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