normally 8, but you can specify a different width with non-@code{nil} | |
3573 | @var{width}. The width must be an integer between 1 and 16. | |
3574 | ||
3575 | The argument @var{align} specifies the positioning of the bitmap | |
3576 | relative to the range of rows where it is used; the default is to | |
3577 | center the bitmap. The allowed values are @code{top}, @code{center}, | |
3578 | or @code{bottom}. | |
3579 | ||
3580 | The @var{align} argument may also be a list @code{(@var{align} | |
3581 | @var{periodic})} where @var{align} is interpreted as described above. | |
3582 | If @var{periodic} is non-@code{nil}, it specifies that the rows in | |
3583 | @code{bits} should be repeated enough times to reach the specified | |
3584 | height. | |
3585 | @end defun | |
3586 | ||
3587 | @defun destroy-fringe-bitmap bitmap | |
3588 | This function destroy the fringe bitmap identified by @var{bitmap}. | |
3589 | If @var{bitmap} identifies a standard fringe bitmap, it actually | |
3590 | restores the standard definition of that bitmap, instead of | |
3591 | eliminating it entirely. | |
3592 | @end defun | |
3593 | ||
3594 | @defun set-fringe-bitmap-face bitmap &optional face | |
3595 | This sets the face for the fringe bitmap @var{bitmap} to @var{face}. | |
3596 | If @var{face} is @code{nil}, it selects the @code{fringe} face. The | |
3597 | bitmap's face controls the color to draw it in. | |
3598 | ||
3599 | @var{face} is merged with the @code{fringe} face, so normally | |
3600 | @var{face} should specify only the foreground color. | |
3601 | @end defun | |
3602 | ||
3603 | @node Overlay Arrow | |
3604 | @subsection The Overlay Arrow | |
3605 | @c @cindex overlay arrow Duplicates variable names | |
3606 | ||
3607 | The @dfn{overlay arrow} is useful for directing the user's attention | |
3608 | to a particular line in a buffer. For example, in the modes used for | |
3609 | interface to debuggers, the overlay arrow indicates the line of code | |
3610 | about to be executed. This feature has nothing to do with | |
3611 | @dfn{overlays} (@pxref{Overlays}). | |
3612 | ||
3613 | @defvar overlay-arrow-string | |
3614 | This variable holds the string to display to call attention to a | |
3615 | particular line, or @code{nil} if the arrow feature is not in use. | |
3616 | On a graphical display the contents of the string are ignored; instead a | |
3617 | glyph is displayed in the fringe area to the left of the display area. | |
3618 | @end defvar | |
3619 | ||
3620 | @defvar overlay-arrow-position | |
3621 | This variable holds a marker that indicates where to display the overlay | |
3622 | arrow. It should point at the beginning of a line. On a non-graphical | |
3623 | display the arrow text | |
3624 | appears at the beginning of that line, overlaying any text that would | |
3625 | otherwise appear. Since the arrow is usually short, and the line | |
3626 | usually begins with indentation, normally nothing significant is | |
3627 | overwritten. | |
3628 | ||
3629 | The overlay-arrow string is displayed in any given buffer if the value | |
3630 | of @code{overlay-arrow-position} in that buffer points into that | |
3631 | buffer. Thus, it is possible to display multiple overlay arrow strings | |
3632 | by creating buffer-local bindings of @code{overlay-arrow-position}. | |
3633 | However, it is usually cleaner to use | |
3634 | @code{overlay-arrow-variable-list} to achieve this result. | |
3635 | @c !!! overlay-arrow-position: but the overlay string may remain in the display | |
3636 | @c of some other buffer until an update is required. This should be fixed | |
3637 | @c now. Is it? | |
3638 | @end defvar | |
3639 | ||
3640 | You can do a similar job by creating an overlay with a | |
3641 | @code{before-string} property. @xref{Overlay Properties}. | |
3642 | ||
3643 | You can define multiple overlay arrows via the variable | |
3644 | @code{overlay-arrow-variable-list}. | |
3645 | ||
3646 | @defvar overlay-arrow-variable-list | |
3647 | This variable's value is a list of variables, each of which specifies | |
3648 | the position of an overlay arrow. The variable | |
3649 | @code{overlay-arrow-position} has its normal meaning because it is on | |
3650 | this list. | |
3651 | @end defvar | |
3652 | ||
3653 | Each variable on this list can have properties | |
3654 | @code{overlay-arrow-string} and @code{overlay-arrow-bitmap} that | |
a08a07e3 CY |
3655 | specify an overlay arrow string (for text terminals) or fringe bitmap |
3656 | (for graphical terminals) to display at the corresponding overlay | |
3657 | arrow position. If either property is not set, the default | |
b8d4c8d0 GM |
3658 | @code{overlay-arrow-string} or @code{overlay-arrow} fringe indicator |
3659 | is used. | |
3660 | ||
3661 | @node Scroll Bars | |
3662 | @section Scroll Bars | |
3663 | @cindex scroll bars | |
3664 | ||
3665 | Normally the frame parameter @code{vertical-scroll-bars} controls | |
3666 | whether the windows in the frame have vertical scroll bars, and | |
3667 | whether they are on the left or right. The frame parameter | |
3668 | @code{scroll-bar-width} specifies how wide they are (@code{nil} | |
3669 | meaning the default). @xref{Layout Parameters}. | |
3670 | ||
3671 | @defun frame-current-scroll-bars &optional frame | |
3672 | This function reports the scroll bar type settings for frame | |
3673 | @var{frame}. The value is a cons cell | |
3674 | @code{(@var{vertical-type} .@: @var{horizontal-type})}, where | |
3675 | @var{vertical-type} is either @code{left}, @code{right}, or @code{nil} | |
3676 | (which means no scroll bar.) @var{horizontal-type} is meant to | |
3677 | specify the horizontal scroll bar type, but since they are not | |
3678 | implemented, it is always @code{nil}. | |
3679 | @end defun | |
3680 | ||
3681 | @vindex vertical-scroll-bar | |
3682 | You can enable or disable scroll bars for a particular buffer, | |
3683 | by setting the variable @code{vertical-scroll-bar}. This variable | |
3684 | automatically becomes buffer-local when set. The possible values are | |
3685 | @code{left}, @code{right}, @code{t}, which means to use the | |
3686 | frame's default, and @code{nil} for no scroll bar. | |
3687 | ||
3688 | You can also control this for individual windows. Call the function | |
3689 | @code{set-window-scroll-bars} to specify what to do for a specific window: | |
3690 | ||
3691 | @defun set-window-scroll-bars window width &optional vertical-type horizontal-type | |
3692 | This function sets the width and type of scroll bars for window | |
3693 | @var{window}. | |
3694 | ||
3695 | @var{width} specifies the scroll bar width in pixels (@code{nil} means | |
3696 | use the width specified for the frame). @var{vertical-type} specifies | |
3697 | whether to have a vertical scroll bar and, if so, where. The possible | |
3698 | values are @code{left}, @code{right} and @code{nil}, just like the | |
3699 | values of the @code{vertical-scroll-bars} frame parameter. | |
3700 | ||
3701 | The argument @var{horizontal-type} is meant to specify whether and | |
3702 | where to have horizontal scroll bars, but since they are not | |
3703 | implemented, it has no effect. If @var{window} is @code{nil}, the | |
3704 | selected window is used. | |
3705 | @end defun | |
3706 | ||
3707 | @defun window-scroll-bars &optional window | |
3708 | Report the width and type of scroll bars specified for @var{window}. | |
3709 | If @var{window} is omitted or @code{nil}, the selected window is used. | |
3710 | The value is a list of the form @code{(@var{width} | |
3711 | @var{cols} @var{vertical-type} @var{horizontal-type})}. The value | |
3712 | @var{width} is the value that was specified for the width (which may | |
3713 | be @code{nil}); @var{cols} is the number of columns that the scroll | |
3714 | bar actually occupies. | |
3715 | ||
3716 | @var{horizontal-type} is not actually meaningful. | |
3717 | @end defun | |
3718 | ||
3719 | If you don't specify these values for a window with | |
3720 | @code{set-window-scroll-bars}, the buffer-local variables | |
3721 | @code{scroll-bar-mode} and @code{scroll-bar-width} in the buffer being | |
3722 | displayed control the window's vertical scroll bars. The function | |
3723 | @code{set-window-buffer} examines these variables. If you change them | |
3724 | in a buffer that is already visible in a window, you can make the | |
3725 | window take note of the new values by calling @code{set-window-buffer} | |
3726 | specifying the same buffer that is already displayed. | |
3727 | ||
01f17ae2 | 3728 | @defopt scroll-bar-mode |
b8d4c8d0 GM |
3729 | This variable, always local in all buffers, controls whether and where |
3730 | to put scroll bars in windows displaying the buffer. The possible values | |
3731 | are @code{nil} for no scroll bar, @code{left} to put a scroll bar on | |
3732 | the left, and @code{right} to put a scroll bar on the right. | |
01f17ae2 | 3733 | @end defopt |
b8d4c8d0 GM |
3734 | |
3735 | @defun window-current-scroll-bars &optional window | |
3736 | This function reports the scroll bar type for window @var{window}. | |
3737 | If @var{window} is omitted or @code{nil}, the selected window is used. | |
3738 | The value is a cons cell | |
3739 | @code{(@var{vertical-type} .@: @var{horizontal-type})}. Unlike | |
3740 | @code{window-scroll-bars}, this reports the scroll bar type actually | |
3741 | used, once frame defaults and @code{scroll-bar-mode} are taken into | |
3742 | account. | |
3743 | @end defun | |
3744 | ||
3745 | @defvar scroll-bar-width | |
3746 | This variable, always local in all buffers, specifies the width of the | |
3747 | buffer's scroll bars, measured in pixels. A value of @code{nil} means | |
3748 | to use the value specified by the frame. | |
3749 | @end defvar | |
3750 | ||
3751 | @node Display Property | |
3752 | @section The @code{display} Property | |
3753 | @cindex display specification | |
3754 | @kindex display @r{(text property)} | |
3755 | ||
3756 | The @code{display} text property (or overlay property) is used to | |
9a69676a | 3757 | insert images into text, and to control other aspects of how text |
b8d4c8d0 GM |
3758 | displays. The value of the @code{display} property should be a |
3759 | display specification, or a list or vector containing several display | |
fb33e6a9 RS |
3760 | specifications. Display specifications in the same @code{display} |
3761 | property value generally apply in parallel to the text they cover. | |
3762 | ||
3763 | If several sources (overlays and/or a text property) specify values | |
3764 | for the @code{display} property, only one of the values takes effect, | |
3765 | following the rules of @code{get-char-property}. @xref{Examining | |
3766 | Properties}. | |
3767 | ||
3768 | The rest of this section describes several kinds of | |
3769 | display specifications and what they mean. | |
3770 | ||
3771 | @menu | |
3772 | * Replacing Specs:: Display specs that replace the text. | |
3773 | * Specified Space:: Displaying one space with a specified width. | |
3774 | * Pixel Specification:: Specifying space width or height in pixels. | |
61db307f CY |
3775 | * Other Display Specs:: Displaying an image; adjusting the height, |
3776 | spacing, and other properties of text. | |
fb33e6a9 RS |
3777 | * Display Margins:: Displaying text or images to the side of the main text. |
3778 | @end menu | |
3779 | ||
3780 | @node Replacing Specs | |
3781 | @subsection Display Specs That Replace The Text | |
4db6da64 | 3782 | |
9a69676a CY |
3783 | Some kinds of display specifications specify something to display |
3784 | instead of the text that has the property. These are called | |
fb33e6a9 RS |
3785 | @dfn{replacing} display specifications. Emacs does not allow the user |
3786 | to interactively move point into the middle of buffer text that is | |
3787 | replaced in this way. | |
3788 | ||
3789 | If a list of display specifications includes more than one replacing | |
3790 | display specification, the first overrides the rest. Replacing | |
3791 | display specifications make most other display specifications | |
3792 | irrelevant, since those don't apply to the replacement. | |
3793 | ||
3794 | For replacing display specifications, ``the text that has the | |
3795 | property'' means all the consecutive characters that have the same | |
3796 | Lisp object as their @code{display} property; these characters are | |
9a69676a CY |
3797 | replaced as a single unit. If two characters have different Lisp |
3798 | objects as their @code{display} properties (i.e.@: objects which are | |
3799 | not @code{eq}), they are handled separately. | |
b8d4c8d0 | 3800 | |
9a69676a CY |
3801 | Here is an example which illustrates this point. A string serves as |
3802 | a replacing display specification, which replaces the text that has | |
3803 | the property with the specified string (@pxref{Other Display Specs}). | |
3804 | Consider the following function: | |
b8d4c8d0 GM |
3805 | |
3806 | @smallexample | |
3807 | (defun foo () | |
b8d4c8d0 | 3808 | (dotimes (i 5) |
9a69676a CY |
3809 | (let ((string (concat "A")) |
3810 | (start (+ i i (point-min)))) | |
3811 | (put-text-property start (1+ start) 'display string) | |
3812 | (put-text-property start (+ 2 start) 'display string)))) | |
b8d4c8d0 GM |
3813 | @end smallexample |
3814 | ||
3815 | @noindent | |
9a69676a CY |
3816 | This function gives each of the first ten characters in the buffer a |
3817 | @code{display} property which is a string @code{"A"}, but they don't | |
3818 | all get the same string object. The first two characters get the same | |
3819 | string object, so they are replaced with one @samp{A}; the fact that | |
3820 | the display property was assigned in two separate calls to | |
3821 | @code{put-text-property} is irrelevant. Similarly, the next two | |
3822 | characters get a second string (@code{concat} creates a new string | |
3823 | object), so they are replaced with one @samp{A}; and so on. Thus, the | |
3824 | ten characters appear as five A's. | |
b8d4c8d0 | 3825 | |
b8d4c8d0 GM |
3826 | @node Specified Space |
3827 | @subsection Specified Spaces | |
3828 | @cindex spaces, specified height or width | |
3829 | @cindex variable-width spaces | |
3830 | ||
3831 | To display a space of specified width and/or height, use a display | |
3832 | specification of the form @code{(space . @var{props})}, where | |
3833 | @var{props} is a property list (a list of alternating properties and | |
3834 | values). You can put this property on one or more consecutive | |
3835 | characters; a space of the specified height and width is displayed in | |
3836 | place of @emph{all} of those characters. These are the properties you | |
3837 | can use in @var{props} to specify the weight of the space: | |
3838 | ||
3839 | @table @code | |
3840 | @item :width @var{width} | |
3841 | If @var{width} is an integer or floating point number, it specifies | |
3842 | that the space width should be @var{width} times the normal character | |
3843 | width. @var{width} can also be a @dfn{pixel width} specification | |
3844 | (@pxref{Pixel Specification}). | |
3845 | ||
3846 | @item :relative-width @var{factor} | |
3847 | Specifies that the width of the stretch should be computed from the | |
3848 | first character in the group of consecutive characters that have the | |
3849 | same @code{display} property. The space width is the width of that | |
3850 | character, multiplied by @var{factor}. | |
3851 | ||
3852 | @item :align-to @var{hpos} | |
3853 | Specifies that the space should be wide enough to reach @var{hpos}. | |
3854 | If @var{hpos} is a number, it is measured in units of the normal | |
3855 | character width. @var{hpos} can also be a @dfn{pixel width} | |
3856 | specification (@pxref{Pixel Specification}). | |
3857 | @end table | |
3858 | ||
3859 | You should use one and only one of the above properties. You can | |
3860 | also specify the height of the space, with these properties: | |
3861 | ||
3862 | @table @code | |
3863 | @item :height @var{height} | |
3864 | Specifies the height of the space. | |
3865 | If @var{height} is an integer or floating point number, it specifies | |
3866 | that the space height should be @var{height} times the normal character | |
3867 | height. The @var{height} may also be a @dfn{pixel height} specification | |
3868 | (@pxref{Pixel Specification}). | |
3869 | ||
3870 | @item :relative-height @var{factor} | |
3871 | Specifies the height of the space, multiplying the ordinary height | |
3872 | of the text having this display specification by @var{factor}. | |
3873 | ||
3874 | @item :ascent @var{ascent} | |
3875 | If the value of @var{ascent} is a non-negative number no greater than | |
3876 | 100, it specifies that @var{ascent} percent of the height of the space | |
3877 | should be considered as the ascent of the space---that is, the part | |
3878 | above the baseline. The ascent may also be specified in pixel units | |
3879 | with a @dfn{pixel ascent} specification (@pxref{Pixel Specification}). | |
3880 | ||
3881 | @end table | |
3882 | ||
3883 | Don't use both @code{:height} and @code{:relative-height} together. | |
3884 | ||
3885 | The @code{:width} and @code{:align-to} properties are supported on | |
3886 | non-graphic terminals, but the other space properties in this section | |
3887 | are not. | |
3888 | ||
0c95fcf7 EZ |
3889 | Note that space properties are treated as paragraph separators for |
3890 | the purposes of reordering bidirectional text for display. | |
3891 | @xref{Bidirectional Display}, for the details. | |
3892 | ||
b8d4c8d0 GM |
3893 | @node Pixel Specification |
3894 | @subsection Pixel Specification for Spaces | |
3895 | @cindex spaces, pixel specification | |
3896 | ||
3897 | The value of the @code{:width}, @code{:align-to}, @code{:height}, | |
3898 | and @code{:ascent} properties can be a special kind of expression that | |
3899 | is evaluated during redisplay. The result of the evaluation is used | |
3900 | as an absolute number of pixels. | |
3901 | ||
3902 | The following expressions are supported: | |
3903 | ||
3904 | @smallexample | |
3905 | @group | |
3906 | @var{expr} ::= @var{num} | (@var{num}) | @var{unit} | @var{elem} | @var{pos} | @var{image} | @var{form} | |
3907 | @var{num} ::= @var{integer} | @var{float} | @var{symbol} | |
3908 | @var{unit} ::= in | mm | cm | width | height | |
3909 | @end group | |
3910 | @group | |
3911 | @var{elem} ::= left-fringe | right-fringe | left-margin | right-margin | |
3912 | | scroll-bar | text | |
3913 | @var{pos} ::= left | center | right | |
3914 | @var{form} ::= (@var{num} . @var{expr}) | (@var{op} @var{expr} ...) | |
3915 | @var{op} ::= + | - | |
3916 | @end group | |
3917 | @end smallexample | |
3918 | ||
3919 | The form @var{num} specifies a fraction of the default frame font | |
3920 | height or width. The form @code{(@var{num})} specifies an absolute | |
3921 | number of pixels. If @var{num} is a symbol, @var{symbol}, its | |
3922 | buffer-local variable binding is used. | |
3923 | ||
3924 | The @code{in}, @code{mm}, and @code{cm} units specify the number of | |
3925 | pixels per inch, millimeter, and centimeter, respectively. The | |
3926 | @code{width} and @code{height} units correspond to the default width | |
3927 | and height of the current face. An image specification @code{image} | |
3928 | corresponds to the width or height of the image. | |
3929 | ||
049bcbcb CY |
3930 | The elements @code{left-fringe}, @code{right-fringe}, |
3931 | @code{left-margin}, @code{right-margin}, @code{scroll-bar}, and | |
3932 | @code{text} specify to the width of the corresponding area of the | |
3933 | window. | |
b8d4c8d0 GM |
3934 | |
3935 | The @code{left}, @code{center}, and @code{right} positions can be | |
3936 | used with @code{:align-to} to specify a position relative to the left | |
3937 | edge, center, or right edge of the text area. | |
3938 | ||
3939 | Any of the above window elements (except @code{text}) can also be | |
3940 | used with @code{:align-to} to specify that the position is relative to | |
3941 | the left edge of the given area. Once the base offset for a relative | |
3942 | position has been set (by the first occurrence of one of these | |
3943 | symbols), further occurrences of these symbols are interpreted as the | |
3944 | width of the specified area. For example, to align to the center of | |
3945 | the left-margin, use | |
3946 | ||
3947 | @example | |
3948 | :align-to (+ left-margin (0.5 . left-margin)) | |
3949 | @end example | |
3950 | ||
3951 | If no specific base offset is set for alignment, it is always relative | |
3952 | to the left edge of the text area. For example, @samp{:align-to 0} in a | |
3953 | header-line aligns with the first text column in the text area. | |
3954 | ||
3955 | A value of the form @code{(@var{num} . @var{expr})} stands for the | |
3956 | product of the values of @var{num} and @var{expr}. For example, | |
3957 | @code{(2 . in)} specifies a width of 2 inches, while @code{(0.5 . | |
3958 | @var{image})} specifies half the width (or height) of the specified | |
3959 | image. | |
3960 | ||
3961 | The form @code{(+ @var{expr} ...)} adds up the value of the | |
3962 | expressions. The form @code{(- @var{expr} ...)} negates or subtracts | |
3963 | the value of the expressions. | |
3964 | ||
3965 | @node Other Display Specs | |
3966 | @subsection Other Display Specifications | |
3967 | ||
3968 | Here are the other sorts of display specifications that you can use | |
3969 | in the @code{display} text property. | |
3970 | ||
3971 | @table @code | |
3972 | @item @var{string} | |
3973 | Display @var{string} instead of the text that has this property. | |
3974 | ||
3975 | Recursive display specifications are not supported---@var{string}'s | |
3976 | @code{display} properties, if any, are not used. | |
3977 | ||
3978 | @item (image . @var{image-props}) | |
3979 | This kind of display specification is an image descriptor (@pxref{Images}). | |
3980 | When used as a display specification, it means to display the image | |
3981 | instead of the text that has the display specification. | |
3982 | ||
3983 | @item (slice @var{x} @var{y} @var{width} @var{height}) | |
3984 | This specification together with @code{image} specifies a @dfn{slice} | |
3985 | (a partial area) of the image to display. The elements @var{y} and | |
3986 | @var{x} specify the top left corner of the slice, within the image; | |
3987 | @var{width} and @var{height} specify the width and height of the | |
3988 | slice. Integer values are numbers of pixels. A floating point number | |
3989 | in the range 0.0--1.0 stands for that fraction of the width or height | |
3990 | of the entire image. | |
3991 | ||
3992 | @item ((margin nil) @var{string}) | |
3993 | A display specification of this form means to display @var{string} | |
3994 | instead of the text that has the display specification, at the same | |
3995 | position as that text. It is equivalent to using just @var{string}, | |
3996 | but it is done as a special case of marginal display (@pxref{Display | |
3997 | Margins}). | |
3998 | ||
bdef6a77 EZ |
3999 | @item (left-fringe @var{bitmap} @r{[}@var{face}@r{]}) |
4000 | @itemx (right-fringe @var{bitmap} @r{[}@var{face}@r{]}) | |
4001 | This display specification on any character of a line of text causes | |
4002 | the specified @var{bitmap} be displayed in the left or right fringes | |
a2eaa31d EZ |
4003 | for that line, instead of the characters that have the display |
4004 | specification. The optional @var{face} specifies the colors to be | |
bdef6a77 EZ |
4005 | used for the bitmap. @xref{Fringe Bitmaps}, for the details. |
4006 | ||
b8d4c8d0 GM |
4007 | @item (space-width @var{factor}) |
4008 | This display specification affects all the space characters within the | |
4009 | text that has the specification. It displays all of these spaces | |
4010 | @var{factor} times as wide as normal. The element @var{factor} should | |
4011 | be an integer or float. Characters other than spaces are not affected | |
4012 | at all; in particular, this has no effect on tab characters. | |
4013 | ||
4014 | @item (height @var{height}) | |
4015 | This display specification makes the text taller or shorter. | |
4016 | Here are the possibilities for @var{height}: | |
4017 | ||
4018 | @table @asis | |
4019 | @item @code{(+ @var{n})} | |
4020 | This means to use a font that is @var{n} steps larger. A ``step'' is | |
4021 | defined by the set of available fonts---specifically, those that match | |
4022 | what was otherwise specified for this text, in all attributes except | |
4023 | height. Each size for which a suitable font is available counts as | |
4024 | another step. @var{n} should be an integer. | |
4025 | ||
4026 | @item @code{(- @var{n})} | |
4027 | This means to use a font that is @var{n} steps smaller. | |
4028 | ||
4029 | @item a number, @var{factor} | |
4030 | A number, @var{factor}, means to use a font that is @var{factor} times | |
4031 | as tall as the default font. | |
4032 | ||
4033 | @item a symbol, @var{function} | |
4034 | A symbol is a function to compute the height. It is called with the | |
4035 | current height as argument, and should return the new height to use. | |
4036 | ||
4037 | @item anything else, @var{form} | |
4038 | If the @var{height} value doesn't fit the previous possibilities, it is | |
4039 | a form. Emacs evaluates it to get the new height, with the symbol | |
4040 | @code{height} bound to the current specified font height. | |
4041 | @end table | |
4042 | ||
4043 | @item (raise @var{factor}) | |
4044 | This kind of display specification raises or lowers the text | |
4045 | it applies to, relative to the baseline of the line. | |
4046 | ||
4047 | @var{factor} must be a number, which is interpreted as a multiple of the | |
4048 | height of the affected text. If it is positive, that means to display | |
4049 | the characters raised. If it is negative, that means to display them | |
4050 | lower down. | |
4051 | ||
4052 | If the text also has a @code{height} display specification, that does | |
4053 | not affect the amount of raising or lowering, which is based on the | |
4054 | faces used for the text. | |
4055 | @end table | |
4056 | ||
4057 | @c We put all the `@code{(when ...)}' on one line to encourage | |
4058 | @c makeinfo's end-of-sentence heuristics to DTRT. Previously, the dot | |
4059 | @c was at eol; the info file ended up w/ two spaces rendered after it. | |
4060 | You can make any display specification conditional. To do that, | |
4061 | package it in another list of the form | |
4062 | @code{(when @var{condition} . @var{spec})}. | |
4063 | Then the specification @var{spec} applies only when | |
4064 | @var{condition} evaluates to a non-@code{nil} value. During the | |
4065 | evaluation, @code{object} is bound to the string or buffer having the | |
4066 | conditional @code{display} property. @code{position} and | |
4067 | @code{buffer-position} are bound to the position within @code{object} | |
4068 | and the buffer position where the @code{display} property was found, | |
4069 | respectively. Both positions can be different when @code{object} is a | |
4070 | string. | |
4071 | ||
4072 | @node Display Margins | |
4073 | @subsection Displaying in the Margins | |
4074 | @cindex display margins | |
4075 | @cindex margins, display | |
4076 | ||
fb33e6a9 RS |
4077 | A buffer can have blank areas called @dfn{display margins} on the |
4078 | left and on the right. Ordinary text never appears in these areas, | |
4079 | but you can put things into the display margins using the | |
4080 | @code{display} property. There is currently no way to make text or | |
4081 | images in the margin mouse-sensitive. | |
4082 | ||
4083 | The way to display something in the margins is to specify it in a | |
4084 | margin display specification in the @code{display} property of some | |
4085 | text. This is a replacing display specification, meaning that the | |
4086 | text you put it on does not get displayed; the margin display appears, | |
4087 | but that text does not. | |
4088 | ||
4089 | A margin display specification looks like @code{((margin | |
d25ed7db | 4090 | right-margin) @var{spec})} or @code{((margin left-margin) @var{spec})}. |
fb33e6a9 RS |
4091 | Here, @var{spec} is another display specification that says what to |
4092 | display in the margin. Typically it is a string of text to display, | |
4093 | or an image descriptor. | |
4094 | ||
4095 | To display something in the margin @emph{in association with} | |
4096 | certain buffer text, without altering or preventing the display of | |
4097 | that text, put a @code{before-string} property on the text and put the | |
4098 | margin display specification on the contents of the before-string. | |
b8d4c8d0 GM |
4099 | |
4100 | Before the display margins can display anything, you must give | |
4101 | them a nonzero width. The usual way to do that is to set these | |
4102 | variables: | |
4103 | ||
4104 | @defvar left-margin-width | |
4105 | This variable specifies the width of the left margin. | |
4106 | It is buffer-local in all buffers. | |
4107 | @end defvar | |
4108 | ||
4109 | @defvar right-margin-width | |
4110 | This variable specifies the width of the right margin. | |
4111 | It is buffer-local in all buffers. | |
4112 | @end defvar | |
4113 | ||
4114 | Setting these variables does not immediately affect the window. These | |
4115 | variables are checked when a new buffer is displayed in the window. | |
4116 | Thus, you can make changes take effect by calling | |
4117 | @code{set-window-buffer}. | |
4118 | ||
4119 | You can also set the margin widths immediately. | |
4120 | ||
4121 | @defun set-window-margins window left &optional right | |
4122 | This function specifies the margin widths for window @var{window}. | |
4123 | The argument @var{left} controls the left margin and | |
4124 | @var{right} controls the right margin (default @code{0}). | |
4125 | @end defun | |
4126 | ||
4127 | @defun window-margins &optional window | |
4128 | This function returns the left and right margins of @var{window} | |
4129 | as a cons cell of the form @code{(@var{left} . @var{right})}. | |
4130 | If @var{window} is @code{nil}, the selected window is used. | |
4131 | @end defun | |
4132 | ||
4133 | @node Images | |
4134 | @section Images | |
4135 | @cindex images in buffers | |
4136 | ||
4137 | To display an image in an Emacs buffer, you must first create an image | |
4138 | descriptor, then use it as a display specifier in the @code{display} | |
4139 | property of text that is displayed (@pxref{Display Property}). | |
4140 | ||
4141 | Emacs is usually able to display images when it is run on a | |
4142 | graphical terminal. Images cannot be displayed in a text terminal, on | |
4143 | certain graphical terminals that lack the support for this, or if | |
4144 | Emacs is compiled without image support. You can use the function | |
4145 | @code{display-images-p} to determine if images can in principle be | |
4146 | displayed (@pxref{Display Feature Testing}). | |
4147 | ||
4148 | @menu | |
4149 | * Image Formats:: Supported image formats. | |
4150 | * Image Descriptors:: How to specify an image for use in @code{:display}. | |
4151 | * XBM Images:: Special features for XBM format. | |
4152 | * XPM Images:: Special features for XPM format. | |
4153 | * GIF Images:: Special features for GIF format. | |
905a9adb | 4154 | * TIFF Images:: Special features for TIFF format. |
2833b3ff | 4155 | * PostScript Images:: Special features for PostScript format. |
16a91140 | 4156 | * ImageMagick Images:: Special features available through ImageMagick. |
b8d4c8d0 GM |
4157 | * Other Image Types:: Various other formats are supported. |
4158 | * Defining Images:: Convenient ways to define an image for later use. | |
4159 | * Showing Images:: Convenient ways to display an image once it is defined. | |
eea14f31 | 4160 | * Animated Images:: Some image formats can be animated. |
b8d4c8d0 GM |
4161 | * Image Cache:: Internal mechanisms of image display. |
4162 | @end menu | |
4163 | ||
4164 | @node Image Formats | |
4165 | @subsection Image Formats | |
4166 | @cindex image formats | |
4167 | @cindex image types | |
4168 | ||
5319014e CY |
4169 | Emacs can display a number of different image formats. Some of |
4170 | these image formats are supported only if particular support libraries | |
4171 | are installed. On some platforms, Emacs can load support libraries on | |
4172 | demand; if so, the variable @code{dynamic-library-alist} can be used | |
4173 | to modify the set of known names for these dynamic libraries. | |
4174 | @xref{Dynamic Libraries}. | |
4175 | ||
4176 | Supported image formats (and the required support libraries) include | |
4177 | PBM and XBM (which do not depend on support libraries and are always | |
4178 | available), XPM (@code{libXpm}), GIF (@code{libgif} or | |
4179 | @code{libungif}), PostScript (@code{gs}), JPEG (@code{libjpeg}), TIFF | |
4f5a10ef | 4180 | (@code{libtiff}), PNG (@code{libpng}), and SVG (@code{librsvg}). |
b8d4c8d0 | 4181 | |
5319014e CY |
4182 | Each of these image formats is associated with an @dfn{image type |
4183 | symbol}. The symbols for the above formats are, respectively, | |
4184 | @code{pbm}, @code{xbm}, @code{xpm}, @code{gif}, @code{postscript}, | |
4185 | @code{jpeg}, @code{tiff}, @code{png}, and @code{svg}. | |
4186 | ||
4187 | Furthermore, if you build Emacs with ImageMagick | |
4188 | (@code{libMagickWand}) support, Emacs can display any image format | |
4189 | that ImageMagick can. @xref{ImageMagick Images}. All images | |
4190 | displayed via ImageMagick have type symbol @code{imagemagick}. | |
b8d4c8d0 GM |
4191 | |
4192 | @defvar image-types | |
5319014e CY |
4193 | This variable contains a list of type symbols for image formats which |
4194 | are potentially supported in the current configuration. | |
4195 | ||
4196 | ``Potentially'' means that Emacs knows about the image types, not | |
4197 | necessarily that they can be used (for example, they could depend on | |
4198 | unavailable dynamic libraries). To know which image types are really | |
4199 | available, use @code{image-type-available-p}. | |
b8d4c8d0 GM |
4200 | @end defvar |
4201 | ||
b8d4c8d0 | 4202 | @defun image-type-available-p type |
5319014e CY |
4203 | This function returns non-@code{nil} if images of type @var{type} can |
4204 | be loaded and displayed. @var{type} must be an image type symbol. | |
b8d4c8d0 GM |
4205 | |
4206 | For image types whose support libraries are statically linked, this | |
5319014e CY |
4207 | function always returns @code{t}. For image types whose support |
4208 | libraries are dynamically loaded, it returns @code{t} if the library | |
4209 | could be loaded and @code{nil} otherwise. | |
b8d4c8d0 GM |
4210 | @end defun |
4211 | ||
4212 | @node Image Descriptors | |
4213 | @subsection Image Descriptors | |
4214 | @cindex image descriptor | |
4215 | ||
5319014e CY |
4216 | An @dfn{image descriptor} is a list which specifies the underlying |
4217 | data for an image, and how to display it. It is typically used as the | |
4218 | value of a @code{display} overlay or text property (@pxref{Other | |
4219 | Display Specs}); but @xref{Showing Images}, for convenient helper | |
4220 | functions to insert images into buffers. | |
b8d4c8d0 | 4221 | |
5319014e CY |
4222 | Each image descriptor has the form @code{(image . @var{props})}, |
4223 | where @var{props} is a property list of alternating keyword symbols | |
4224 | and values, including at least the pair @code{:type @var{TYPE}} which | |
4225 | specifies the image type. | |
b8d4c8d0 | 4226 | |
5319014e CY |
4227 | The following is a list of properties that are meaningful for all |
4228 | image types (there are also properties which are meaningful only for | |
4229 | certain image types, as documented in the following subsections): | |
b8d4c8d0 GM |
4230 | |
4231 | @table @code | |
5319014e CY |
4232 | @item :type @var{type} |
4233 | The image type. | |
4234 | @ifnottex | |
4235 | @xref{Image Formats}. | |
4236 | @end ifnottex | |
4237 | Every image descriptor must include this property. | |
4238 | ||
b8d4c8d0 | 4239 | @item :file @var{file} |
5319014e CY |
4240 | This says to load the image from file @var{file}. If @var{file} is |
4241 | not an absolute file name, it is expanded in @code{data-directory}. | |
b8d4c8d0 GM |
4242 | |
4243 | @item :data @var{data} | |
5319014e CY |
4244 | This specifies the raw image data. Each image descriptor must have |
4245 | either @code{:data} or @code{:file}, but not both. | |
b8d4c8d0 | 4246 | |
5319014e CY |
4247 | For most image types, the value of a @code{:data} property should be a |
4248 | string containing the image data. Some image types do not support | |
4249 | @code{:data}; for some others, @code{:data} alone is not enough, so | |
4250 | you need to use other image properties along with @code{:data}. See | |
4251 | the following subsections for details. | |
b8d4c8d0 GM |
4252 | |
4253 | @item :margin @var{margin} | |
5319014e CY |
4254 | This specifies how many pixels to add as an extra margin around the |
4255 | image. The value, @var{margin}, must be a non-negative number, or a | |
4256 | pair @code{(@var{x} . @var{y})} of such numbers. If it is a pair, | |
4257 | @var{x} specifies how many pixels to add horizontally, and @var{y} | |
4258 | specifies how many pixels to add vertically. If @code{:margin} is not | |
4259 | specified, the default is zero. | |
b8d4c8d0 GM |
4260 | |
4261 | @item :ascent @var{ascent} | |
5319014e CY |
4262 | This specifies the amount of the image's height to use for its |
4263 | ascent---that is, the part above the baseline. The value, | |
4264 | @var{ascent}, must be a number in the range 0 to 100, or the symbol | |
4265 | @code{center}. | |
b8d4c8d0 GM |
4266 | |
4267 | If @var{ascent} is a number, that percentage of the image's height is | |
4268 | used for its ascent. | |
4269 | ||
4270 | If @var{ascent} is @code{center}, the image is vertically centered | |
4271 | around a centerline which would be the vertical centerline of text drawn | |
4272 | at the position of the image, in the manner specified by the text | |
4273 | properties and overlays that apply to the image. | |
4274 | ||
4275 | If this property is omitted, it defaults to 50. | |
4276 | ||
4277 | @item :relief @var{relief} | |
5319014e CY |
4278 | This adds a shadow rectangle around the image. The value, |
4279 | @var{relief}, specifies the width of the shadow lines, in pixels. If | |
4280 | @var{relief} is negative, shadows are drawn so that the image appears | |
4281 | as a pressed button; otherwise, it appears as an unpressed button. | |
b8d4c8d0 GM |
4282 | |
4283 | @item :conversion @var{algorithm} | |
5319014e CY |
4284 | This specifies a conversion algorithm that should be applied to the |
4285 | image before it is displayed; the value, @var{algorithm}, specifies | |
4286 | which algorithm. | |
b8d4c8d0 GM |
4287 | |
4288 | @table @code | |
4289 | @item laplace | |
4290 | @itemx emboss | |
4291 | Specifies the Laplace edge detection algorithm, which blurs out small | |
4292 | differences in color while highlighting larger differences. People | |
4293 | sometimes consider this useful for displaying the image for a | |
4294 | ``disabled'' button. | |
4295 | ||
4296 | @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust}) | |
4297 | Specifies a general edge-detection algorithm. @var{matrix} must be | |
4298 | either a nine-element list or a nine-element vector of numbers. A pixel | |
4299 | at position @math{x/y} in the transformed image is computed from | |
4300 | original pixels around that position. @var{matrix} specifies, for each | |
4301 | pixel in the neighborhood of @math{x/y}, a factor with which that pixel | |
4302 | will influence the transformed pixel; element @math{0} specifies the | |
4303 | factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for | |
4304 | the pixel at @math{x/y-1} etc., as shown below: | |
4305 | @iftex | |
4306 | @tex | |
4307 | $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr | |
4308 | x-1/y & x/y & x+1/y \cr | |
4309 | x-1/y+1& x/y+1 & x+1/y+1 \cr}$$ | |
4310 | @end tex | |
4311 | @end iftex | |
4312 | @ifnottex | |
4313 | @display | |
4314 | (x-1/y-1 x/y-1 x+1/y-1 | |
4315 | x-1/y x/y x+1/y | |
4316 | x-1/y+1 x/y+1 x+1/y+1) | |
4317 | @end display | |
4318 | @end ifnottex | |
4319 | ||
4320 | The resulting pixel is computed from the color intensity of the color | |
4321 | resulting from summing up the RGB values of surrounding pixels, | |
4322 | multiplied by the specified factors, and dividing that sum by the sum | |
4323 | of the factors' absolute values. | |
4324 | ||
4325 | Laplace edge-detection currently uses a matrix of | |
4326 | @iftex | |
4327 | @tex | |
4328 | $$\pmatrix{1 & 0 & 0 \cr | |
4329 | 0& 0 & 0 \cr | |
e2c94218 | 4330 | 0 & 0 & -1 \cr}$$ |
b8d4c8d0 GM |
4331 | @end tex |
4332 | @end iftex | |
4333 | @ifnottex | |
4334 | @display | |
4335 | (1 0 0 | |
4336 | 0 0 0 | |
e2c94218 | 4337 | 0 0 -1) |
b8d4c8d0 GM |
4338 | @end display |
4339 | @end ifnottex | |
4340 | ||
4341 | Emboss edge-detection uses a matrix of | |
4342 | @iftex | |
4343 | @tex | |
4344 | $$\pmatrix{ 2 & -1 & 0 \cr | |
4345 | -1 & 0 & 1 \cr | |
4346 | 0 & 1 & -2 \cr}$$ | |
4347 | @end tex | |
4348 | @end iftex | |
4349 | @ifnottex | |
4350 | @display | |
4351 | ( 2 -1 0 | |
4352 | -1 0 1 | |
4353 | 0 1 -2) | |
4354 | @end display | |
4355 | @end ifnottex | |
4356 | ||
4357 | @item disabled | |
4358 | Specifies transforming the image so that it looks ``disabled.'' | |
4359 | @end table | |
4360 | ||
4361 | @item :mask @var{mask} | |
4362 | If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build | |
4363 | a clipping mask for the image, so that the background of a frame is | |
4364 | visible behind the image. If @var{bg} is not specified, or if @var{bg} | |
4365 | is @code{t}, determine the background color of the image by looking at | |
4366 | the four corners of the image, assuming the most frequently occurring | |
4367 | color from the corners is the background color of the image. Otherwise, | |
4368 | @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})} | |
4369 | specifying the color to assume for the background of the image. | |
4370 | ||
4371 | If @var{mask} is @code{nil}, remove a mask from the image, if it has | |
4372 | one. Images in some formats include a mask which can be removed by | |
4373 | specifying @code{:mask nil}. | |
4374 | ||
4375 | @item :pointer @var{shape} | |
4376 | This specifies the pointer shape when the mouse pointer is over this | |
4377 | image. @xref{Pointer Shape}, for available pointer shapes. | |
4378 | ||
4379 | @item :map @var{map} | |
4380 | This associates an image map of @dfn{hot spots} with this image. | |
4381 | ||
4382 | An image map is an alist where each element has the format | |
4383 | @code{(@var{area} @var{id} @var{plist})}. An @var{area} is specified | |
4384 | as either a rectangle, a circle, or a polygon. | |
4385 | ||
4386 | A rectangle is a cons | |
4387 | @code{(rect . ((@var{x0} . @var{y0}) . (@var{x1} . @var{y1})))} | |
4388 | which specifies the pixel coordinates of the upper left and bottom right | |
4389 | corners of the rectangle area. | |
4390 | ||
4391 | A circle is a cons | |
4392 | @code{(circle . ((@var{x0} . @var{y0}) . @var{r}))} | |
4393 | which specifies the center and the radius of the circle; @var{r} may | |
4394 | be a float or integer. | |
4395 | ||
4396 | A polygon is a cons | |
4397 | @code{(poly . [@var{x0} @var{y0} @var{x1} @var{y1} ...])} | |
4398 | where each pair in the vector describes one corner in the polygon. | |
4399 | ||
4400 | When the mouse pointer lies on a hot-spot area of an image, the | |
4401 | @var{plist} of that hot-spot is consulted; if it contains a @code{help-echo} | |
4402 | property, that defines a tool-tip for the hot-spot, and if it contains | |
4403 | a @code{pointer} property, that defines the shape of the mouse cursor when | |
4404 | it is on the hot-spot. | |
4405 | @xref{Pointer Shape}, for available pointer shapes. | |
4406 | ||
4407 | When you click the mouse when the mouse pointer is over a hot-spot, an | |
4408 | event is composed by combining the @var{id} of the hot-spot with the | |
4409 | mouse event; for instance, @code{[area4 mouse-1]} if the hot-spot's | |
4410 | @var{id} is @code{area4}. | |
4411 | @end table | |
4412 | ||
4413 | @defun image-mask-p spec &optional frame | |
4414 | This function returns @code{t} if image @var{spec} has a mask bitmap. | |
4415 | @var{frame} is the frame on which the image will be displayed. | |
4416 | @var{frame} @code{nil} or omitted means to use the selected frame | |
4417 | (@pxref{Input Focus}). | |
4418 | @end defun | |
4419 | ||
4420 | @node XBM Images | |
4421 | @subsection XBM Images | |
4422 | @cindex XBM | |
4423 | ||
4424 | To use XBM format, specify @code{xbm} as the image type. This image | |
4425 | format doesn't require an external library, so images of this type are | |
4426 | always supported. | |
4427 | ||
4428 | Additional image properties supported for the @code{xbm} image type are: | |
4429 | ||
4430 | @table @code | |
4431 | @item :foreground @var{foreground} | |
4432 | The value, @var{foreground}, should be a string specifying the image | |
4433 | foreground color, or @code{nil} for the default color. This color is | |
4434 | used for each pixel in the XBM that is 1. The default is the frame's | |
4435 | foreground color. | |
4436 | ||
4437 | @item :background @var{background} | |
4438 | The value, @var{background}, should be a string specifying the image | |
4439 | background color, or @code{nil} for the default color. This color is | |
4440 | used for each pixel in the XBM that is 0. The default is the frame's | |
4441 | background color. | |
4442 | @end table | |
4443 | ||
4444 | If you specify an XBM image using data within Emacs instead of an | |
4445 | external file, use the following three properties: | |
4446 | ||
4447 | @table @code | |
4448 | @item :data @var{data} | |
4449 | The value, @var{data}, specifies the contents of the image. | |
4450 | There are three formats you can use for @var{data}: | |
4451 | ||
4452 | @itemize @bullet | |
4453 | @item | |
4454 | A vector of strings or bool-vectors, each specifying one line of the | |
4455 | image. Do specify @code{:height} and @code{:width}. | |
4456 | ||
4457 | @item | |
4458 | A string containing the same byte sequence as an XBM file would contain. | |
4459 | You must not specify @code{:height} and @code{:width} in this case, | |
4460 | because omitting them is what indicates the data has the format of an | |
4461 | XBM file. The file contents specify the height and width of the image. | |
4462 | ||
4463 | @item | |
4464 | A string or a bool-vector containing the bits of the image (plus perhaps | |
4465 | some extra bits at the end that will not be used). It should contain at | |
4466 | least @var{width} * @code{height} bits. In this case, you must specify | |
4467 | @code{:height} and @code{:width}, both to indicate that the string | |
4468 | contains just the bits rather than a whole XBM file, and to specify the | |
4469 | size of the image. | |
4470 | @end itemize | |
4471 | ||
4472 | @item :width @var{width} | |
4473 | The value, @var{width}, specifies the width of the image, in pixels. | |
4474 | ||
4475 | @item :height @var{height} | |
4476 | The value, @var{height}, specifies the height of the image, in pixels. | |
4477 | @end table | |
4478 | ||
4479 | @node XPM Images | |
4480 | @subsection XPM Images | |
4481 | @cindex XPM | |
4482 | ||
4483 | To use XPM format, specify @code{xpm} as the image type. The | |
4484 | additional image property @code{:color-symbols} is also meaningful with | |
4485 | the @code{xpm} image type: | |
4486 | ||
4487 | @table @code | |
4488 | @item :color-symbols @var{symbols} | |
4489 | The value, @var{symbols}, should be an alist whose elements have the | |
4490 | form @code{(@var{name} . @var{color})}. In each element, @var{name} is | |
4491 | the name of a color as it appears in the image file, and @var{color} | |
4492 | specifies the actual color to use for displaying that name. | |
4493 | @end table | |
4494 | ||
4495 | @node GIF Images | |
4496 | @subsection GIF Images | |
4497 | @cindex GIF | |
4498 | ||
4499 | For GIF images, specify image type @code{gif}. | |
4500 | ||
4501 | @table @code | |
4502 | @item :index @var{index} | |
204e728d GM |
4503 | You can use @code{:index} to specify image number @var{index} from a |
4504 | GIF file that contains more than one image. If the GIF file doesn't | |
4505 | contain an image with the specified index, the image displays as a | |
eea14f31 GM |
4506 | hollow box. GIF files with more than one image can be animated, |
4507 | @pxref{Animated Images}. | |
b8d4c8d0 GM |
4508 | @end table |
4509 | ||
905a9adb JR |
4510 | @node TIFF Images |
4511 | @subsection TIFF Images | |
4512 | @cindex TIFF | |
4513 | ||
4514 | For TIFF images, specify image type @code{tiff}. | |
4515 | ||
4516 | @table @code | |
4517 | @item :index @var{index} | |
204e728d GM |
4518 | You can use @code{:index} to specify image number @var{index} from a |
4519 | TIFF file that contains more than one image. If the TIFF file doesn't | |
4520 | contain an image with the specified index, the image displays as a | |
4521 | hollow box. | |
905a9adb JR |
4522 | @end table |
4523 | ||
2833b3ff CY |
4524 | @node PostScript Images |
4525 | @subsection PostScript Images | |
4526 | @cindex postscript images | |
4527 | ||
4528 | To use PostScript for an image, specify image type @code{postscript}. | |
4529 | This works only if you have Ghostscript installed. You must always use | |
4530 | these three properties: | |
4531 | ||
4532 | @table @code | |
4533 | @item :pt-width @var{width} | |
4534 | The value, @var{width}, specifies the width of the image measured in | |
4535 | points (1/72 inch). @var{width} must be an integer. | |
4536 | ||
4537 | @item :pt-height @var{height} | |
4538 | The value, @var{height}, specifies the height of the image in points | |
4539 | (1/72 inch). @var{height} must be an integer. | |
4540 | ||
4541 | @item :bounding-box @var{box} | |
4542 | The value, @var{box}, must be a list or vector of four integers, which | |
4543 | specifying the bounding box of the PostScript image, analogous to the | |
4544 | @samp{BoundingBox} comment found in PostScript files. | |
4545 | ||
4546 | @example | |
4547 | %%BoundingBox: 22 171 567 738 | |
4548 | @end example | |
4549 | @end table | |
4550 | ||
16a91140 JV |
4551 | @node ImageMagick Images |
4552 | @subsection ImageMagick Images | |
ca0d44e4 GM |
4553 | @cindex ImageMagick images |
4554 | @cindex images, support for more formats | |
4555 | ||
5319014e CY |
4556 | If you build Emacs with ImageMagick support, you can use the |
4557 | ImageMagick library to load many image formats. The image type symbol | |
4558 | for images loaded via ImageMagick is @code{imagemagick}, regardless of | |
4559 | the actual underlying image format. | |
4560 | ||
4561 | @defun imagemagick-types | |
4562 | This function returns a list of image file extensions supported by the | |
4563 | current ImageMagick installation. | |
4564 | @end defun | |
4565 | ||
4566 | By default, Emacs does not use ImageMagick to display images in | |
4567 | Image mode, e.g.@: when visiting such files with @kbd{C-x C-f}. This | |
4568 | feature is enabled by calling @code{imagemagick-register-types}. | |
4569 | ||
4570 | @defun imagemagick-register-types | |
4571 | This function enables using Image mode to visit image files supported | |
4572 | by ImageMagick. @xref{File Conveniences,,, emacs, The GNU Emacs | |
4573 | Manual}. It also causes @code{create-image} and other helper | |
4574 | functions to associate such file names with the @code{imagemagick} | |
4575 | image type (@pxref{Defining Images}). | |
4576 | ||
4577 | All image file extensions supported by ImageMagick are registered, | |
4578 | except those specified in @code{imagemagick-types-inhibit}. If Emacs | |
4579 | was not compiled with ImageMagick support, this function does nothing. | |
4580 | @end defun | |
4581 | ||
4582 | @defopt imagemagick-types-inhibit | |
4583 | This variable specifies a list of image types that should @emph{not} | |
4584 | be registered by @code{imagemagick-register-types}. Each entry in | |
4585 | this list should be one of the symbols returned by | |
4586 | @code{imagemagick-types}. The default value lists several file types | |
4587 | that are considered ``images'' by ImageMagick, but which should not be | |
4588 | considered as images by Emacs, including C files and HTML files. | |
4589 | @end defopt | |
4590 | ||
e80e1825 GM |
4591 | @ignore |
4592 | @c I don't know what this means. I suspect it means eg loading jpg | |
4593 | @c images via libjpeg or ImageMagick. But it doesn't work. | |
4594 | @c If you don't have libjpeg support compiled in, you cannot | |
4595 | @c view jpeg images, even if you have imagemagick support: | |
4596 | @c http://debbugs.gnu.org/9045 | |
4597 | @c And if you have both compiled in, then you always get | |
4598 | @c the libjpeg version: | |
4599 | @c http://debbugs.gnu.org/10746 | |
4600 | There may be overlap between image loaders in your Emacs installation, | |
4601 | and you may prefer to use a different one for a given image type | |
4602 | (which loader will be used in practice depends on the priority of the | |
4603 | loaders). | |
e80e1825 | 4604 | For example, if you never want to use the ImageMagick loader to view |
93137f94 GM |
4605 | JPEG files, add @code{JPG} to this list. |
4606 | @end ignore | |
ca0d44e4 | 4607 | |
5319014e CY |
4608 | Images loaded with ImageMagick support the following additional |
4609 | image descriptor properties: | |
16a91140 | 4610 | |
ca0d44e4 GM |
4611 | @table @code |
4612 | @item :width, :height | |
4613 | The @code{:width} and @code{:height} keywords are used for scaling the | |
4614 | image. If only one of them is specified, the other one will be | |
4615 | calculated so as to preserve the aspect ratio. If both are specified, | |
4616 | aspect ratio may not be preserved. | |
4617 | ||
4618 | @item :rotation | |
4619 | Specifies a rotation angle in degrees. | |
4620 | ||
4621 | @item :index | |
e80e1825 GM |
4622 | @c Doesn't work: http://debbugs.gnu.org/7978 |
4623 | This has the same meaning as it does for GIF images (@pxref{GIF Images}), | |
4624 | i.e. it specifies which image to view inside an image bundle file format | |
4625 | such as DJVM. You can use the @code{image-metadata} function to | |
4626 | retrieve the total number of images in an image bundle. | |
ca0d44e4 | 4627 | @end table |
16a91140 | 4628 | |
b8d4c8d0 GM |
4629 | @node Other Image Types |
4630 | @subsection Other Image Types | |
4631 | @cindex PBM | |
4632 | ||
4633 | For PBM images, specify image type @code{pbm}. Color, gray-scale and | |
4634 | monochromatic images are supported. For mono PBM images, two additional | |
4635 | image properties are supported. | |
4636 | ||
4637 | @table @code | |
4638 | @item :foreground @var{foreground} | |
4639 | The value, @var{foreground}, should be a string specifying the image | |
4640 | foreground color, or @code{nil} for the default color. This color is | |
3696411e | 4641 | used for each pixel in the PBM that is 1. The default is the frame's |
b8d4c8d0 GM |
4642 | foreground color. |
4643 | ||
4644 | @item :background @var{background} | |
4645 | The value, @var{background}, should be a string specifying the image | |
4646 | background color, or @code{nil} for the default color. This color is | |
3696411e | 4647 | used for each pixel in the PBM that is 0. The default is the frame's |
b8d4c8d0 GM |
4648 | background color. |
4649 | @end table | |
4650 | ||
4651 | For JPEG images, specify image type @code{jpeg}. | |
4652 | ||
4653 | For TIFF images, specify image type @code{tiff}. | |
4654 | ||
4655 | For PNG images, specify image type @code{png}. | |
4656 | ||
4657 | For SVG images, specify image type @code{svg}. | |
4658 | ||
4659 | @node Defining Images | |
4660 | @subsection Defining Images | |
4661 | ||
4662 | The functions @code{create-image}, @code{defimage} and | |
4663 | @code{find-image} provide convenient ways to create image descriptors. | |
4664 | ||
4665 | @defun create-image file-or-data &optional type data-p &rest props | |
4666 | This function creates and returns an image descriptor which uses the | |
4667 | data in @var{file-or-data}. @var{file-or-data} can be a file name or | |
4668 | a string containing the image data; @var{data-p} should be @code{nil} | |
4669 | for the former case, non-@code{nil} for the latter case. | |
4670 | ||
4671 | The optional argument @var{type} is a symbol specifying the image type. | |
4672 | If @var{type} is omitted or @code{nil}, @code{create-image} tries to | |
4673 | determine the image type from the file's first few bytes, or else | |
4674 | from the file's name. | |
4675 | ||
4676 | The remaining arguments, @var{props}, specify additional image | |
4677 | properties---for example, | |
4678 | ||
4679 | @example | |
4680 | (create-image "foo.xpm" 'xpm nil :heuristic-mask t) | |
4681 | @end example | |
4682 | ||
4683 | The function returns @code{nil} if images of this type are not | |
4684 | supported. Otherwise it returns an image descriptor. | |
4685 | @end defun | |
4686 | ||
4687 | @defmac defimage symbol specs &optional doc | |
4688 | This macro defines @var{symbol} as an image name. The arguments | |
4689 | @var{specs} is a list which specifies how to display the image. | |
4690 | The third argument, @var{doc}, is an optional documentation string. | |
4691 | ||
4692 | Each argument in @var{specs} has the form of a property list, and each | |
4693 | one should specify at least the @code{:type} property and either the | |
4694 | @code{:file} or the @code{:data} property. The value of @code{:type} | |
4695 | should be a symbol specifying the image type, the value of | |
4696 | @code{:file} is the file to load the image from, and the value of | |
4697 | @code{:data} is a string containing the actual image data. Here is an | |
4698 | example: | |
4699 | ||
4700 | @example | |
4701 | (defimage test-image | |
4702 | ((:type xpm :file "~/test1.xpm") | |
4703 | (:type xbm :file "~/test1.xbm"))) | |
4704 | @end example | |
4705 | ||
4706 | @code{defimage} tests each argument, one by one, to see if it is | |
4707 | usable---that is, if the type is supported and the file exists. The | |
4708 | first usable argument is used to make an image descriptor which is | |
4709 | stored in @var{symbol}. | |
4710 | ||
4711 | If none of the alternatives will work, then @var{symbol} is defined | |
4712 | as @code{nil}. | |
4713 | @end defmac | |
4714 | ||
4715 | @defun find-image specs | |
4716 | This function provides a convenient way to find an image satisfying one | |
4717 | of a list of image specifications @var{specs}. | |
4718 | ||
4719 | Each specification in @var{specs} is a property list with contents | |
4720 | depending on image type. All specifications must at least contain the | |
4721 | properties @code{:type @var{type}} and either @w{@code{:file @var{file}}} | |
4722 | or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying | |
4723 | the image type, e.g.@: @code{xbm}, @var{file} is the file to load the | |
4724 | image from, and @var{data} is a string containing the actual image data. | |
4725 | The first specification in the list whose @var{type} is supported, and | |
4726 | @var{file} exists, is used to construct the image specification to be | |
4727 | returned. If no specification is satisfied, @code{nil} is returned. | |
4728 | ||
4729 | The image is looked for in @code{image-load-path}. | |
4730 | @end defun | |
4731 | ||
4732 | @defvar image-load-path | |
4733 | This variable's value is a list of locations in which to search for | |
4734 | image files. If an element is a string or a variable symbol whose | |
4735 | value is a string, the string is taken to be the name of a directory | |
4736 | to search. If an element is a variable symbol whose value is a list, | |
4737 | that is taken to be a list of directory names to search. | |
4738 | ||
4739 | The default is to search in the @file{images} subdirectory of the | |
4740 | directory specified by @code{data-directory}, then the directory | |
4741 | specified by @code{data-directory}, and finally in the directories in | |
4742 | @code{load-path}. Subdirectories are not automatically included in | |
4743 | the search, so if you put an image file in a subdirectory, you have to | |
4744 | supply the subdirectory name explicitly. For example, to find the | |
4745 | image @file{images/foo/bar.xpm} within @code{data-directory}, you | |
4746 | should specify the image as follows: | |
4747 | ||
4748 | @example | |
4749 | (defimage foo-image '((:type xpm :file "foo/bar.xpm"))) | |
4750 | @end example | |
4751 | @end defvar | |
4752 | ||
4753 | @defun image-load-path-for-library library image &optional path no-error | |
4754 | This function returns a suitable search path for images used by the | |
4755 | Lisp package @var{library}. | |
4756 | ||
4757 | The function searches for @var{image} first using @code{image-load-path}, | |
4758 | excluding @file{@code{data-directory}/images}, and then in | |
4759 | @code{load-path}, followed by a path suitable for @var{library}, which | |
4760 | includes @file{../../etc/images} and @file{../etc/images} relative to | |
4761 | the library file itself, and finally in | |
4762 | @file{@code{data-directory}/images}. | |
4763 | ||
4764 | Then this function returns a list of directories which contains first | |
4765 | the directory in which @var{image} was found, followed by the value of | |
4766 | @code{load-path}. If @var{path} is given, it is used instead of | |
4767 | @code{load-path}. | |
4768 | ||
4769 | If @var{no-error} is non-@code{nil} and a suitable path can't be | |
4770 | found, don't signal an error. Instead, return a list of directories as | |
4771 | before, except that @code{nil} appears in place of the image directory. | |
4772 | ||
049bcbcb | 4773 | Here is an example of using @code{image-load-path-for-library}: |
b8d4c8d0 GM |
4774 | |
4775 | @example | |
4776 | (defvar image-load-path) ; shush compiler | |
4777 | (let* ((load-path (image-load-path-for-library | |
049bcbcb | 4778 | "mh-e" "mh-logo.xpm")) |
b8d4c8d0 | 4779 | (image-load-path (cons (car load-path) |
049bcbcb | 4780 | image-load-path))) |
b8d4c8d0 GM |
4781 | (mh-tool-bar-folder-buttons-init)) |
4782 | @end example | |
4783 | @end defun | |
4784 | ||
4785 | @node Showing Images | |
4786 | @subsection Showing Images | |
4787 | ||
4788 | You can use an image descriptor by setting up the @code{display} | |
4789 | property yourself, but it is easier to use the functions in this | |
4790 | section. | |
4791 | ||
4792 | @defun insert-image image &optional string area slice | |
4793 | This function inserts @var{image} in the current buffer at point. The | |
4794 | value @var{image} should be an image descriptor; it could be a value | |
4795 | returned by @code{create-image}, or the value of a symbol defined with | |
4796 | @code{defimage}. The argument @var{string} specifies the text to put | |
4797 | in the buffer to hold the image. If it is omitted or @code{nil}, | |
4798 | @code{insert-image} uses @code{" "} by default. | |
4799 | ||
4800 | The argument @var{area} specifies whether to put the image in a margin. | |
4801 | If it is @code{left-margin}, the image appears in the left margin; | |
4802 | @code{right-margin} specifies the right margin. If @var{area} is | |
4803 | @code{nil} or omitted, the image is displayed at point within the | |
4804 | buffer's text. | |
4805 | ||
4806 | The argument @var{slice} specifies a slice of the image to insert. If | |
4807 | @var{slice} is @code{nil} or omitted the whole image is inserted. | |
4808 | Otherwise, @var{slice} is a list @code{(@var{x} @var{y} @var{width} | |
4809 | @var{height})} which specifies the @var{x} and @var{y} positions and | |
4810 | @var{width} and @var{height} of the image area to insert. Integer | |
4811 | values are in units of pixels. A floating point number in the range | |
4812 | 0.0--1.0 stands for that fraction of the width or height of the entire | |
4813 | image. | |
4814 | ||
4815 | Internally, this function inserts @var{string} in the buffer, and gives | |
4816 | it a @code{display} property which specifies @var{image}. @xref{Display | |
4817 | Property}. | |
4818 | @end defun | |
4819 | ||
f68d76d0 LMI |
4820 | @cindex slice, image |
4821 | @cindex image slice | |
b8d4c8d0 GM |
4822 | @defun insert-sliced-image image &optional string area rows cols |
4823 | This function inserts @var{image} in the current buffer at point, like | |
4824 | @code{insert-image}, but splits the image into @var{rows}x@var{cols} | |
4825 | equally sized slices. | |
f68d76d0 | 4826 | |
5319014e CY |
4827 | If an image is inserted ``sliced'', Emacs displays each slice as a |
4828 | separate image, and allow more intuitive scrolling up/down, instead of | |
4829 | jumping up/down the entire image when paging through a buffer that | |
4830 | displays (large) images. | |
b8d4c8d0 GM |
4831 | @end defun |
4832 | ||
4833 | @defun put-image image pos &optional string area | |
4834 | This function puts image @var{image} in front of @var{pos} in the | |
4835 | current buffer. The argument @var{pos} should be an integer or a | |
4836 | marker. It specifies the buffer position where the image should appear. | |
4837 | The argument @var{string} specifies the text that should hold the image | |
4838 | as an alternative to the default. | |
4839 | ||
4840 | The argument @var{image} must be an image descriptor, perhaps returned | |
4841 | by @code{create-image} or stored by @code{defimage}. | |
4842 | ||
4843 | The argument @var{area} specifies whether to put the image in a margin. | |
4844 | If it is @code{left-margin}, the image appears in the left margin; | |
4845 | @code{right-margin} specifies the right margin. If @var{area} is | |
4846 | @code{nil} or omitted, the image is displayed at point within the | |
4847 | buffer's text. | |
4848 | ||
4849 | Internally, this function creates an overlay, and gives it a | |
4850 | @code{before-string} property containing text that has a @code{display} | |
4851 | property whose value is the image. (Whew!) | |
4852 | @end defun | |
4853 | ||
4854 | @defun remove-images start end &optional buffer | |
4855 | This function removes images in @var{buffer} between positions | |
4856 | @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil}, | |
4857 | images are removed from the current buffer. | |
4858 | ||
4859 | This removes only images that were put into @var{buffer} the way | |
4860 | @code{put-image} does it, not images that were inserted with | |
4861 | @code{insert-image} or in other ways. | |
4862 | @end defun | |
4863 | ||
4864 | @defun image-size spec &optional pixels frame | |
4865 | This function returns the size of an image as a pair | |
4866 | @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image | |
4867 | specification. @var{pixels} non-@code{nil} means return sizes | |
4868 | measured in pixels, otherwise return sizes measured in canonical | |
4869 | character units (fractions of the width/height of the frame's default | |
4870 | font). @var{frame} is the frame on which the image will be displayed. | |
4871 | @var{frame} null or omitted means use the selected frame (@pxref{Input | |
4872 | Focus}). | |
4873 | @end defun | |
4874 | ||
4875 | @defvar max-image-size | |
4876 | This variable is used to define the maximum size of image that Emacs | |
4877 | will load. Emacs will refuse to load (and display) any image that is | |
4878 | larger than this limit. | |
4879 | ||
4880 | If the value is an integer, it directly specifies the maximum | |
4881 | image height and width, measured in pixels. If it is a floating | |
4882 | point number, it specifies the maximum image height and width | |
4883 | as a ratio to the frame height and width. If the value is | |
4884 | non-numeric, there is no explicit limit on the size of images. | |
4885 | ||
4886 | The purpose of this variable is to prevent unreasonably large images | |
4887 | from accidentally being loaded into Emacs. It only takes effect the | |
4888 | first time an image is loaded. Once an image is placed in the image | |
4889 | cache, it can always be displayed, even if the value of | |
4890 | @var{max-image-size} is subsequently changed (@pxref{Image Cache}). | |
4891 | @end defvar | |
4892 | ||
eea14f31 GM |
4893 | @node Animated Images |
4894 | @subsection Animated Images | |
4895 | ||
4896 | @cindex animation | |
4897 | @cindex image animation | |
4898 | Some image files can contain more than one image. This can be used to | |
4899 | create animation. Currently, Emacs only supports animated GIF files. | |
4900 | The following functions related to animated images are available. | |
4901 | ||
4902 | @defun image-animated-p image | |
4903 | This function returns non-nil if @var{image} can be animated. | |
4904 | The actual return value is a cons @code{(@var{nimages} . @var{delay})}, | |
4905 | where @var{nimages} is the number of frames and @var{delay} is the | |
4906 | delay in seconds between them. | |
4907 | @end defun | |
4908 | ||
4909 | @defun image-animate image &optional index limit | |
4910 | This function animates @var{image}. The optional integer @var{index} | |
4911 | specifies the frame from which to start (default 0). The optional | |
4912 | argument @var{limit} controls the length of the animation. If omitted | |
4913 | or @code{nil}, the image animates once only; if @code{t} it loops | |
4914 | forever; if a number animation stops after that many seconds. | |
4915 | @end defun | |
4916 | ||
4917 | @noindent Animation operates by means of a timer. Note that Emacs imposes a | |
4918 | minimum frame delay of 0.01 seconds. | |
4919 | ||
4920 | @defun image-animate-timer image | |
4921 | This function returns the timer responsible for animating @var{image}, | |
4922 | if there is one. | |
4923 | @end defun | |
4924 | ||
4925 | ||
b8d4c8d0 GM |
4926 | @node Image Cache |
4927 | @subsection Image Cache | |
4928 | @cindex image cache | |
4929 | ||
0c1cfe01 CY |
4930 | Emacs caches images so that it can display them again more |
4931 | efficiently. When Emacs displays an image, it searches the image | |
4932 | cache for an existing image specification @code{equal} to the desired | |
4933 | specification. If a match is found, the image is displayed from the | |
110683ad CY |
4934 | cache. Otherwise, Emacs loads the image normally. |
4935 | ||
4936 | @defun image-flush spec &optional frame | |
4937 | This function removes the image with specification @var{spec} from the | |
4938 | image cache of frame @var{frame}. Image specifications are compared | |
4939 | using @code{equal}. If @var{frame} is @code{nil}, it defaults to the | |
4940 | selected frame. If @var{frame} is @code{t}, the image is flushed on | |
4941 | all existing frames. | |
4942 | ||
44e97401 | 4943 | In Emacs's current implementation, each graphical terminal possesses an |
110683ad | 4944 | image cache, which is shared by all the frames on that terminal |
0c1cfe01 CY |
4945 | (@pxref{Multiple Terminals}). Thus, refreshing an image in one frame |
4946 | also refreshes it in all other frames on the same terminal. | |
b8d4c8d0 GM |
4947 | @end defun |
4948 | ||
110683ad CY |
4949 | One use for @code{image-flush} is to tell Emacs about a change in an |
4950 | image file. If an image specification contains a @code{:file} | |
4951 | property, the image is cached based on the file's contents when the | |
4952 | image is first displayed. Even if the file subsequently changes, | |
4953 | Emacs continues displaying the old version of the image. Calling | |
4954 | @code{image-flush} flushes the image from the cache, forcing Emacs to | |
4955 | re-read the file the next time it needs to display that image. | |
4956 | ||
4957 | Another use for @code{image-flush} is for memory conservation. If | |
4958 | your Lisp program creates a large number of temporary images over a | |
4959 | period much shorter than @code{image-cache-eviction-delay} (see | |
4960 | below), you can opt to flush unused images yourself, instead of | |
4961 | waiting for Emacs to do it automatically. | |
4962 | ||
a2bc5bdd | 4963 | @defun clear-image-cache &optional filter |
0c1cfe01 CY |
4964 | This function clears an image cache, removing all the images stored in |
4965 | it. If @var{filter} is omitted or @code{nil}, it clears the cache for | |
4966 | the selected frame. If @var{filter} is a frame, it clears the cache | |
4967 | for that frame. If @var{filter} is @code{t}, all image caches are | |
4968 | cleared. Otherwise, @var{filter} is taken to be a file name, and all | |
4969 | images associated with that file name are removed from all image | |
4970 | caches. | |
b8d4c8d0 GM |
4971 | @end defun |
4972 | ||
4973 | If an image in the image cache has not been displayed for a specified | |
4974 | period of time, Emacs removes it from the cache and frees the | |
4975 | associated memory. | |
4976 | ||
4977 | @defvar image-cache-eviction-delay | |
110683ad CY |
4978 | This variable specifies the number of seconds an image can remain in |
4979 | the cache without being displayed. When an image is not displayed for | |
4980 | this length of time, Emacs removes it from the image cache. | |
4981 | ||
4982 | Under some circumstances, if the number of images in the cache grows | |
4983 | too large, the actual eviction delay may be shorter than this. | |
b8d4c8d0 GM |
4984 | |
4985 | If the value is @code{nil}, Emacs does not remove images from the cache | |
4986 | except when you explicitly clear it. This mode can be useful for | |
4987 | debugging. | |
4988 | @end defvar | |
4989 | ||
4990 | @node Buttons | |
4991 | @section Buttons | |
4992 | @cindex buttons in buffers | |
4993 | @cindex clickable buttons in buffers | |
4994 | ||
9a69676a CY |
4995 | The Button package defines functions for inserting and manipulating |
4996 | @dfn{buttons} that can be activated with the mouse or via keyboard | |
4997 | commands. These buttons are typically used for various kinds of | |
4998 | hyperlinks. | |
4999 | ||
5000 | A button is essentially a set of text or overlay properties, | |
5001 | attached to a stretch of text in a buffer. These properties are | |
5002 | called @dfn{button properties}. One of these properties, the | |
5003 | @dfn{action property}, specifies a function which is called when the | |
5004 | user invokes the button using the keyboard or the mouse. The action | |
5005 | function may examine the button and use its other properties as | |
5006 | desired. | |
5007 | ||
5008 | In some ways, the Button package duplicates the functionality in the | |
5009 | Widget package. @xref{Top, , Introduction, widget, The Emacs Widget | |
5010 | Library}. The advantage of the Button package is that it is faster, | |
5011 | smaller, and simpler to program. From the point of view of the user, | |
5012 | the interfaces produced by the two packages are very similar. | |
b8d4c8d0 GM |
5013 | |
5014 | @menu | |
5015 | * Button Properties:: Button properties with special meanings. | |
5016 | * Button Types:: Defining common properties for classes of buttons. | |
5017 | * Making Buttons:: Adding buttons to Emacs buffers. | |
5018 | * Manipulating Buttons:: Getting and setting properties of buttons. | |
5019 | * Button Buffer Commands:: Buffer-wide commands and bindings for buttons. | |
5020 | @end menu | |
5021 | ||
5022 | @node Button Properties | |
5023 | @subsection Button Properties | |
5024 | @cindex button properties | |
5025 | ||
9a69676a | 5026 | Each button has an associated list of properties defining its |
b8d4c8d0 | 5027 | appearance and behavior, and other arbitrary properties may be used |
9a69676a CY |
5028 | for application specific purposes. The following properties have |
5029 | special meaning to the Button package: | |
b8d4c8d0 GM |
5030 | |
5031 | @table @code | |
5032 | @item action | |
5033 | @kindex action @r{(button property)} | |
5034 | The function to call when the user invokes the button, which is passed | |
5035 | the single argument @var{button}. By default this is @code{ignore}, | |
5036 | which does nothing. | |
5037 | ||
5038 | @item mouse-action | |
5039 | @kindex mouse-action @r{(button property)} | |
5040 | This is similar to @code{action}, and when present, will be used | |
5041 | instead of @code{action} for button invocations resulting from | |
5042 | mouse-clicks (instead of the user hitting @key{RET}). If not | |
5043 | present, mouse-clicks use @code{action} instead. | |
5044 | ||
5045 | @item face | |
5046 | @kindex face @r{(button property)} | |
5047 | This is an Emacs face controlling how buttons of this type are | |
5048 | displayed; by default this is the @code{button} face. | |
5049 | ||
5050 | @item mouse-face | |
5051 | @kindex mouse-face @r{(button property)} | |
5052 | This is an additional face which controls appearance during | |
5053 | mouse-overs (merged with the usual button face); by default this is | |
5054 | the usual Emacs @code{highlight} face. | |
5055 | ||
5056 | @item keymap | |
5057 | @kindex keymap @r{(button property)} | |
5058 | The button's keymap, defining bindings active within the button | |
5059 | region. By default this is the usual button region keymap, stored | |
5060 | in the variable @code{button-map}, which defines @key{RET} and | |
5061 | @key{mouse-2} to invoke the button. | |
5062 | ||
5063 | @item type | |
5064 | @kindex type @r{(button property)} | |
9a69676a | 5065 | The button type. @xref{Button Types}. |
b8d4c8d0 GM |
5066 | |
5067 | @item help-echo | |
5068 | @kindex help-index @r{(button property)} | |
5069 | A string displayed by the Emacs tool-tip help system; by default, | |
5070 | @code{"mouse-2, RET: Push this button"}. | |
5071 | ||
5072 | @item follow-link | |
5073 | @kindex follow-link @r{(button property)} | |
5074 | The follow-link property, defining how a @key{Mouse-1} click behaves | |
2bad3299 | 5075 | on this button, @xref{Clickable Text}. |
b8d4c8d0 GM |
5076 | |
5077 | @item button | |
5078 | @kindex button @r{(button property)} | |
5079 | All buttons have a non-@code{nil} @code{button} property, which may be useful | |
5080 | in finding regions of text that comprise buttons (which is what the | |
5081 | standard button functions do). | |
5082 | @end table | |
5083 | ||
5084 | There are other properties defined for the regions of text in a | |
5085 | button, but these are not generally interesting for typical uses. | |
5086 | ||
5087 | @node Button Types | |
5088 | @subsection Button Types | |
5089 | @cindex button types | |
5090 | ||
9a69676a | 5091 | Every button has a @dfn{button type}, which defines default values |
b8d4c8d0 GM |
5092 | for the button's properties. Button types are arranged in a |
5093 | hierarchy, with specialized types inheriting from more general types, | |
5094 | so that it's easy to define special-purpose types of buttons for | |
5095 | specific tasks. | |
5096 | ||
5097 | @defun define-button-type name &rest properties | |
1a256502 TTN |
5098 | Define a `button type' called @var{name} (a symbol). |
5099 | The remaining arguments | |
b8d4c8d0 GM |
5100 | form a sequence of @var{property value} pairs, specifying default |
5101 | property values for buttons with this type (a button's type may be set | |
5102 | by giving it a @code{type} property when creating the button, using | |
5103 | the @code{:type} keyword argument). | |
5104 | ||
5105 | In addition, the keyword argument @code{:supertype} may be used to | |
5106 | specify a button-type from which @var{name} inherits its default | |
5107 | property values. Note that this inheritance happens only when | |
5108 | @var{name} is defined; subsequent changes to a supertype are not | |
5109 | reflected in its subtypes. | |
5110 | @end defun | |
5111 | ||
5112 | Using @code{define-button-type} to define default properties for | |
5113 | buttons is not necessary---buttons without any specified type use the | |
5114 | built-in button-type @code{button}---but it is encouraged, since | |
5115 | doing so usually makes the resulting code clearer and more efficient. | |
5116 | ||
5117 | @node Making Buttons | |
5118 | @subsection Making Buttons | |
5119 | @cindex making buttons | |
5120 | ||
5121 | Buttons are associated with a region of text, using an overlay or | |
5122 | text properties to hold button-specific information, all of which are | |
5123 | initialized from the button's type (which defaults to the built-in | |
5124 | button type @code{button}). Like all Emacs text, the appearance of | |
5125 | the button is governed by the @code{face} property; by default (via | |
5126 | the @code{face} property inherited from the @code{button} button-type) | |
5127 | this is a simple underline, like a typical web-page link. | |
5128 | ||
5129 | For convenience, there are two sorts of button-creation functions, | |
5130 | those that add button properties to an existing region of a buffer, | |
5131 | called @code{make-...button}, and those that also insert the button | |
5132 | text, called @code{insert-...button}. | |
5133 | ||
5134 | The button-creation functions all take the @code{&rest} argument | |
5135 | @var{properties}, which should be a sequence of @var{property value} | |
5136 | pairs, specifying properties to add to the button; see @ref{Button | |
5137 | Properties}. In addition, the keyword argument @code{:type} may be | |
5138 | used to specify a button-type from which to inherit other properties; | |
5139 | see @ref{Button Types}. Any properties not explicitly specified | |
5140 | during creation will be inherited from the button's type (if the type | |
5141 | defines such a property). | |
5142 | ||
5143 | The following functions add a button using an overlay | |
5144 | (@pxref{Overlays}) to hold the button properties: | |
5145 | ||
5146 | @defun make-button beg end &rest properties | |
5147 | This makes a button from @var{beg} to @var{end} in the | |
5148 | current buffer, and returns it. | |
5149 | @end defun | |
5150 | ||
5151 | @defun insert-button label &rest properties | |
5152 | This insert a button with the label @var{label} at point, | |
5153 | and returns it. | |
5154 | @end defun | |
5155 | ||
9a69676a CY |
5156 | The following functions are similar, but using text properties |
5157 | (@pxref{Text Properties}) to hold the button properties. Such buttons | |
5158 | do not add markers to the buffer, so editing in the buffer does not | |
5159 | slow down if there is an extremely large numbers of buttons. However, | |
5160 | if there is an existing face text property on the text (e.g.@: a face | |
5161 | assigned by Font Lock mode), the button face may not be visible. Both | |
5162 | of these functions return the starting position of the new button. | |
b8d4c8d0 GM |
5163 | |
5164 | @defun make-text-button beg end &rest properties | |
9a69676a CY |
5165 | This makes a button from @var{beg} to @var{end} in the current buffer, |
5166 | using text properties. | |
b8d4c8d0 GM |
5167 | @end defun |
5168 | ||
5169 | @defun insert-text-button label &rest properties | |
5170 | This inserts a button with the label @var{label} at point, using text | |
5171 | properties. | |
5172 | @end defun | |
5173 | ||
5174 | @node Manipulating Buttons | |
5175 | @subsection Manipulating Buttons | |
5176 | @cindex manipulating buttons | |
5177 | ||
5178 | These are functions for getting and setting properties of buttons. | |
5179 | Often these are used by a button's invocation function to determine | |
5180 | what to do. | |
5181 | ||
5182 | Where a @var{button} parameter is specified, it means an object | |
5183 | referring to a specific button, either an overlay (for overlay | |
5184 | buttons), or a buffer-position or marker (for text property buttons). | |
5185 | Such an object is passed as the first argument to a button's | |
5186 | invocation function when it is invoked. | |
5187 | ||
5188 | @defun button-start button | |
5189 | Return the position at which @var{button} starts. | |
5190 | @end defun | |
5191 | ||
5192 | @defun button-end button | |
5193 | Return the position at which @var{button} ends. | |
5194 | @end defun | |
5195 | ||
5196 | @defun button-get button prop | |
5197 | Get the property of button @var{button} named @var{prop}. | |
5198 | @end defun | |
5199 | ||
5200 | @defun button-put button prop val | |
5201 | Set @var{button}'s @var{prop} property to @var{val}. | |
5202 | @end defun | |
5203 | ||
5204 | @defun button-activate button &optional use-mouse-action | |
5205 | Call @var{button}'s @code{action} property (i.e., invoke it). If | |
5206 | @var{use-mouse-action} is non-@code{nil}, try to invoke the button's | |
5207 | @code{mouse-action} property instead of @code{action}; if the button | |
5208 | has no @code{mouse-action} property, use @code{action} as normal. | |
5209 | @end defun | |
5210 | ||
5211 | @defun button-label button | |
5212 | Return @var{button}'s text label. | |
5213 | @end defun | |
5214 | ||
5215 | @defun button-type button | |
5216 | Return @var{button}'s button-type. | |
5217 | @end defun | |
5218 | ||
5219 | @defun button-has-type-p button type | |
5220 | Return @code{t} if @var{button} has button-type @var{type}, or one of | |
5221 | @var{type}'s subtypes. | |
5222 | @end defun | |
5223 | ||
5224 | @defun button-at pos | |
9a69676a CY |
5225 | Return the button at position @var{pos} in the current buffer, or |
5226 | @code{nil}. If the button at @var{pos} is a text property button, the | |
5227 | return value is a marker pointing to @var{pos}. | |
b8d4c8d0 GM |
5228 | @end defun |
5229 | ||
5230 | @defun button-type-put type prop val | |
5231 | Set the button-type @var{type}'s @var{prop} property to @var{val}. | |
5232 | @end defun | |
5233 | ||
5234 | @defun button-type-get type prop | |
5235 | Get the property of button-type @var{type} named @var{prop}. | |
5236 | @end defun | |
5237 | ||
5238 | @defun button-type-subtype-p type supertype | |
5239 | Return @code{t} if button-type @var{type} is a subtype of @var{supertype}. | |
5240 | @end defun | |
5241 | ||
5242 | @node Button Buffer Commands | |
5243 | @subsection Button Buffer Commands | |
5244 | @cindex button buffer commands | |
5245 | ||
5246 | These are commands and functions for locating and operating on | |
5247 | buttons in an Emacs buffer. | |
5248 | ||
5249 | @code{push-button} is the command that a user uses to actually `push' | |
5250 | a button, and is bound by default in the button itself to @key{RET} | |
9a69676a CY |
5251 | and to @key{mouse-2} using a local keymap in the button's overlay or |
5252 | text properties. Commands that are useful outside the buttons itself, | |
5253 | such as @code{forward-button} and @code{backward-button} are | |
5254 | additionally available in the keymap stored in | |
5255 | @code{button-buffer-map}; a mode which uses buttons may want to use | |
5256 | @code{button-buffer-map} as a parent keymap for its keymap. | |
b8d4c8d0 GM |
5257 | |
5258 | If the button has a non-@code{nil} @code{follow-link} property, and | |
5259 | @var{mouse-1-click-follows-link} is set, a quick @key{Mouse-1} click | |
5260 | will also activate the @code{push-button} command. | |
2bad3299 | 5261 | @xref{Clickable Text}. |
b8d4c8d0 GM |
5262 | |
5263 | @deffn Command push-button &optional pos use-mouse-action | |
5264 | Perform the action specified by a button at location @var{pos}. | |
5265 | @var{pos} may be either a buffer position or a mouse-event. If | |
5266 | @var{use-mouse-action} is non-@code{nil}, or @var{pos} is a | |
5267 | mouse-event (@pxref{Mouse Events}), try to invoke the button's | |
5268 | @code{mouse-action} property instead of @code{action}; if the button | |
5269 | has no @code{mouse-action} property, use @code{action} as normal. | |
5270 | @var{pos} defaults to point, except when @code{push-button} is invoked | |
5271 | interactively as the result of a mouse-event, in which case, the mouse | |
5272 | event's position is used. If there's no button at @var{pos}, do | |
5273 | nothing and return @code{nil}, otherwise return @code{t}. | |
5274 | @end deffn | |
5275 | ||
5276 | @deffn Command forward-button n &optional wrap display-message | |
5277 | Move to the @var{n}th next button, or @var{n}th previous button if | |
5278 | @var{n} is negative. If @var{n} is zero, move to the start of any | |
5279 | button at point. If @var{wrap} is non-@code{nil}, moving past either | |
5280 | end of the buffer continues from the other end. If | |
5281 | @var{display-message} is non-@code{nil}, the button's help-echo string | |
5282 | is displayed. Any button with a non-@code{nil} @code{skip} property | |
5283 | is skipped over. Returns the button found. | |
5284 | @end deffn | |
5285 | ||
5286 | @deffn Command backward-button n &optional wrap display-message | |
5287 | Move to the @var{n}th previous button, or @var{n}th next button if | |
5288 | @var{n} is negative. If @var{n} is zero, move to the start of any | |
5289 | button at point. If @var{wrap} is non-@code{nil}, moving past either | |
5290 | end of the buffer continues from the other end. If | |
5291 | @var{display-message} is non-@code{nil}, the button's help-echo string | |
5292 | is displayed. Any button with a non-@code{nil} @code{skip} property | |
5293 | is skipped over. Returns the button found. | |
5294 | @end deffn | |
5295 | ||
5296 | @defun next-button pos &optional count-current | |
5297 | @defunx previous-button pos &optional count-current | |
5298 | Return the next button after (for @code{next-button} or before (for | |
5299 | @code{previous-button}) position @var{pos} in the current buffer. If | |
5300 | @var{count-current} is non-@code{nil}, count any button at @var{pos} | |
5301 | in the search, instead of starting at the next button. | |
5302 | @end defun | |
5303 | ||
5304 | @node Abstract Display | |
5305 | @section Abstract Display | |
5306 | @cindex ewoc | |
5307 | @cindex display, abstract | |
5308 | @cindex display, arbitrary objects | |
5309 | @cindex model/view/controller | |
5310 | @cindex view part, model/view/controller | |
5311 | ||
5312 | The Ewoc package constructs buffer text that represents a structure | |
5313 | of Lisp objects, and updates the text to follow changes in that | |
5314 | structure. This is like the ``view'' component in the | |
5315 | ``model/view/controller'' design paradigm. | |
5316 | ||
5317 | An @dfn{ewoc} is a structure that organizes information required to | |
5318 | construct buffer text that represents certain Lisp data. The buffer | |
5319 | text of the ewoc has three parts, in order: first, fixed @dfn{header} | |
5320 | text; next, textual descriptions of a series of data elements (Lisp | |
5321 | objects that you specify); and last, fixed @dfn{footer} text. | |
5322 | Specifically, an ewoc contains information on: | |
5323 | ||
5324 | @itemize @bullet | |
5325 | @item | |
5326 | The buffer which its text is generated in. | |
5327 | ||
5328 | @item | |
5329 | The text's start position in the buffer. | |
5330 | ||
5331 | @item | |
5332 | The header and footer strings. | |
5333 | ||
5334 | @item | |
5335 | A doubly-linked chain of @dfn{nodes}, each of which contains: | |
5336 | ||
5337 | @itemize | |
5338 | @item | |
5339 | A @dfn{data element}, a single Lisp object. | |
5340 | ||
5341 | @item | |
5342 | Links to the preceding and following nodes in the chain. | |
5343 | @end itemize | |
5344 | ||
5345 | @item | |
5346 | A @dfn{pretty-printer} function which is responsible for | |
5347 | inserting the textual representation of a data | |
5348 | element value into the current buffer. | |
5349 | @end itemize | |
5350 | ||
5351 | Typically, you define an ewoc with @code{ewoc-create}, and then pass | |
5352 | the resulting ewoc structure to other functions in the Ewoc package to | |
5353 | build nodes within it, and display it in the buffer. Once it is | |
35a30759 | 5354 | displayed in the buffer, other functions determine the correspondence |
b8d4c8d0 GM |
5355 | between buffer positions and nodes, move point from one node's textual |
5356 | representation to another, and so forth. @xref{Abstract Display | |
5357 | Functions}. | |
5358 | ||
5359 | A node @dfn{encapsulates} a data element much the way a variable | |
5360 | holds a value. Normally, encapsulation occurs as a part of adding a | |
5361 | node to the ewoc. You can retrieve the data element value and place a | |
5362 | new value in its place, like so: | |
5363 | ||
5364 | @lisp | |
5365 | (ewoc-data @var{node}) | |
5366 | @result{} value | |
5367 | ||
5368 | (ewoc-set-data @var{node} @var{new-value}) | |
5369 | @result{} @var{new-value} | |
5370 | @end lisp | |
5371 | ||
5372 | @noindent | |
5373 | You can also use, as the data element value, a Lisp object (list or | |
5374 | vector) that is a container for the ``real'' value, or an index into | |
5375 | some other structure. The example (@pxref{Abstract Display Example}) | |
5376 | uses the latter approach. | |
5377 | ||
5378 | When the data changes, you will want to update the text in the | |
5379 | buffer. You can update all nodes by calling @code{ewoc-refresh}, or | |
5380 | just specific nodes using @code{ewoc-invalidate}, or all nodes | |
5381 | satisfying a predicate using @code{ewoc-map}. Alternatively, you can | |
5382 | delete invalid nodes using @code{ewoc-delete} or @code{ewoc-filter}, | |
5383 | and add new nodes in their place. Deleting a node from an ewoc deletes | |
5384 | its associated textual description from buffer, as well. | |
5385 | ||
5386 | @menu | |
5b594a58 GM |
5387 | * Abstract Display Functions:: Functions in the Ewoc package. |
5388 | * Abstract Display Example:: Example of using Ewoc. | |
b8d4c8d0 GM |
5389 | @end menu |
5390 | ||
5391 | @node Abstract Display Functions | |
5392 | @subsection Abstract Display Functions | |
5393 | ||
5394 | In this subsection, @var{ewoc} and @var{node} stand for the | |
5395 | structures described above (@pxref{Abstract Display}), while | |
5396 | @var{data} stands for an arbitrary Lisp object used as a data element. | |
5397 | ||
5398 | @defun ewoc-create pretty-printer &optional header footer nosep | |
5399 | This constructs and returns a new ewoc, with no nodes (and thus no data | |
5400 | elements). @var{pretty-printer} should be a function that takes one | |
5401 | argument, a data element of the sort you plan to use in this ewoc, and | |
5402 | inserts its textual description at point using @code{insert} (and never | |
5403 | @code{insert-before-markers}, because that would interfere with the | |
5404 | Ewoc package's internal mechanisms). | |
5405 | ||
5406 | Normally, a newline is automatically inserted after the header, | |
5407 | the footer and every node's textual description. If @var{nosep} | |
5408 | is non-@code{nil}, no newline is inserted. This may be useful for | |
5409 | displaying an entire ewoc on a single line, for example, or for | |
5410 | making nodes ``invisible'' by arranging for @var{pretty-printer} | |
5411 | to do nothing for those nodes. | |
5412 | ||
5413 | An ewoc maintains its text in the buffer that is current when | |
5414 | you create it, so switch to the intended buffer before calling | |
5415 | @code{ewoc-create}. | |
5416 | @end defun | |
5417 | ||
5418 | @defun ewoc-buffer ewoc | |
5419 | This returns the buffer where @var{ewoc} maintains its text. | |
5420 | @end defun | |
5421 | ||
5422 | @defun ewoc-get-hf ewoc | |
5423 | This returns a cons cell @code{(@var{header} . @var{footer})} | |
5424 | made from @var{ewoc}'s header and footer. | |
5425 | @end defun | |
5426 | ||
5427 | @defun ewoc-set-hf ewoc header footer | |
5428 | This sets the header and footer of @var{ewoc} to the strings | |
5429 | @var{header} and @var{footer}, respectively. | |
5430 | @end defun | |
5431 | ||
5432 | @defun ewoc-enter-first ewoc data | |
5433 | @defunx ewoc-enter-last ewoc data | |
5434 | These add a new node encapsulating @var{data}, putting it, respectively, | |
5435 | at the beginning or end of @var{ewoc}'s chain of nodes. | |
5436 | @end defun | |
5437 | ||
5438 | @defun ewoc-enter-before ewoc node data | |
5439 | @defunx ewoc-enter-after ewoc node data | |
5440 | These add a new node encapsulating @var{data}, adding it to | |
5441 | @var{ewoc} before or after @var{node}, respectively. | |
5442 | @end defun | |
5443 | ||
5444 | @defun ewoc-prev ewoc node | |
5445 | @defunx ewoc-next ewoc node | |
5446 | These return, respectively, the previous node and the next node of @var{node} | |
5447 | in @var{ewoc}. | |
5448 | @end defun | |
5449 | ||
5450 | @defun ewoc-nth ewoc n | |
5451 | This returns the node in @var{ewoc} found at zero-based index @var{n}. | |
5452 | A negative @var{n} means count from the end. @code{ewoc-nth} returns | |
5453 | @code{nil} if @var{n} is out of range. | |
5454 | @end defun | |
5455 | ||
5456 | @defun ewoc-data node | |
5457 | This extracts the data encapsulated by @var{node} and returns it. | |
5458 | @end defun | |
5459 | ||
5460 | @defun ewoc-set-data node data | |
5461 | This sets the data encapsulated by @var{node} to @var{data}. | |
5462 | @end defun | |
5463 | ||
5464 | @defun ewoc-locate ewoc &optional pos guess | |
5465 | This determines the node in @var{ewoc} which contains point (or | |
5466 | @var{pos} if specified), and returns that node. If @var{ewoc} has no | |
5467 | nodes, it returns @code{nil}. If @var{pos} is before the first node, | |
5468 | it returns the first node; if @var{pos} is after the last node, it returns | |
5469 | the last node. The optional third arg @var{guess} | |
5470 | should be a node that is likely to be near @var{pos}; this doesn't | |
5471 | alter the result, but makes the function run faster. | |
5472 | @end defun | |
5473 | ||
5474 | @defun ewoc-location node | |
5475 | This returns the start position of @var{node}. | |
5476 | @end defun | |
5477 | ||
5478 | @defun ewoc-goto-prev ewoc arg | |
5479 | @defunx ewoc-goto-next ewoc arg | |
5480 | These move point to the previous or next, respectively, @var{arg}th node | |
5481 | in @var{ewoc}. @code{ewoc-goto-prev} does not move if it is already at | |
5482 | the first node or if @var{ewoc} is empty, whereas @code{ewoc-goto-next} | |
5483 | moves past the last node, returning @code{nil}. Excepting this special | |
5484 | case, these functions return the node moved to. | |
5485 | @end defun | |
5486 | ||
5487 | @defun ewoc-goto-node ewoc node | |
5488 | This moves point to the start of @var{node} in @var{ewoc}. | |
5489 | @end defun | |
5490 | ||
5491 | @defun ewoc-refresh ewoc | |
5492 | This function regenerates the text of @var{ewoc}. It works by | |
5493 | deleting the text between the header and the footer, i.e., all the | |
5494 | data elements' representations, and then calling the pretty-printer | |
5495 | function for each node, one by one, in order. | |
5496 | @end defun | |
5497 | ||
5498 | @defun ewoc-invalidate ewoc &rest nodes | |
5499 | This is similar to @code{ewoc-refresh}, except that only @var{nodes} in | |
5500 | @var{ewoc} are updated instead of the entire set. | |
5501 | @end defun | |
5502 | ||
5503 | @defun ewoc-delete ewoc &rest nodes | |
5504 | This deletes each node in @var{nodes} from @var{ewoc}. | |
5505 | @end defun | |
5506 | ||
5507 | @defun ewoc-filter ewoc predicate &rest args | |
5508 | This calls @var{predicate} for each data element in @var{ewoc} and | |
5509 | deletes those nodes for which @var{predicate} returns @code{nil}. | |
5510 | Any @var{args} are passed to @var{predicate}. | |
5511 | @end defun | |
5512 | ||
5513 | @defun ewoc-collect ewoc predicate &rest args | |
5514 | This calls @var{predicate} for each data element in @var{ewoc} | |
5515 | and returns a list of those elements for which @var{predicate} | |
5516 | returns non-@code{nil}. The elements in the list are ordered | |
5517 | as in the buffer. Any @var{args} are passed to @var{predicate}. | |
5518 | @end defun | |
5519 | ||
5520 | @defun ewoc-map map-function ewoc &rest args | |
5521 | This calls @var{map-function} for each data element in @var{ewoc} and | |
5522 | updates those nodes for which @var{map-function} returns non-@code{nil}. | |
5523 | Any @var{args} are passed to @var{map-function}. | |
5524 | @end defun | |
5525 | ||
5526 | @node Abstract Display Example | |
5527 | @subsection Abstract Display Example | |
5528 | ||
5529 | Here is a simple example using functions of the ewoc package to | |
5530 | implement a ``color components display,'' an area in a buffer that | |
5531 | represents a vector of three integers (itself representing a 24-bit RGB | |
5532 | value) in various ways. | |
5533 | ||
5534 | @example | |
5535 | (setq colorcomp-ewoc nil | |
5536 | colorcomp-data nil | |
5537 | colorcomp-mode-map nil | |
5538 | colorcomp-labels ["Red" "Green" "Blue"]) | |
5539 | ||
5540 | (defun colorcomp-pp (data) | |
5541 | (if data | |
5542 | (let ((comp (aref colorcomp-data data))) | |
5543 | (insert (aref colorcomp-labels data) "\t: #x" | |
5544 | (format "%02X" comp) " " | |
5545 | (make-string (ash comp -2) ?#) "\n")) | |
5546 | (let ((cstr (format "#%02X%02X%02X" | |
5547 | (aref colorcomp-data 0) | |
5548 | (aref colorcomp-data 1) | |
5549 | (aref colorcomp-data 2))) | |
5550 | (samp " (sample text) ")) | |
5551 | (insert "Color\t: " | |
049bcbcb CY |
5552 | (propertize samp 'face |
5553 | `(foreground-color . ,cstr)) | |
5554 | (propertize samp 'face | |
5555 | `(background-color . ,cstr)) | |
b8d4c8d0 GM |
5556 | "\n")))) |
5557 | ||
5558 | (defun colorcomp (color) | |
5559 | "Allow fiddling with COLOR in a new buffer. | |
5560 | The buffer is in Color Components mode." | |
5561 | (interactive "sColor (name or #RGB or #RRGGBB): ") | |
5562 | (when (string= "" color) | |
5563 | (setq color "green")) | |
5564 | (unless (color-values color) | |
5565 | (error "No such color: %S" color)) | |
5566 | (switch-to-buffer | |
5567 | (generate-new-buffer (format "originally: %s" color))) | |
5568 | (kill-all-local-variables) | |
5569 | (setq major-mode 'colorcomp-mode | |
5570 | mode-name "Color Components") | |
5571 | (use-local-map colorcomp-mode-map) | |
5572 | (erase-buffer) | |
5573 | (buffer-disable-undo) | |
5574 | (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8)) | |
5575 | (color-values color)))) | |
5576 | (ewoc (ewoc-create 'colorcomp-pp | |
5577 | "\nColor Components\n\n" | |
5578 | (substitute-command-keys | |
5579 | "\n\\@{colorcomp-mode-map@}")))) | |
5580 | (set (make-local-variable 'colorcomp-data) data) | |
5581 | (set (make-local-variable 'colorcomp-ewoc) ewoc) | |
5582 | (ewoc-enter-last ewoc 0) | |
5583 | (ewoc-enter-last ewoc 1) | |
5584 | (ewoc-enter-last ewoc 2) | |
5585 | (ewoc-enter-last ewoc nil))) | |
5586 | @end example | |
5587 | ||
5588 | @cindex controller part, model/view/controller | |
5589 | This example can be extended to be a ``color selection widget'' (in | |
5590 | other words, the controller part of the ``model/view/controller'' | |
5591 | design paradigm) by defining commands to modify @code{colorcomp-data} | |
5592 | and to ``finish'' the selection process, and a keymap to tie it all | |
5593 | together conveniently. | |
5594 | ||
5595 | @smallexample | |
5596 | (defun colorcomp-mod (index limit delta) | |
5597 | (let ((cur (aref colorcomp-data index))) | |
5598 | (unless (= limit cur) | |
5599 | (aset colorcomp-data index (+ cur delta))) | |
5600 | (ewoc-invalidate | |
5601 | colorcomp-ewoc | |
5602 | (ewoc-nth colorcomp-ewoc index) | |
5603 | (ewoc-nth colorcomp-ewoc -1)))) | |
5604 | ||
5605 | (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1)) | |
5606 | (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1)) | |
5607 | (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1)) | |
5608 | (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1)) | |
5609 | (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1)) | |
5610 | (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1)) | |
5611 | ||
5612 | (defun colorcomp-copy-as-kill-and-exit () | |
5613 | "Copy the color components into the kill ring and kill the buffer. | |
5614 | The string is formatted #RRGGBB (hash followed by six hex digits)." | |
5615 | (interactive) | |
5616 | (kill-new (format "#%02X%02X%02X" | |
5617 | (aref colorcomp-data 0) | |
5618 | (aref colorcomp-data 1) | |
5619 | (aref colorcomp-data 2))) | |
5620 | (kill-buffer nil)) | |
5621 | ||
5622 | (setq colorcomp-mode-map | |
5623 | (let ((m (make-sparse-keymap))) | |
5624 | (suppress-keymap m) | |
5625 | (define-key m "i" 'colorcomp-R-less) | |
5626 | (define-key m "o" 'colorcomp-R-more) | |
5627 | (define-key m "k" 'colorcomp-G-less) | |
5628 | (define-key m "l" 'colorcomp-G-more) | |
5629 | (define-key m "," 'colorcomp-B-less) | |
5630 | (define-key m "." 'colorcomp-B-more) | |
5631 | (define-key m " " 'colorcomp-copy-as-kill-and-exit) | |
5632 | m)) | |
5633 | @end smallexample | |
5634 | ||
5635 | Note that we never modify the data in each node, which is fixed when the | |
5636 | ewoc is created to be either @code{nil} or an index into the vector | |
5637 | @code{colorcomp-data}, the actual color components. | |
5638 | ||
5639 | @node Blinking | |
5640 | @section Blinking Parentheses | |
5641 | @cindex parenthesis matching | |
5642 | @cindex blinking parentheses | |
5643 | @cindex balancing parentheses | |
5644 | ||
5645 | This section describes the mechanism by which Emacs shows a matching | |
5646 | open parenthesis when the user inserts a close parenthesis. | |
5647 | ||
5648 | @defvar blink-paren-function | |
5649 | The value of this variable should be a function (of no arguments) to | |
5650 | be called whenever a character with close parenthesis syntax is inserted. | |
5651 | The value of @code{blink-paren-function} may be @code{nil}, in which | |
5652 | case nothing is done. | |
5653 | @end defvar | |
5654 | ||
5655 | @defopt blink-matching-paren | |
5656 | If this variable is @code{nil}, then @code{blink-matching-open} does | |
5657 | nothing. | |
5658 | @end defopt | |
5659 | ||
5660 | @defopt blink-matching-paren-distance | |
5661 | This variable specifies the maximum distance to scan for a matching | |
5662 | parenthesis before giving up. | |
5663 | @end defopt | |
5664 | ||
5665 | @defopt blink-matching-delay | |
5666 | This variable specifies the number of seconds for the cursor to remain | |
5667 | at the matching parenthesis. A fraction of a second often gives | |
5668 | good results, but the default is 1, which works on all systems. | |
5669 | @end defopt | |
5670 | ||
5671 | @deffn Command blink-matching-open | |
5672 | This function is the default value of @code{blink-paren-function}. It | |
5673 | assumes that point follows a character with close parenthesis syntax and | |
5674 | moves the cursor momentarily to the matching opening character. If that | |
5675 | character is not already on the screen, it displays the character's | |
5676 | context in the echo area. To avoid long delays, this function does not | |
5677 | search farther than @code{blink-matching-paren-distance} characters. | |
5678 | ||
5679 | Here is an example of calling this function explicitly. | |
5680 | ||
5681 | @smallexample | |
5682 | @group | |
5683 | (defun interactive-blink-matching-open () | |
b8d4c8d0 GM |
5684 | "Indicate momentarily the start of sexp before point." |
5685 | (interactive) | |
5686 | @end group | |
5687 | @group | |
5688 | (let ((blink-matching-paren-distance | |
5689 | (buffer-size)) | |
5690 | (blink-matching-paren t)) | |
5691 | (blink-matching-open))) | |
5692 | @end group | |
5693 | @end smallexample | |
5694 | @end deffn | |
5695 | ||
9a69676a CY |
5696 | @node Character Display |
5697 | @section Character Display | |
5698 | ||
5319014e CY |
5699 | This section describes how characters are actually displayed by |
5700 | Emacs. Typically, a character is displayed as a @dfn{glyph} (a | |
5701 | graphical symbol which occupies one character position on the screen), | |
5702 | whose appearance corresponds to the character itself. For example, | |
5703 | the character @samp{a} (character code 97) is displayed as @samp{a}. | |
5704 | Some characters, however, are displayed specially. For example, the | |
9a69676a CY |
5705 | formfeed character (character code 12) is usually displayed as a |
5706 | sequence of two glyphs, @samp{^L}, while the newline character | |
5707 | (character code 10) starts a new screen line. | |
5708 | ||
5709 | You can modify how each character is displayed by defining a | |
5710 | @dfn{display table}, which maps each character code into a sequence of | |
5319014e | 5711 | glyphs. @xref{Display Tables}. |
9a69676a CY |
5712 | |
5713 | @menu | |
5714 | * Usual Display:: The usual conventions for displaying characters. | |
5715 | * Display Tables:: What a display table consists of. | |
5716 | * Active Display Table:: How Emacs selects a display table to use. | |
5717 | * Glyphs:: How to define a glyph, and what glyphs mean. | |
5718 | * Glyphless Chars:: How glyphless characters are drawn. | |
5719 | @end menu | |
5720 | ||
b8d4c8d0 | 5721 | @node Usual Display |
9a69676a | 5722 | @subsection Usual Display Conventions |
b8d4c8d0 | 5723 | |
5319014e CY |
5724 | Here are the conventions for displaying each character code (in the |
5725 | absence of a display table, which can override these | |
9a69676a CY |
5726 | @iftex |
5727 | conventions). | |
5728 | @end iftex | |
5729 | @ifnottex | |
5730 | conventions; @pxref{Display Tables}). | |
5731 | @end ifnottex | |
b8d4c8d0 | 5732 | |
9a69676a | 5733 | @cindex printable ASCII characters |
b8d4c8d0 GM |
5734 | @itemize @bullet |
5735 | @item | |
9a69676a CY |
5736 | The @dfn{printable @acronym{ASCII} characters}, character codes 32 |
5737 | through 126 (consisting of numerals, English letters, and symbols like | |
5319014e | 5738 | @samp{#}) are displayed literally. |
b8d4c8d0 GM |
5739 | |
5740 | @item | |
9a69676a CY |
5741 | The tab character (character code 9) displays as whitespace stretching |
5742 | up to the next tab stop column. @xref{Text Display,,, emacs, The GNU | |
5743 | Emacs Manual}. The variable @code{tab-width} controls the number of | |
5744 | spaces per tab stop (see below). | |
b8d4c8d0 GM |
5745 | |
5746 | @item | |
5319014e CY |
5747 | The newline character (character code 10) has a special effect: it |
5748 | ends the preceding line and starts a new line. | |
b8d4c8d0 | 5749 | |
9a69676a | 5750 | @cindex ASCII control characters |
b8d4c8d0 | 5751 | @item |
9a69676a CY |
5752 | The non-printable @dfn{@acronym{ASCII} control characters}---character |
5753 | codes 0 through 31, as well as the @key{DEL} character (character code | |
5754 | 127)---display in one of two ways according to the variable | |
5755 | @code{ctl-arrow}. If this variable is non-@code{nil} (the default), | |
5756 | these characters are displayed as sequences of two glyphs, where the | |
5757 | first glyph is @samp{^} (a display table can specify a glyph to use | |
5758 | instead of @samp{^}); e.g.@: the @key{DEL} character is displayed as | |
5759 | @samp{^?}. | |
5760 | ||
5761 | If @code{ctl-arrow} is @code{nil}, these characters are displayed as | |
5762 | octal escapes (see below). | |
5763 | ||
5764 | This rule also applies to carriage return (character code 13), if that | |
5765 | character appears in the buffer. But carriage returns usually do not | |
5766 | appear in buffer text; they are eliminated as part of end-of-line | |
5767 | conversion (@pxref{Coding System Basics}). | |
a3dcc84e EZ |
5768 | |
5769 | @cindex octal escapes | |
b8d4c8d0 | 5770 | @item |
9a69676a CY |
5771 | @dfn{Raw bytes} are non-@acronym{ASCII} characters with codes 128 |
5772 | through 255 (@pxref{Text Representations}). These characters display | |
5773 | as @dfn{octal escapes}: sequences of four glyphs, where the first | |
5774 | glyph is the @acronym{ASCII} code for @samp{\}, and the others are | |
5775 | digit characters representing the character code in octal. (A display | |
5776 | table can specify a glyph to use instead of @samp{\}.) | |
b8d4c8d0 GM |
5777 | |
5778 | @item | |
9a69676a CY |
5779 | Each non-@acronym{ASCII} character with code above 255 is displayed |
5780 | literally, if the terminal supports it. If the terminal does not | |
5781 | support it, the character is said to be @dfn{glyphless}, and it is | |
5782 | usually displayed using a placeholder glyph. For example, if a | |
5783 | graphical terminal has no font for a character, Emacs usually displays | |
5784 | a box containing the character code in hexadecimal. @xref{Glyphless | |
5785 | Chars}. | |
b8d4c8d0 GM |
5786 | @end itemize |
5787 | ||
9a69676a | 5788 | The above display conventions apply even when there is a display |
b8d4c8d0 GM |
5789 | table, for any character whose entry in the active display table is |
5790 | @code{nil}. Thus, when you set up a display table, you need only | |
5791 | specify the characters for which you want special behavior. | |
5792 | ||
9a69676a CY |
5793 | The following variables affect how certain characters are displayed |
5794 | on the screen. Since they change the number of columns the characters | |
5795 | occupy, they also affect the indentation functions. They also affect | |
b8d4c8d0 GM |
5796 | how the mode line is displayed; if you want to force redisplay of the |
5797 | mode line using the new values, call the function | |
5798 | @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
5799 | ||
5800 | @defopt ctl-arrow | |
5801 | @cindex control characters in display | |
5802 | This buffer-local variable controls how control characters are | |
5803 | displayed. If it is non-@code{nil}, they are displayed as a caret | |
5804 | followed by the character: @samp{^A}. If it is @code{nil}, they are | |
a3dcc84e EZ |
5805 | displayed as octal escapes: a backslash followed by three octal |
5806 | digits, as in @samp{\001}. | |
b8d4c8d0 GM |
5807 | @end defopt |
5808 | ||
b8d4c8d0 GM |
5809 | @defopt tab-width |
5810 | The value of this buffer-local variable is the spacing between tab | |
5811 | stops used for displaying tab characters in Emacs buffers. The value | |
5812 | is in units of columns, and the default is 8. Note that this feature | |
5813 | is completely independent of the user-settable tab stops used by the | |
5814 | command @code{tab-to-tab-stop}. @xref{Indent Tabs}. | |
5815 | @end defopt | |
5816 | ||
5817 | @node Display Tables | |
9a69676a | 5818 | @subsection Display Tables |
b8d4c8d0 GM |
5819 | |
5820 | @cindex display table | |
9a69676a CY |
5821 | A display table is a special-purpose char-table |
5822 | (@pxref{Char-Tables}), with @code{display-table} as its subtype, which | |
5823 | is used to override the usual character display conventions. This | |
5824 | section describes how to make, inspect, and assign elements to a | |
5825 | display table object. | |
b8d4c8d0 GM |
5826 | |
5827 | @defun make-display-table | |
5828 | This creates and returns a display table. The table initially has | |
5829 | @code{nil} in all elements. | |
5830 | @end defun | |
5831 | ||
5832 | The ordinary elements of the display table are indexed by character | |
5833 | codes; the element at index @var{c} says how to display the character | |
9a69676a CY |
5834 | code @var{c}. The value should be @code{nil} (which means to display |
5835 | the character @var{c} according to the usual display conventions; | |
5836 | @pxref{Usual Display}), or a vector of glyph codes (which means to | |
5837 | display the character @var{c} as those glyphs; @pxref{Glyphs}). | |
b8d4c8d0 GM |
5838 | |
5839 | @strong{Warning:} if you use the display table to change the display | |
5840 | of newline characters, the whole buffer will be displayed as one long | |
5841 | ``line.'' | |
5842 | ||
5843 | The display table also has six ``extra slots'' which serve special | |
5844 | purposes. Here is a table of their meanings; @code{nil} in any slot | |
5845 | means to use the default for that slot, as stated below. | |
5846 | ||
5847 | @table @asis | |
5848 | @item 0 | |
5849 | The glyph for the end of a truncated screen line (the default for this | |
5850 | is @samp{$}). @xref{Glyphs}. On graphical terminals, Emacs uses | |
5851 | arrows in the fringes to indicate truncation, so the display table has | |
5852 | no effect. | |
5853 | ||
5854 | @item 1 | |
5855 | The glyph for the end of a continued line (the default is @samp{\}). | |
5856 | On graphical terminals, Emacs uses curved arrows in the fringes to | |
5857 | indicate continuation, so the display table has no effect. | |
5858 | ||
5859 | @item 2 | |
5860 | The glyph for indicating a character displayed as an octal character | |
5861 | code (the default is @samp{\}). | |
5862 | ||
5863 | @item 3 | |
5864 | The glyph for indicating a control character (the default is @samp{^}). | |
5865 | ||
5866 | @item 4 | |
5867 | A vector of glyphs for indicating the presence of invisible lines (the | |
5868 | default is @samp{...}). @xref{Selective Display}. | |
5869 | ||
5870 | @item 5 | |
5871 | The glyph used to draw the border between side-by-side windows (the | |
5872 | default is @samp{|}). @xref{Splitting Windows}. This takes effect only | |
5873 | when there are no scroll bars; if scroll bars are supported and in use, | |
5874 | a scroll bar separates the two windows. | |
5875 | @end table | |
5876 | ||
5319014e CY |
5877 | For example, here is how to construct a display table that mimics |
5878 | the effect of setting @code{ctl-arrow} to a non-@code{nil} value | |
5879 | (@pxref{Glyphs}, for the function @code{make-glyph-code}): | |
b8d4c8d0 GM |
5880 | |
5881 | @example | |
5882 | (setq disptab (make-display-table)) | |
9a69676a CY |
5883 | (dotimes (i 32) |
5884 | (or (= i ?\t) | |
5885 | (= i ?\n) | |
5319014e CY |
5886 | (aset disptab i |
5887 | (vector (make-glyph-code ?^ 'escape-glyph) | |
5888 | (make-glyph-code (+ i 64) 'escape-glyph))))) | |
5889 | (aset disptab 127 | |
5890 | (vector (make-glyph-code ?^ 'escape-glyph) | |
5891 | (make-glyph-code ?? 'escape-glyph))))) | |
b8d4c8d0 GM |
5892 | @end example |
5893 | ||
5894 | @defun display-table-slot display-table slot | |
5895 | This function returns the value of the extra slot @var{slot} of | |
5896 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
5897 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
5898 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
5899 | @code{selective-display}, and @code{vertical-border}. | |
5900 | @end defun | |
5901 | ||
5902 | @defun set-display-table-slot display-table slot value | |
5903 | This function stores @var{value} in the extra slot @var{slot} of | |
5904 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
5905 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
5906 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
5907 | @code{selective-display}, and @code{vertical-border}. | |
5908 | @end defun | |
5909 | ||
5910 | @defun describe-display-table display-table | |
5911 | This function displays a description of the display table | |
5912 | @var{display-table} in a help buffer. | |
5913 | @end defun | |
5914 | ||
5915 | @deffn Command describe-current-display-table | |
5916 | This command displays a description of the current display table in a | |
5917 | help buffer. | |
5918 | @end deffn | |
5919 | ||
5920 | @node Active Display Table | |
5921 | @subsection Active Display Table | |
5922 | @cindex active display table | |
5923 | ||
9a69676a CY |
5924 | Each window can specify a display table, and so can each buffer. |
5925 | The window's display table, if there is one, takes precedence over the | |
5926 | buffer's display table. If neither exists, Emacs tries to use the | |
5927 | standard display table; if that is @code{nil}, Emacs uses the usual | |
5928 | character display conventions (@pxref{Usual Display}). | |
5929 | ||
5930 | Note that display tables affect how the mode line is displayed, so | |
5931 | if you want to force redisplay of the mode line using a new display | |
5932 | table, call @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
b8d4c8d0 GM |
5933 | |
5934 | @defun window-display-table &optional window | |
9a69676a CY |
5935 | This function returns @var{window}'s display table, or @code{nil} if |
5936 | there is none. The default for @var{window} is the selected window. | |
b8d4c8d0 GM |
5937 | @end defun |
5938 | ||
5939 | @defun set-window-display-table window table | |
5940 | This function sets the display table of @var{window} to @var{table}. | |
5941 | The argument @var{table} should be either a display table or | |
5942 | @code{nil}. | |
5943 | @end defun | |
5944 | ||
5945 | @defvar buffer-display-table | |
9a69676a CY |
5946 | This variable is automatically buffer-local in all buffers; its value |
5947 | specifies the buffer's display table. If it is @code{nil}, there is | |
5948 | no buffer display table. | |
b8d4c8d0 GM |
5949 | @end defvar |
5950 | ||
5951 | @defvar standard-display-table | |
9a69676a CY |
5952 | The value of this variable is the standard display table, which is |
5953 | used when Emacs is displaying a buffer in a window with neither a | |
5954 | window display table nor a buffer display table defined. Its default | |
5955 | is @code{nil}. | |
b8d4c8d0 GM |
5956 | @end defvar |
5957 | ||
9a69676a CY |
5958 | The @file{disp-table} library defines several functions for changing |
5959 | the standard display table. | |
b8d4c8d0 GM |
5960 | |
5961 | @node Glyphs | |
5962 | @subsection Glyphs | |
5319014e | 5963 | @cindex glyph |
b8d4c8d0 | 5964 | |
9a69676a CY |
5965 | A @dfn{glyph} is a graphical symbol which occupies a single |
5966 | character position on the screen. Each glyph is represented in Lisp | |
5319014e CY |
5967 | as a @dfn{glyph code}, which specifies a character and optionally a |
5968 | face to display it in (@pxref{Faces}). The main use of glyph codes is | |
5969 | as the entries of display tables (@pxref{Display Tables}). The | |
5970 | following functions are used to manipulate glyph codes: | |
b8d4c8d0 GM |
5971 | |
5972 | @defun make-glyph-code char &optional face | |
5319014e CY |
5973 | This function returns a glyph code representing char @var{char} with |
5974 | face @var{face}. If @var{face} is omitted or @code{nil}, the glyph | |
5975 | uses the default face; in that case, the glyph code is an integer. If | |
5976 | @var{face} is non-@code{nil}, the glyph code is not necessarily an | |
5977 | integer object. | |
b8d4c8d0 GM |
5978 | @end defun |
5979 | ||
5980 | @defun glyph-char glyph | |
5319014e | 5981 | This function returns the character of glyph code @var{glyph}. |
b8d4c8d0 GM |
5982 | @end defun |
5983 | ||
5984 | @defun glyph-face glyph | |
5319014e CY |
5985 | This function returns face of glyph code @var{glyph}, or @code{nil} if |
5986 | @var{glyph} uses the default face. | |
b8d4c8d0 GM |
5987 | @end defun |
5988 | ||
5319014e CY |
5989 | @ifnottex |
5990 | You can set up a @dfn{glyph table} to change how glyph codes are | |
5991 | actually displayed on text terminals. This feature is semi-obsolete; | |
5992 | use @code{glyphless-char-display} instead (@pxref{Glyphless Chars}). | |
b8d4c8d0 GM |
5993 | |
5994 | @defvar glyph-table | |
5319014e CY |
5995 | The value of this variable, if non-@code{nil}, is the current glyph |
5996 | table. It takes effect only on character terminals; on graphical | |
5997 | displays, all glyphs are displayed literally. The glyph table should | |
5998 | be a vector whose @var{g}th element specifies how to display glyph | |
5999 | code @var{g}, where @var{g} is the glyph code for a glyph whose face | |
6000 | is unspecified. Each element should be one of the following: | |
b8d4c8d0 GM |
6001 | |
6002 | @table @asis | |
b8d4c8d0 | 6003 | @item @code{nil} |
5319014e | 6004 | Display this glyph literally. |
b8d4c8d0 | 6005 | |
5319014e CY |
6006 | @item a string |
6007 | Display this glyph by sending the specified string to the terminal. | |
b8d4c8d0 | 6008 | |
5319014e CY |
6009 | @item a glyph code |
6010 | Display the specified glyph code instead. | |
6011 | @end table | |
b8d4c8d0 | 6012 | |
5319014e CY |
6013 | Any integer glyph code greater than or equal to the length of the |
6014 | glyph table is displayed literally. | |
b8d4c8d0 | 6015 | @end defvar |
5319014e | 6016 | @end ifnottex |
b8d4c8d0 | 6017 | |
9a69676a CY |
6018 | @node Glyphless Chars |
6019 | @subsection Glyphless Character Display | |
6020 | @cindex glyphless characters | |
6021 | ||
5319014e CY |
6022 | @dfn{Glyphless characters} are characters which are displayed in a |
6023 | special way, e.g.@: as a box containing a hexadecimal code, instead of | |
6024 | being displayed literally. These include characters which are | |
6025 | explicitly defined to be glyphless, as well as characters for which | |
6026 | there is no available font (on a graphical display), and characters | |
6027 | which cannot be encoded by the terminal's coding system (on a text | |
6028 | terminal). | |
9a69676a CY |
6029 | |
6030 | @defvar glyphless-char-display | |
5319014e CY |
6031 | The value of this variable is a char-table which defines glyphless |
6032 | characters and how they are displayed. Each entry must be one of the | |
6033 | following display methods: | |
9a69676a CY |
6034 | |
6035 | @table @asis | |
5319014e CY |
6036 | @item @code{nil} |
6037 | Display the character in the usual way. | |
6038 | ||
9a69676a CY |
6039 | @item @code{zero-width} |
6040 | Don't display the character. | |
6041 | ||
6042 | @item @code{thin-space} | |
6043 | Display a thin space, 1-pixel wide on graphical displays, or | |
6044 | 1-character wide on text terminals. | |
6045 | ||
6046 | @item @code{empty-box} | |
6047 | Display an empty box. | |
6048 | ||
6049 | @item @code{hex-code} | |
6050 | Display a box containing the Unicode codepoint of the character, in | |
6051 | hexadecimal notation. | |
6052 | ||
6053 | @item an @acronym{ASCII} string | |
6054 | Display a box containing that string. | |
5319014e CY |
6055 | |
6056 | @item a cons cell @code{(@var{graphical} . @var{text})} | |
6057 | Display with @var{graphical} on graphical displays, and with | |
6058 | @var{text} on text terminals. Both @var{graphical} and @var{text} | |
6059 | must be one of the display methods described above. | |
9a69676a CY |
6060 | @end table |
6061 | ||
6062 | @noindent | |
5319014e CY |
6063 | The @code{thin-space}, @code{empty-box}, @code{hex-code}, and |
6064 | @acronym{ASCII} string display methods are drawn with the | |
9a69676a CY |
6065 | @code{glyphless-char} face. |
6066 | ||
9a69676a CY |
6067 | The char-table has one extra slot, which determines how to display any |
6068 | character that cannot be displayed with any available font, or cannot | |
6069 | be encoded by the terminal's coding system. Its value should be one | |
6070 | of the above display methods, except @code{zero-width} or a cons cell. | |
5319014e CY |
6071 | |
6072 | If a character has a non-@code{nil} entry in an active display table, | |
6073 | the display table takes effect; in this case, Emacs does not consult | |
6074 | @code{glyphless-char-display} at all. | |
9a69676a CY |
6075 | @end defvar |
6076 | ||
6077 | @defopt glyphless-char-display-control | |
6078 | This user option provides a convenient way to set | |
5319014e CY |
6079 | @code{glyphless-char-display} for groups of similar characters. Do |
6080 | not set its value directly from Lisp code; the value takes effect only | |
6081 | via a custom @code{:set} function (@pxref{Variable Definitions}), | |
6082 | which updates @code{glyphless-char-display}. | |
9a69676a CY |
6083 | |
6084 | Its value should be an alist of elements @code{(@var{group} | |
6085 | . @var{method})}, where @var{group} is a symbol specifying a group of | |
6086 | characters, and @var{method} is a symbol specifying how to display | |
6087 | them. | |
6088 | ||
6089 | @var{group} should be one of the following: | |
6090 | ||
6091 | @table @code | |
6092 | @item c0-control | |
6093 | @acronym{ASCII} control characters @code{U+0000} to @code{U+001F}, | |
6094 | excluding the newline and tab characters (normally displayed as escape | |
6095 | sequences like @samp{^A}; @pxref{Text Display,, How Text Is Displayed, | |
6096 | emacs, The GNU Emacs Manual}). | |
6097 | ||
6098 | @item c1-control | |
6099 | Non-@acronym{ASCII}, non-printing characters @code{U+0080} to | |
6100 | @code{U+009F} (normally displayed as octal escape sequences like | |
6101 | @samp{\230}). | |
6102 | ||
6103 | @item format-control | |
6104 | Characters of Unicode General Category `Cf', such as @samp{U+200E} | |
6105 | (Left-to-Right Mark), but excluding characters that have graphic | |
6106 | images, such as @samp{U+00AD} (Soft Hyphen). | |
6107 | ||
6108 | @item no-font | |
6109 | Characters for there is no suitable font, or which cannot be encoded | |
6110 | by the terminal's coding system. | |
6111 | @end table | |
6112 | ||
6113 | @c FIXME: this can also be `acronym', but that's not currently | |
6114 | @c completely implemented; it applies only to the format-control | |
6115 | @c group, and only works if the acronym is in `char-acronym-table'. | |
6116 | The @var{method} symbol should be one of @code{zero-width}, | |
6117 | @code{thin-space}, @code{empty-box}, or @code{hex-code}. These have | |
6118 | the same meanings as in @code{glyphless-char-display}, above. | |
6119 | @end defopt | |
6120 | ||
5319014e CY |
6121 | @node Beeping |
6122 | @section Beeping | |
6123 | @cindex bell | |
6124 | ||
6125 | This section describes how to make Emacs ring the bell (or blink the | |
6126 | screen) to attract the user's attention. Be conservative about how | |
6127 | often you do this; frequent bells can become irritating. Also be | |
6128 | careful not to use just beeping when signaling an error is more | |
6129 | appropriate (@pxref{Errors}). | |
6130 | ||
6131 | @defun ding &optional do-not-terminate | |
6132 | @cindex keyboard macro termination | |
6133 | This function beeps, or flashes the screen (see @code{visible-bell} below). | |
6134 | It also terminates any keyboard macro currently executing unless | |
6135 | @var{do-not-terminate} is non-@code{nil}. | |
6136 | @end defun | |
6137 | ||
6138 | @defun beep &optional do-not-terminate | |
6139 | This is a synonym for @code{ding}. | |
6140 | @end defun | |
6141 | ||
6142 | @defopt visible-bell | |
6143 | This variable determines whether Emacs should flash the screen to | |
6144 | represent a bell. Non-@code{nil} means yes, @code{nil} means no. | |
6145 | This is effective on graphical displays, and on text terminals | |
6146 | provided the terminal's Termcap entry defines the visible bell | |
6147 | capability (@samp{vb}). | |
6148 | @end defopt | |
6149 | ||
6150 | @defvar ring-bell-function | |
6151 | If this is non-@code{nil}, it specifies how Emacs should ``ring the | |
6152 | bell.'' Its value should be a function of no arguments. If this is | |
6153 | non-@code{nil}, it takes precedence over the @code{visible-bell} | |
6154 | variable. | |
6155 | @end defvar | |
6156 | ||
b8d4c8d0 GM |
6157 | @node Window Systems |
6158 | @section Window Systems | |
6159 | ||
6160 | Emacs works with several window systems, most notably the X Window | |
6161 | System. Both Emacs and X use the term ``window,'' but use it | |
6162 | differently. An Emacs frame is a single window as far as X is | |
6163 | concerned; the individual Emacs windows are not known to X at all. | |
6164 | ||
6165 | @defvar window-system | |
c830e5ae CY |
6166 | This terminal-local variable tells Lisp programs what window system |
6167 | Emacs is using for displaying the frame. The possible values are | |
b8d4c8d0 GM |
6168 | |
6169 | @table @code | |
6170 | @item x | |
6171 | @cindex X Window System | |
77bb0476 | 6172 | Emacs is displaying the frame using X. |
b8d4c8d0 | 6173 | @item w32 |
77bb0476 | 6174 | Emacs is displaying the frame using native MS-Windows GUI. |
ca27c21b CY |
6175 | @item ns |
6176 | Emacs is displaying the frame using the Nextstep interface (used on | |
6177 | GNUstep and Mac OS X). | |
77bb0476 EZ |
6178 | @item pc |
6179 | Emacs is displaying the frame using MS-DOS direct screen writes. | |
b8d4c8d0 | 6180 | @item nil |
77bb0476 | 6181 | Emacs is displaying the frame on a character-based terminal. |
b8d4c8d0 GM |
6182 | @end table |
6183 | @end defvar | |
6184 | ||
4267d515 EZ |
6185 | @defvar initial-window-system |
6186 | This variable holds the value of @code{window-system} used for the | |
f721deda EZ |
6187 | first frame created by Emacs during startup. (When Emacs is invoked |
6188 | with the @option{--daemon} option, it does not create any initial | |
6189 | frames, so @code{initial-window-system} is @code{nil}. @xref{Initial | |
6190 | Options, daemon,, emacs, The GNU Emacs Manual}.) | |
4267d515 EZ |
6191 | @end defvar |
6192 | ||
77bb0476 EZ |
6193 | @defun window-system &optional frame |
6194 | This function returns a symbol whose name tells what window system is | |
6195 | used for displaying @var{frame} (which defaults to the currently | |
6196 | selected frame). The list of possible symbols it returns is the same | |
6197 | one documented for the variable @code{window-system} above. | |
6198 | @end defun | |
6199 | ||
89baa1df EZ |
6200 | Do @emph{not} use @code{window-system} and |
6201 | @code{initial-window-system} as predicates or boolean flag variables, | |
6202 | if you want to write code that works differently on text terminals and | |
6203 | graphic displays. That is because @code{window-system} is not a good | |
6204 | indicator of Emacs capabilities on a given display type. Instead, use | |
6205 | @code{display-graphic-p} or any of the other @code{display-*-p} | |
6206 | predicates described in @ref{Display Feature Testing}. | |
6207 | ||
b8d4c8d0 GM |
6208 | @defvar window-setup-hook |
6209 | This variable is a normal hook which Emacs runs after handling the | |
6210 | initialization files. Emacs runs this hook after it has completed | |
6211 | loading your init file, the default initialization file (if | |
6212 | any), and the terminal-specific Lisp code, and running the hook | |
6213 | @code{term-setup-hook}. | |
6214 | ||
6215 | This hook is used for internal purposes: setting up communication with | |
6216 | the window system, and creating the initial window. Users should not | |
6217 | interfere with it. | |
6218 | @end defvar | |
5deb92fd EZ |
6219 | |
6220 | @node Bidirectional Display | |
6221 | @section Bidirectional Display | |
6222 | @cindex bidirectional display | |
6223 | @cindex right-to-left text | |
6224 | ||
6225 | Emacs can display text written in scripts, such as Arabic, Farsi, | |
5319014e CY |
6226 | and Hebrew, whose natural ordering for horizontal text display runs |
6227 | from right to left. Furthermore, segments of Latin script and digits | |
6228 | embedded in right-to-left text are displayed left-to-right, while | |
6229 | segments of right-to-left script embedded in left-to-right text | |
6230 | (e.g.@: Arabic or Hebrew text in comments or strings in a program | |
6231 | source file) are appropriately displayed right-to-left. We call such | |
6232 | mixtures of left-to-right and right-to-left text @dfn{bidirectional | |
6233 | text}. This section describes the facilities and options for editing | |
6234 | and displaying bidirectional text. | |
5deb92fd EZ |
6235 | |
6236 | @cindex logical order | |
c094bb0c | 6237 | @cindex reading order |
5deb92fd EZ |
6238 | @cindex visual order |
6239 | @cindex unicode bidirectional algorithm | |
5319014e CY |
6240 | @cindex bidirectional reordering |
6241 | Text is stored in Emacs buffers and strings in @dfn{logical} (or | |
6242 | @dfn{reading}) order, i.e.@: the order in which a human would read | |
6243 | each character. In right-to-left and bidirectional text, the order in | |
6244 | which characters are displayed on the screen (called @dfn{visual | |
6245 | order}) is not the same as logical order; the characters' screen | |
6246 | positions do not increase monotonically with string or buffer | |
6247 | position. In performing this @dfn{bidirectional reordering}, Emacs | |
6248 | follows the Unicode Bidirectional Algorithm (a.k.a.@: @acronym{UBA}), | |
6249 | which is described in Annex #9 of the Unicode standard | |
6250 | (@url{http://www.unicode.org/reports/tr9/}). Emacs provides a ``Full | |
6251 | Bidirectionality'' class implementation of the @acronym{UBA}. | |
5deb92fd EZ |
6252 | |
6253 | @defvar bidi-display-reordering | |
5319014e CY |
6254 | If the value of this buffer-local variable is non-@code{nil} (the |
6255 | default), Emacs performs bidirectional reordering for display. The | |
6256 | reordering affects buffer text, as well as display strings and overlay | |
6257 | strings from text and overlay properties in the buffer (@pxref{Overlay | |
6258 | Properties}, and @pxref{Display Property}). If the value is | |
6259 | @code{nil}, Emacs does not perform bidirectional reordering in the | |
6260 | buffer. | |
6261 | ||
6262 | The default value of @code{bidi-display-reordering} controls the | |
6263 | reordering of strings which are not directly supplied by a buffer, | |
6264 | including the text displayed in mode lines (@pxref{Mode Line Format}) | |
6265 | and header lines (@pxref{Header Lines}). | |
5deb92fd EZ |
6266 | @end defvar |
6267 | ||
6268 | @cindex unibyte buffers, and bidi reordering | |
5319014e CY |
6269 | Emacs never reorders the text of a unibyte buffer, even if |
6270 | @code{bidi-display-reordering} is non-@code{nil} in the buffer. This | |
6271 | is because unibyte buffers contain raw bytes, not characters, and thus | |
6272 | lack the directionality properties required for reordering. | |
6273 | Therefore, to test whether text in a buffer will be reordered for | |
6274 | display, it is not enough to test the value of | |
6275 | @code{bidi-display-reordering} alone. The correct test is this: | |
5deb92fd EZ |
6276 | |
6277 | @example | |
6278 | (if (and enable-multibyte-characters | |
6279 | bidi-display-reordering) | |
6280 | ;; Buffer is being reordered for display | |
6281 | ) | |
6282 | @end example | |
6283 | ||
5319014e CY |
6284 | However, unibyte display and overlay strings @emph{are} reordered if |
6285 | their parent buffer is reordered. This is because plain-@sc{ascii} | |
6286 | strings are stored by Emacs as unibyte strings. If a unibyte display | |
6287 | or overlay string includes non-@sc{ascii} characters, these characters | |
6288 | are assumed to have left-to-right direction. | |
5deb92fd EZ |
6289 | |
6290 | @cindex display properties, and bidi reordering of text | |
6291 | Text covered by @code{display} text properties, by overlays with | |
6292 | @code{display} properties whose value is a string, and by any other | |
6293 | properties that replace buffer text, is treated as a single unit when | |
6294 | it is reordered for display. That is, the entire chunk of text | |
6295 | covered by these properties is reordered together. Moreover, the | |
5319014e | 6296 | bidirectional properties of the characters in such a chunk of text are |
5deb92fd | 6297 | ignored, and Emacs reorders them as if they were replaced with a |
c094bb0c | 6298 | single character @code{U+FFFC}, known as the @dfn{Object Replacement |
5deb92fd EZ |
6299 | Character}. This means that placing a display property over a portion |
6300 | of text may change the way that the surrounding text is reordered for | |
6301 | display. To prevent this unexpected effect, always place such | |
6302 | properties on text whose directionality is identical with text that | |
6303 | surrounds it. | |
6304 | ||
6305 | @cindex base direction of a paragraph | |
5319014e CY |
6306 | Each paragraph of bidirectional text has a @dfn{base direction}, |
6307 | either right-to-left or left-to-right. Left-to-right paragraphs are | |
6308 | displayed beginning at the left margin of the window, and are | |
6309 | truncated or continued when the text reaches the right margin. | |
6310 | Right-to-left paragraphs are displayed beginning at the right margin, | |
6311 | and are continued or truncated at the left margin. | |
6312 | ||
6313 | By default, Emacs determines the base direction of each paragraph by | |
6314 | looking at the text at its beginning. The precise method of | |
6315 | determining the base direction is specified by the @acronym{UBA}; in a | |
6316 | nutshell, the first character in a paragraph that has an explicit | |
6317 | directionality determines the base direction of the paragraph. | |
6318 | However, sometimes a buffer may need to force a certain base direction | |
6319 | for its paragraphs. For example, buffers containing program source | |
6320 | code should force all paragraphs to be displayed left-to-right. You | |
6321 | can use following variable to do this: | |
5deb92fd EZ |
6322 | |
6323 | @defvar bidi-paragraph-direction | |
5319014e CY |
6324 | If the value of this buffer-local variable is the symbol |
6325 | @code{right-to-left} or @code{left-to-right}, all paragraphs in the | |
6326 | buffer are assumed to have that specified direction. Any other value | |
6327 | is equivalent to @code{nil} (the default), which means to determine | |
6328 | the base direction of each paragraph from its contents. | |
c094bb0c EZ |
6329 | |
6330 | @cindex @code{prog-mode}, and @code{bidi-paragraph-direction} | |
5319014e CY |
6331 | Modes for program source code should set this to @code{left-to-right}. |
6332 | Prog mode does this by default, so modes derived from Prog mode do not | |
6333 | need to set this explicitly (@pxref{Basic Major Modes}). | |
5deb92fd EZ |
6334 | @end defvar |
6335 | ||
6336 | @defun current-bidi-paragraph-direction &optional buffer | |
6337 | This function returns the paragraph direction at point in the named | |
6338 | @var{buffer}. The returned value is a symbol, either | |
6339 | @code{left-to-right} or @code{right-to-left}. If @var{buffer} is | |
6340 | omitted or @code{nil}, it defaults to the current buffer. If the | |
6341 | buffer-local value of the variable @code{bidi-paragraph-direction} is | |
6342 | non-@code{nil}, the returned value will be identical to that value; | |
6343 | otherwise, the returned value reflects the paragraph direction | |
5980d4c6 EZ |
6344 | determined dynamically by Emacs. For buffers whose value of |
6345 | @code{bidi-display-reordering} is @code{nil} as well as unibyte | |
6346 | buffers, this function always returns @code{left-to-right}. | |
5deb92fd | 6347 | @end defun |
c094bb0c EZ |
6348 | |
6349 | @cindex layout on display, and bidirectional text | |
6350 | @cindex jumbled display of bidirectional text | |
6351 | @cindex concatenating bidirectional strings | |
5319014e CY |
6352 | Bidirectional reordering can have surprising and unpleasant effects |
6353 | when two strings with bidirectional content are juxtaposed in a | |
6354 | buffer, or otherwise programmatically concatenated into a string of | |
6355 | text. A typical problematic case is when a buffer consists of | |
6356 | sequences of text ``fields'' separated by whitespace or punctuation | |
6357 | characters, like Buffer Menu mode or Rmail Summary Mode. Because the | |
6358 | punctuation characters used as separators have @dfn{weak | |
6359 | directionality}, they take on the directionality of surrounding text. | |
6360 | As result, a numeric field that follows a field with bidirectional | |
6361 | content can be displayed @emph{to the left} of the preceding field, | |
6362 | messing up the expected layout. There are several ways to avoid this | |
6363 | problem: | |
c094bb0c EZ |
6364 | |
6365 | @itemize @minus | |
6366 | @item | |
6367 | Append the special character @code{U+200E}, LEFT-TO-RIGHT MARK, or | |
6368 | @acronym{LRM}, to the end of each field that may have bidirectional | |
6369 | content, or prepend it to the beginning of the following field. The | |
92b71444 EZ |
6370 | function @code{bidi-string-mark-left-to-right}, described below, comes |
6371 | in handy for this purpose. (In a right-to-left paragraph, use | |
c094bb0c | 6372 | @code{U+200F}, RIGHT-TO-LEFT MARK, or @acronym{RLM}, instead.) This |
5319014e | 6373 | is one of the solutions recommended by the UBA. |
c094bb0c EZ |
6374 | |
6375 | @item | |
6376 | Include the tab character in the field separator. The tab character | |
5319014e CY |
6377 | plays the role of @dfn{segment separator} in bidirectional reordering, |
6378 | causing the text on either side to be reordered separately. | |
0c95fcf7 EZ |
6379 | |
6380 | @cindex @code{space} display spec, and bidirectional text | |
6381 | @item | |
5319014e | 6382 | Separate fields with a @code{display} property or overlay with a |
0c95fcf7 | 6383 | property value of the form @code{(space . PROPS)} (@pxref{Specified |
5319014e CY |
6384 | Space}). Emacs treats this display specification as a @dfn{paragraph |
6385 | separator}, and reorders the text on either side separately. | |
c094bb0c EZ |
6386 | @end itemize |
6387 | ||
92b71444 | 6388 | @defun bidi-string-mark-left-to-right string |
5319014e | 6389 | This function returns its argument @var{string}, possibly modified, |
c094bb0c EZ |
6390 | such that the result can be safely concatenated with another string, |
6391 | or juxtaposed with another string in a buffer, without disrupting the | |
6392 | relative layout of this string and the next one on display. If the | |
6393 | string returned by this function is displayed as part of a | |
6394 | left-to-right paragraph, it will always appear on display to the left | |
6395 | of the text that follows it. The function works by examining the | |
6396 | characters of its argument, and if any of those characters could cause | |
6397 | reordering on display, the function appends the @acronym{LRM} | |
6398 | character to the string. The appended @acronym{LRM} character is made | |
5319014e CY |
6399 | invisible by giving it an @code{invisible} text property of @code{t} |
6400 | (@pxref{Invisible Text}). | |
c094bb0c EZ |
6401 | @end defun |
6402 | ||
6403 | The reordering algorithm uses the bidirectional properties of the | |
6404 | characters stored as their @code{bidi-class} property | |
6405 | (@pxref{Character Properties}). Lisp programs can change these | |
6406 | properties by calling the @code{put-char-code-property} function. | |
6407 | However, doing this requires a thorough understanding of the | |
6408 | @acronym{UBA}, and is therefore not recommended. Any changes to the | |
6409 | bidirectional properties of a character have global effect: they | |
6410 | affect all Emacs frames and windows. | |
6411 | ||
6412 | Similarly, the @code{mirroring} property is used to display the | |
6413 | appropriate mirrored character in the reordered text. Lisp programs | |
6414 | can affect the mirrored display by changing this property. Again, any | |
6415 | such changes affect all of Emacs display. |