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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
e3b9fc91 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000 |
fd897522 | 4 | @c Free Software Foundation, Inc. |
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5 | @c See the file elisp.texi for copying conditions. |
6 | @setfilename ../info/display | |
969fe9b5 | 7 | @node Display, Calendar, Processes, Top |
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8 | @chapter Emacs Display |
9 | ||
10 | This chapter describes a number of features related to the display | |
11 | that Emacs presents to the user. | |
12 | ||
13 | @menu | |
14 | * Refresh Screen:: Clearing the screen and redrawing everything on it. | |
8241495d | 15 | * Forcing Redisplay:: Forcing redisplay. |
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16 | * Truncation:: Folding or wrapping long text lines. |
17 | * The Echo Area:: Where messages are displayed. | |
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18 | * Invisible Text:: Hiding part of the buffer text. |
19 | * Selective Display:: Hiding part of the buffer text (the old way). | |
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20 | * Overlay Arrow:: Display of an arrow to indicate position. |
21 | * Temporary Displays:: Displays that go away automatically. | |
22 | * Overlays:: Use overlays to highlight parts of the buffer. | |
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23 | * Width:: How wide a character or string is on the screen. |
24 | * Faces:: A face defines a graphics style for text characters: | |
25 | font, colors, etc. | |
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26 | * Display Property:: Enabling special display features. |
27 | * Images:: Displaying images in Emacs buffers. | |
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28 | * Blinking:: How Emacs shows the matching open parenthesis. |
29 | * Inverse Video:: Specifying how the screen looks. | |
30 | * Usual Display:: The usual conventions for displaying nonprinting chars. | |
31 | * Display Tables:: How to specify other conventions. | |
32 | * Beeping:: Audible signal to the user. | |
33 | * Window Systems:: Which window system is being used. | |
34 | @end menu | |
35 | ||
36 | @node Refresh Screen | |
37 | @section Refreshing the Screen | |
38 | ||
39 | The function @code{redraw-frame} redisplays the entire contents of a | |
1911e6e5 | 40 | given frame (@pxref{Frames}). |
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41 | |
42 | @c Emacs 19 feature | |
43 | @defun redraw-frame frame | |
44 | This function clears and redisplays frame @var{frame}. | |
45 | @end defun | |
46 | ||
47 | Even more powerful is @code{redraw-display}: | |
48 | ||
49 | @deffn Command redraw-display | |
50 | This function clears and redisplays all visible frames. | |
51 | @end deffn | |
52 | ||
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53 | Processing user input takes absolute priority over redisplay. If you |
54 | call these functions when input is available, they do nothing | |
55 | immediately, but a full redisplay does happen eventually---after all the | |
56 | input has been processed. | |
57 | ||
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58 | Normally, suspending and resuming Emacs also refreshes the screen. |
59 | Some terminal emulators record separate contents for display-oriented | |
60 | programs such as Emacs and for ordinary sequential display. If you are | |
61 | using such a terminal, you might want to inhibit the redisplay on | |
78608595 | 62 | resumption. |
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63 | |
64 | @defvar no-redraw-on-reenter | |
65 | @cindex suspend (cf. @code{no-redraw-on-reenter}) | |
66 | @cindex resume (cf. @code{no-redraw-on-reenter}) | |
67 | This variable controls whether Emacs redraws the entire screen after it | |
f9f59935 | 68 | has been suspended and resumed. Non-@code{nil} means there is no need |
969fe9b5 | 69 | to redraw, @code{nil} means redrawing is needed. The default is @code{nil}. |
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70 | @end defvar |
71 | ||
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72 | @node Forcing Redisplay |
73 | @section Forcing Redisplay | |
74 | @cindex forcing redisplay | |
75 | ||
76 | Emacs redisplay normally stops if input arrives, and does not happen | |
77 | at all if input is available before it starts. Most of the time, this | |
78 | is exactly what you want. However, you can prevent preemption by | |
79 | binding @code{redisplay-dont-pause} to a non-@code{nil} value. | |
80 | ||
81 | @tindex redisplay-dont-pause | |
82 | @defvar redisplay-dont-pause | |
83 | If this variable is non-@code{nil}, pending input does not | |
84 | prevent or halt redisplay; redisplay occurs, and finishes, | |
85 | regardless of whether input is available. This feature is available | |
86 | as of Emacs 21. | |
87 | @end defvar | |
88 | ||
89 | You can request a display update, but only if no input is pending, | |
90 | with @code{(sit-for 0)}. To force a display update even when input is | |
91 | pending, do this: | |
92 | ||
93 | @example | |
94 | (let ((redisplay-dont-pause t)) | |
95 | (sit-for 0)) | |
96 | @end example | |
97 | ||
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98 | @node Truncation |
99 | @section Truncation | |
100 | @cindex line wrapping | |
101 | @cindex continuation lines | |
102 | @cindex @samp{$} in display | |
103 | @cindex @samp{\} in display | |
104 | ||
105 | When a line of text extends beyond the right edge of a window, the | |
106 | line can either be continued on the next screen line, or truncated to | |
107 | one screen line. The additional screen lines used to display a long | |
108 | text line are called @dfn{continuation} lines. Normally, a @samp{$} in | |
109 | the rightmost column of the window indicates truncation; a @samp{\} on | |
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110 | the rightmost column indicates a line that ``wraps'' onto the next line, |
111 | which is also called @dfn{continuing} the line. (The display table can | |
112 | specify alternative indicators; see @ref{Display Tables}.) | |
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113 | |
114 | Note that continuation is different from filling; continuation happens | |
115 | on the screen only, not in the buffer contents, and it breaks a line | |
116 | precisely at the right margin, not at a word boundary. @xref{Filling}. | |
117 | ||
118 | @defopt truncate-lines | |
119 | This buffer-local variable controls how Emacs displays lines that extend | |
120 | beyond the right edge of the window. The default is @code{nil}, which | |
121 | specifies continuation. If the value is non-@code{nil}, then these | |
122 | lines are truncated. | |
123 | ||
124 | If the variable @code{truncate-partial-width-windows} is non-@code{nil}, | |
125 | then truncation is always used for side-by-side windows (within one | |
126 | frame) regardless of the value of @code{truncate-lines}. | |
127 | @end defopt | |
128 | ||
bfe721d1 | 129 | @defopt default-truncate-lines |
42b85554 | 130 | This variable is the default value for @code{truncate-lines}, for |
969fe9b5 | 131 | buffers that do not have buffer-local values for it. |
bfe721d1 | 132 | @end defopt |
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133 | |
134 | @defopt truncate-partial-width-windows | |
135 | This variable controls display of lines that extend beyond the right | |
136 | edge of the window, in side-by-side windows (@pxref{Splitting Windows}). | |
137 | If it is non-@code{nil}, these lines are truncated; otherwise, | |
138 | @code{truncate-lines} says what to do with them. | |
139 | @end defopt | |
140 | ||
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141 | When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in |
142 | a window, that forces truncation. | |
143 | ||
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144 | You can override the glyphs that indicate continuation or truncation |
145 | using the display table; see @ref{Display Tables}. | |
42b85554 | 146 | |
1911e6e5 | 147 | If your buffer contains @emph{very} long lines, and you use |
22697dac | 148 | continuation to display them, just thinking about them can make Emacs |
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149 | redisplay slow. The column computation and indentation functions also |
150 | become slow. Then you might find it advisable to set | |
151 | @code{cache-long-line-scans} to @code{t}. | |
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152 | |
153 | @defvar cache-long-line-scans | |
154 | If this variable is non-@code{nil}, various indentation and motion | |
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155 | functions, and Emacs redisplay, cache the results of scanning the |
156 | buffer, and consult the cache to avoid rescanning regions of the buffer | |
157 | unless they are modified. | |
22697dac | 158 | |
bfe721d1 | 159 | Turning on the cache slows down processing of short lines somewhat. |
22697dac | 160 | |
969fe9b5 | 161 | This variable is automatically buffer-local in every buffer. |
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162 | @end defvar |
163 | ||
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164 | @node The Echo Area |
165 | @section The Echo Area | |
166 | @cindex error display | |
167 | @cindex echo area | |
168 | ||
22697dac | 169 | The @dfn{echo area} is used for displaying messages made with the |
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170 | @code{message} primitive, and for echoing keystrokes. It is not the |
171 | same as the minibuffer, despite the fact that the minibuffer appears | |
172 | (when active) in the same place on the screen as the echo area. The | |
173 | @cite{GNU Emacs Manual} specifies the rules for resolving conflicts | |
174 | between the echo area and the minibuffer for use of that screen space | |
175 | (@pxref{Minibuffer,, The Minibuffer, emacs, The GNU Emacs Manual}). | |
176 | Error messages appear in the echo area; see @ref{Errors}. | |
177 | ||
178 | You can write output in the echo area by using the Lisp printing | |
179 | functions with @code{t} as the stream (@pxref{Output Functions}), or as | |
180 | follows: | |
181 | ||
182 | @defun message string &rest arguments | |
22697dac | 183 | This function displays a one-line message in the echo area. The |
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184 | argument @var{string} is similar to a C language @code{printf} control |
185 | string. See @code{format} in @ref{String Conversion}, for the details | |
186 | on the conversion specifications. @code{message} returns the | |
187 | constructed string. | |
188 | ||
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189 | In batch mode, @code{message} prints the message text on the standard |
190 | error stream, followed by a newline. | |
191 | ||
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192 | If @var{string}, or strings among the @var{arguments}, have @code{face} |
193 | text properties, these affect the way the message is displayed. | |
194 | ||
42b85554 | 195 | @c Emacs 19 feature |
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196 | If @var{string} is @code{nil}, @code{message} clears the echo area; if |
197 | the echo area has been expanded automatically, this brings it back to | |
198 | its normal size. If the minibuffer is active, this brings the | |
199 | minibuffer contents back onto the screen immediately. | |
b22f3a19 | 200 | |
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201 | @example |
202 | @group | |
203 | (message "Minibuffer depth is %d." | |
204 | (minibuffer-depth)) | |
205 | @print{} Minibuffer depth is 0. | |
206 | @result{} "Minibuffer depth is 0." | |
207 | @end group | |
208 | ||
209 | @group | |
210 | ---------- Echo Area ---------- | |
211 | Minibuffer depth is 0. | |
212 | ---------- Echo Area ---------- | |
213 | @end group | |
214 | @end example | |
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215 | |
216 | To automatically display a message in the echo area or in a pop-buffer, | |
217 | depending on its size, use @code{display-message-or-buffer}. | |
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218 | @end defun |
219 | ||
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220 | @tindex with-temp-message |
221 | @defmac with-temp-message message &rest body | |
222 | This construct displays a message in the echo area temporarily, during | |
223 | the execution of @var{body}. It displays @var{message}, executes | |
224 | @var{body}, then returns the value of the last body form while restoring | |
225 | the previous echo area contents. | |
226 | @end defmac | |
227 | ||
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228 | @defun message-or-box string &rest arguments |
229 | This function displays a message like @code{message}, but may display it | |
230 | in a dialog box instead of the echo area. If this function is called in | |
231 | a command that was invoked using the mouse---more precisely, if | |
232 | @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either | |
233 | @code{nil} or a list---then it uses a dialog box or pop-up menu to | |
234 | display the message. Otherwise, it uses the echo area. (This is the | |
235 | same criterion that @code{y-or-n-p} uses to make a similar decision; see | |
236 | @ref{Yes-or-No Queries}.) | |
237 | ||
238 | You can force use of the mouse or of the echo area by binding | |
239 | @code{last-nonmenu-event} to a suitable value around the call. | |
240 | @end defun | |
241 | ||
242 | @defun message-box string &rest arguments | |
243 | This function displays a message like @code{message}, but uses a dialog | |
244 | box (or a pop-up menu) whenever that is possible. If it is impossible | |
245 | to use a dialog box or pop-up menu, because the terminal does not | |
246 | support them, then @code{message-box} uses the echo area, like | |
247 | @code{message}. | |
248 | @end defun | |
249 | ||
a43709e6 | 250 | @defun display-message-or-buffer message &optional buffer-name not-this-window frame |
26f42fed | 251 | @tindex display-message-or-buffer |
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252 | This function displays the message @var{message}, which may be either a |
253 | string or a buffer. If it is shorter than the maximum height of the | |
254 | echo area, as defined by @code{max-mini-window-height}, it is displayed | |
255 | in the echo area, using @code{message}. Otherwise, | |
256 | @code{display-buffer} is used to show it in a pop-up buffer. | |
257 | ||
258 | Returns either the string shown in the echo area, or when a pop-up | |
259 | buffer is used, the window used to display it. | |
260 | ||
261 | If @var{message} is a string, then the optional argument | |
262 | @var{buffer-name} is the name of the buffer used to display it when a | |
263 | pop-up buffer is used, defaulting to @samp{*Message*}. In the case | |
264 | where @var{message} is a string and displayed in the echo area, it is | |
265 | not specified whether the contents are inserted into the buffer anyway. | |
266 | ||
267 | The optional arguments @var{not-this-window} and @var{frame} are as for | |
268 | @code{display-buffer}, and only used if a buffer is displayed. | |
269 | @end defun | |
270 | ||
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271 | @defun current-message |
272 | This function returns the message currently being displayed in the | |
273 | echo area, or @code{nil} if there is none. | |
274 | @end defun | |
275 | ||
969fe9b5 RS |
276 | @defvar cursor-in-echo-area |
277 | This variable controls where the cursor appears when a message is | |
278 | displayed in the echo area. If it is non-@code{nil}, then the cursor | |
279 | appears at the end of the message. Otherwise, the cursor appears at | |
280 | point---not in the echo area at all. | |
281 | ||
282 | The value is normally @code{nil}; Lisp programs bind it to @code{t} | |
283 | for brief periods of time. | |
284 | @end defvar | |
285 | ||
f9f59935 RS |
286 | @defvar echo-area-clear-hook |
287 | This normal hook is run whenever the echo area is cleared---either by | |
288 | @code{(message nil)} or for any other reason. | |
289 | @end defvar | |
290 | ||
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291 | Almost all the messages displayed in the echo area are also recorded |
292 | in the @samp{*Messages*} buffer. | |
293 | ||
294 | @defopt message-log-max | |
295 | This variable specifies how many lines to keep in the @samp{*Messages*} | |
296 | buffer. The value @code{t} means there is no limit on how many lines to | |
297 | keep. The value @code{nil} disables message logging entirely. Here's | |
298 | how to display a message and prevent it from being logged: | |
299 | ||
300 | @example | |
301 | (let (message-log-max) | |
302 | (message @dots{})) | |
303 | @end example | |
304 | @end defopt | |
305 | ||
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306 | @defvar echo-keystrokes |
307 | This variable determines how much time should elapse before command | |
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308 | characters echo. Its value must be an integer or floating point number, |
309 | which specifies the | |
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310 | number of seconds to wait before echoing. If the user types a prefix |
311 | key (such as @kbd{C-x}) and then delays this many seconds before | |
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312 | continuing, the prefix key is echoed in the echo area. (Once echoing |
313 | begins in a key sequence, all subsequent characters in the same key | |
314 | sequence are echoed immediately.) | |
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315 | |
316 | If the value is zero, then command input is not echoed. | |
317 | @end defvar | |
318 | ||
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319 | @node Invisible Text |
320 | @section Invisible Text | |
321 | ||
322 | @cindex invisible text | |
323 | You can make characters @dfn{invisible}, so that they do not appear on | |
324 | the screen, with the @code{invisible} property. This can be either a | |
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325 | text property (@pxref{Text Properties}) or a property of an overlay |
326 | (@pxref{Overlays}). | |
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327 | |
328 | In the simplest case, any non-@code{nil} @code{invisible} property makes | |
329 | a character invisible. This is the default case---if you don't alter | |
330 | the default value of @code{buffer-invisibility-spec}, this is how the | |
969fe9b5 | 331 | @code{invisible} property works. |
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332 | |
333 | More generally, you can use the variable @code{buffer-invisibility-spec} | |
334 | to control which values of the @code{invisible} property make text | |
335 | invisible. This permits you to classify the text into different subsets | |
336 | in advance, by giving them different @code{invisible} values, and | |
337 | subsequently make various subsets visible or invisible by changing the | |
338 | value of @code{buffer-invisibility-spec}. | |
339 | ||
340 | Controlling visibility with @code{buffer-invisibility-spec} is | |
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341 | especially useful in a program to display the list of entries in a |
342 | database. It permits the implementation of convenient filtering | |
343 | commands to view just a part of the entries in the database. Setting | |
344 | this variable is very fast, much faster than scanning all the text in | |
345 | the buffer looking for properties to change. | |
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346 | |
347 | @defvar buffer-invisibility-spec | |
348 | This variable specifies which kinds of @code{invisible} properties | |
349 | actually make a character invisible. | |
350 | ||
351 | @table @asis | |
352 | @item @code{t} | |
353 | A character is invisible if its @code{invisible} property is | |
354 | non-@code{nil}. This is the default. | |
355 | ||
356 | @item a list | |
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357 | Each element of the list specifies a criterion for invisibility; if a |
358 | character's @code{invisible} property fits any one of these criteria, | |
359 | the character is invisible. The list can have two kinds of elements: | |
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360 | |
361 | @table @code | |
362 | @item @var{atom} | |
969fe9b5 | 363 | A character is invisible if its @code{invisible} property value |
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364 | is @var{atom} or if it is a list with @var{atom} as a member. |
365 | ||
366 | @item (@var{atom} . t) | |
969fe9b5 | 367 | A character is invisible if its @code{invisible} property value |
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368 | is @var{atom} or if it is a list with @var{atom} as a member. |
369 | Moreover, if this character is at the end of a line and is followed | |
370 | by a visible newline, it displays an ellipsis. | |
371 | @end table | |
372 | @end table | |
373 | @end defvar | |
374 | ||
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375 | Two functions are specifically provided for adding elements to |
376 | @code{buffer-invisibility-spec} and removing elements from it. | |
377 | ||
f9f59935 RS |
378 | @defun add-to-invisibility-spec element |
379 | Add the element @var{element} to @code{buffer-invisibility-spec} | |
380 | (if it is not already present in that list). | |
381 | @end defun | |
382 | ||
f9f59935 RS |
383 | @defun remove-from-invisibility-spec element |
384 | Remove the element @var{element} from @code{buffer-invisibility-spec}. | |
a40d4712 | 385 | This does nothing if @var{element} is not in the list. |
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386 | @end defun |
387 | ||
388 | One convention about the use of @code{buffer-invisibility-spec} is | |
389 | that a major mode should use the mode's own name as an element of | |
390 | @code{buffer-invisibility-spec} and as the value of the @code{invisible} | |
391 | property: | |
392 | ||
393 | @example | |
969fe9b5 | 394 | ;; @r{If you want to display an ellipsis:} |
f9f59935 | 395 | (add-to-invisibility-spec '(my-symbol . t)) |
969fe9b5 | 396 | ;; @r{If you don't want ellipsis:} |
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397 | (add-to-invisibility-spec 'my-symbol) |
398 | ||
399 | (overlay-put (make-overlay beginning end) | |
400 | 'invisible 'my-symbol) | |
401 | ||
969fe9b5 | 402 | ;; @r{When done with the overlays:} |
f9f59935 | 403 | (remove-from-invisibility-spec '(my-symbol . t)) |
969fe9b5 | 404 | ;; @r{Or respectively:} |
f9f59935 RS |
405 | (remove-from-invisibility-spec 'my-symbol) |
406 | @end example | |
407 | ||
5e8ae792 | 408 | @vindex line-move-ignore-invisible |
bfe721d1 | 409 | Ordinarily, commands that operate on text or move point do not care |
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410 | whether the text is invisible. The user-level line motion commands |
411 | explicitly ignore invisible newlines if | |
412 | @code{line-move-ignore-invisible} is non-@code{nil}, but only because | |
413 | they are explicitly programmed to do so. | |
bfe721d1 | 414 | |
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415 | Incremental search can make invisible overlays visible temporarily |
416 | and/or permanently when a match includes invisible text. To enable | |
417 | this, the overlay should have a non-@code{nil} | |
418 | @code{isearch-open-invisible} property. The property value should be a | |
419 | function to be called with the overlay as an argument. This function | |
420 | should make the overlay visible permanently; it is used when the match | |
421 | overlaps the overlay on exit from the search. | |
422 | ||
423 | During the search, such overlays are made temporarily visible by | |
424 | temporarily modifying their invisible and intangible properties. If you | |
ebc6903b | 425 | want this to be done differently for a certain overlay, give it an |
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426 | @code{isearch-open-invisible-temporary} property which is a function. |
427 | The function is called with two arguments: the first is the overlay, and | |
f21b06b7 | 428 | the second is @code{nil} to make the overlay visible, or @code{t} to |
a9f0a989 | 429 | make it invisible again. |
f9f59935 | 430 | |
42b85554 RS |
431 | @node Selective Display |
432 | @section Selective Display | |
433 | @cindex selective display | |
434 | ||
969fe9b5 RS |
435 | @dfn{Selective display} refers to a pair of related features for |
436 | hiding certain lines on the screen. | |
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437 | |
438 | The first variant, explicit selective display, is designed for use in | |
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439 | a Lisp program: it controls which lines are hidden by altering the text. |
440 | The invisible text feature (@pxref{Invisible Text}) has partially | |
441 | replaced this feature. | |
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442 | |
443 | In the second variant, the choice of lines to hide is made | |
bfe721d1 | 444 | automatically based on indentation. This variant is designed to be a |
22697dac | 445 | user-level feature. |
42b85554 RS |
446 | |
447 | The way you control explicit selective display is by replacing a | |
78608595 | 448 | newline (control-j) with a carriage return (control-m). The text that |
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449 | was formerly a line following that newline is now invisible. Strictly |
450 | speaking, it is temporarily no longer a line at all, since only newlines | |
451 | can separate lines; it is now part of the previous line. | |
452 | ||
453 | Selective display does not directly affect editing commands. For | |
454 | example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly into | |
455 | invisible text. However, the replacement of newline characters with | |
456 | carriage return characters affects some editing commands. For example, | |
457 | @code{next-line} skips invisible lines, since it searches only for | |
458 | newlines. Modes that use selective display can also define commands | |
459 | that take account of the newlines, or that make parts of the text | |
460 | visible or invisible. | |
461 | ||
462 | When you write a selectively displayed buffer into a file, all the | |
463 | control-m's are output as newlines. This means that when you next read | |
464 | in the file, it looks OK, with nothing invisible. The selective display | |
465 | effect is seen only within Emacs. | |
466 | ||
467 | @defvar selective-display | |
468 | This buffer-local variable enables selective display. This means that | |
469 | lines, or portions of lines, may be made invisible. | |
470 | ||
471 | @itemize @bullet | |
472 | @item | |
a40d4712 PR |
473 | If the value of @code{selective-display} is @code{t}, then the character |
474 | control-m marks the start of invisible text; the control-m, and the rest | |
475 | of the line following it, are not displayed. This is explicit selective | |
476 | display. | |
42b85554 RS |
477 | |
478 | @item | |
479 | If the value of @code{selective-display} is a positive integer, then | |
480 | lines that start with more than that many columns of indentation are not | |
481 | displayed. | |
482 | @end itemize | |
483 | ||
484 | When some portion of a buffer is invisible, the vertical movement | |
485 | commands operate as if that portion did not exist, allowing a single | |
486 | @code{next-line} command to skip any number of invisible lines. | |
487 | However, character movement commands (such as @code{forward-char}) do | |
488 | not skip the invisible portion, and it is possible (if tricky) to insert | |
489 | or delete text in an invisible portion. | |
490 | ||
491 | In the examples below, we show the @emph{display appearance} of the | |
492 | buffer @code{foo}, which changes with the value of | |
493 | @code{selective-display}. The @emph{contents} of the buffer do not | |
494 | change. | |
495 | ||
496 | @example | |
497 | @group | |
498 | (setq selective-display nil) | |
499 | @result{} nil | |
500 | ||
501 | ---------- Buffer: foo ---------- | |
502 | 1 on this column | |
503 | 2on this column | |
504 | 3n this column | |
505 | 3n this column | |
506 | 2on this column | |
507 | 1 on this column | |
508 | ---------- Buffer: foo ---------- | |
509 | @end group | |
510 | ||
511 | @group | |
512 | (setq selective-display 2) | |
513 | @result{} 2 | |
514 | ||
515 | ---------- Buffer: foo ---------- | |
516 | 1 on this column | |
517 | 2on this column | |
518 | 2on this column | |
519 | 1 on this column | |
520 | ---------- Buffer: foo ---------- | |
521 | @end group | |
522 | @end example | |
523 | @end defvar | |
524 | ||
525 | @defvar selective-display-ellipses | |
526 | If this buffer-local variable is non-@code{nil}, then Emacs displays | |
527 | @samp{@dots{}} at the end of a line that is followed by invisible text. | |
528 | This example is a continuation of the previous one. | |
529 | ||
530 | @example | |
531 | @group | |
532 | (setq selective-display-ellipses t) | |
533 | @result{} t | |
534 | ||
535 | ---------- Buffer: foo ---------- | |
536 | 1 on this column | |
537 | 2on this column ... | |
538 | 2on this column | |
539 | 1 on this column | |
540 | ---------- Buffer: foo ---------- | |
541 | @end group | |
542 | @end example | |
543 | ||
544 | You can use a display table to substitute other text for the ellipsis | |
545 | (@samp{@dots{}}). @xref{Display Tables}. | |
546 | @end defvar | |
547 | ||
548 | @node Overlay Arrow | |
549 | @section The Overlay Arrow | |
550 | @cindex overlay arrow | |
551 | ||
552 | The @dfn{overlay arrow} is useful for directing the user's attention | |
553 | to a particular line in a buffer. For example, in the modes used for | |
554 | interface to debuggers, the overlay arrow indicates the line of code | |
555 | about to be executed. | |
556 | ||
557 | @defvar overlay-arrow-string | |
78608595 RS |
558 | This variable holds the string to display to call attention to a |
559 | particular line, or @code{nil} if the arrow feature is not in use. | |
bb2337f5 DL |
560 | On a graphical display the contents of the string are ignored; instead a |
561 | glyph is displayed in the fringe area to the left of the display area. | |
42b85554 RS |
562 | @end defvar |
563 | ||
564 | @defvar overlay-arrow-position | |
78608595 | 565 | This variable holds a marker that indicates where to display the overlay |
bb2337f5 DL |
566 | arrow. It should point at the beginning of a line. On a non-graphical |
567 | display the arrow text | |
78608595 RS |
568 | appears at the beginning of that line, overlaying any text that would |
569 | otherwise appear. Since the arrow is usually short, and the line | |
570 | usually begins with indentation, normally nothing significant is | |
571 | overwritten. | |
572 | ||
573 | The overlay string is displayed only in the buffer that this marker | |
42b85554 RS |
574 | points into. Thus, only one buffer can have an overlay arrow at any |
575 | given time. | |
576 | @c !!! overlay-arrow-position: but the overlay string may remain in the display | |
577 | @c of some other buffer until an update is required. This should be fixed | |
578 | @c now. Is it? | |
579 | @end defvar | |
580 | ||
969fe9b5 | 581 | You can do a similar job by creating an overlay with a |
22697dac KH |
582 | @code{before-string} property. @xref{Overlay Properties}. |
583 | ||
42b85554 RS |
584 | @node Temporary Displays |
585 | @section Temporary Displays | |
586 | ||
969fe9b5 RS |
587 | Temporary displays are used by Lisp programs to put output into a |
588 | buffer and then present it to the user for perusal rather than for | |
589 | editing. Many help commands use this feature. | |
42b85554 RS |
590 | |
591 | @defspec with-output-to-temp-buffer buffer-name forms@dots{} | |
b6954afd RS |
592 | This function executes @var{forms} while arranging to insert any output |
593 | they print into the buffer named @var{buffer-name}, which is first | |
594 | created if necessary, and put into Help mode. Finally, the buffer is | |
595 | displayed in some window, but not selected. | |
596 | ||
597 | If the @var{forms} do not change the major mode in the output buffer, so | |
598 | that it is still Help mode at the end of their execution, then | |
599 | @code{with-output-to-temp-buffer} makes this buffer read-only at the | |
600 | end, and also scans it for function and variable names to make them into | |
601 | clickable cross-references. | |
42b85554 RS |
602 | |
603 | The string @var{buffer-name} specifies the temporary buffer, which | |
604 | need not already exist. The argument must be a string, not a buffer. | |
605 | The buffer is erased initially (with no questions asked), and it is | |
606 | marked as unmodified after @code{with-output-to-temp-buffer} exits. | |
607 | ||
608 | @code{with-output-to-temp-buffer} binds @code{standard-output} to the | |
609 | temporary buffer, then it evaluates the forms in @var{forms}. Output | |
610 | using the Lisp output functions within @var{forms} goes by default to | |
611 | that buffer (but screen display and messages in the echo area, although | |
612 | they are ``output'' in the general sense of the word, are not affected). | |
613 | @xref{Output Functions}. | |
614 | ||
b6954afd RS |
615 | Several hooks are available for customizing the behavior |
616 | of this construct; they are listed below. | |
617 | ||
42b85554 RS |
618 | The value of the last form in @var{forms} is returned. |
619 | ||
620 | @example | |
621 | @group | |
622 | ---------- Buffer: foo ---------- | |
623 | This is the contents of foo. | |
624 | ---------- Buffer: foo ---------- | |
625 | @end group | |
626 | ||
627 | @group | |
628 | (with-output-to-temp-buffer "foo" | |
629 | (print 20) | |
630 | (print standard-output)) | |
631 | @result{} #<buffer foo> | |
632 | ||
633 | ---------- Buffer: foo ---------- | |
634 | 20 | |
635 | ||
636 | #<buffer foo> | |
637 | ||
638 | ---------- Buffer: foo ---------- | |
639 | @end group | |
640 | @end example | |
641 | @end defspec | |
642 | ||
643 | @defvar temp-buffer-show-function | |
78608595 | 644 | If this variable is non-@code{nil}, @code{with-output-to-temp-buffer} |
42b85554 RS |
645 | calls it as a function to do the job of displaying a help buffer. The |
646 | function gets one argument, which is the buffer it should display. | |
a9f0a989 RS |
647 | |
648 | It is a good idea for this function to run @code{temp-buffer-show-hook} | |
649 | just as @code{with-output-to-temp-buffer} normally would, inside of | |
b6954afd | 650 | @code{save-selected-window} and with the chosen window and buffer |
a9f0a989 RS |
651 | selected. |
652 | @end defvar | |
653 | ||
b6954afd RS |
654 | @defvar temp-buffer-setup-hook |
655 | @tindex temp-buffer-setup-hook | |
656 | This normal hook is run by @code{with-output-to-temp-buffer} before | |
657 | evaluating @var{body}. When the hook runs, the help buffer is current. | |
658 | This hook is normally set up with a function to put the buffer in Help | |
659 | mode. | |
660 | @end defvar | |
661 | ||
a9f0a989 RS |
662 | @defvar temp-buffer-show-hook |
663 | This normal hook is run by @code{with-output-to-temp-buffer} after | |
664 | displaying the help buffer. When the hook runs, the help buffer is | |
b6954afd RS |
665 | current, and the window it was displayed in is selected. This hook is |
666 | normally set up with a function to make the buffer read only, and find | |
667 | function names and variable names in it, provided the major mode is | |
668 | still Help mode. | |
42b85554 RS |
669 | @end defvar |
670 | ||
671 | @defun momentary-string-display string position &optional char message | |
672 | This function momentarily displays @var{string} in the current buffer at | |
673 | @var{position}. It has no effect on the undo list or on the buffer's | |
674 | modification status. | |
675 | ||
676 | The momentary display remains until the next input event. If the next | |
677 | input event is @var{char}, @code{momentary-string-display} ignores it | |
678 | and returns. Otherwise, that event remains buffered for subsequent use | |
679 | as input. Thus, typing @var{char} will simply remove the string from | |
680 | the display, while typing (say) @kbd{C-f} will remove the string from | |
681 | the display and later (presumably) move point forward. The argument | |
682 | @var{char} is a space by default. | |
683 | ||
684 | The return value of @code{momentary-string-display} is not meaningful. | |
685 | ||
bfe721d1 | 686 | If the string @var{string} does not contain control characters, you can |
969fe9b5 RS |
687 | do the same job in a more general way by creating (and then subsequently |
688 | deleting) an overlay with a @code{before-string} property. | |
689 | @xref{Overlay Properties}. | |
bfe721d1 | 690 | |
42b85554 RS |
691 | If @var{message} is non-@code{nil}, it is displayed in the echo area |
692 | while @var{string} is displayed in the buffer. If it is @code{nil}, a | |
693 | default message says to type @var{char} to continue. | |
694 | ||
695 | In this example, point is initially located at the beginning of the | |
696 | second line: | |
697 | ||
698 | @example | |
699 | @group | |
700 | ---------- Buffer: foo ---------- | |
701 | This is the contents of foo. | |
702 | @point{}Second line. | |
703 | ---------- Buffer: foo ---------- | |
704 | @end group | |
705 | ||
706 | @group | |
707 | (momentary-string-display | |
708 | "**** Important Message! ****" | |
709 | (point) ?\r | |
710 | "Type RET when done reading") | |
711 | @result{} t | |
712 | @end group | |
713 | ||
714 | @group | |
715 | ---------- Buffer: foo ---------- | |
716 | This is the contents of foo. | |
717 | **** Important Message! ****Second line. | |
718 | ---------- Buffer: foo ---------- | |
719 | ||
720 | ---------- Echo Area ---------- | |
721 | Type RET when done reading | |
722 | ---------- Echo Area ---------- | |
723 | @end group | |
724 | @end example | |
725 | @end defun | |
726 | ||
727 | @node Overlays | |
728 | @section Overlays | |
729 | @cindex overlays | |
730 | ||
731 | You can use @dfn{overlays} to alter the appearance of a buffer's text on | |
bfe721d1 KH |
732 | the screen, for the sake of presentation features. An overlay is an |
733 | object that belongs to a particular buffer, and has a specified | |
734 | beginning and end. It also has properties that you can examine and set; | |
735 | these affect the display of the text within the overlay. | |
42b85554 RS |
736 | |
737 | @menu | |
738 | * Overlay Properties:: How to read and set properties. | |
739 | What properties do to the screen display. | |
eda77a0f DL |
740 | * Managing Overlays:: Creating and moving overlays. |
741 | * Finding Overlays:: Searching for overlays. | |
42b85554 RS |
742 | @end menu |
743 | ||
744 | @node Overlay Properties | |
745 | @subsection Overlay Properties | |
746 | ||
8241495d | 747 | Overlay properties are like text properties in that the properties that |
a9f0a989 RS |
748 | alter how a character is displayed can come from either source. But in |
749 | most respects they are different. Text properties are considered a part | |
750 | of the text; overlays are specifically considered not to be part of the | |
751 | text. Thus, copying text between various buffers and strings preserves | |
752 | text properties, but does not try to preserve overlays. Changing a | |
753 | buffer's text properties marks the buffer as modified, while moving an | |
754 | overlay or changing its properties does not. Unlike text property | |
755 | changes, overlay changes are not recorded in the buffer's undo list. | |
756 | @xref{Text Properties}, for comparison. | |
42b85554 | 757 | |
8241495d RS |
758 | These functions are used for reading and writing the properties of an |
759 | overlay: | |
760 | ||
761 | @defun overlay-get overlay prop | |
762 | This function returns the value of property @var{prop} recorded in | |
763 | @var{overlay}, if any. If @var{overlay} does not record any value for | |
764 | that property, but it does have a @code{category} property which is a | |
765 | symbol, that symbol's @var{prop} property is used. Otherwise, the value | |
766 | is @code{nil}. | |
767 | @end defun | |
768 | ||
769 | @defun overlay-put overlay prop value | |
770 | This function sets the value of property @var{prop} recorded in | |
771 | @var{overlay} to @var{value}. It returns @var{value}. | |
772 | @end defun | |
773 | ||
774 | See also the function @code{get-char-property} which checks both | |
775 | overlay properties and text properties for a given character. | |
776 | @xref{Examining Properties}. | |
777 | ||
778 | Many overlay properties have special meanings; here is a table | |
779 | of them: | |
780 | ||
42b85554 RS |
781 | @table @code |
782 | @item priority | |
783 | @kindex priority @r{(overlay property)} | |
784 | This property's value (which should be a nonnegative number) determines | |
785 | the priority of the overlay. The priority matters when two or more | |
786 | overlays cover the same character and both specify a face for display; | |
787 | the one whose @code{priority} value is larger takes priority over the | |
788 | other, and its face attributes override the face attributes of the lower | |
789 | priority overlay. | |
790 | ||
791 | Currently, all overlays take priority over text properties. Please | |
792 | avoid using negative priority values, as we have not yet decided just | |
793 | what they should mean. | |
794 | ||
795 | @item window | |
796 | @kindex window @r{(overlay property)} | |
797 | If the @code{window} property is non-@code{nil}, then the overlay | |
798 | applies only on that window. | |
799 | ||
22697dac KH |
800 | @item category |
801 | @kindex category @r{(overlay property)} | |
802 | If an overlay has a @code{category} property, we call it the | |
bfe721d1 | 803 | @dfn{category} of the overlay. It should be a symbol. The properties |
22697dac KH |
804 | of the symbol serve as defaults for the properties of the overlay. |
805 | ||
42b85554 RS |
806 | @item face |
807 | @kindex face @r{(overlay property)} | |
f9f59935 | 808 | This property controls the way text is displayed---for example, which |
8241495d | 809 | font and which colors. @xref{Faces}, for more information. |
f9f59935 | 810 | |
8241495d | 811 | In the simplest case, the value is a face name. It can also be a list; |
a40d4712 | 812 | then each element can be any of these possibilities: |
8241495d RS |
813 | |
814 | @itemize @bullet | |
815 | @item | |
816 | A face name (a symbol or string). | |
817 | ||
818 | @item | |
819 | Starting in Emacs 21, a property list of face attributes. This has the | |
820 | form (@var{keyword} @var{value} @dots{}), where each @var{keyword} is a | |
821 | face attribute name and @var{value} is a meaningful value for that | |
822 | attribute. With this feature, you do not need to create a face each | |
823 | time you want to specify a particular attribute for certain text. | |
824 | @xref{Face Attributes}. | |
825 | ||
826 | @item | |
827 | A cons cell of the form @code{(foreground-color . @var{color-name})} or | |
828 | @code{(background-color . @var{color-name})}. These elements specify | |
829 | just the foreground color or just the background color. | |
830 | ||
831 | @code{(foreground-color . @var{color-name})} is equivalent to | |
832 | @code{(:foreground @var{color-name})}, and likewise for the background. | |
833 | @end itemize | |
42b85554 RS |
834 | |
835 | @item mouse-face | |
836 | @kindex mouse-face @r{(overlay property)} | |
837 | This property is used instead of @code{face} when the mouse is within | |
f9f59935 | 838 | the range of the overlay. |
42b85554 | 839 | |
8241495d RS |
840 | @item display |
841 | @kindex display @r{(overlay property)} | |
842 | This property activates various features that change the | |
843 | way text is displayed. For example, it can make text appear taller | |
844 | or shorter, higher or lower, wider or narror, or replaced with an image. | |
845 | @xref{Display Property}. | |
846 | ||
847 | @item help-echo | |
848 | @kindex help-echo @r{(text property)} | |
e3b9fc91 DL |
849 | If an overlay has a @code{help-echo} property, then when you move the |
850 | mouse onto the text in the overlay, Emacs displays a help string in the | |
851 | echo area, or in the tooltip window. For details see @ref{Text | |
852 | help-echo}. This feature is available starting in Emacs 21. | |
8241495d | 853 | |
42b85554 RS |
854 | @item modification-hooks |
855 | @kindex modification-hooks @r{(overlay property)} | |
856 | This property's value is a list of functions to be called if any | |
857 | character within the overlay is changed or if text is inserted strictly | |
22697dac KH |
858 | within the overlay. |
859 | ||
860 | The hook functions are called both before and after each change. | |
861 | If the functions save the information they receive, and compare notes | |
862 | between calls, they can determine exactly what change has been made | |
863 | in the buffer text. | |
864 | ||
865 | When called before a change, each function receives four arguments: the | |
866 | overlay, @code{nil}, and the beginning and end of the text range to be | |
a890e1b0 | 867 | modified. |
42b85554 | 868 | |
22697dac KH |
869 | When called after a change, each function receives five arguments: the |
870 | overlay, @code{t}, the beginning and end of the text range just | |
871 | modified, and the length of the pre-change text replaced by that range. | |
872 | (For an insertion, the pre-change length is zero; for a deletion, that | |
873 | length is the number of characters deleted, and the post-change | |
bfe721d1 | 874 | beginning and end are equal.) |
22697dac | 875 | |
42b85554 RS |
876 | @item insert-in-front-hooks |
877 | @kindex insert-in-front-hooks @r{(overlay property)} | |
22697dac KH |
878 | This property's value is a list of functions to be called before and |
879 | after inserting text right at the beginning of the overlay. The calling | |
880 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
881 | |
882 | @item insert-behind-hooks | |
883 | @kindex insert-behind-hooks @r{(overlay property)} | |
22697dac KH |
884 | This property's value is a list of functions to be called before and |
885 | after inserting text right at the end of the overlay. The calling | |
886 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
887 | |
888 | @item invisible | |
889 | @kindex invisible @r{(overlay property)} | |
22697dac KH |
890 | The @code{invisible} property can make the text in the overlay |
891 | invisible, which means that it does not appear on the screen. | |
892 | @xref{Invisible Text}, for details. | |
893 | ||
894 | @item intangible | |
895 | @kindex intangible @r{(overlay property)} | |
896 | The @code{intangible} property on an overlay works just like the | |
bfe721d1 | 897 | @code{intangible} text property. @xref{Special Properties}, for details. |
f9f59935 RS |
898 | |
899 | @item isearch-open-invisible | |
a9f0a989 RS |
900 | This property tells incremental search how to make an invisible overlay |
901 | visible, permanently, if the final match overlaps it. @xref{Invisible | |
f9f59935 | 902 | Text}. |
42b85554 | 903 | |
a9f0a989 RS |
904 | @item isearch-open-invisible-temporary |
905 | This property tells incremental search how to make an invisible overlay | |
906 | visible, temporarily, during the search. @xref{Invisible Text}. | |
907 | ||
42b85554 RS |
908 | @item before-string |
909 | @kindex before-string @r{(overlay property)} | |
910 | This property's value is a string to add to the display at the beginning | |
911 | of the overlay. The string does not appear in the buffer in any | |
a40d4712 | 912 | sense---only on the screen. |
42b85554 RS |
913 | |
914 | @item after-string | |
915 | @kindex after-string @r{(overlay property)} | |
916 | This property's value is a string to add to the display at the end of | |
917 | the overlay. The string does not appear in the buffer in any | |
a40d4712 | 918 | sense---only on the screen. |
22697dac KH |
919 | |
920 | @item evaporate | |
921 | @kindex evaporate @r{(overlay property)} | |
922 | If this property is non-@code{nil}, the overlay is deleted automatically | |
923 | if it ever becomes empty (i.e., if it spans no characters). | |
d2609065 | 924 | |
ce75fd23 | 925 | @item local-map |
969fe9b5 | 926 | @cindex keymap of character (and overlays) |
ce75fd23 | 927 | @kindex local-map @r{(overlay property)} |
d2609065 RS |
928 | If this property is non-@code{nil}, it specifies a keymap for a portion |
929 | of the text. The property's value replaces the buffer's local map, when | |
930 | the character after point is within the overlay. @xref{Active Keymaps}. | |
62fb5c66 DL |
931 | |
932 | @item keymap | |
933 | @kindex keymap @r{(overlay property)} | |
934 | The @code{keymap} property is similar to @code{local-map} but overrides the | |
935 | buffer's local map (and the map specified by the @code{local-map} | |
936 | property) rather than replacing it. | |
42b85554 RS |
937 | @end table |
938 | ||
42b85554 RS |
939 | @node Managing Overlays |
940 | @subsection Managing Overlays | |
941 | ||
942 | This section describes the functions to create, delete and move | |
943 | overlays, and to examine their contents. | |
944 | ||
f9f59935 | 945 | @defun make-overlay start end &optional buffer front-advance rear-advance |
78608595 | 946 | This function creates and returns an overlay that belongs to |
42b85554 RS |
947 | @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start} |
948 | and @var{end} must specify buffer positions; they may be integers or | |
949 | markers. If @var{buffer} is omitted, the overlay is created in the | |
950 | current buffer. | |
f9f59935 RS |
951 | |
952 | The arguments @var{front-advance} and @var{rear-advance} specify the | |
953 | insertion type for the start of the overlay and for the end of the | |
2468d0c0 | 954 | overlay, respectively. @xref{Marker Insertion Types}. |
42b85554 RS |
955 | @end defun |
956 | ||
957 | @defun overlay-start overlay | |
f9f59935 RS |
958 | This function returns the position at which @var{overlay} starts, |
959 | as an integer. | |
42b85554 RS |
960 | @end defun |
961 | ||
962 | @defun overlay-end overlay | |
f9f59935 RS |
963 | This function returns the position at which @var{overlay} ends, |
964 | as an integer. | |
42b85554 RS |
965 | @end defun |
966 | ||
967 | @defun overlay-buffer overlay | |
968 | This function returns the buffer that @var{overlay} belongs to. | |
969 | @end defun | |
970 | ||
971 | @defun delete-overlay overlay | |
972 | This function deletes @var{overlay}. The overlay continues to exist as | |
2468d0c0 DL |
973 | a Lisp object, and its property list is unchanged, but it ceases to be |
974 | attached to the buffer it belonged to, and ceases to have any effect on | |
975 | display. | |
a9f0a989 | 976 | |
2468d0c0 DL |
977 | A deleted overlay is not permanently disconnected. You can give it a |
978 | position in a buffer again by calling @code{move-overlay}. | |
42b85554 RS |
979 | @end defun |
980 | ||
981 | @defun move-overlay overlay start end &optional buffer | |
982 | This function moves @var{overlay} to @var{buffer}, and places its bounds | |
983 | at @var{start} and @var{end}. Both arguments @var{start} and @var{end} | |
2468d0c0 DL |
984 | must specify buffer positions; they may be integers or markers. |
985 | ||
986 | If @var{buffer} is omitted, @var{overlay} stays in the same buffer it | |
987 | was already associated with; if @var{overlay} was deleted, it goes into | |
988 | the current buffer. | |
42b85554 RS |
989 | |
990 | The return value is @var{overlay}. | |
991 | ||
992 | This is the only valid way to change the endpoints of an overlay. Do | |
993 | not try modifying the markers in the overlay by hand, as that fails to | |
994 | update other vital data structures and can cause some overlays to be | |
995 | ``lost''. | |
996 | @end defun | |
997 | ||
2468d0c0 DL |
998 | Here are some examples: |
999 | ||
1000 | @example | |
1001 | ;; @r{Create an overlay.} | |
1002 | (setq foo (make-overlay 1 10)) | |
1003 | @result{} #<overlay from 1 to 10 in display.texi> | |
1004 | (overlay-start foo) | |
1005 | @result{} 1 | |
1006 | (overlay-end foo) | |
1007 | @result{} 10 | |
1008 | (overlay-buffer foo) | |
1009 | @result{} #<buffer display.texi> | |
1010 | ;; @r{Give it a property we can check later.} | |
1011 | (overlay-put foo 'happy t) | |
1012 | @result{} t | |
1013 | ;; @r{Verify the property is present.} | |
1014 | (overlay-get foo 'happy) | |
1015 | @result{} t | |
1016 | ;; @r{Move the overlay.} | |
1017 | (move-overlay foo 5 20) | |
1018 | @result{} #<overlay from 5 to 20 in display.texi> | |
1019 | (overlay-start foo) | |
1020 | @result{} 5 | |
1021 | (overlay-end foo) | |
1022 | @result{} 20 | |
1023 | ;; @r{Delete the overlay.} | |
1024 | (delete-overlay foo) | |
1025 | @result{} nil | |
1026 | ;; @r{Verify it is deleted.} | |
1027 | foo | |
1028 | @result{} #<overlay in no buffer> | |
1029 | ;; @r{A deleted overlay has no position.} | |
1030 | (overlay-start foo) | |
1031 | @result{} nil | |
1032 | (overlay-end foo) | |
1033 | @result{} nil | |
1034 | (overlay-buffer foo) | |
1035 | @result{} nil | |
1036 | ;; @r{Undelete the overlay.} | |
1037 | (move-overlay foo 1 20) | |
1038 | @result{} #<overlay from 1 to 20 in display.texi> | |
1039 | ;; @r{Verify the results.} | |
1040 | (overlay-start foo) | |
1041 | @result{} 1 | |
1042 | (overlay-end foo) | |
1043 | @result{} 20 | |
1044 | (overlay-buffer foo) | |
1045 | @result{} #<buffer display.texi> | |
05aea714 | 1046 | ;; @r{Moving and deleting the overlay does not change its properties.} |
2468d0c0 DL |
1047 | (overlay-get foo 'happy) |
1048 | @result{} t | |
1049 | @end example | |
1050 | ||
1051 | @node Finding Overlays | |
1052 | @subsection Searching for Overlays | |
1053 | ||
42b85554 | 1054 | @defun overlays-at pos |
2468d0c0 DL |
1055 | This function returns a list of all the overlays that cover the |
1056 | character at position @var{pos} in the current buffer. The list is in | |
1057 | no particular order. An overlay contains position @var{pos} if it | |
1058 | begins at or before @var{pos}, and ends after @var{pos}. | |
1059 | ||
1060 | To illustrate usage, here is a Lisp function that returns a list of the | |
1061 | overlays that specify property @var{prop} for the character at point: | |
1062 | ||
1063 | @smallexample | |
1064 | (defun find-overlays-specifying (prop) | |
1065 | (let ((overlays (overlays-at (point))) | |
1066 | found) | |
1067 | (while overlays | |
1068 | (let ((overlay (cdr overlays))) | |
1069 | (if (overlay-get overlay prop) | |
1070 | (setq found (cons overlay found)))) | |
1071 | (setq overlays (cdr overlays))) | |
1072 | found)) | |
1073 | @end smallexample | |
42b85554 RS |
1074 | @end defun |
1075 | ||
f9f59935 RS |
1076 | @defun overlays-in beg end |
1077 | This function returns a list of the overlays that overlap the region | |
1078 | @var{beg} through @var{end}. ``Overlap'' means that at least one | |
1079 | character is contained within the overlay and also contained within the | |
1080 | specified region; however, empty overlays are included in the result if | |
2468d0c0 | 1081 | they are located at @var{beg}, or strictly between @var{beg} and @var{end}. |
f9f59935 RS |
1082 | @end defun |
1083 | ||
42b85554 RS |
1084 | @defun next-overlay-change pos |
1085 | This function returns the buffer position of the next beginning or end | |
1086 | of an overlay, after @var{pos}. | |
1087 | @end defun | |
1088 | ||
22697dac KH |
1089 | @defun previous-overlay-change pos |
1090 | This function returns the buffer position of the previous beginning or | |
1091 | end of an overlay, before @var{pos}. | |
1092 | @end defun | |
1093 | ||
2468d0c0 DL |
1094 | Here's an easy way to use @code{next-overlay-change} to search for the |
1095 | next character which gets a non-@code{nil} @code{happy} property from | |
1096 | either its overlays or its text properties (@pxref{Property Search}): | |
1097 | ||
1098 | @smallexample | |
1099 | (defun find-overlay-prop (prop) | |
1100 | (save-excursion | |
1101 | (while (and (not (eobp)) | |
1102 | (not (get-char-property (point) 'happy))) | |
1103 | (goto-char (min (next-overlay-change (point)) | |
1104 | (next-single-property-change (point) 'happy)))) | |
1105 | (point))) | |
1106 | @end smallexample | |
1107 | ||
f9f59935 RS |
1108 | @node Width |
1109 | @section Width | |
1110 | ||
1111 | Since not all characters have the same width, these functions let you | |
969fe9b5 RS |
1112 | check the width of a character. @xref{Primitive Indent}, and |
1113 | @ref{Screen Lines}, for related functions. | |
f9f59935 | 1114 | |
f9f59935 RS |
1115 | @defun char-width char |
1116 | This function returns the width in columns of the character @var{char}, | |
1117 | if it were displayed in the current buffer and the selected window. | |
1118 | @end defun | |
1119 | ||
f9f59935 RS |
1120 | @defun string-width string |
1121 | This function returns the width in columns of the string @var{string}, | |
1122 | if it were displayed in the current buffer and the selected window. | |
1123 | @end defun | |
1124 | ||
f9f59935 RS |
1125 | @defun truncate-string-to-width string width &optional start-column padding |
1126 | This function returns the part of @var{string} that fits within | |
1127 | @var{width} columns, as a new string. | |
1128 | ||
1129 | If @var{string} does not reach @var{width}, then the result ends where | |
1130 | @var{string} ends. If one multi-column character in @var{string} | |
1131 | extends across the column @var{width}, that character is not included in | |
1132 | the result. Thus, the result can fall short of @var{width} but cannot | |
1133 | go beyond it. | |
1134 | ||
1135 | The optional argument @var{start-column} specifies the starting column. | |
1136 | If this is non-@code{nil}, then the first @var{start-column} columns of | |
1137 | the string are omitted from the value. If one multi-column character in | |
1138 | @var{string} extends across the column @var{start-column}, that | |
1139 | character is not included. | |
1140 | ||
1141 | The optional argument @var{padding}, if non-@code{nil}, is a padding | |
1142 | character added at the beginning and end of the result string, to extend | |
1143 | it to exactly @var{width} columns. The padding character is used at the | |
1144 | end of the result if it falls short of @var{width}. It is also used at | |
1145 | the beginning of the result if one multi-column character in | |
1146 | @var{string} extends across the column @var{start-column}. | |
1147 | ||
1148 | @example | |
1149 | (truncate-string-to-width "\tab\t" 12 4) | |
1150 | @result{} "ab" | |
1151 | (truncate-string-to-width "\tab\t" 12 4 ?\ ) | |
1152 | @result{} " ab " | |
1153 | @end example | |
1154 | @end defun | |
1155 | ||
42b85554 RS |
1156 | @node Faces |
1157 | @section Faces | |
1158 | @cindex face | |
1159 | ||
8241495d RS |
1160 | A @dfn{face} is a named collection of graphical attributes: font |
1161 | family, foreground color, background color, optional underlining, and | |
1162 | many others. Faces are used in Emacs to control the style of display of | |
1163 | particular parts of the text or the frame. | |
42b85554 RS |
1164 | |
1165 | @cindex face id | |
969fe9b5 | 1166 | Each face has its own @dfn{face number}, which distinguishes faces at |
8241495d | 1167 | low levels within Emacs. However, for most purposes, you refer to |
42b85554 RS |
1168 | faces in Lisp programs by their names. |
1169 | ||
22697dac KH |
1170 | @defun facep object |
1171 | This function returns @code{t} if @var{object} is a face name symbol (or | |
1172 | if it is a vector of the kind used internally to record face data). It | |
1173 | returns @code{nil} otherwise. | |
1174 | @end defun | |
1175 | ||
42b85554 RS |
1176 | Each face name is meaningful for all frames, and by default it has the |
1177 | same meaning in all frames. But you can arrange to give a particular | |
1178 | face name a special meaning in one frame if you wish. | |
1179 | ||
1180 | @menu | |
1181 | * Standard Faces:: The faces Emacs normally comes with. | |
969fe9b5 | 1182 | * Defining Faces:: How to define a face with @code{defface}. |
8241495d RS |
1183 | * Face Attributes:: What is in a face? |
1184 | * Attribute Functions:: Functions to examine and set face attributes. | |
1185 | * Merging Faces:: How Emacs combines the faces specified for a character. | |
1186 | * Font Selection:: Finding the best available font for a face. | |
42b85554 | 1187 | * Face Functions:: How to define and examine faces. |
8241495d RS |
1188 | * Auto Faces:: Hook for automatic face assignment. |
1189 | * Font Lookup:: Looking up the names of available fonts | |
1190 | and information about them. | |
1191 | * Fontsets:: A fontset is a collection of fonts | |
1192 | that handle a range of character sets. | |
42b85554 RS |
1193 | @end menu |
1194 | ||
1195 | @node Standard Faces | |
1196 | @subsection Standard Faces | |
1197 | ||
8241495d RS |
1198 | This table lists all the standard faces and their uses. Most of them |
1199 | are used for displaying certain parts of the frames or certain kinds of | |
1200 | text; you can control how those places look by customizing these faces. | |
42b85554 RS |
1201 | |
1202 | @table @code | |
1203 | @item default | |
1204 | @kindex default @r{(face name)} | |
1205 | This face is used for ordinary text. | |
1206 | ||
8241495d RS |
1207 | @item mode-line |
1208 | @kindex mode-line @r{(face name)} | |
a40d4712 PR |
1209 | This face is used for mode lines, and for menu bars when toolkit menus |
1210 | are not used---but only if @code{mode-line-inverse-video} is | |
1211 | non-@code{nil}. | |
8241495d | 1212 | |
42b85554 RS |
1213 | @item modeline |
1214 | @kindex modeline @r{(face name)} | |
8241495d RS |
1215 | This is an alias for the @code{mode-line} face, for compatibility with |
1216 | old Emacs versions. | |
1217 | ||
1218 | @item header-line | |
1219 | @kindex header-line @r{(face name)} | |
1220 | This face is used for the header lines of windows that have them. | |
1221 | ||
a40d4712 PR |
1222 | @item menu |
1223 | This face controls the display of menus, both their colors and their | |
1224 | font. (This works only on certain systems.) | |
1225 | ||
8241495d RS |
1226 | @item fringe |
1227 | @kindex fringe @r{(face name)} | |
1228 | This face controls the colors of window fringes, the thin areas on | |
1229 | either side that are used to display continuation and truncation glyphs. | |
1230 | ||
1231 | @item scroll-bar | |
1232 | @kindex scroll-bar @r{(face name)} | |
1233 | This face controls the colors for display of scroll bars. | |
1234 | ||
1235 | @item tool-bar | |
1236 | @kindex tool-bar @r{(face name)} | |
1237 | This face is used for display of the tool bar, if any. | |
42b85554 RS |
1238 | |
1239 | @item region | |
1240 | @kindex region @r{(face name)} | |
1241 | This face is used for highlighting the region in Transient Mark mode. | |
1242 | ||
1243 | @item secondary-selection | |
1244 | @kindex secondary-selection @r{(face name)} | |
1245 | This face is used to show any secondary selection you have made. | |
1246 | ||
1247 | @item highlight | |
1248 | @kindex highlight @r{(face name)} | |
1249 | This face is meant to be used for highlighting for various purposes. | |
1250 | ||
8241495d RS |
1251 | @item trailing-whitespace |
1252 | @kindex trailing-whitespace @r{(face name)} | |
a40d4712 PR |
1253 | This face is used to display excess whitespace at the end of a line, |
1254 | if @code{show-trailing-whitespace} is non-@code{nil}. | |
8241495d | 1255 | @end table |
42b85554 | 1256 | |
8241495d RS |
1257 | In contrast, these faces are provided to change the appearance of text |
1258 | in specific ways. You can use them on specific text, when you want | |
1259 | the effects they produce. | |
1260 | ||
1261 | @table @code | |
42b85554 RS |
1262 | @item bold |
1263 | @kindex bold @r{(face name)} | |
1264 | This face uses a bold font, if possible. It uses the bold variant of | |
1265 | the frame's font, if it has one. It's up to you to choose a default | |
1266 | font that has a bold variant, if you want to use one. | |
1267 | ||
1268 | @item italic | |
1269 | @kindex italic @r{(face name)} | |
1270 | This face uses the italic variant of the frame's font, if it has one. | |
1271 | ||
1272 | @item bold-italic | |
1273 | @kindex bold-italic @r{(face name)} | |
1274 | This face uses the bold italic variant of the frame's font, if it has | |
1275 | one. | |
8241495d RS |
1276 | |
1277 | @item underline | |
1278 | @kindex underline @r{(face name)} | |
1279 | This face underlines text. | |
1280 | ||
1281 | @item fixed-patch | |
1282 | @kindex fixed-patch @r{(face name)} | |
1283 | This face forces use of a particular fixed-width font. | |
1284 | ||
1285 | @item variable-patch | |
1286 | @kindex variable-patch @r{(face name)} | |
1287 | This face forces use of a particular variable-width font. It's | |
a40d4712 | 1288 | reasonable to customize this to use a different variable-width font, if |
8241495d | 1289 | you like, but you should not make it a fixed-width font. |
42b85554 RS |
1290 | @end table |
1291 | ||
a40d4712 PR |
1292 | @defvar show-trailing-whitespace |
1293 | @tindex show-trailing-whitespace | |
1294 | If this variable is non-@code{nil}, Emacs uses the | |
1295 | @code{trailing-whitespace} face to display any spaces and tabs at the | |
1296 | end of a line. | |
1297 | @end defvar | |
1298 | ||
969fe9b5 | 1299 | @node Defining Faces |
a9f0a989 | 1300 | @subsection Defining Faces |
969fe9b5 RS |
1301 | |
1302 | The way to define a new face is with @code{defface}. This creates a | |
1303 | kind of customization item (@pxref{Customization}) which the user can | |
1304 | customize using the Customization buffer (@pxref{Easy Customization,,, | |
1305 | emacs, The GNU Emacs Manual}). | |
1306 | ||
969fe9b5 | 1307 | @defmac defface face spec doc [keyword value]... |
a40d4712 PR |
1308 | This declares @var{face} as a customizable face that defaults according |
1309 | to @var{spec}. You should not quote the symbol @var{face}. The | |
1310 | argument @var{doc} specifies the face documentation. The keywords you | |
1311 | can use in @code{defface} are the same ones that are meaningful in both | |
1312 | @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}). | |
969fe9b5 RS |
1313 | |
1314 | When @code{defface} executes, it defines the face according to | |
a9f0a989 | 1315 | @var{spec}, then uses any customizations that were read from the |
a40d4712 | 1316 | init file (@pxref{Init File}) to override that specification. |
969fe9b5 RS |
1317 | |
1318 | The purpose of @var{spec} is to specify how the face should appear on | |
1319 | different kinds of terminals. It should be an alist whose elements have | |
a40d4712 PR |
1320 | the form @code{(@var{display} @var{atts})}. Each element's @sc{car}, |
1321 | @var{display}, specifies a class of terminals. The element's second element, | |
969fe9b5 RS |
1322 | @var{atts}, is a list of face attributes and their values; it specifies |
1323 | what the face should look like on that kind of terminal. The possible | |
1324 | attributes are defined in the value of @code{custom-face-attributes}. | |
1325 | ||
1326 | The @var{display} part of an element of @var{spec} determines which | |
1327 | frames the element applies to. If more than one element of @var{spec} | |
1328 | matches a given frame, the first matching element is the only one used | |
1329 | for that frame. There are two possibilities for @var{display}: | |
1330 | ||
1331 | @table @asis | |
1332 | @item @code{t} | |
1333 | This element of @var{spec} matches all frames. Therefore, any | |
1334 | subsequent elements of @var{spec} are never used. Normally | |
1335 | @code{t} is used in the last (or only) element of @var{spec}. | |
1336 | ||
a9f0a989 | 1337 | @item a list |
1911e6e5 | 1338 | If @var{display} is a list, each element should have the form |
969fe9b5 RS |
1339 | @code{(@var{characteristic} @var{value}@dots{})}. Here |
1340 | @var{characteristic} specifies a way of classifying frames, and the | |
1341 | @var{value}s are possible classifications which @var{display} should | |
1342 | apply to. Here are the possible values of @var{characteristic}: | |
1343 | ||
1344 | @table @code | |
1345 | @item type | |
9a6b7dcd MB |
1346 | The kind of window system the frame uses---either @code{graphic} (any |
1347 | graphics-capable display), @code{x}, @code{pc} (for the MS-DOS console), | |
1348 | @code{w32} (for MS Windows 9X/NT), or @code{tty} (a non-graphics-capable | |
1349 | display). | |
969fe9b5 RS |
1350 | |
1351 | @item class | |
1352 | What kinds of colors the frame supports---either @code{color}, | |
1353 | @code{grayscale}, or @code{mono}. | |
1354 | ||
1355 | @item background | |
1911e6e5 | 1356 | The kind of background---either @code{light} or @code{dark}. |
969fe9b5 RS |
1357 | @end table |
1358 | ||
1359 | If an element of @var{display} specifies more than one @var{value} for a | |
1360 | given @var{characteristic}, any of those values is acceptable. If | |
1361 | @var{display} has more than one element, each element should specify a | |
1362 | different @var{characteristic}; then @emph{each} characteristic of the | |
1363 | frame must match one of the @var{value}s specified for it in | |
1364 | @var{display}. | |
1365 | @end table | |
1366 | @end defmac | |
1367 | ||
a40d4712 | 1368 | Here's how the standard face @code{region} is defined: |
969fe9b5 RS |
1369 | |
1370 | @example | |
a40d4712 | 1371 | @group |
969fe9b5 | 1372 | (defface region |
a40d4712 PR |
1373 | `((((type tty) (class color)) |
1374 | (:background "blue" :foreground "white")) | |
1375 | @end group | |
1376 | (((type tty) (class mono)) | |
1377 | (:inverse-video t)) | |
1378 | (((class color) (background dark)) | |
1379 | (:background "blue")) | |
1380 | (((class color) (background light)) | |
1381 | (:background "lightblue")) | |
1382 | (t (:background "gray"))) | |
1383 | @group | |
1384 | "Basic face for highlighting the region." | |
1385 | :group 'basic-faces) | |
1386 | @end group | |
969fe9b5 RS |
1387 | @end example |
1388 | ||
1389 | Internally, @code{defface} uses the symbol property | |
1390 | @code{face-defface-spec} to record the face attributes specified in | |
1391 | @code{defface}, @code{saved-face} for the attributes saved by the user | |
1392 | with the customization buffer, and @code{face-documentation} for the | |
1393 | documentation string. | |
1394 | ||
1911e6e5 RS |
1395 | @defopt frame-background-mode |
1396 | This option, if non-@code{nil}, specifies the background type to use for | |
1397 | interpreting face definitions. If it is @code{dark}, then Emacs treats | |
1398 | all frames as if they had a dark background, regardless of their actual | |
1399 | background colors. If it is @code{light}, then Emacs treats all frames | |
1400 | as if they had a light background. | |
1401 | @end defopt | |
1402 | ||
8241495d RS |
1403 | @node Face Attributes |
1404 | @subsection Face Attributes | |
1405 | @cindex face attributes | |
42b85554 | 1406 | |
8241495d RS |
1407 | The effect of using a face is determined by a fixed set of @dfn{face |
1408 | attributes}. This table lists all the face attributes, and what they | |
a40d4712 PR |
1409 | mean. Note that in general, more than one face can be specified for a |
1410 | given piece of text; when that happens, the attributes of all the faces | |
1411 | are merged to specify how to display the text. @xref{Merging Faces}. | |
42b85554 | 1412 | |
8241495d RS |
1413 | In Emacs 21, any attribute in a face can have the value |
1414 | @code{unspecified}. This means the face doesn't specify that attribute. | |
1415 | In face merging, when the first face fails to specify a particular | |
1416 | attribute, that means the next face gets a chance. However, the | |
1417 | @code{default} face must specify all attributes. | |
42b85554 | 1418 | |
a40d4712 PR |
1419 | Some of these font attributes are meaningful only on certain kinds of |
1420 | displays---if your display cannot handle a certain attribute, the | |
1421 | attribute is ignored. (The attributes @code{:family}, @code{:width}, | |
1422 | @code{:height}, @code{:weight}, and @code{:slant} correspond to parts of | |
1423 | an X Logical Font Descriptor.) | |
42b85554 | 1424 | |
8241495d RS |
1425 | @table @code |
1426 | @item :family | |
1427 | Font family name, or fontset name (@pxref{Fontsets}). If you specify a | |
a40d4712 PR |
1428 | font family name, the wild-card characters @samp{*} and @samp{?} are |
1429 | allowed. | |
8241495d RS |
1430 | |
1431 | @item :width | |
1432 | Relative proportionate width, also known as the character set width or | |
1433 | set width. This should be one of the symbols @code{ultra-condensed}, | |
1434 | @code{extra-condensed}, @code{condensed}, @code{semi-condensed}, | |
1435 | @code{normal}, @code{semi-expanded}, @code{expanded}, | |
1436 | @code{extra-expanded}, or @code{ultra-expanded}. | |
1437 | ||
1438 | @item :height | |
96f71a49 MB |
1439 | Either the font height, an integer in units of 1/10 point, a floating |
1440 | point number specifying the amount by which to scale the height of any | |
1441 | underlying face, or a function, which is called with the old height | |
1442 | (from the underlying face), and should return the new height. | |
8241495d RS |
1443 | |
1444 | @item :weight | |
1445 | Font weight---a symbol from this series (from most dense to most faint): | |
1446 | @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold}, | |
1447 | @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, | |
a40d4712 | 1448 | or @code{ultra-light}. |
66f54605 | 1449 | |
a40d4712 PR |
1450 | On a text-only terminal, any weight greater than normal is displayed as |
1451 | extra bright, and any weight less than normal is displayed as | |
1452 | half-bright (provided the terminal supports the feature). | |
1453 | ||
8241495d RS |
1454 | @item :slant |
1455 | Font slant---one of the symbols @code{italic}, @code{oblique}, @code{normal}, | |
1456 | @code{reverse-italic}, or @code{reverse-oblique}. | |
66f54605 PR |
1457 | |
1458 | On a text-only terminal, slanted text is displayed as half-bright, if | |
1459 | the terminal supports the feature. | |
1460 | ||
8241495d RS |
1461 | @item :foreground |
1462 | Foreground color, a string. | |
1463 | ||
1464 | @item :background | |
1465 | Background color, a string. | |
1466 | ||
1467 | @item :inverse-video | |
1468 | Whether or not characters should be displayed in inverse video. The | |
1469 | value should be @code{t} (yes) or @code{nil} (no). | |
1470 | ||
1471 | @item :stipple | |
a40d4712 | 1472 | The background stipple, a bitmap. |
8241495d | 1473 | |
a40d4712 PR |
1474 | The value can be a string; that should be the name of a file containing |
1475 | external-format X bitmap data. The file is found in the directories | |
1476 | listed in the variable @code{x-bitmap-file-path}. | |
8241495d | 1477 | |
a40d4712 PR |
1478 | Alternatively, the value can specify the bitmap directly, with a list of |
1479 | the form @code{(@var{width} @var{height} @var{data})}. Here, | |
1480 | @var{width} and @var{height} specify the size in pixels, and @var{data} | |
1481 | is a string containing the raw bits of the bitmap, row by row. Each row | |
1482 | occupies @math{(@var{width} + 7) / 8} consecutie bytes in the string | |
1483 | (which should be a unibyte string for best results). | |
8241495d RS |
1484 | |
1485 | If the value is @code{nil}, that means use no stipple pattern. | |
1486 | ||
1487 | Normally you do not need to set the stipple attribute, because it is | |
1488 | used automatically to handle certain shades of gray. | |
1489 | ||
1490 | @item :underline | |
1491 | Whether or not characters should be underlined, and in what color. If | |
1492 | the value is @code{t}, underlining uses the foreground color of the | |
1493 | face. If the value is a string, underlining uses that color. The | |
1494 | value @code{nil} means do not underline. | |
1495 | ||
1496 | @item :overline | |
1497 | Whether or not characters should be overlined, and in what color. | |
1498 | The value is used like that of @code{:underline}. | |
1499 | ||
1500 | @item :strike-through | |
1501 | Whether or not characters should be strike-through, and in what | |
1502 | color. The value is used like that of @code{:underline}. | |
1503 | ||
96f71a49 MB |
1504 | @item :inherit |
1505 | The name of a face from which to inherit attributes, or a list of face | |
1506 | names. Attributes from inherited faces are merged into the face like an | |
1507 | underlying face would be, with higher priority than underlying faces. | |
1508 | ||
8241495d RS |
1509 | @item :box |
1510 | Whether or not a box should be drawn around characters, its color, the | |
a40d4712 | 1511 | width of the box lines, and 3D appearance. |
8241495d | 1512 | @end table |
42b85554 | 1513 | |
8241495d RS |
1514 | Here are the possible values of the @code{:box} attribute, and what |
1515 | they mean: | |
42b85554 | 1516 | |
8241495d RS |
1517 | @table @asis |
1518 | @item @code{nil} | |
1519 | Don't draw a box. | |
bfe721d1 | 1520 | |
8241495d RS |
1521 | @item @code{t} |
1522 | Draw a box with lines of width 1, in the foreground color. | |
42b85554 | 1523 | |
8241495d RS |
1524 | @item @var{color} |
1525 | Draw a box with lines of width 1, in color @var{color}. | |
42b85554 | 1526 | |
8241495d RS |
1527 | @item @code{(:line-width @var{width} :color @var{color} :style @var{style})} |
1528 | This way you can explicitly specify all aspects of the box. The value | |
1529 | @var{width} specifies the width of the lines to draw; it defaults to 1. | |
42b85554 | 1530 | |
8241495d RS |
1531 | The value @var{color} specifies the color to draw with. The default is |
1532 | the foreground color of the face for simple boxes, and the background | |
1533 | color of the face for 3D boxes. | |
42b85554 | 1534 | |
8241495d RS |
1535 | The value @var{style} specifies whether to draw a 3D box. If it is |
1536 | @code{released-button}, the box looks like a 3D button that is not being | |
1537 | pressed. If it is @code{pressed-button}, the box looks like a 3D button | |
1538 | that is being pressed. If it is @code{nil} or omitted, a plain 2D box | |
1539 | is used. | |
1540 | @end table | |
42b85554 | 1541 | |
8241495d RS |
1542 | The attributes @code{:overline}, @code{:strike-through} and |
1543 | @code{:box} are new in Emacs 21. The attributes @code{:family}, | |
1544 | @code{:height}, @code{:width}, @code{:weight}, @code{:slant} are also | |
a40d4712 PR |
1545 | new; previous versions used the following attributes, now semi-obsolete, |
1546 | to specify some of the same information: | |
42b85554 | 1547 | |
8241495d RS |
1548 | @table @code |
1549 | @item :font | |
a40d4712 | 1550 | This attribute specifies the font name. |
42b85554 | 1551 | |
8241495d RS |
1552 | @item :bold |
1553 | A non-@code{nil} value specifies a bold font. | |
42b85554 | 1554 | |
8241495d RS |
1555 | @item :italic |
1556 | A non-@code{nil} value specifies an italic font. | |
1557 | @end table | |
42b85554 | 1558 | |
8241495d RS |
1559 | For compatibility, you can still set these ``attributes'' in Emacs 21, |
1560 | even though they are not real face attributes. Here is what that does: | |
42b85554 | 1561 | |
8241495d RS |
1562 | @table @code |
1563 | @item :font | |
a40d4712 PR |
1564 | You can specify an X font name as the ``value'' of this ``attribute''; |
1565 | that sets the @code{:family}, @code{:width}, @code{:height}, | |
1566 | @code{:weight}, and @code{:slant} attributes according to the font name. | |
8241495d RS |
1567 | |
1568 | If the value is a pattern with wildcards, the first font that matches | |
1569 | the pattern is used to set these attributes. | |
1570 | ||
1571 | @item :bold | |
1572 | A non-@code{nil} makes the face bold; @code{nil} makes it normal. | |
1573 | This actually works by setting the @code{:weight} attribute. | |
1574 | ||
1575 | @item :italic | |
1576 | A non-@code{nil} makes the face italic; @code{nil} makes it normal. | |
1577 | This actually works by setting the @code{:slant} attribute. | |
1578 | @end table | |
42b85554 | 1579 | |
8241495d RS |
1580 | @defvar x-bitmap-file-path |
1581 | This variable specifies a list of directories for searching | |
1582 | for bitmap files, for the @code{:stipple} attribute. | |
1583 | @end defvar | |
1584 | ||
ea7220f8 | 1585 | @defun bitmap-spec-p object |
a40d4712 PR |
1586 | This returns @code{t} if @var{object} is a valid bitmap |
1587 | specification, suitable for use with @code{:stipple}. | |
1588 | It returns @code{nil} otherwise. | |
1589 | @end defun | |
1590 | ||
8241495d RS |
1591 | @node Attribute Functions |
1592 | @subsection Face Attribute Functions | |
42b85554 RS |
1593 | |
1594 | You can modify the attributes of an existing face with the following | |
1595 | functions. If you specify @var{frame}, they affect just that frame; | |
1596 | otherwise, they affect all frames as well as the defaults that apply to | |
1597 | new frames. | |
1598 | ||
8241495d RS |
1599 | @tindex set-face-attribute |
1600 | @defun set-face-attribute face frame &rest arguments | |
1601 | This function sets one or more attributes of face @var{face} | |
1602 | for frame @var{frame}. If @var{frame} is @code{nil}, it sets | |
1603 | the attribute for all frames, and the defaults for new frames. | |
1604 | ||
1605 | The extra arguments @var{arguments} specify the attributes to set, and | |
1606 | the values for them. They should consist of alternating attribute names | |
a40d4712 | 1607 | (such as @code{:family} or @code{:underline}) and corresponding values. |
8241495d RS |
1608 | Thus, |
1609 | ||
1610 | @example | |
1611 | (set-face-attribute 'foo nil | |
1612 | :width :extended | |
1613 | :weight :bold | |
1614 | :underline "red") | |
1615 | @end example | |
1616 | ||
1617 | @noindent | |
1618 | sets the attributes @code{:width}, @code{:weight} and @code{:underline} | |
1619 | to the corresponding values. | |
1620 | @end defun | |
1621 | ||
1622 | @tindex face-attribute | |
1623 | @defun face-attribute face attribute &optional frame | |
1624 | This returns the value of the @var{attribute} attribute of face | |
1625 | @var{face} on @var{frame}. If @var{frame} is @code{nil}, | |
1626 | that means the selected frame. | |
1627 | ||
1628 | If @var{frame} is @code{t}, the value is the default for | |
1629 | @var{face} for new frames. | |
1630 | ||
1631 | For example, | |
1632 | ||
1633 | @example | |
1634 | (face-attribute 'bold :weight) | |
1635 | @result{} bold | |
1636 | @end example | |
1637 | @end defun | |
1638 | ||
a40d4712 PR |
1639 | The functions above did not exist before Emacs 21. For compatibility |
1640 | with older Emacs versions, you can use the following functions to set | |
8241495d RS |
1641 | and examine the face attributes which existed in those versions. |
1642 | ||
42b85554 RS |
1643 | @defun set-face-foreground face color &optional frame |
1644 | @defunx set-face-background face color &optional frame | |
78608595 RS |
1645 | These functions set the foreground (or background, respectively) color |
1646 | of face @var{face} to @var{color}. The argument @var{color} should be a | |
42b85554 | 1647 | string, the name of a color. |
bfe721d1 KH |
1648 | |
1649 | Certain shades of gray are implemented by stipple patterns on | |
1650 | black-and-white screens. | |
1651 | @end defun | |
1652 | ||
1653 | @defun set-face-stipple face pattern &optional frame | |
1654 | This function sets the background stipple pattern of face @var{face} to | |
1655 | @var{pattern}. The argument @var{pattern} should be the name of a | |
1656 | stipple pattern defined by the X server, or @code{nil} meaning don't use | |
1657 | stipple. | |
1658 | ||
1659 | Normally there is no need to pay attention to stipple patterns, because | |
1660 | they are used automatically to handle certain shades of gray. | |
42b85554 RS |
1661 | @end defun |
1662 | ||
1663 | @defun set-face-font face font &optional frame | |
8241495d RS |
1664 | This function sets the font of face @var{face}. |
1665 | ||
1666 | In Emacs 21, this actually sets the attributes @code{:family}, | |
1667 | @code{:width}, @code{:height}, @code{:weight}, and @code{:slant} | |
1668 | according to the font name @var{font}. | |
1669 | ||
1670 | In Emacs 20, this sets the font attribute. Once you set the font | |
a9f0a989 | 1671 | explicitly, the bold and italic attributes cease to have any effect, |
8241495d | 1672 | because the precise font that you specified is used. |
21cffb83 RS |
1673 | @end defun |
1674 | ||
f9f59935 | 1675 | @defun set-face-bold-p face bold-p &optional frame |
8241495d RS |
1676 | This function specifies whether @var{face} should be bold. If |
1677 | @var{bold-p} is non-@code{nil}, that means yes; @code{nil} means no. | |
1678 | ||
1679 | In Emacs 21, this sets the @code{:weight} attribute. | |
1680 | In Emacs 20, it sets the @code{:bold} attribute. | |
21cffb83 RS |
1681 | @end defun |
1682 | ||
f9f59935 | 1683 | @defun set-face-italic-p face italic-p &optional frame |
8241495d RS |
1684 | This function specifies whether @var{face} should be italic. If |
1685 | @var{italic-p} is non-@code{nil}, that means yes; @code{nil} means no. | |
1686 | ||
1687 | In Emacs 21, this sets the @code{:slant} attribute. | |
1688 | In Emacs 20, it sets the @code{:italic} attribute. | |
42b85554 RS |
1689 | @end defun |
1690 | ||
969fe9b5 RS |
1691 | @defun set-face-underline-p face underline-p &optional frame |
1692 | This function sets the underline attribute of face @var{face}. | |
1693 | Non-@code{nil} means do underline; @code{nil} means don't. | |
1694 | @end defun | |
1695 | ||
42b85554 | 1696 | @defun invert-face face &optional frame |
8241495d RS |
1697 | This function inverts the @code{:inverse-video} attribute of face |
1698 | @var{face}. If the attribute is @code{nil}, this function sets it to | |
1699 | @code{t}, and vice versa. | |
42b85554 RS |
1700 | @end defun |
1701 | ||
1702 | These functions examine the attributes of a face. If you don't | |
1703 | specify @var{frame}, they refer to the default data for new frames. | |
a40d4712 PR |
1704 | They return the symbol @code{unspecified} if the face doesn't define any |
1705 | value for that attribute. | |
42b85554 RS |
1706 | |
1707 | @defun face-foreground face &optional frame | |
1708 | @defunx face-background face &optional frame | |
78608595 RS |
1709 | These functions return the foreground color (or background color, |
1710 | respectively) of face @var{face}, as a string. | |
42b85554 RS |
1711 | @end defun |
1712 | ||
bfe721d1 KH |
1713 | @defun face-stipple face &optional frame |
1714 | This function returns the name of the background stipple pattern of face | |
1715 | @var{face}, or @code{nil} if it doesn't have one. | |
1716 | @end defun | |
1717 | ||
42b85554 RS |
1718 | @defun face-font face &optional frame |
1719 | This function returns the name of the font of face @var{face}. | |
1720 | @end defun | |
1721 | ||
f9f59935 | 1722 | @defun face-bold-p face &optional frame |
8241495d RS |
1723 | This function returns @code{t} if @var{face} is bold---that is, if it is |
1724 | bolder than normal. It returns @code{nil} otherwise. | |
f9f59935 RS |
1725 | @end defun |
1726 | ||
f9f59935 | 1727 | @defun face-italic-p face &optional frame |
8241495d RS |
1728 | This function returns @code{t} if @var{face} is italic or oblique, |
1729 | @code{nil} otherwise. | |
f9f59935 RS |
1730 | @end defun |
1731 | ||
969fe9b5 | 1732 | @defun face-underline-p face &optional frame |
8241495d RS |
1733 | This function returns the @code{:underline} attribute of face @var{face}. |
1734 | @end defun | |
1735 | ||
1736 | @defun face-inverse-video-p face &optional frame | |
1737 | This function returns the @code{:inverse-video} attribute of face @var{face}. | |
1738 | @end defun | |
1739 | ||
1740 | @node Merging Faces | |
1741 | @subsection Merging Faces for Display | |
1742 | ||
1743 | Here are the ways to specify which faces to use for display of text: | |
1744 | ||
1745 | @itemize @bullet | |
1746 | @item | |
1747 | With defaults. The @code{default} face is used as the ultimate | |
1748 | default for all text. (In Emacs 19 and 20, the @code{default} | |
1749 | face is used only when no other face is specified.) | |
1750 | ||
1751 | For a mode line or header line, the face @code{modeline} or | |
1752 | @code{header-line} is used just before @code{default}. | |
1753 | ||
1754 | @item | |
1755 | With text properties. A character can have a @code{face} property; if | |
1756 | so, the faces and face attributes specified there apply. @xref{Special | |
1757 | Properties}. | |
1758 | ||
1759 | If the character has a @code{mouse-face} property, that is used instead | |
1760 | of the @code{face} property when the mouse is ``near enough'' to the | |
1761 | character. | |
1762 | ||
1763 | @item | |
1764 | With overlays. An overlay can have @code{face} and @code{mouse-face} | |
1765 | properties too; they apply to all the text covered by the overlay. | |
1766 | ||
1767 | @item | |
1768 | With a region that is active. In Transient Mark mode, the region is | |
1769 | highlighted with the face @code{region} (@pxref{Standard Faces}). | |
1770 | ||
1771 | @item | |
1772 | With special glyphs. Each glyph can specify a particular face | |
1773 | number. @xref{Glyphs}. | |
1774 | @end itemize | |
1775 | ||
1776 | If these various sources together specify more than one face for a | |
1777 | particular character, Emacs merges the attributes of the various faces | |
1778 | specified. The attributes of the faces of special glyphs come first; | |
1779 | then comes the face for region highlighting, if appropriate; | |
1780 | then come attributes of faces from overlays, followed by those from text | |
1781 | properties, and last the default face. | |
1782 | ||
1783 | When multiple overlays cover one character, an overlay with higher | |
1784 | priority overrides those with lower priority. @xref{Overlays}. | |
1785 | ||
1786 | In Emacs 20, if an attribute such as the font or a color is not | |
1787 | specified in any of the above ways, the frame's own font or color is | |
1788 | used. In newer Emacs versions, this cannot happen, because the | |
1789 | @code{default} face specifies all attributes---in fact, the frame's own | |
1790 | font and colors are synonymous with those of the default face. | |
1791 | ||
1792 | @node Font Selection | |
1793 | @subsection Font Selection | |
1794 | ||
1795 | @dfn{Selecting a font} means mapping the specified face attributes for | |
1796 | a character to a font that is available on a particular display. The | |
1797 | face attributes, as determined by face merging, specify most of the | |
1798 | font choice, but not all. Part of the choice depends on what character | |
1799 | it is. | |
1800 | ||
1801 | For multibyte characters, typically each font covers only one | |
1802 | character set. So each character set (@pxref{Character Sets}) specifies | |
1803 | a registry and encoding to use, with the character set's | |
1804 | @code{x-charset-registry} property. Its value is a string containing | |
1805 | the registry and the encoding, with a dash between them: | |
1806 | ||
1807 | @example | |
1808 | (plist-get (charset-plist 'latin-iso8859-1) | |
1809 | 'x-charset-registry) | |
1810 | @result{} "ISO8859-1" | |
1811 | @end example | |
1812 | ||
1813 | Unibyte text does not have character sets, so displaying a unibyte | |
1814 | character takes the registry and encoding from the variable | |
1815 | @code{face-default-registry}. | |
1816 | ||
1817 | @defvar face-default-registry | |
1818 | This variable specifies which registry and encoding to use in choosing | |
1819 | fonts for unibyte characters. The value is initialized at Emacs startup | |
1820 | time from the font the user specified for Emacs. | |
1821 | @end defvar | |
1822 | ||
1823 | If the face specifies a fontset name, that fontset determines a | |
1824 | pattern for fonts of the given charset. If the face specifies a font | |
1825 | family, a font pattern is constructed. | |
1826 | ||
1827 | Emacs tries to find an available font for the given face attributes | |
1828 | and character's registry and encoding. If there is a font that matches | |
1829 | exactly, it is used, of course. The hard case is when no available font | |
1830 | exactly fits the specification. Then Emacs looks for one that is | |
1dffc5db RS |
1831 | ``close''---one attribute at a time. You can specify the order to |
1832 | consider the attributes. In the case where a specified font family is | |
1833 | not available, you can specify a set of mappings for alternatives to | |
1834 | try. | |
8241495d RS |
1835 | |
1836 | @defvar face-font-selection-order | |
1837 | @tindex face-font-selection-order | |
1838 | This variable specifies the order of importance of the face attributes | |
1839 | @code{:width}, @code{:height}, @code{:weight}, and @code{:slant}. The | |
1840 | value should be a list containing those four symbols, in order of | |
1841 | decreasing importance. | |
1842 | ||
1843 | Font selection first finds the best available matches for the first | |
1844 | attribute listed; then, among the fonts which are best in that way, it | |
1845 | searches for the best matches in the second attribute, and so on. | |
1846 | ||
1847 | The attributes @code{:weight} and @code{:width} have symbolic values in | |
1848 | a range centered around @code{normal}. Matches that are more extreme | |
1849 | (farther from @code{normal}) are somewhat preferred to matches that are | |
1850 | less extreme (closer to @code{normal}); this is designed to ensure that | |
1851 | non-normal faces contrast with normal ones, whenever possible. | |
1852 | ||
1853 | The default is @code{(:width :height :weight :slant)}, which means first | |
1854 | find the fonts closest to the specified @code{:width}, then---among the | |
1855 | fonts with that width---find a best match for the specified font height, | |
1856 | and so on. | |
1857 | ||
1858 | One example of a case where this variable makes a difference is when the | |
1859 | default font has no italic equivalent. With the default ordering, the | |
1860 | @code{italic} face will use a non-italic font that is similar to the | |
1861 | default one. But if you put @code{:slant} before @code{:height}, the | |
1862 | @code{italic} face will use an italic font, even if its height is not | |
1863 | quite right. | |
1864 | @end defvar | |
1865 | ||
52d89894 GM |
1866 | @defvar face-font-family-alternatives |
1867 | @tindex face-font-family-alternatives | |
8241495d RS |
1868 | This variable lets you specify alternative font families to try, if a |
1869 | given family is specified and doesn't exist. Each element should have | |
1870 | this form: | |
1871 | ||
1872 | @example | |
1873 | (@var{family} @var{alternate-families}@dots{}) | |
1874 | @end example | |
1875 | ||
1876 | If @var{family} is specified but not available, Emacs will try the other | |
1877 | families given in @var{alternate-families}, one by one, until it finds a | |
1878 | family that does exist. | |
52d89894 GM |
1879 | @end defvar |
1880 | ||
1881 | @defvar face-font-registry-alternatives | |
1882 | @tindex face-font-registry-alternatives | |
1883 | This variable lets you specify alternative font registries to try, if a | |
1884 | given registry is specified and doesn't exist. Each element should have | |
1885 | this form: | |
1886 | ||
1887 | @example | |
1888 | (@var{registry} @var{alternate-registries}@dots{}) | |
1889 | @end example | |
1890 | ||
1891 | If @var{registry} is specified but not available, Emacs will try the | |
1892 | other registries given in @var{alternate-registries}, one by one, | |
1893 | until it finds a registry that does exist. | |
8241495d RS |
1894 | @end defvar |
1895 | ||
1896 | Emacs can make use of scalable fonts, but by default it does not use | |
1897 | them, since the use of too many or too big scalable fonts can crash | |
1898 | XFree86 servers. | |
1899 | ||
1900 | @defvar scalable-fonts-allowed | |
1901 | @tindex scalable-fonts-allowed | |
1902 | This variable controls which scalable fonts to use. A value of | |
1903 | @code{nil}, the default, means do not use scalable fonts. @code{t} | |
1904 | means to use any scalable font that seems appropriate for the text. | |
1905 | ||
1906 | Otherwise, the value must be a list of regular expressions. Then a | |
1907 | scalable font is enabled for use if its name matches any regular | |
1908 | expression in the list. For example, | |
1909 | ||
1910 | @example | |
1911 | (setq scalable-fonts-allowed '("muleindian-2$")) | |
1912 | @end example | |
1913 | ||
1914 | @noindent | |
1915 | allows the use of scalable fonts with registry @code{muleindian-2}. | |
eda77a0f | 1916 | @end defvar |
8241495d RS |
1917 | |
1918 | @defun clear-face-cache &optional unload-p | |
1919 | @tindex clear-face-cache | |
1920 | This function clears the face cache for all frames. | |
1921 | If @var{unload-p} is non-@code{nil}, that means to unload | |
1922 | all unused fonts as well. | |
1923 | @end defun | |
1924 | ||
1925 | @node Face Functions | |
1926 | @subsection Functions for Working with Faces | |
1927 | ||
1928 | Here are additional functions for creating and working with faces. | |
1929 | ||
1930 | @defun make-face name | |
1931 | This function defines a new face named @var{name}, initially with all | |
1932 | attributes @code{nil}. It does nothing if there is already a face named | |
1933 | @var{name}. | |
1934 | @end defun | |
1935 | ||
1936 | @defun face-list | |
1937 | This function returns a list of all defined face names. | |
1938 | @end defun | |
1939 | ||
1940 | @defun copy-face old-face new-name &optional frame new-frame | |
1941 | This function defines the face @var{new-name} as a copy of the existing | |
1942 | face named @var{old-face}. It creates the face @var{new-name} if that | |
1943 | doesn't already exist. | |
1944 | ||
1945 | If the optional argument @var{frame} is given, this function applies | |
1946 | only to that frame. Otherwise it applies to each frame individually, | |
1947 | copying attributes from @var{old-face} in each frame to @var{new-face} | |
1948 | in the same frame. | |
1949 | ||
1950 | If the optional argument @var{new-frame} is given, then @code{copy-face} | |
1951 | copies the attributes of @var{old-face} in @var{frame} to @var{new-name} | |
1952 | in @var{new-frame}. | |
969fe9b5 RS |
1953 | @end defun |
1954 | ||
bfe721d1 | 1955 | @defun face-id face |
969fe9b5 | 1956 | This function returns the face number of face @var{face}. |
42b85554 RS |
1957 | @end defun |
1958 | ||
f9f59935 RS |
1959 | @defun face-documentation face |
1960 | This function returns the documentation string of face @var{face}, or | |
1961 | @code{nil} if none was specified for it. | |
1962 | @end defun | |
1963 | ||
42b85554 RS |
1964 | @defun face-equal face1 face2 &optional frame |
1965 | This returns @code{t} if the faces @var{face1} and @var{face2} have the | |
1966 | same attributes for display. | |
1967 | @end defun | |
1968 | ||
1969 | @defun face-differs-from-default-p face &optional frame | |
1970 | This returns @code{t} if the face @var{face} displays differently from | |
a40d4712 PR |
1971 | the default face. A face is considered to be ``the same'' as the |
1972 | default face if each attribute is either the same as that of the default | |
1973 | face, or unspecified (meaning to inherit from the default). | |
1911e6e5 RS |
1974 | @end defun |
1975 | ||
8241495d RS |
1976 | @node Auto Faces |
1977 | @subsection Automatic Face Assignment | |
1978 | @cindex automatic face assignment | |
1979 | @cindex faces, automatic choice | |
1980 | ||
1981 | @cindex Font-Lock mode | |
1982 | Starting with Emacs 21, a hook is available for automatically | |
1983 | assigning faces to text in the buffer. This hook is used for part of | |
1984 | the implementation of Font-Lock mode. | |
1985 | ||
1986 | @tindex fontification-functions | |
1987 | @defvar fontification-functions | |
1988 | This variable holds a list of functions that are called by Emacs | |
1989 | redisplay as needed to assign faces automatically to text in the buffer. | |
1990 | ||
1991 | The functions are called in the order listed, with one argument, a | |
1992 | buffer position @var{pos}. Each function should attempt to assign faces | |
1993 | to the text in the current buffer starting at @var{pos}. | |
1994 | ||
1995 | Each function should record the faces they assign by setting the | |
1996 | @code{face} property. It should also add a non-@code{nil} | |
1997 | @code{fontified} property for all the text it has assigned faces to. | |
1998 | That property tells redisplay that faces have been assigned to that text | |
1999 | already. | |
2000 | ||
2001 | It is probably a good idea for each function to do nothing if the | |
2002 | character after @var{pos} already has a non-@code{nil} @code{fontified} | |
2003 | property, but this is not required. If one function overrides the | |
2004 | assignments made by a previous one, the properties as they are | |
2005 | after the last function finishes are the ones that really matter. | |
2006 | ||
2007 | For efficiency, we recommend writing these functions so that they | |
2008 | usually assign faces to around 400 to 600 characters at each call. | |
2009 | @end defvar | |
2010 | ||
2011 | @node Font Lookup | |
2012 | @subsection Looking Up Fonts | |
2013 | ||
2014 | @defun x-list-fonts pattern &optional face frame maximum | |
2015 | This function returns a list of available font names that match | |
2016 | @var{pattern}. If the optional arguments @var{face} and @var{frame} are | |
2017 | specified, then the list is limited to fonts that are the same size as | |
2018 | @var{face} currently is on @var{frame}. | |
2019 | ||
2020 | The argument @var{pattern} should be a string, perhaps with wildcard | |
2021 | characters: the @samp{*} character matches any substring, and the | |
2022 | @samp{?} character matches any single character. Pattern matching | |
2023 | of font names ignores case. | |
2024 | ||
2025 | If you specify @var{face} and @var{frame}, @var{face} should be a face name | |
2026 | (a symbol) and @var{frame} should be a frame. | |
2027 | ||
2028 | The optional argument @var{maximum} sets a limit on how many fonts to | |
2029 | return. If this is non-@code{nil}, then the return value is truncated | |
2030 | after the first @var{maximum} matching fonts. Specifying a small value | |
2031 | for @var{maximum} can make this function much faster, in cases where | |
2032 | many fonts match the pattern. | |
2033 | @end defun | |
2034 | ||
2035 | These additional functions are available starting in Emacs 21. | |
2036 | ||
2037 | @defun x-family-fonts &optional family frame | |
2038 | @tindex x-family-fonts | |
2039 | This function returns a list describing the available fonts for family | |
2040 | @var{family} on @var{frame}. If @var{family} is omitted or @code{nil}, | |
2041 | this list applies to all families, and therefore, it contains all | |
2042 | available fonts. Otherwise, @var{family} must be a string; it may | |
2043 | contain the wildcards @samp{?} and @samp{*}. | |
2044 | ||
2045 | The list describes the display that @var{frame} is on; if @var{frame} is | |
2046 | omitted or @code{nil}, it applies to the selected frame's display. | |
2047 | ||
2048 | The list contains a vector of the following form for each font: | |
2049 | ||
2050 | @example | |
2051 | [@var{family} @var{width} @var{point-size} @var{weight} @var{slant} | |
2052 | @var{fixed-p} @var{full} @var{registry-and-encoding}] | |
2053 | @end example | |
2054 | ||
2055 | The first five elements correspond to face attributes; if you | |
2056 | specify these attributes for a face, it will use this font. | |
2057 | ||
2058 | The last three elements give additional information about the font. | |
2059 | @var{fixed-p} is non-nil if the font is fixed-pitch. @var{full} is the | |
2060 | full name of the font, and @var{registry-and-encoding} is a string | |
2061 | giving the registry and encoding of the font. | |
2062 | ||
2063 | The result list is sorted according to the current face font sort order. | |
2064 | @end defun | |
2065 | ||
2066 | @defun x-font-family-list &optional frame | |
2067 | @tindex x-font-family-list | |
2068 | This function returns a list of the font families available for | |
2069 | @var{frame}'s display. If @var{frame} is omitted or @code{nil}, it | |
2070 | describes the selected frame's display. | |
2071 | ||
2072 | The value is a list of elements of this form: | |
2073 | ||
2074 | @example | |
2075 | (@var{family} . @var{fixed-p}) | |
2076 | @end example | |
2077 | ||
2078 | @noindent | |
2079 | Here @var{family} is a font family, and @var{fixed-p} is | |
2080 | non-@code{nil} if fonts of that family are fixed-pitch. | |
2081 | @end defun | |
2082 | ||
2083 | @defvar font-list-limit | |
2084 | @tindex font-list-limit | |
2085 | This variable specifies maximum number of fonts to consider in font | |
2086 | matching. The function @code{x-family-fonts} will not return more than | |
2087 | that many fonts, and font selection will consider only that many fonts | |
2088 | when searching a matching font for face attributes. The default is | |
2089 | currently 100. | |
2090 | @end defvar | |
2091 | ||
2092 | @node Fontsets | |
2093 | @subsection Fontsets | |
2094 | ||
2095 | A @dfn{fontset} is a list of fonts, each assigned to a range of | |
2096 | character codes. An individual font cannot display the whole range of | |
2097 | characters that Emacs supports, but a fontset can. Fontsets have names, | |
2098 | just as fonts do, and you can use a fontset name in place of a font name | |
2099 | when you specify the ``font'' for a frame or a face. Here is | |
2100 | information about defining a fontset under Lisp program control. | |
2101 | ||
2102 | @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror | |
2103 | This function defines a new fontset according to the specification | |
2104 | string @var{fontset-spec}. The string should have this format: | |
2105 | ||
2106 | @smallexample | |
2107 | @var{fontpattern}, @r{[}@var{charsetname}:@var{fontname}@r{]@dots{}} | |
2108 | @end smallexample | |
2109 | ||
2110 | @noindent | |
2111 | Whitespace characters before and after the commas are ignored. | |
2112 | ||
2113 | The first part of the string, @var{fontpattern}, should have the form of | |
2114 | a standard X font name, except that the last two fields should be | |
2115 | @samp{fontset-@var{alias}}. | |
2116 | ||
2117 | The new fontset has two names, one long and one short. The long name is | |
2118 | @var{fontpattern} in its entirety. The short name is | |
2119 | @samp{fontset-@var{alias}}. You can refer to the fontset by either | |
2120 | name. If a fontset with the same name already exists, an error is | |
2121 | signaled, unless @var{noerror} is non-@code{nil}, in which case this | |
2122 | function does nothing. | |
2123 | ||
2124 | If optional argument @var{style-variant-p} is non-@code{nil}, that says | |
2125 | to create bold, italic and bold-italic variants of the fontset as well. | |
2126 | These variant fontsets do not have a short name, only a long one, which | |
2127 | is made by altering @var{fontpattern} to indicate the bold or italic | |
2128 | status. | |
2129 | ||
2130 | The specification string also says which fonts to use in the fontset. | |
2131 | See below for the details. | |
2132 | @end defun | |
2133 | ||
2134 | The construct @samp{@var{charset}:@var{font}} specifies which font to | |
2135 | use (in this fontset) for one particular character set. Here, | |
2136 | @var{charset} is the name of a character set, and @var{font} is the font | |
2137 | to use for that character set. You can use this construct any number of | |
2138 | times in the specification string. | |
2139 | ||
2140 | For the remaining character sets, those that you don't specify | |
2141 | explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces | |
2142 | @samp{fontset-@var{alias}} with a value that names one character set. | |
2143 | For the @sc{ascii} character set, @samp{fontset-@var{alias}} is replaced | |
2144 | with @samp{ISO8859-1}. | |
2145 | ||
2146 | In addition, when several consecutive fields are wildcards, Emacs | |
2147 | collapses them into a single wildcard. This is to prevent use of | |
2148 | auto-scaled fonts. Fonts made by scaling larger fonts are not usable | |
2149 | for editing, and scaling a smaller font is not useful because it is | |
2150 | better to use the smaller font in its own size, which Emacs does. | |
2151 | ||
2152 | Thus if @var{fontpattern} is this, | |
2153 | ||
2154 | @example | |
2155 | -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24 | |
2156 | @end example | |
2157 | ||
2158 | @noindent | |
75708135 | 2159 | the font specification for @sc{ascii} characters would be this: |
8241495d RS |
2160 | |
2161 | @example | |
2162 | -*-fixed-medium-r-normal-*-24-*-ISO8859-1 | |
2163 | @end example | |
2164 | ||
2165 | @noindent | |
2166 | and the font specification for Chinese GB2312 characters would be this: | |
2167 | ||
2168 | @example | |
2169 | -*-fixed-medium-r-normal-*-24-*-gb2312*-* | |
2170 | @end example | |
2171 | ||
2172 | You may not have any Chinese font matching the above font | |
2173 | specification. Most X distributions include only Chinese fonts that | |
2174 | have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In | |
2175 | such a case, @samp{Fontset-@var{n}} can be specified as below: | |
2176 | ||
2177 | @smallexample | |
2178 | Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\ | |
2179 | chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-* | |
2180 | @end smallexample | |
2181 | ||
2182 | @noindent | |
2183 | Then, the font specifications for all but Chinese GB2312 characters have | |
2184 | @samp{fixed} in the @var{family} field, and the font specification for | |
2185 | Chinese GB2312 characters has a wild card @samp{*} in the @var{family} | |
2186 | field. | |
2187 | ||
2188 | @node Display Property | |
2189 | @section The @code{display} Property | |
2190 | @cindex display specification | |
2191 | @kindex display @r{(text property)} | |
2192 | ||
a40d4712 PR |
2193 | The @code{display} text property (or overlay property) is used to |
2194 | insert images into text, and also control other aspects of how text | |
2195 | displays. These features are available starting in Emacs 21. The value | |
2196 | of the @code{display} property should be a display specification, or a | |
2197 | list or vector containing several display specifications. The rest of | |
2198 | this section describes several kinds of display specifications and what | |
2199 | they mean. | |
8241495d RS |
2200 | |
2201 | @menu | |
a40d4712 PR |
2202 | * Specified Space:: Displaying one space with a specified width. |
2203 | * Other Display Specs:: Displaying an image; magnifying text; moving it | |
2204 | up or down on the page; adjusting the width | |
2205 | of spaces within text. | |
2206 | * Display Margins:: Displaying text or images to the side of the main text. | |
2207 | * Conditional Display:: Making any of the above features conditional | |
2208 | depending on some Lisp expression. | |
8241495d RS |
2209 | @end menu |
2210 | ||
2211 | @node Specified Space | |
2212 | @subsection Specified Spaces | |
2213 | @cindex spaces, specified height or width | |
2214 | @cindex specified spaces | |
2215 | @cindex variable-width spaces | |
2216 | ||
2217 | To display a space of specified width and/or height, use a display | |
a40d4712 PR |
2218 | specification of the form @code{(space . @var{props})}, where |
2219 | @var{props} is a property list (a list of alternating properties and | |
2220 | values). You can put this property on one or more consecutive | |
2221 | characters; a space of the specified height and width is displayed in | |
2222 | place of @emph{all} of those characters. These are the properties you | |
2223 | can use to specify the weight of the space: | |
8241495d RS |
2224 | |
2225 | @table @code | |
2226 | @item :width @var{width} | |
2227 | Specifies that the space width should be @var{width} times the normal | |
2228 | character width. @var{width} can be an integer or floating point | |
2229 | number. | |
2230 | ||
2231 | @item :relative-width @var{factor} | |
2232 | Specifies that the width of the stretch should be computed from the | |
2233 | first character in the group of consecutive characters that have the | |
2234 | same @code{display} property. The space width is the width of that | |
2235 | character, multiplied by @var{factor}. | |
2236 | ||
2237 | @item :align-to @var{hpos} | |
2238 | Specifies that the space should be wide enough to reach @var{hpos}. The | |
a40d4712 PR |
2239 | value @var{hpos} is measured in units of the normal character width. It |
2240 | may be an interer or a floating point number. | |
8241495d RS |
2241 | @end table |
2242 | ||
2243 | Exactly one of the above properties should be used. You can also | |
2244 | specify the height of the space, with other properties: | |
2245 | ||
2246 | @table @code | |
2247 | @item :height @var{height} | |
2248 | Specifies the height of the space, as @var{height}, | |
2249 | measured in terms of the normal line height. | |
2250 | ||
2251 | @item :relative-height @var{factor} | |
2252 | Specifies the height of the space, multiplying the ordinary height | |
2253 | of the text having this display specification by @var{factor}. | |
2254 | ||
2255 | @item :ascent @var{ascent} | |
2256 | Specifies that @var{ascent} percent of the height of the space should be | |
a40d4712 PR |
2257 | considered as the ascent of the space---that is, the part above the |
2258 | baseline. The value of @var{ascent} must be a non-negative number no | |
2259 | greater than 100. | |
8241495d RS |
2260 | @end table |
2261 | ||
2262 | You should not use both @code{:height} and @code{:relative-height} | |
2263 | together. | |
2264 | ||
2265 | @node Other Display Specs | |
2266 | @subsection Other Display Specifications | |
2267 | ||
2268 | @table @code | |
2269 | @item (image . @var{image-props}) | |
2270 | This is in fact an image descriptor (@pxref{Images}). When used as a | |
2271 | display specification, it means to display the image instead of the text | |
2272 | that has the display specification. | |
2273 | ||
1574933b DL |
2274 | @item ((margin nil) @var{string}) |
2275 | @itemx @var{string} | |
2276 | A display specification of this form means to display @var{string} | |
2277 | instead of the text that has the display specification, at the same | |
2278 | position as that text. This is a special case of marginal display | |
2279 | (@pxref{Display Margins}). | |
2280 | ||
8241495d | 2281 | @item (space-width @var{factor}) |
a40d4712 PR |
2282 | This display specification affects all the space characters within the |
2283 | text that has the specification. It displays all of these spaces | |
2284 | @var{factor} times as wide as normal. The element @var{factor} should | |
2285 | be an integer or float. Characters other than spaces are not affected | |
2286 | at all; in particular, this has no effect on tab characters. | |
8241495d RS |
2287 | |
2288 | @item (height @var{height}) | |
2289 | This display specification makes the text taller or shorter. | |
2290 | Here are the possibilities for @var{height}: | |
2291 | ||
2292 | @table @asis | |
2293 | @item @code{(+ @var{n})} | |
2294 | This means to use a font that is @var{n} steps larger. A ``step'' is | |
a40d4712 PR |
2295 | defined by the set of available fonts---specifically, those that match |
2296 | what was otherwise specified for this text, in all attributes except | |
2297 | height. Each size for which a suitable font is available counts as | |
2298 | another step. @var{n} should be an integer. | |
8241495d RS |
2299 | |
2300 | @item @code{(- @var{n})} | |
2301 | This means to use a font that is @var{n} steps smaller. | |
2302 | ||
2303 | @item a number, @var{factor} | |
2304 | A number, @var{factor}, means to use a font that is @var{factor} times | |
2305 | as tall as the default font. | |
2306 | ||
2307 | @item a symbol, @var{function} | |
2308 | A symbol is a function to compute the height. It is called with the | |
2309 | current height as argument, and should return the new height to use. | |
2310 | ||
2311 | @item anything else, @var{form} | |
2312 | If the @var{height} value doesn't fit the previous possibilities, it is | |
2313 | a form. Emacs evaluates it to get the new height, with the symbol | |
2314 | @code{height} bound to the current specified font height. | |
2315 | @end table | |
2316 | ||
2317 | @item (raise @var{factor}) | |
2318 | This kind of display specification raises or lowers the text | |
2319 | it applies to, relative to the baseline of the line. | |
2320 | ||
2321 | @var{factor} must be a number, which is interpreted as a multiple of the | |
2322 | height of the affected text. If it is positive, that means to display | |
2323 | the characters raised. If it is negative, that means to display them | |
2324 | lower down. | |
2325 | ||
2326 | If the text also has a @code{height} display specification, that does | |
2327 | not affect the amount of raising or lowering, which is based on the | |
2328 | faces used for the text. | |
2329 | @end table | |
2330 | ||
2331 | @node Display Margins | |
2332 | @subsection Displaying in the Margins | |
2333 | @cindex display margins | |
2334 | @cindex margins, display | |
2335 | ||
2336 | A buffer can have blank areas called @dfn{display margins} on the left | |
2337 | and on the right. Ordinary text never appears in these areas, but you | |
2338 | can put things into the display margins using the @code{display} | |
2339 | property. | |
2340 | ||
2341 | To put text in the left or right display margin of the window, use a | |
2342 | display specification of the form @code{(margin right-margin)} or | |
2343 | @code{(margin left-margin)} on it. To put an image in a display margin, | |
2344 | use that display specification along with the display specification for | |
2345 | the image. | |
2346 | ||
2347 | Before the display margins can display anything, you must give | |
2348 | them a nonzero width. The usual way to do that is to set these | |
2349 | variables: | |
2350 | ||
2351 | @defvar left-margin-width | |
2352 | @tindex left-margin-width | |
2353 | This variable specifies the width of the left margin. | |
2354 | It is buffer-local in all buffers. | |
2355 | @end defvar | |
2356 | ||
2357 | @defvar right-margin-width | |
2358 | @tindex right-margin-width | |
2359 | This variable specifies the width of the right margin. | |
2360 | It is buffer-local in all buffers. | |
2361 | @end defvar | |
2362 | ||
2363 | Setting these variables does not immediately affect the window. These | |
2364 | variables are checked when a new buffer is displayed in the window. | |
2365 | Thus, you can make changes take effect by calling | |
2366 | @code{set-window-buffer}. | |
2367 | ||
2368 | You can also set the margin widths immediately. | |
2369 | ||
2370 | @defun set-window-margins window left right | |
2371 | @tindex set-window-margins | |
2372 | This function specifies the margin widths for window @var{window}. | |
2373 | The argument @var{left} controls the left margin and | |
2374 | @var{right} controls the right margin. | |
2375 | @end defun | |
2376 | ||
2377 | @defun window-margins &optional window | |
2378 | @tindex window-margins | |
2379 | This function returns the left and right margins of @var{window} | |
2380 | as a cons cell of the form @code{(@var{left} . @var{right})}. | |
2381 | If @var{window} is @code{nil}, the selected window is used. | |
2382 | @end defun | |
2383 | ||
2384 | @node Conditional Display | |
2385 | @subsection Conditional Display Specifications | |
2386 | @cindex conditional display specifications | |
2387 | ||
2388 | You can make any display specification conditional. To do that, | |
bb2337f5 | 2389 | package it in another list of the form @code{(when @var{condition} . |
8241495d RS |
2390 | @var{spec})}. Then the specification @var{spec} applies only when |
2391 | @var{condition} evaluates to a non-@code{nil} value. During the | |
2392 | evaluation, point is temporarily set at the end position of the text | |
2393 | having this conditional display specification. | |
2394 | ||
2395 | @node Images | |
2396 | @section Images | |
2397 | @cindex images in buffers | |
2398 | ||
2399 | To display an image in an Emacs buffer, you must first create an image | |
2400 | descriptor, then use it as a display specifier in the @code{display} | |
2401 | property of text that is displayed (@pxref{Display Property}). Like the | |
2402 | @code{display} property, this feature is available starting in Emacs 21. | |
2403 | ||
2404 | Emacs can display a number of different image formats; some of them | |
2405 | are supported only if particular support libraries are installed on your | |
2406 | machine. The supported image formats include XBM, XPM (needing the | |
2407 | libraries @code{libXpm} version 3.4k and @code{libz}), GIF (needing | |
2408 | @code{libungif} 4.1.0), Postscript, PBM, JPEG (needing the | |
2409 | @code{libjpeg} library version v6a), TIFF (needing @code{libtiff} v3.4), | |
2410 | and PNG (needing @code{libpng} 1.0.2). | |
2411 | ||
2412 | You specify one of these formats with an image type symbol. The image | |
2413 | type symbols are @code{xbm}, @code{xpm}, @code{gif}, @code{postscript}, | |
2414 | @code{pbm}, @code{jpeg}, @code{tiff}, and @code{png}. | |
2415 | ||
2416 | @defvar image-types | |
2417 | This variable contains a list of those image type symbols that are | |
2418 | supported in the current configuration. | |
2419 | @end defvar | |
2420 | ||
2421 | @menu | |
a40d4712 PR |
2422 | * Image Descriptors:: How to specify an image for use in @code{:display}. |
2423 | * XBM Images:: Special features for XBM format. | |
2424 | * XPM Images:: Special features for XPM format. | |
2425 | * GIF Images:: Special features for GIF format. | |
2426 | * Postscript Images:: Special features for Postscript format. | |
2427 | * Other Image Types:: Various other formats are supported. | |
2428 | * Defining Images:: Convenient ways to define an image for later use. | |
2429 | * Showing Images:: Convenient ways to display an image once it is defined. | |
2430 | * Image Cache:: Internal mechanisms of image display. | |
8241495d RS |
2431 | @end menu |
2432 | ||
2433 | @node Image Descriptors | |
2434 | @subsection Image Descriptors | |
2435 | @cindex image descriptor | |
2436 | ||
2437 | An image description is a list of the form @code{(image | |
2438 | . @var{props})}, where @var{props} is a property list containing | |
2439 | alternating keyword symbols (symbols whose names start with a colon) and | |
14ac7224 GM |
2440 | their values. You can use any Lisp object as a property, but the only |
2441 | properties that have any special meaning are certain symbols, all of | |
2442 | them keywords. | |
2443 | ||
2444 | Every image descriptor must contain the property @code{:type | |
2445 | @var{type}} to specify the format of the image. The value of @var{type} | |
2446 | should be an image type symbol; for example, @code{xpm} for an image in | |
2447 | XPM format. | |
8241495d RS |
2448 | |
2449 | Here is a list of other properties that are meaningful for all image | |
2450 | types: | |
2451 | ||
2452 | @table @code | |
2453 | @item :ascent @var{ascent} | |
04545643 GM |
2454 | The @code{:ascent} property specifies the amount of the image's |
2455 | height to use for its ascent---that is, the part above the baseline. | |
2456 | The value, @var{ascent}, must be a number in the range 0 to 100, or | |
2457 | the symbol @code{center}. | |
2458 | ||
2459 | If @var{ascent} is a number, that percentage of the image's height is | |
2460 | used for its ascent. | |
2461 | ||
2462 | If @var{ascent} is @code{center}, the image is vertically centered | |
2463 | around a centerline which would be the vertical centerline of text drawn | |
2464 | at the position of the image, in the manner specified by the text | |
2465 | properties and overlays that apply to the image. | |
2466 | ||
2467 | If this property is omitted, it defaults to 50. | |
8241495d RS |
2468 | |
2469 | @item :margin @var{margin} | |
2470 | The @code{:margin} property specifies how many pixels to add as an extra | |
2471 | margin around the image. The value, @var{margin}, must be a | |
2472 | non-negative number; if it is not specified, the default is zero. | |
2473 | ||
2474 | @item :relief @var{relief} | |
2475 | The @code{:relief} property, if non-@code{nil}, adds a shadow rectangle | |
2476 | around the image. The value, @var{relief}, specifies the width of the | |
2477 | shadow lines, in pixels. If @var{relief} is negative, shadows are drawn | |
2478 | so that the image appears as a pressed button; otherwise, it appears as | |
2479 | an unpressed button. | |
2480 | ||
2481 | @item :algorithm @var{algorithm} | |
2482 | The @code{:algorithm} property, if non-@code{nil}, specifies a | |
2483 | conversion algorithm that should be applied to the image before it is | |
2484 | displayed; the value, @var{algorithm}, specifies which algorithm. | |
2485 | ||
62fb5c66 DL |
2486 | @table @code |
2487 | @item laplace | |
2488 | @itemx emboss | |
2489 | Specifies the Laplace edge detection algorithm, which blurs out small | |
2490 | differences in color while highlighting larger differences. People | |
2491 | sometimes consider this useful for displaying the image for a | |
2492 | ``disabled'' button. | |
2493 | ||
2494 | @item (edge-detection :matrix @var{matrix} :color-adjust @var{adjust}) | |
2495 | Specifies a general edge-detection algorithm. @var{matrix} must be | |
2496 | either a nine-element list or a nine-element vector of numbers. A pixel | |
2497 | at position @math{x/y} in the transformed image is computed from | |
2498 | original pixels around that position. @var{matrix} specifies, for each | |
2499 | pixel in the neighborhood of @math{x/y}, a factor with which that pixel | |
2500 | will influence the transformed pixel; element @math{0} specifies the | |
2501 | factor for the pixel at @math{x-1/y-1}, element @math{1} the factor for | |
2502 | the pixel at @math{x/y-1} etc., as shown below: | |
2503 | @iftex | |
2504 | @tex | |
2505 | $$\pmatrix{x-1/y-1 & x/y-1 & x+1/y-1 \cr | |
2506 | x-1/y & x/y & x+1/y \cr | |
2507 | x-1/y+1& x/y+1 & x+1/y+1 \cr}$$ | |
2508 | @end tex | |
2509 | @end iftex | |
2510 | @ifnottex | |
2511 | @display | |
2512 | (x-1/y-1 x/y-1 x+1/y-1 | |
2513 | x-1/y x/y x+1/y | |
2514 | x-1/y+1 x/y+1 x+1/y+1) | |
2515 | @end display | |
2516 | @end ifnottex | |
2517 | ||
2518 | The resulting pixel is computed from the color intensity of the color | |
2519 | resulting from summing up the RGB values of surrounding pixels, | |
2520 | multiplied by the specified factors, and dividing that sum by the sum | |
2521 | of the factors' absolute values. | |
2522 | ||
2523 | Laplace edge-detection currently uses a matrix of | |
2524 | @iftex | |
2525 | @tex | |
2526 | $$\pmatrix{1 & 0 & 0 \cr | |
2527 | 0& 0 & 0 \cr | |
2528 | 9 & 9 & -1 \cr}$$ | |
2529 | @end tex | |
2530 | @end iftex | |
2531 | @ifnottex | |
2532 | @display | |
2533 | (1 0 0 | |
2534 | 0 0 0 | |
2535 | 9 9 -1) | |
2536 | @end display | |
2537 | @end ifnottex | |
2538 | ||
2539 | Emboss edge-detection uses a matrix of | |
2540 | @iftex | |
2541 | @tex | |
2542 | $$\pmatrix{ 2 & -1 & 0 \cr | |
2543 | -1 & 0 & 1 \cr | |
2544 | 0 & 1 & -2 \cr}$$ | |
2545 | @end tex | |
2546 | @end iftex | |
2547 | @ifnottex | |
2548 | @display | |
2549 | ( 2 -1 0 | |
2550 | -1 0 1 | |
2551 | 0 1 -2) | |
2552 | @end display | |
2553 | @end ifnottex | |
2554 | ||
2555 | @item disabled | |
2556 | Specifies transforming the image so that it looks ``disabled''. | |
2557 | @end table | |
8241495d | 2558 | |
62fb5c66 DL |
2559 | @item :mask @var{mask} |
2560 | If @var{mask} is @code{heuristic} or @code{(heuristic @var{bg})}, build | |
2561 | a clipping mask for the image, so that the background of a frame is | |
2562 | visible behind the image. If @var{bg} is not specified, or if @var{bg} | |
2563 | is @code{t}, determine the background color of the image by looking at | |
2564 | the four corners of the image, assuming the most frequently occurring | |
2565 | color from the corners is the background color of the image. Otherwise, | |
2566 | @var{bg} must be a list @code{(@var{red} @var{green} @var{blue})} | |
2567 | specifying the color to assume for the background of the image. | |
8241495d | 2568 | |
62fb5c66 DL |
2569 | If @var{mask} is nil, remove a mask from the image, if it has one. Images |
2570 | in some formats include a mask which can be removed by specifying | |
2571 | @code{:mask nil}. | |
8241495d RS |
2572 | |
2573 | @item :file @var{file} | |
2574 | The @code{:file} property specifies to load the image from file | |
2575 | @var{file}. If @var{file} is not an absolute file name, it is expanded | |
2576 | in @code{data-directory}. | |
2577 | ||
2578 | @item :data @var{data} | |
2579 | The @code{:data} property specifies the actual contents of the image. | |
2580 | Each image must use either @code{:data} or @code{:file}, but not both. | |
72821190 RS |
2581 | For most image types, the value of the @code{:data} property should be a |
2582 | string containing the image data; we recommend using a unibyte string. | |
2583 | ||
2584 | Before using @code{:data}, look for further information in the section | |
2585 | below describing the specific image format. For some image types, | |
2586 | @code{:data} may not be supported; for some, it allows other data types; | |
2587 | for some, @code{:data} alone is not enough, so you need to use other | |
2588 | image properties along with @code{:data}. | |
8241495d RS |
2589 | @end table |
2590 | ||
62fb5c66 DL |
2591 | @defun image-mask-p spec &optional frame |
2592 | @tindex image-mask-p | |
2593 | This function returns @code{t} if image @var{spec} has a mask bitmap. | |
2594 | @var{frame} is the frame on which the image will be displayed. | |
2595 | @var{frame} @code{nil} or omitted means to use the selected frame. | |
2596 | @end defun | |
2597 | ||
8241495d RS |
2598 | @node XBM Images |
2599 | @subsection XBM Images | |
2600 | @cindex XBM | |
2601 | ||
2602 | To use XBM format, specify @code{xbm} as the image type. This image | |
2603 | format doesn't require an external library, so images of this type are | |
2604 | always supported. | |
2605 | ||
2606 | Additional image properties supported for the @code{xbm} image type are: | |
2607 | ||
2608 | @table @code | |
2609 | @item :foreground @var{foreground} | |
2610 | The value, @var{foreground}, should be a string specifying the image | |
2611 | foreground color. This color is used for each pixel in the XBM that is | |
2612 | 1. The default is the frame's foreground color. | |
2613 | ||
2614 | @item :background @var{background} | |
2615 | The value, @var{background}, should be a string specifying the image | |
2616 | background color. This color is used for each pixel in the XBM that is | |
2617 | 0. The default is the frame's background color. | |
2618 | @end table | |
2619 | ||
72821190 | 2620 | If you specify an XBM image using data within Emacs instead of an |
96f66dc5 | 2621 | external file, use the following three properties: |
8241495d RS |
2622 | |
2623 | @table @code | |
96f66dc5 GM |
2624 | @item :data @var{data} |
2625 | The value, @var{data}, specifies the contents of the image. | |
2626 | There are three formats you can use for @var{data}: | |
8241495d | 2627 | |
96f66dc5 GM |
2628 | @itemize @bullet |
2629 | @item | |
2630 | A vector of strings or bool-vectors, each specifying one line of the | |
2631 | image. Do specify @code{:height} and @code{:width}. | |
8241495d | 2632 | |
96f66dc5 GM |
2633 | @item |
2634 | A string containing the same byte sequence as an XBM file would contain. | |
2635 | You must not specify @code{:height} and @code{:width} in this case, | |
2636 | because omitting them is what indicates the data has the format of an | |
2637 | XBM file. The file contents specify the height and width of the image. | |
8241495d | 2638 | |
96f66dc5 GM |
2639 | @item |
2640 | A string or a bool-vector containing the bits of the image (plus perhaps | |
2641 | some extra bits at the end that will not be used). It should contain at | |
2642 | least @var{width} * @code{height} bits. In this case, you must specify | |
2643 | @code{:height} and @code{:width}, both to indicate that the string | |
2644 | contains just the bits rather than a whole XBM file, and to specify the | |
2645 | size of the image. | |
2646 | @end itemize | |
2647 | ||
2648 | @item :width @var{width} | |
2649 | The value, @var{width}, specifies the width of the image, in pixels. | |
2650 | ||
2651 | @item :height @var{height} | |
2652 | The value, @var{height}, specifies the height of the image, in pixels. | |
8241495d RS |
2653 | @end table |
2654 | ||
2655 | @node XPM Images | |
2656 | @subsection XPM Images | |
2657 | @cindex XPM | |
2658 | ||
72821190 RS |
2659 | To use XPM format, specify @code{xpm} as the image type. The |
2660 | additional image property @code{:color-symbols} is also meaningful with | |
2661 | the @code{xpm} image type: | |
8241495d RS |
2662 | |
2663 | @table @code | |
2664 | @item :color-symbols @var{symbols} | |
2665 | The value, @var{symbols}, should be an alist whose elements have the | |
2666 | form @code{(@var{name} . @var{color})}. In each element, @var{name} is | |
2667 | the name of a color as it appears in the image file, and @var{color} | |
2668 | specifies the actual color to use for displaying that name. | |
8241495d RS |
2669 | @end table |
2670 | ||
2671 | @node GIF Images | |
2672 | @subsection GIF Images | |
2673 | @cindex GIF | |
2674 | ||
2675 | For GIF images, specify image type @code{gif}. Because of the patents | |
2676 | in the US covering the LZW algorithm, the continued use of GIF format is | |
2677 | a problem for the whole Internet; to end this problem, it is a good idea | |
2678 | for everyone, even outside the US, to stop using GIFS right away | |
2679 | (@uref{http://www.burnallgifs.org/}). But if you still want to use | |
2680 | them, Emacs can display them. | |
2681 | ||
2682 | @table @code | |
2683 | @item :index @var{index} | |
2684 | You can use @code{:index} to specify one image from a GIF file that | |
2685 | contains more than one image. This property specifies use of image | |
2686 | number @var{index} from the file. An error is signaled if the GIF file | |
2687 | doesn't contain an image with index @var{index}. | |
2688 | @end table | |
2689 | ||
2690 | @ignore | |
2691 | This could be used to implement limited support for animated GIFs. | |
2692 | For example, the following function displays a multi-image GIF file | |
2693 | at point-min in the current buffer, switching between sub-images | |
2694 | every 0.1 seconds. | |
2695 | ||
2696 | (defun show-anim (file max) | |
2697 | "Display multi-image GIF file FILE which contains MAX subimages." | |
2698 | (display-anim (current-buffer) file 0 max t)) | |
2699 | ||
2700 | (defun display-anim (buffer file idx max first-time) | |
2701 | (when (= idx max) | |
2702 | (setq idx 0)) | |
2703 | (let ((img (create-image file nil :image idx))) | |
2704 | (save-excursion | |
2705 | (set-buffer buffer) | |
2706 | (goto-char (point-min)) | |
2707 | (unless first-time (delete-char 1)) | |
2708 | (insert-image img)) | |
2709 | (run-with-timer 0.1 nil 'display-anim buffer file (1+ idx) max nil))) | |
2710 | @end ignore | |
2711 | ||
2712 | @node Postscript Images | |
2713 | @subsection Postscript Images | |
2714 | @cindex Postscript images | |
2715 | ||
2716 | To use Postscript for an image, specify image type @code{postscript}. | |
2717 | This works only if you have Ghostscript installed. You must always use | |
2718 | these three properties: | |
2719 | ||
2720 | @table @code | |
2721 | @item :pt-width @var{width} | |
2722 | The value, @var{width}, specifies the width of the image measured in | |
2723 | points (1/72 inch). @var{width} must be an integer. | |
2724 | ||
2725 | @item :pt-height @var{height} | |
2726 | The value, @var{height}, specifies the height of the image in points | |
2727 | (1/72 inch). @var{height} must be an integer. | |
2728 | ||
2729 | @item :bounding-box @var{box} | |
2730 | The value, @var{box}, must be a list or vector of four integers, which | |
2731 | specifying the bounding box of the Postscript image, analogous to the | |
2732 | @samp{BoundingBox} comment found in Postscript files. | |
2733 | ||
2734 | @example | |
2735 | %%BoundingBox: 22 171 567 738 | |
2736 | @end example | |
2737 | @end table | |
2738 | ||
72821190 RS |
2739 | Displaying Postscript images from Lisp data is not currently |
2740 | implemented, but it may be implemented by the time you read this. | |
2741 | See the @file{etc/NEWS} file to make sure. | |
2742 | ||
8241495d RS |
2743 | @node Other Image Types |
2744 | @subsection Other Image Types | |
2745 | @cindex PBM | |
2746 | ||
2747 | For PBM images, specify image type @code{pbm}. Color, gray-scale and | |
7ccd82bd GM |
2748 | monochromatic images are supported. For mono PBM images, two additional |
2749 | image properties are supported. | |
2750 | ||
2751 | @table @code | |
2752 | @item :foreground @var{foreground} | |
2753 | The value, @var{foreground}, should be a string specifying the image | |
2754 | foreground color. This color is used for each pixel in the XBM that is | |
2755 | 1. The default is the frame's foreground color. | |
2756 | ||
2757 | @item :background @var{background} | |
2758 | The value, @var{background}, should be a string specifying the image | |
2759 | background color. This color is used for each pixel in the XBM that is | |
2760 | 0. The default is the frame's background color. | |
2761 | @end table | |
8241495d | 2762 | |
72821190 | 2763 | For JPEG images, specify image type @code{jpeg}. |
8241495d RS |
2764 | |
2765 | For TIFF images, specify image type @code{tiff}. | |
2766 | ||
2767 | For PNG images, specify image type @code{png}. | |
2768 | ||
2769 | @node Defining Images | |
2770 | @subsection Defining Images | |
2771 | ||
e3b9fc91 DL |
2772 | The functions @code{create-image}, @code{defimage} and |
2773 | @code{find-image} provide convenient ways to create image descriptors. | |
8241495d RS |
2774 | |
2775 | @defun create-image file &optional type &rest props | |
2776 | @tindex create-image | |
2777 | This function creates and returns an image descriptor which uses the | |
2778 | data in @var{file}. | |
2779 | ||
2780 | The optional argument @var{type} is a symbol specifying the image type. | |
2781 | If @var{type} is omitted or @code{nil}, @code{create-image} tries to | |
2782 | determine the image type from the file's first few bytes, or else | |
2783 | from the file's name. | |
2784 | ||
2785 | The remaining arguments, @var{props}, specify additional image | |
2786 | properties---for example, | |
2787 | ||
2788 | @example | |
2789 | (create-image "foo.xpm" 'xpm :heuristic-mask t) | |
2790 | @end example | |
2791 | ||
2792 | The function returns @code{nil} if images of this type are not | |
2793 | supported. Otherwise it returns an image descriptor. | |
2794 | @end defun | |
2795 | ||
2796 | @defmac defimage variable doc &rest specs | |
2797 | @tindex defimage | |
2798 | This macro defines @var{variable} as an image name. The second argument, | |
2799 | @var{doc}, is an optional documentation string. The remaining | |
2800 | arguments, @var{specs}, specify alternative ways to display the image. | |
2801 | ||
2802 | Each argument in @var{specs} has the form of a property list, and each | |
2803 | one should specify at least the @code{:type} property and the | |
2804 | @code{:file} property. Here is an example: | |
2805 | ||
a40d4712 PR |
2806 | @example |
2807 | (defimage test-image | |
2808 | '((:type xpm :file "~/test1.xpm") | |
2809 | (:type xbm :file "~/test1.xbm"))) | |
2810 | @end example | |
8241495d RS |
2811 | |
2812 | @code{defimage} tests each argument, one by one, to see if it is | |
2813 | usable---that is, if the type is supported and the file exists. The | |
2814 | first usable argument is used to make an image descriptor which is | |
2815 | stored in the variable @var{variable}. | |
2816 | ||
2817 | If none of the alternatives will work, then @var{variable} is defined | |
2818 | as @code{nil}. | |
2819 | @end defmac | |
2820 | ||
e3b9fc91 DL |
2821 | @defun find-image specs |
2822 | @tindex find-image | |
2823 | This function provides a convenient way to find an image satisfying one | |
2824 | of a list of image specifications @var{specs}. | |
2825 | ||
2826 | Each specification in @var{specs} is a property list with contents | |
2827 | depending on image type. All specifications must at least contain the | |
2828 | properties @code{:type @var{type}} and either @w{@code{:file @var{file}}} | |
2829 | or @w{@code{:data @var{DATA}}}, where @var{type} is a symbol specifying | |
2830 | the image type, e.g.@: @code{xbm}, @var{file} is the file to load the | |
2831 | image from, and @var{data} is a string containing the actual image data. | |
2832 | The first specification in the list whose @var{type} is supported, and | |
2833 | @var{file} exists, is used to construct the image specification to be | |
2834 | returned. If no specification is satisfied, @code{nil} is returned. | |
2835 | ||
2836 | The image is looked for first on @code{load-path} and then in | |
2837 | @code{data-directory}. | |
2838 | @end defun | |
2839 | ||
8241495d RS |
2840 | @node Showing Images |
2841 | @subsection Showing Images | |
2842 | ||
2843 | You can use an image descriptor by setting up the @code{display} | |
2844 | property yourself, but it is easier to use the functions in this | |
2845 | section. | |
2846 | ||
bb2337f5 | 2847 | @defun insert-image image &optional string area |
8241495d RS |
2848 | This function inserts @var{image} in the current buffer at point. The |
2849 | value @var{image} should be an image descriptor; it could be a value | |
2850 | returned by @code{create-image}, or the value of a symbol defined with | |
a40d4712 PR |
2851 | @code{defimage}. The argument @var{string} specifies the text to put in |
2852 | the buffer to hold the image. | |
8241495d RS |
2853 | |
2854 | The argument @var{area} specifies whether to put the image in a margin. | |
2855 | If it is @code{left-margin}, the image appears in the left margin; | |
2856 | @code{right-margin} specifies the right margin. If @var{area} is | |
2857 | @code{nil} or omitted, the image is displayed at point within the | |
2858 | buffer's text. | |
2859 | ||
a40d4712 PR |
2860 | Internally, this function inserts @var{string} in the buffer, and gives |
2861 | it a @code{display} property which specifies @var{image}. @xref{Display | |
8241495d RS |
2862 | Property}. |
2863 | @end defun | |
2864 | ||
bb2337f5 | 2865 | @defun put-image image pos &optional string area |
8241495d RS |
2866 | This function puts image @var{image} in front of @var{pos} in the |
2867 | current buffer. The argument @var{pos} should be an integer or a | |
2868 | marker. It specifies the buffer position where the image should appear. | |
bb2337f5 DL |
2869 | The argument @var{string} specifies the text that should hold the image |
2870 | as an alternative to the default. | |
8241495d RS |
2871 | |
2872 | The argument @var{image} must be an image descriptor, perhaps returned | |
2873 | by @code{create-image} or stored by @code{defimage}. | |
2874 | ||
2875 | The argument @var{area} specifies whether to put the image in a margin. | |
2876 | If it is @code{left-margin}, the image appears in the left margin; | |
2877 | @code{right-margin} specifies the right margin. If @var{area} is | |
2878 | @code{nil} or omitted, the image is displayed at point within the | |
2879 | buffer's text. | |
2880 | ||
2881 | Internally, this function creates an overlay, and gives it a | |
2882 | @code{before-string} property containing text that has a @code{display} | |
2883 | property whose value is the image. (Whew!) | |
2884 | @end defun | |
2885 | ||
2886 | @defun remove-images start end &optional buffer | |
2887 | This function removes images in @var{buffer} between positions | |
2888 | @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil}, | |
2889 | images are removed from the current buffer. | |
2890 | ||
05aea714 | 2891 | This removes only images that were put into @var{buffer} the way |
8241495d RS |
2892 | @code{put-image} does it, not images that were inserted with |
2893 | @code{insert-image} or in other ways. | |
2894 | @end defun | |
2895 | ||
e3b9fc91 DL |
2896 | @defun image-size spec &optional pixels frame |
2897 | @tindex image-size | |
2898 | This function returns the size of an image as a pair | |
2899 | @w{@code{(@var{width} . @var{height})}}. @var{spec} is an image | |
2900 | specification. @var{pixels} non-nil means return sizes measured in | |
2901 | pixels, otherwise return sizes measured in canonical character units | |
2902 | (fractions of the width/height of the frame's default font). | |
2903 | @var{frame} is the frame on which the image will be displayed. | |
2904 | @var{frame} null or omitted means use the selected frame. | |
2905 | @end defun | |
2906 | ||
8241495d RS |
2907 | @node Image Cache |
2908 | @subsection Image Cache | |
2909 | ||
2910 | Emacs stores images in an image cache when it displays them, so it can | |
2911 | display them again more efficiently. It removes an image from the cache | |
2912 | when it hasn't been displayed for a specified period of time. | |
2913 | ||
3e8b2a01 GM |
2914 | When an image is looked up in the cache, its specification is compared |
2915 | with cached image specifications using @code{equal}. This means that | |
2916 | all images with equal specifications share the same image in the cache. | |
2917 | ||
8241495d RS |
2918 | @defvar image-cache-eviction-delay |
2919 | @tindex image-cache-eviction-delay | |
2920 | This variable specifies the number of seconds an image can remain in the | |
2921 | cache without being displayed. When an image is not displayed for this | |
2922 | length of time, Emacs removes it from the image cache. | |
2923 | ||
2924 | If the value is @code{nil}, Emacs does not remove images from the cache | |
2925 | except when you explicitly clear it. This mode can be useful for | |
2926 | debugging. | |
2927 | @end defvar | |
2928 | ||
2929 | @defun clear-image-cache &optional frame | |
2930 | @tindex clear-image-cache | |
2931 | This function clears the image cache. If @var{frame} is non-@code{nil}, | |
2932 | only the cache for that frame is cleared. Otherwise all frames' caches | |
2933 | are cleared. | |
2934 | @end defun | |
a065c889 | 2935 | |
42b85554 RS |
2936 | @node Blinking |
2937 | @section Blinking Parentheses | |
2938 | @cindex parenthesis matching | |
2939 | @cindex blinking | |
2940 | @cindex balancing parentheses | |
2941 | @cindex close parenthesis | |
2942 | ||
2943 | This section describes the mechanism by which Emacs shows a matching | |
2944 | open parenthesis when the user inserts a close parenthesis. | |
2945 | ||
42b85554 RS |
2946 | @defvar blink-paren-function |
2947 | The value of this variable should be a function (of no arguments) to | |
2948 | be called whenever a character with close parenthesis syntax is inserted. | |
2949 | The value of @code{blink-paren-function} may be @code{nil}, in which | |
2950 | case nothing is done. | |
42b85554 RS |
2951 | @end defvar |
2952 | ||
1911e6e5 | 2953 | @defopt blink-matching-paren |
42b85554 RS |
2954 | If this variable is @code{nil}, then @code{blink-matching-open} does |
2955 | nothing. | |
1911e6e5 | 2956 | @end defopt |
42b85554 | 2957 | |
1911e6e5 | 2958 | @defopt blink-matching-paren-distance |
42b85554 RS |
2959 | This variable specifies the maximum distance to scan for a matching |
2960 | parenthesis before giving up. | |
1911e6e5 | 2961 | @end defopt |
42b85554 | 2962 | |
1911e6e5 | 2963 | @defopt blink-matching-delay |
bfe721d1 KH |
2964 | This variable specifies the number of seconds for the cursor to remain |
2965 | at the matching parenthesis. A fraction of a second often gives | |
2966 | good results, but the default is 1, which works on all systems. | |
1911e6e5 | 2967 | @end defopt |
bfe721d1 | 2968 | |
1911e6e5 | 2969 | @deffn Command blink-matching-open |
42b85554 RS |
2970 | This function is the default value of @code{blink-paren-function}. It |
2971 | assumes that point follows a character with close parenthesis syntax and | |
2972 | moves the cursor momentarily to the matching opening character. If that | |
2973 | character is not already on the screen, it displays the character's | |
2974 | context in the echo area. To avoid long delays, this function does not | |
2975 | search farther than @code{blink-matching-paren-distance} characters. | |
2976 | ||
2977 | Here is an example of calling this function explicitly. | |
2978 | ||
2979 | @smallexample | |
2980 | @group | |
2981 | (defun interactive-blink-matching-open () | |
2982 | @c Do not break this line! -- rms. | |
2983 | @c The first line of a doc string | |
2984 | @c must stand alone. | |
2985 | "Indicate momentarily the start of sexp before point." | |
2986 | (interactive) | |
2987 | @end group | |
2988 | @group | |
2989 | (let ((blink-matching-paren-distance | |
2990 | (buffer-size)) | |
2991 | (blink-matching-paren t)) | |
2992 | (blink-matching-open))) | |
2993 | @end group | |
2994 | @end smallexample | |
1911e6e5 | 2995 | @end deffn |
42b85554 RS |
2996 | |
2997 | @node Inverse Video | |
2998 | @section Inverse Video | |
2999 | @cindex Inverse Video | |
3000 | ||
3001 | @defopt inverse-video | |
3002 | @cindex highlighting | |
3003 | This variable controls whether Emacs uses inverse video for all text | |
3004 | on the screen. Non-@code{nil} means yes, @code{nil} means no. The | |
3005 | default is @code{nil}. | |
3006 | @end defopt | |
3007 | ||
3008 | @defopt mode-line-inverse-video | |
a40d4712 PR |
3009 | This variable controls the use of inverse video for mode lines and menu |
3010 | bars. If it is non-@code{nil}, then these lines are displayed in | |
05aea714 | 3011 | inverse video. Otherwise, these lines are displayed normally, just like |
a40d4712 PR |
3012 | other text. The default is @code{t}. |
3013 | ||
3014 | For window frames, this feature actually applies the face named | |
3015 | @code{mode-line}; that face is normally set up as the inverse of the | |
3016 | default face, unless you change it. | |
42b85554 RS |
3017 | @end defopt |
3018 | ||
3019 | @node Usual Display | |
3020 | @section Usual Display Conventions | |
3021 | ||
3022 | The usual display conventions define how to display each character | |
3023 | code. You can override these conventions by setting up a display table | |
3024 | (@pxref{Display Tables}). Here are the usual display conventions: | |
3025 | ||
3026 | @itemize @bullet | |
3027 | @item | |
3028 | Character codes 32 through 126 map to glyph codes 32 through 126. | |
3029 | Normally this means they display as themselves. | |
3030 | ||
3031 | @item | |
3032 | Character code 9 is a horizontal tab. It displays as whitespace | |
3033 | up to a position determined by @code{tab-width}. | |
3034 | ||
3035 | @item | |
3036 | Character code 10 is a newline. | |
3037 | ||
3038 | @item | |
3039 | All other codes in the range 0 through 31, and code 127, display in one | |
78608595 | 3040 | of two ways according to the value of @code{ctl-arrow}. If it is |
42b85554 | 3041 | non-@code{nil}, these codes map to sequences of two glyphs, where the |
8241495d | 3042 | first glyph is the @sc{ascii} code for @samp{^}. (A display table can |
42b85554 RS |
3043 | specify a glyph to use instead of @samp{^}.) Otherwise, these codes map |
3044 | just like the codes in the range 128 to 255. | |
3045 | ||
8241495d RS |
3046 | On MS-DOS terminals, Emacs arranges by default for the character code |
3047 | 127 to be mapped to the glyph code 127, which normally displays as an | |
3048 | empty polygon. This glyph is used to display non-@sc{ascii} characters | |
3049 | that the MS-DOS terminal doesn't support. @xref{MS-DOS and MULE,,, | |
3050 | emacs, The GNU Emacs Manual}. | |
3051 | ||
42b85554 RS |
3052 | @item |
3053 | Character codes 128 through 255 map to sequences of four glyphs, where | |
8241495d | 3054 | the first glyph is the @sc{ascii} code for @samp{\}, and the others are |
a9f0a989 | 3055 | digit characters representing the character code in octal. (A display |
969fe9b5 RS |
3056 | table can specify a glyph to use instead of @samp{\}.) |
3057 | ||
3058 | @item | |
3059 | Multibyte character codes above 256 are displayed as themselves, or as a | |
3060 | question mark or empty box if the terminal cannot display that | |
3061 | character. | |
42b85554 RS |
3062 | @end itemize |
3063 | ||
3064 | The usual display conventions apply even when there is a display | |
3065 | table, for any character whose entry in the active display table is | |
3066 | @code{nil}. Thus, when you set up a display table, you need only | |
969fe9b5 | 3067 | specify the characters for which you want special behavior. |
42b85554 | 3068 | |
b6954afd RS |
3069 | These display rules apply to carriage return (character code 13), when |
3070 | it appears in the buffer. But that character may not appear in the | |
3071 | buffer where you expect it, if it was eliminated as part of end-of-line | |
15da7853 | 3072 | conversion (@pxref{Coding System Basics}). |
b6954afd | 3073 | |
42b85554 RS |
3074 | These variables affect the way certain characters are displayed on the |
3075 | screen. Since they change the number of columns the characters occupy, | |
f9f59935 RS |
3076 | they also affect the indentation functions. These variables also affect |
3077 | how the mode line is displayed; if you want to force redisplay of the | |
3078 | mode line using the new values, call the function | |
3079 | @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
42b85554 RS |
3080 | |
3081 | @defopt ctl-arrow | |
3082 | @cindex control characters in display | |
3083 | This buffer-local variable controls how control characters are | |
3084 | displayed. If it is non-@code{nil}, they are displayed as a caret | |
3085 | followed by the character: @samp{^A}. If it is @code{nil}, they are | |
3086 | displayed as a backslash followed by three octal digits: @samp{\001}. | |
3087 | @end defopt | |
3088 | ||
3089 | @c Following may have overfull hbox. | |
3090 | @defvar default-ctl-arrow | |
3091 | The value of this variable is the default value for @code{ctl-arrow} in | |
3092 | buffers that do not override it. @xref{Default Value}. | |
3093 | @end defvar | |
3094 | ||
2468d0c0 DL |
3095 | @defopt indicate-empty-lines |
3096 | @tindex indicate-empty-lines | |
3097 | When this is non-@code{nil}, Emacs displays a special glyph in | |
3098 | each empty line at the end of the buffer, on terminals that | |
3099 | support it (window systems). | |
3100 | @end defopt | |
3101 | ||
42b85554 RS |
3102 | @defopt tab-width |
3103 | The value of this variable is the spacing between tab stops used for | |
a40d4712 PR |
3104 | displaying tab characters in Emacs buffers. The value is in units of |
3105 | columns, and the default is 8. Note that this feature is completely | |
3106 | independent of the user-settable tab stops used by the command | |
3107 | @code{tab-to-tab-stop}. @xref{Indent Tabs}. | |
42b85554 RS |
3108 | @end defopt |
3109 | ||
3110 | @node Display Tables | |
3111 | @section Display Tables | |
3112 | ||
3113 | @cindex display table | |
969fe9b5 RS |
3114 | You can use the @dfn{display table} feature to control how all possible |
3115 | character codes display on the screen. This is useful for displaying | |
8241495d | 3116 | European languages that have letters not in the @sc{ascii} character |
969fe9b5 | 3117 | set. |
42b85554 RS |
3118 | |
3119 | The display table maps each character code into a sequence of | |
8241495d | 3120 | @dfn{glyphs}, each glyph being a graphic that takes up one character |
42b85554 RS |
3121 | position on the screen. You can also define how to display each glyph |
3122 | on your terminal, using the @dfn{glyph table}. | |
3123 | ||
f9f59935 RS |
3124 | Display tables affect how the mode line is displayed; if you want to |
3125 | force redisplay of the mode line using a new display table, call | |
3126 | @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
3127 | ||
42b85554 RS |
3128 | @menu |
3129 | * Display Table Format:: What a display table consists of. | |
3130 | * Active Display Table:: How Emacs selects a display table to use. | |
3131 | * Glyphs:: How to define a glyph, and what glyphs mean. | |
42b85554 RS |
3132 | @end menu |
3133 | ||
3134 | @node Display Table Format | |
3135 | @subsection Display Table Format | |
3136 | ||
a9f0a989 RS |
3137 | A display table is actually a char-table (@pxref{Char-Tables}) with |
3138 | @code{display-table} as its subtype. | |
42b85554 RS |
3139 | |
3140 | @defun make-display-table | |
3141 | This creates and returns a display table. The table initially has | |
3142 | @code{nil} in all elements. | |
3143 | @end defun | |
3144 | ||
f9f59935 RS |
3145 | The ordinary elements of the display table are indexed by character |
3146 | codes; the element at index @var{c} says how to display the character | |
3147 | code @var{c}. The value should be @code{nil} or a vector of glyph | |
3148 | values (@pxref{Glyphs}). If an element is @code{nil}, it says to | |
3149 | display that character according to the usual display conventions | |
3150 | (@pxref{Usual Display}). | |
22697dac KH |
3151 | |
3152 | If you use the display table to change the display of newline | |
3153 | characters, the whole buffer will be displayed as one long ``line.'' | |
42b85554 | 3154 | |
f9f59935 | 3155 | The display table also has six ``extra slots'' which serve special |
969fe9b5 RS |
3156 | purposes. Here is a table of their meanings; @code{nil} in any slot |
3157 | means to use the default for that slot, as stated below. | |
42b85554 RS |
3158 | |
3159 | @table @asis | |
f9f59935 | 3160 | @item 0 |
42b85554 | 3161 | The glyph for the end of a truncated screen line (the default for this |
8241495d RS |
3162 | is @samp{$}). @xref{Glyphs}. Newer Emacs versions, on some platforms, |
3163 | display arrows to indicate truncation---the display table has no effect | |
3164 | in these situations. | |
f9f59935 | 3165 | @item 1 |
42b85554 | 3166 | The glyph for the end of a continued line (the default is @samp{\}). |
8241495d RS |
3167 | Newer Emacs versions, on some platforms, display curved arrows to |
3168 | indicate truncation---the display table has no effect in these | |
3169 | situations. | |
f9f59935 | 3170 | @item 2 |
42b85554 RS |
3171 | The glyph for indicating a character displayed as an octal character |
3172 | code (the default is @samp{\}). | |
f9f59935 | 3173 | @item 3 |
42b85554 | 3174 | The glyph for indicating a control character (the default is @samp{^}). |
f9f59935 | 3175 | @item 4 |
42b85554 RS |
3176 | A vector of glyphs for indicating the presence of invisible lines (the |
3177 | default is @samp{...}). @xref{Selective Display}. | |
f9f59935 | 3178 | @item 5 |
50b04c36 | 3179 | The glyph used to draw the border between side-by-side windows (the |
8241495d RS |
3180 | default is @samp{|}). @xref{Splitting Windows}. This takes effect only |
3181 | when there are no scroll bars; if scroll bars are supported and in use, | |
3182 | a scroll bar separates the two windows. | |
42b85554 RS |
3183 | @end table |
3184 | ||
3185 | For example, here is how to construct a display table that mimics the | |
3186 | effect of setting @code{ctl-arrow} to a non-@code{nil} value: | |
3187 | ||
3188 | @example | |
3189 | (setq disptab (make-display-table)) | |
3190 | (let ((i 0)) | |
3191 | (while (< i 32) | |
3192 | (or (= i ?\t) (= i ?\n) | |
3193 | (aset disptab i (vector ?^ (+ i 64)))) | |
3194 | (setq i (1+ i))) | |
3195 | (aset disptab 127 (vector ?^ ??))) | |
3196 | @end example | |
3197 | ||
f9f59935 RS |
3198 | @defun display-table-slot display-table slot |
3199 | This function returns the value of the extra slot @var{slot} of | |
3200 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
3201 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
3202 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
3203 | @code{selective-display}, and @code{vertical-border}. | |
3204 | @end defun | |
3205 | ||
f9f59935 RS |
3206 | @defun set-display-table-slot display-table slot value |
3207 | This function stores @var{value} in the extra slot @var{slot} of | |
3208 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
3209 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
3210 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
3211 | @code{selective-display}, and @code{vertical-border}. | |
3212 | @end defun | |
3213 | ||
8241495d RS |
3214 | @defun describe-display-table display-table |
3215 | @tindex describe-display-table | |
3216 | This function displays a description of the display table | |
3217 | @var{display-table} in a help buffer. | |
3218 | @end defun | |
3219 | ||
3220 | @deffn Command describe-current-display-table | |
3221 | @tindex describe-current-display-table | |
3222 | This command displays a description of the current display table in a | |
3223 | help buffer. | |
3224 | @end deffn | |
3225 | ||
42b85554 RS |
3226 | @node Active Display Table |
3227 | @subsection Active Display Table | |
3228 | @cindex active display table | |
3229 | ||
3230 | Each window can specify a display table, and so can each buffer. When | |
3231 | a buffer @var{b} is displayed in window @var{w}, display uses the | |
3232 | display table for window @var{w} if it has one; otherwise, the display | |
3233 | table for buffer @var{b} if it has one; otherwise, the standard display | |
3234 | table if any. The display table chosen is called the @dfn{active} | |
3235 | display table. | |
3236 | ||
3237 | @defun window-display-table window | |
3238 | This function returns @var{window}'s display table, or @code{nil} | |
3239 | if @var{window} does not have an assigned display table. | |
3240 | @end defun | |
3241 | ||
3242 | @defun set-window-display-table window table | |
3243 | This function sets the display table of @var{window} to @var{table}. | |
3244 | The argument @var{table} should be either a display table or | |
3245 | @code{nil}. | |
3246 | @end defun | |
3247 | ||
3248 | @defvar buffer-display-table | |
969fe9b5 RS |
3249 | This variable is automatically buffer-local in all buffers; its value in |
3250 | a particular buffer specifies the display table for that buffer. If it | |
3251 | is @code{nil}, that means the buffer does not have an assigned display | |
3252 | table. | |
42b85554 RS |
3253 | @end defvar |
3254 | ||
3255 | @defvar standard-display-table | |
3256 | This variable's value is the default display table, used whenever a | |
3257 | window has no display table and neither does the buffer displayed in | |
3258 | that window. This variable is @code{nil} by default. | |
3259 | @end defvar | |
3260 | ||
3261 | If there is no display table to use for a particular window---that is, | |
f9f59935 RS |
3262 | if the window specifies none, its buffer specifies none, and |
3263 | @code{standard-display-table} is @code{nil}---then Emacs uses the usual | |
42b85554 RS |
3264 | display conventions for all character codes in that window. @xref{Usual |
3265 | Display}. | |
3266 | ||
8241495d RS |
3267 | A number of functions for changing the standard display table |
3268 | are defined in the library @file{disp-table}. | |
3269 | ||
42b85554 RS |
3270 | @node Glyphs |
3271 | @subsection Glyphs | |
3272 | ||
3273 | @cindex glyph | |
3274 | A @dfn{glyph} is a generalization of a character; it stands for an | |
3275 | image that takes up a single character position on the screen. Glyphs | |
3276 | are represented in Lisp as integers, just as characters are. | |
3277 | ||
3278 | @cindex glyph table | |
3279 | The meaning of each integer, as a glyph, is defined by the glyph | |
3280 | table, which is the value of the variable @code{glyph-table}. | |
3281 | ||
3282 | @defvar glyph-table | |
3283 | The value of this variable is the current glyph table. It should be a | |
3284 | vector; the @var{g}th element defines glyph code @var{g}. If the value | |
3285 | is @code{nil} instead of a vector, then all glyphs are simple (see | |
3286 | below). | |
3287 | @end defvar | |
3288 | ||
3289 | Here are the possible types of elements in the glyph table: | |
3290 | ||
1911e6e5 RS |
3291 | @table @asis |
3292 | @item @var{string} | |
42b85554 RS |
3293 | Send the characters in @var{string} to the terminal to output |
3294 | this glyph. This alternative is available on character terminals, | |
969fe9b5 | 3295 | but not under a window system. |
42b85554 | 3296 | |
1911e6e5 | 3297 | @item @var{integer} |
969fe9b5 RS |
3298 | Define this glyph code as an alias for glyph code @var{integer}. You |
3299 | can use an alias to specify a face code for the glyph; see below. | |
42b85554 RS |
3300 | |
3301 | @item @code{nil} | |
969fe9b5 RS |
3302 | This glyph is simple. On an ordinary terminal, the glyph code mod |
3303 | 524288 is the character to output. In a window system, the glyph code | |
3304 | mod 524288 is the character to output, and the glyph code divided by | |
3305 | 524288 specifies the face number (@pxref{Face Functions}) to use while | |
3306 | outputting it. (524288 is | |
37680279 | 3307 | @ifnottex |
969fe9b5 | 3308 | 2**19.) |
37680279 | 3309 | @end ifnottex |
f9f59935 | 3310 | @tex |
969fe9b5 | 3311 | $2^{19}$.) |
f9f59935 RS |
3312 | @end tex |
3313 | @xref{Faces}. | |
42b85554 RS |
3314 | @end table |
3315 | ||
3316 | If a glyph code is greater than or equal to the length of the glyph | |
3317 | table, that code is automatically simple. | |
3318 | ||
8241495d RS |
3319 | @defun create-glyph string |
3320 | @tindex create-glyph | |
3321 | This function returns a newly-allocated glyph code which is set up to | |
3322 | display by sending @var{string} to the terminal. | |
3323 | @end defun | |
3324 | ||
42b85554 RS |
3325 | @node Beeping |
3326 | @section Beeping | |
3327 | @cindex beeping | |
3328 | @cindex bell | |
3329 | ||
f9f59935 RS |
3330 | This section describes how to make Emacs ring the bell (or blink the |
3331 | screen) to attract the user's attention. Be conservative about how | |
3332 | often you do this; frequent bells can become irritating. Also be | |
3333 | careful not to use just beeping when signaling an error is more | |
3334 | appropriate. (@xref{Errors}.) | |
42b85554 | 3335 | |
a9f0a989 | 3336 | @defun ding &optional do-not-terminate |
42b85554 RS |
3337 | @cindex keyboard macro termination |
3338 | This function beeps, or flashes the screen (see @code{visible-bell} below). | |
3339 | It also terminates any keyboard macro currently executing unless | |
a9f0a989 | 3340 | @var{do-not-terminate} is non-@code{nil}. |
42b85554 RS |
3341 | @end defun |
3342 | ||
a9f0a989 | 3343 | @defun beep &optional do-not-terminate |
42b85554 RS |
3344 | This is a synonym for @code{ding}. |
3345 | @end defun | |
3346 | ||
1911e6e5 | 3347 | @defopt visible-bell |
42b85554 RS |
3348 | This variable determines whether Emacs should flash the screen to |
3349 | represent a bell. Non-@code{nil} means yes, @code{nil} means no. This | |
969fe9b5 RS |
3350 | is effective on a window system, and on a character-only terminal |
3351 | provided the terminal's Termcap entry defines the visible bell | |
3352 | capability (@samp{vb}). | |
1911e6e5 | 3353 | @end defopt |
42b85554 | 3354 | |
f9f59935 RS |
3355 | @defvar ring-bell-function |
3356 | If this is non-@code{nil}, it specifies how Emacs should ``ring the | |
a40d4712 PR |
3357 | bell.'' Its value should be a function of no arguments. If this is |
3358 | non-@code{nil}, it takes precedence over the @code{visible-bell} | |
3359 | variable. | |
f9f59935 RS |
3360 | @end defvar |
3361 | ||
42b85554 RS |
3362 | @node Window Systems |
3363 | @section Window Systems | |
3364 | ||
3365 | Emacs works with several window systems, most notably the X Window | |
3366 | System. Both Emacs and X use the term ``window'', but use it | |
3367 | differently. An Emacs frame is a single window as far as X is | |
3368 | concerned; the individual Emacs windows are not known to X at all. | |
3369 | ||
3370 | @defvar window-system | |
42b85554 | 3371 | This variable tells Lisp programs what window system Emacs is running |
1911e6e5 RS |
3372 | under. The possible values are |
3373 | ||
3374 | @table @code | |
3375 | @item x | |
3376 | @cindex X Window System | |
3377 | Emacs is displaying using X. | |
3378 | @item pc | |
8241495d | 3379 | Emacs is displaying using MS-DOS. |
1911e6e5 | 3380 | @item w32 |
05aea714 | 3381 | Emacs is displaying using Windows. |
8241495d RS |
3382 | @item mac |
3383 | Emacs is displaying using a Macintosh. | |
1911e6e5 RS |
3384 | @item nil |
3385 | Emacs is using a character-based terminal. | |
3386 | @end table | |
42b85554 RS |
3387 | @end defvar |
3388 | ||
42b85554 | 3389 | @defvar window-setup-hook |
f9f59935 RS |
3390 | This variable is a normal hook which Emacs runs after handling the |
3391 | initialization files. Emacs runs this hook after it has completed | |
a40d4712 | 3392 | loading your init file, the default initialization file (if |
a9f0a989 | 3393 | any), and the terminal-specific Lisp code, and running the hook |
42b85554 RS |
3394 | @code{term-setup-hook}. |
3395 | ||
3396 | This hook is used for internal purposes: setting up communication with | |
3397 | the window system, and creating the initial window. Users should not | |
3398 | interfere with it. | |
3399 | @end defvar |