Commit | Line | Data |
---|---|---|
42b85554 RS |
1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
f9f59935 | 3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998 Free Software Foundation, Inc. |
42b85554 RS |
4 | @c See the file elisp.texi for copying conditions. |
5 | @setfilename ../info/display | |
969fe9b5 | 6 | @node Display, Calendar, Processes, Top |
42b85554 RS |
7 | @chapter Emacs Display |
8 | ||
9 | This chapter describes a number of features related to the display | |
10 | that Emacs presents to the user. | |
11 | ||
12 | @menu | |
13 | * Refresh Screen:: Clearing the screen and redrawing everything on it. | |
8241495d | 14 | * Forcing Redisplay:: Forcing redisplay. |
42b85554 RS |
15 | * Truncation:: Folding or wrapping long text lines. |
16 | * The Echo Area:: Where messages are displayed. | |
22697dac KH |
17 | * Invisible Text:: Hiding part of the buffer text. |
18 | * Selective Display:: Hiding part of the buffer text (the old way). | |
42b85554 RS |
19 | * Overlay Arrow:: Display of an arrow to indicate position. |
20 | * Temporary Displays:: Displays that go away automatically. | |
21 | * Overlays:: Use overlays to highlight parts of the buffer. | |
a40d4712 PR |
22 | * Width:: How wide a character or string is on the screen. |
23 | * Faces:: A face defines a graphics style for text characters: | |
24 | font, colors, etc. | |
8241495d RS |
25 | * Display Property:: Enabling special display features. |
26 | * Images:: Displaying images in Emacs buffers. | |
42b85554 RS |
27 | * Blinking:: How Emacs shows the matching open parenthesis. |
28 | * Inverse Video:: Specifying how the screen looks. | |
29 | * Usual Display:: The usual conventions for displaying nonprinting chars. | |
30 | * Display Tables:: How to specify other conventions. | |
31 | * Beeping:: Audible signal to the user. | |
32 | * Window Systems:: Which window system is being used. | |
33 | @end menu | |
34 | ||
35 | @node Refresh Screen | |
36 | @section Refreshing the Screen | |
37 | ||
38 | The function @code{redraw-frame} redisplays the entire contents of a | |
1911e6e5 | 39 | given frame (@pxref{Frames}). |
42b85554 RS |
40 | |
41 | @c Emacs 19 feature | |
42 | @defun redraw-frame frame | |
43 | This function clears and redisplays frame @var{frame}. | |
44 | @end defun | |
45 | ||
46 | Even more powerful is @code{redraw-display}: | |
47 | ||
48 | @deffn Command redraw-display | |
49 | This function clears and redisplays all visible frames. | |
50 | @end deffn | |
51 | ||
bfe721d1 KH |
52 | Processing user input takes absolute priority over redisplay. If you |
53 | call these functions when input is available, they do nothing | |
54 | immediately, but a full redisplay does happen eventually---after all the | |
55 | input has been processed. | |
56 | ||
42b85554 RS |
57 | Normally, suspending and resuming Emacs also refreshes the screen. |
58 | Some terminal emulators record separate contents for display-oriented | |
59 | programs such as Emacs and for ordinary sequential display. If you are | |
60 | using such a terminal, you might want to inhibit the redisplay on | |
78608595 | 61 | resumption. |
42b85554 RS |
62 | |
63 | @defvar no-redraw-on-reenter | |
64 | @cindex suspend (cf. @code{no-redraw-on-reenter}) | |
65 | @cindex resume (cf. @code{no-redraw-on-reenter}) | |
66 | This variable controls whether Emacs redraws the entire screen after it | |
f9f59935 | 67 | has been suspended and resumed. Non-@code{nil} means there is no need |
969fe9b5 | 68 | to redraw, @code{nil} means redrawing is needed. The default is @code{nil}. |
42b85554 RS |
69 | @end defvar |
70 | ||
8241495d RS |
71 | @node Forcing Redisplay |
72 | @section Forcing Redisplay | |
73 | @cindex forcing redisplay | |
74 | ||
75 | Emacs redisplay normally stops if input arrives, and does not happen | |
76 | at all if input is available before it starts. Most of the time, this | |
77 | is exactly what you want. However, you can prevent preemption by | |
78 | binding @code{redisplay-dont-pause} to a non-@code{nil} value. | |
79 | ||
80 | @tindex redisplay-dont-pause | |
81 | @defvar redisplay-dont-pause | |
82 | If this variable is non-@code{nil}, pending input does not | |
83 | prevent or halt redisplay; redisplay occurs, and finishes, | |
84 | regardless of whether input is available. This feature is available | |
85 | as of Emacs 21. | |
86 | @end defvar | |
87 | ||
88 | You can request a display update, but only if no input is pending, | |
89 | with @code{(sit-for 0)}. To force a display update even when input is | |
90 | pending, do this: | |
91 | ||
92 | @example | |
93 | (let ((redisplay-dont-pause t)) | |
94 | (sit-for 0)) | |
95 | @end example | |
96 | ||
42b85554 RS |
97 | @node Truncation |
98 | @section Truncation | |
99 | @cindex line wrapping | |
100 | @cindex continuation lines | |
101 | @cindex @samp{$} in display | |
102 | @cindex @samp{\} in display | |
103 | ||
104 | When a line of text extends beyond the right edge of a window, the | |
105 | line can either be continued on the next screen line, or truncated to | |
106 | one screen line. The additional screen lines used to display a long | |
107 | text line are called @dfn{continuation} lines. Normally, a @samp{$} in | |
108 | the rightmost column of the window indicates truncation; a @samp{\} on | |
969fe9b5 RS |
109 | the rightmost column indicates a line that ``wraps'' onto the next line, |
110 | which is also called @dfn{continuing} the line. (The display table can | |
111 | specify alternative indicators; see @ref{Display Tables}.) | |
42b85554 RS |
112 | |
113 | Note that continuation is different from filling; continuation happens | |
114 | on the screen only, not in the buffer contents, and it breaks a line | |
115 | precisely at the right margin, not at a word boundary. @xref{Filling}. | |
116 | ||
117 | @defopt truncate-lines | |
118 | This buffer-local variable controls how Emacs displays lines that extend | |
119 | beyond the right edge of the window. The default is @code{nil}, which | |
120 | specifies continuation. If the value is non-@code{nil}, then these | |
121 | lines are truncated. | |
122 | ||
123 | If the variable @code{truncate-partial-width-windows} is non-@code{nil}, | |
124 | then truncation is always used for side-by-side windows (within one | |
125 | frame) regardless of the value of @code{truncate-lines}. | |
126 | @end defopt | |
127 | ||
bfe721d1 | 128 | @defopt default-truncate-lines |
42b85554 | 129 | This variable is the default value for @code{truncate-lines}, for |
969fe9b5 | 130 | buffers that do not have buffer-local values for it. |
bfe721d1 | 131 | @end defopt |
42b85554 RS |
132 | |
133 | @defopt truncate-partial-width-windows | |
134 | This variable controls display of lines that extend beyond the right | |
135 | edge of the window, in side-by-side windows (@pxref{Splitting Windows}). | |
136 | If it is non-@code{nil}, these lines are truncated; otherwise, | |
137 | @code{truncate-lines} says what to do with them. | |
138 | @end defopt | |
139 | ||
a9f0a989 RS |
140 | When horizontal scrolling (@pxref{Horizontal Scrolling}) is in use in |
141 | a window, that forces truncation. | |
142 | ||
f9f59935 RS |
143 | You can override the glyphs that indicate continuation or truncation |
144 | using the display table; see @ref{Display Tables}. | |
42b85554 | 145 | |
1911e6e5 | 146 | If your buffer contains @emph{very} long lines, and you use |
22697dac | 147 | continuation to display them, just thinking about them can make Emacs |
bfe721d1 KH |
148 | redisplay slow. The column computation and indentation functions also |
149 | become slow. Then you might find it advisable to set | |
150 | @code{cache-long-line-scans} to @code{t}. | |
22697dac KH |
151 | |
152 | @defvar cache-long-line-scans | |
153 | If this variable is non-@code{nil}, various indentation and motion | |
bfe721d1 KH |
154 | functions, and Emacs redisplay, cache the results of scanning the |
155 | buffer, and consult the cache to avoid rescanning regions of the buffer | |
156 | unless they are modified. | |
22697dac | 157 | |
bfe721d1 | 158 | Turning on the cache slows down processing of short lines somewhat. |
22697dac | 159 | |
969fe9b5 | 160 | This variable is automatically buffer-local in every buffer. |
22697dac KH |
161 | @end defvar |
162 | ||
42b85554 RS |
163 | @node The Echo Area |
164 | @section The Echo Area | |
165 | @cindex error display | |
166 | @cindex echo area | |
167 | ||
22697dac | 168 | The @dfn{echo area} is used for displaying messages made with the |
42b85554 RS |
169 | @code{message} primitive, and for echoing keystrokes. It is not the |
170 | same as the minibuffer, despite the fact that the minibuffer appears | |
171 | (when active) in the same place on the screen as the echo area. The | |
172 | @cite{GNU Emacs Manual} specifies the rules for resolving conflicts | |
173 | between the echo area and the minibuffer for use of that screen space | |
174 | (@pxref{Minibuffer,, The Minibuffer, emacs, The GNU Emacs Manual}). | |
175 | Error messages appear in the echo area; see @ref{Errors}. | |
176 | ||
177 | You can write output in the echo area by using the Lisp printing | |
178 | functions with @code{t} as the stream (@pxref{Output Functions}), or as | |
179 | follows: | |
180 | ||
181 | @defun message string &rest arguments | |
22697dac | 182 | This function displays a one-line message in the echo area. The |
42b85554 RS |
183 | argument @var{string} is similar to a C language @code{printf} control |
184 | string. See @code{format} in @ref{String Conversion}, for the details | |
185 | on the conversion specifications. @code{message} returns the | |
186 | constructed string. | |
187 | ||
b22f3a19 RS |
188 | In batch mode, @code{message} prints the message text on the standard |
189 | error stream, followed by a newline. | |
190 | ||
8241495d RS |
191 | If @var{string}, or strings among the @var{arguments}, have @code{face} |
192 | text properties, these affect the way the message is displayed. | |
193 | ||
42b85554 | 194 | @c Emacs 19 feature |
8241495d RS |
195 | If @var{string} is @code{nil}, @code{message} clears the echo area; if |
196 | the echo area has been expanded automatically, this brings it back to | |
197 | its normal size. If the minibuffer is active, this brings the | |
198 | minibuffer contents back onto the screen immediately. | |
b22f3a19 | 199 | |
42b85554 RS |
200 | @example |
201 | @group | |
202 | (message "Minibuffer depth is %d." | |
203 | (minibuffer-depth)) | |
204 | @print{} Minibuffer depth is 0. | |
205 | @result{} "Minibuffer depth is 0." | |
206 | @end group | |
207 | ||
208 | @group | |
209 | ---------- Echo Area ---------- | |
210 | Minibuffer depth is 0. | |
211 | ---------- Echo Area ---------- | |
212 | @end group | |
213 | @end example | |
214 | @end defun | |
215 | ||
b6954afd RS |
216 | @tindex with-temp-message |
217 | @defmac with-temp-message message &rest body | |
218 | This construct displays a message in the echo area temporarily, during | |
219 | the execution of @var{body}. It displays @var{message}, executes | |
220 | @var{body}, then returns the value of the last body form while restoring | |
221 | the previous echo area contents. | |
222 | @end defmac | |
223 | ||
39d6d9bd RS |
224 | @defun message-or-box string &rest arguments |
225 | This function displays a message like @code{message}, but may display it | |
226 | in a dialog box instead of the echo area. If this function is called in | |
227 | a command that was invoked using the mouse---more precisely, if | |
228 | @code{last-nonmenu-event} (@pxref{Command Loop Info}) is either | |
229 | @code{nil} or a list---then it uses a dialog box or pop-up menu to | |
230 | display the message. Otherwise, it uses the echo area. (This is the | |
231 | same criterion that @code{y-or-n-p} uses to make a similar decision; see | |
232 | @ref{Yes-or-No Queries}.) | |
233 | ||
234 | You can force use of the mouse or of the echo area by binding | |
235 | @code{last-nonmenu-event} to a suitable value around the call. | |
236 | @end defun | |
237 | ||
238 | @defun message-box string &rest arguments | |
239 | This function displays a message like @code{message}, but uses a dialog | |
240 | box (or a pop-up menu) whenever that is possible. If it is impossible | |
241 | to use a dialog box or pop-up menu, because the terminal does not | |
242 | support them, then @code{message-box} uses the echo area, like | |
243 | @code{message}. | |
244 | @end defun | |
245 | ||
f9f59935 | 246 | @defun current-message |
a9f0a989 | 247 | @tindex current-message |
f9f59935 RS |
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 | ||
f9f59935 | 262 | @defvar echo-area-clear-hook |
a9f0a989 | 263 | @tindex echo-area-clear-hook |
f9f59935 RS |
264 | This normal hook is run whenever the echo area is cleared---either by |
265 | @code{(message nil)} or for any other reason. | |
266 | @end defvar | |
267 | ||
22697dac KH |
268 | Almost all the messages displayed in the echo area are also recorded |
269 | in the @samp{*Messages*} buffer. | |
270 | ||
271 | @defopt message-log-max | |
272 | This variable specifies how many lines to keep in the @samp{*Messages*} | |
273 | buffer. The value @code{t} means there is no limit on how many lines to | |
274 | keep. The value @code{nil} disables message logging entirely. Here's | |
275 | how to display a message and prevent it from being logged: | |
276 | ||
277 | @example | |
278 | (let (message-log-max) | |
279 | (message @dots{})) | |
280 | @end example | |
281 | @end defopt | |
282 | ||
bfe721d1 KH |
283 | @defvar echo-keystrokes |
284 | This variable determines how much time should elapse before command | |
285 | characters echo. Its value must be an integer, which specifies the | |
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 | |
a9f0a989 RS |
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.) | |
bfe721d1 KH |
291 | |
292 | If the value is zero, then command input is not echoed. | |
293 | @end defvar | |
294 | ||
22697dac KH |
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 | |
a9f0a989 RS |
301 | text property (@pxref{Text Properties}) or a property of an overlay |
302 | (@pxref{Overlays}). | |
22697dac KH |
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. |
22697dac KH |
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 | |
a40d4712 PR |
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. | |
22697dac KH |
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 | |
969fe9b5 RS |
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: | |
22697dac KH |
336 | |
337 | @table @code | |
338 | @item @var{atom} | |
969fe9b5 | 339 | A character is invisible if its @code{invisible} property value |
22697dac KH |
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 |
22697dac KH |
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 | 354 | @defun add-to-invisibility-spec element |
a9f0a989 | 355 | @tindex add-to-invisibility-spec |
f9f59935 RS |
356 | Add the element @var{element} to @code{buffer-invisibility-spec} |
357 | (if it is not already present in that list). | |
358 | @end defun | |
359 | ||
f9f59935 | 360 | @defun remove-from-invisibility-spec element |
a9f0a989 | 361 | @tindex remove-from-invisibility-spec |
f9f59935 | 362 | Remove the element @var{element} from @code{buffer-invisibility-spec}. |
a40d4712 | 363 | This does nothing if @var{element} is not in the list. |
f9f59935 RS |
364 | @end defun |
365 | ||
366 | One convention about the use of @code{buffer-invisibility-spec} is | |
367 | that a major mode should use the mode's own name as an element of | |
368 | @code{buffer-invisibility-spec} and as the value of the @code{invisible} | |
369 | property: | |
370 | ||
371 | @example | |
969fe9b5 | 372 | ;; @r{If you want to display an ellipsis:} |
f9f59935 | 373 | (add-to-invisibility-spec '(my-symbol . t)) |
969fe9b5 | 374 | ;; @r{If you don't want ellipsis:} |
f9f59935 RS |
375 | (add-to-invisibility-spec 'my-symbol) |
376 | ||
377 | (overlay-put (make-overlay beginning end) | |
378 | 'invisible 'my-symbol) | |
379 | ||
969fe9b5 | 380 | ;; @r{When done with the overlays:} |
f9f59935 | 381 | (remove-from-invisibility-spec '(my-symbol . t)) |
969fe9b5 | 382 | ;; @r{Or respectively:} |
f9f59935 RS |
383 | (remove-from-invisibility-spec 'my-symbol) |
384 | @end example | |
385 | ||
5e8ae792 | 386 | @vindex line-move-ignore-invisible |
bfe721d1 | 387 | Ordinarily, commands that operate on text or move point do not care |
5e8ae792 RS |
388 | whether the text is invisible. The user-level line motion commands |
389 | explicitly ignore invisible newlines if | |
390 | @code{line-move-ignore-invisible} is non-@code{nil}, but only because | |
391 | they are explicitly programmed to do so. | |
bfe721d1 | 392 | |
f9f59935 RS |
393 | Incremental search can make invisible overlays visible temporarily |
394 | and/or permanently when a match includes invisible text. To enable | |
395 | this, the overlay should have a non-@code{nil} | |
396 | @code{isearch-open-invisible} property. The property value should be a | |
397 | function to be called with the overlay as an argument. This function | |
398 | should make the overlay visible permanently; it is used when the match | |
399 | overlaps the overlay on exit from the search. | |
400 | ||
401 | During the search, such overlays are made temporarily visible by | |
402 | temporarily modifying their invisible and intangible properties. If you | |
ebc6903b | 403 | want this to be done differently for a certain overlay, give it an |
f9f59935 RS |
404 | @code{isearch-open-invisible-temporary} property which is a function. |
405 | The function is called with two arguments: the first is the overlay, and | |
a9f0a989 RS |
406 | the second is @code{t} to make the overlay visible, or @code{nil} to |
407 | make it invisible again. | |
f9f59935 | 408 | |
42b85554 RS |
409 | @node Selective Display |
410 | @section Selective Display | |
411 | @cindex selective display | |
412 | ||
969fe9b5 RS |
413 | @dfn{Selective display} refers to a pair of related features for |
414 | hiding certain lines on the screen. | |
42b85554 RS |
415 | |
416 | The first variant, explicit selective display, is designed for use in | |
969fe9b5 RS |
417 | a Lisp program: it controls which lines are hidden by altering the text. |
418 | The invisible text feature (@pxref{Invisible Text}) has partially | |
419 | replaced this feature. | |
22697dac KH |
420 | |
421 | In the second variant, the choice of lines to hide is made | |
bfe721d1 | 422 | automatically based on indentation. This variant is designed to be a |
22697dac | 423 | user-level feature. |
42b85554 RS |
424 | |
425 | The way you control explicit selective display is by replacing a | |
78608595 | 426 | newline (control-j) with a carriage return (control-m). The text that |
42b85554 RS |
427 | was formerly a line following that newline is now invisible. Strictly |
428 | speaking, it is temporarily no longer a line at all, since only newlines | |
429 | can separate lines; it is now part of the previous line. | |
430 | ||
431 | Selective display does not directly affect editing commands. For | |
432 | example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly into | |
433 | invisible text. However, the replacement of newline characters with | |
434 | carriage return characters affects some editing commands. For example, | |
435 | @code{next-line} skips invisible lines, since it searches only for | |
436 | newlines. Modes that use selective display can also define commands | |
437 | that take account of the newlines, or that make parts of the text | |
438 | visible or invisible. | |
439 | ||
440 | When you write a selectively displayed buffer into a file, all the | |
441 | control-m's are output as newlines. This means that when you next read | |
442 | in the file, it looks OK, with nothing invisible. The selective display | |
443 | effect is seen only within Emacs. | |
444 | ||
445 | @defvar selective-display | |
446 | This buffer-local variable enables selective display. This means that | |
447 | lines, or portions of lines, may be made invisible. | |
448 | ||
449 | @itemize @bullet | |
450 | @item | |
a40d4712 PR |
451 | If the value of @code{selective-display} is @code{t}, then the character |
452 | control-m marks the start of invisible text; the control-m, and the rest | |
453 | of the line following it, are not displayed. This is explicit selective | |
454 | display. | |
42b85554 RS |
455 | |
456 | @item | |
457 | If the value of @code{selective-display} is a positive integer, then | |
458 | lines that start with more than that many columns of indentation are not | |
459 | displayed. | |
460 | @end itemize | |
461 | ||
462 | When some portion of a buffer is invisible, the vertical movement | |
463 | commands operate as if that portion did not exist, allowing a single | |
464 | @code{next-line} command to skip any number of invisible lines. | |
465 | However, character movement commands (such as @code{forward-char}) do | |
466 | not skip the invisible portion, and it is possible (if tricky) to insert | |
467 | or delete text in an invisible portion. | |
468 | ||
469 | In the examples below, we show the @emph{display appearance} of the | |
470 | buffer @code{foo}, which changes with the value of | |
471 | @code{selective-display}. The @emph{contents} of the buffer do not | |
472 | change. | |
473 | ||
474 | @example | |
475 | @group | |
476 | (setq selective-display nil) | |
477 | @result{} nil | |
478 | ||
479 | ---------- Buffer: foo ---------- | |
480 | 1 on this column | |
481 | 2on this column | |
482 | 3n this column | |
483 | 3n this column | |
484 | 2on this column | |
485 | 1 on this column | |
486 | ---------- Buffer: foo ---------- | |
487 | @end group | |
488 | ||
489 | @group | |
490 | (setq selective-display 2) | |
491 | @result{} 2 | |
492 | ||
493 | ---------- Buffer: foo ---------- | |
494 | 1 on this column | |
495 | 2on this column | |
496 | 2on this column | |
497 | 1 on this column | |
498 | ---------- Buffer: foo ---------- | |
499 | @end group | |
500 | @end example | |
501 | @end defvar | |
502 | ||
503 | @defvar selective-display-ellipses | |
504 | If this buffer-local variable is non-@code{nil}, then Emacs displays | |
505 | @samp{@dots{}} at the end of a line that is followed by invisible text. | |
506 | This example is a continuation of the previous one. | |
507 | ||
508 | @example | |
509 | @group | |
510 | (setq selective-display-ellipses t) | |
511 | @result{} t | |
512 | ||
513 | ---------- Buffer: foo ---------- | |
514 | 1 on this column | |
515 | 2on this column ... | |
516 | 2on this column | |
517 | 1 on this column | |
518 | ---------- Buffer: foo ---------- | |
519 | @end group | |
520 | @end example | |
521 | ||
522 | You can use a display table to substitute other text for the ellipsis | |
523 | (@samp{@dots{}}). @xref{Display Tables}. | |
524 | @end defvar | |
525 | ||
526 | @node Overlay Arrow | |
527 | @section The Overlay Arrow | |
528 | @cindex overlay arrow | |
529 | ||
530 | The @dfn{overlay arrow} is useful for directing the user's attention | |
531 | to a particular line in a buffer. For example, in the modes used for | |
532 | interface to debuggers, the overlay arrow indicates the line of code | |
533 | about to be executed. | |
534 | ||
535 | @defvar overlay-arrow-string | |
78608595 RS |
536 | This variable holds the string to display to call attention to a |
537 | particular line, or @code{nil} if the arrow feature is not in use. | |
42b85554 RS |
538 | @end defvar |
539 | ||
540 | @defvar overlay-arrow-position | |
78608595 RS |
541 | This variable holds a marker that indicates where to display the overlay |
542 | arrow. It should point at the beginning of a line. The arrow text | |
543 | appears at the beginning of that line, overlaying any text that would | |
544 | otherwise appear. Since the arrow is usually short, and the line | |
545 | usually begins with indentation, normally nothing significant is | |
546 | overwritten. | |
547 | ||
548 | The overlay string is displayed only in the buffer that this marker | |
42b85554 RS |
549 | points into. Thus, only one buffer can have an overlay arrow at any |
550 | given time. | |
551 | @c !!! overlay-arrow-position: but the overlay string may remain in the display | |
552 | @c of some other buffer until an update is required. This should be fixed | |
553 | @c now. Is it? | |
554 | @end defvar | |
555 | ||
969fe9b5 | 556 | You can do a similar job by creating an overlay with a |
22697dac KH |
557 | @code{before-string} property. @xref{Overlay Properties}. |
558 | ||
42b85554 RS |
559 | @node Temporary Displays |
560 | @section Temporary Displays | |
561 | ||
969fe9b5 RS |
562 | Temporary displays are used by Lisp programs to put output into a |
563 | buffer and then present it to the user for perusal rather than for | |
564 | editing. Many help commands use this feature. | |
42b85554 RS |
565 | |
566 | @defspec with-output-to-temp-buffer buffer-name forms@dots{} | |
b6954afd RS |
567 | This function executes @var{forms} while arranging to insert any output |
568 | they print into the buffer named @var{buffer-name}, which is first | |
569 | created if necessary, and put into Help mode. Finally, the buffer is | |
570 | displayed in some window, but not selected. | |
571 | ||
572 | If the @var{forms} do not change the major mode in the output buffer, so | |
573 | that it is still Help mode at the end of their execution, then | |
574 | @code{with-output-to-temp-buffer} makes this buffer read-only at the | |
575 | end, and also scans it for function and variable names to make them into | |
576 | clickable cross-references. | |
42b85554 RS |
577 | |
578 | The string @var{buffer-name} specifies the temporary buffer, which | |
579 | need not already exist. The argument must be a string, not a buffer. | |
580 | The buffer is erased initially (with no questions asked), and it is | |
581 | marked as unmodified after @code{with-output-to-temp-buffer} exits. | |
582 | ||
583 | @code{with-output-to-temp-buffer} binds @code{standard-output} to the | |
584 | temporary buffer, then it evaluates the forms in @var{forms}. Output | |
585 | using the Lisp output functions within @var{forms} goes by default to | |
586 | that buffer (but screen display and messages in the echo area, although | |
587 | they are ``output'' in the general sense of the word, are not affected). | |
588 | @xref{Output Functions}. | |
589 | ||
b6954afd RS |
590 | Several hooks are available for customizing the behavior |
591 | of this construct; they are listed below. | |
592 | ||
42b85554 RS |
593 | The value of the last form in @var{forms} is returned. |
594 | ||
595 | @example | |
596 | @group | |
597 | ---------- Buffer: foo ---------- | |
598 | This is the contents of foo. | |
599 | ---------- Buffer: foo ---------- | |
600 | @end group | |
601 | ||
602 | @group | |
603 | (with-output-to-temp-buffer "foo" | |
604 | (print 20) | |
605 | (print standard-output)) | |
606 | @result{} #<buffer foo> | |
607 | ||
608 | ---------- Buffer: foo ---------- | |
609 | 20 | |
610 | ||
611 | #<buffer foo> | |
612 | ||
613 | ---------- Buffer: foo ---------- | |
614 | @end group | |
615 | @end example | |
616 | @end defspec | |
617 | ||
618 | @defvar temp-buffer-show-function | |
78608595 | 619 | If this variable is non-@code{nil}, @code{with-output-to-temp-buffer} |
42b85554 RS |
620 | calls it as a function to do the job of displaying a help buffer. The |
621 | function gets one argument, which is the buffer it should display. | |
a9f0a989 RS |
622 | |
623 | It is a good idea for this function to run @code{temp-buffer-show-hook} | |
624 | just as @code{with-output-to-temp-buffer} normally would, inside of | |
b6954afd | 625 | @code{save-selected-window} and with the chosen window and buffer |
a9f0a989 RS |
626 | selected. |
627 | @end defvar | |
628 | ||
b6954afd RS |
629 | @defvar temp-buffer-setup-hook |
630 | @tindex temp-buffer-setup-hook | |
631 | This normal hook is run by @code{with-output-to-temp-buffer} before | |
632 | evaluating @var{body}. When the hook runs, the help buffer is current. | |
633 | This hook is normally set up with a function to put the buffer in Help | |
634 | mode. | |
635 | @end defvar | |
636 | ||
a9f0a989 RS |
637 | @defvar temp-buffer-show-hook |
638 | This normal hook is run by @code{with-output-to-temp-buffer} after | |
639 | displaying the help buffer. When the hook runs, the help buffer is | |
b6954afd RS |
640 | current, and the window it was displayed in is selected. This hook is |
641 | normally set up with a function to make the buffer read only, and find | |
642 | function names and variable names in it, provided the major mode is | |
643 | still Help mode. | |
42b85554 RS |
644 | @end defvar |
645 | ||
646 | @defun momentary-string-display string position &optional char message | |
647 | This function momentarily displays @var{string} in the current buffer at | |
648 | @var{position}. It has no effect on the undo list or on the buffer's | |
649 | modification status. | |
650 | ||
651 | The momentary display remains until the next input event. If the next | |
652 | input event is @var{char}, @code{momentary-string-display} ignores it | |
653 | and returns. Otherwise, that event remains buffered for subsequent use | |
654 | as input. Thus, typing @var{char} will simply remove the string from | |
655 | the display, while typing (say) @kbd{C-f} will remove the string from | |
656 | the display and later (presumably) move point forward. The argument | |
657 | @var{char} is a space by default. | |
658 | ||
659 | The return value of @code{momentary-string-display} is not meaningful. | |
660 | ||
bfe721d1 | 661 | If the string @var{string} does not contain control characters, you can |
969fe9b5 RS |
662 | do the same job in a more general way by creating (and then subsequently |
663 | deleting) an overlay with a @code{before-string} property. | |
664 | @xref{Overlay Properties}. | |
bfe721d1 | 665 | |
42b85554 RS |
666 | If @var{message} is non-@code{nil}, it is displayed in the echo area |
667 | while @var{string} is displayed in the buffer. If it is @code{nil}, a | |
668 | default message says to type @var{char} to continue. | |
669 | ||
670 | In this example, point is initially located at the beginning of the | |
671 | second line: | |
672 | ||
673 | @example | |
674 | @group | |
675 | ---------- Buffer: foo ---------- | |
676 | This is the contents of foo. | |
677 | @point{}Second line. | |
678 | ---------- Buffer: foo ---------- | |
679 | @end group | |
680 | ||
681 | @group | |
682 | (momentary-string-display | |
683 | "**** Important Message! ****" | |
684 | (point) ?\r | |
685 | "Type RET when done reading") | |
686 | @result{} t | |
687 | @end group | |
688 | ||
689 | @group | |
690 | ---------- Buffer: foo ---------- | |
691 | This is the contents of foo. | |
692 | **** Important Message! ****Second line. | |
693 | ---------- Buffer: foo ---------- | |
694 | ||
695 | ---------- Echo Area ---------- | |
696 | Type RET when done reading | |
697 | ---------- Echo Area ---------- | |
698 | @end group | |
699 | @end example | |
700 | @end defun | |
701 | ||
702 | @node Overlays | |
703 | @section Overlays | |
704 | @cindex overlays | |
705 | ||
706 | You can use @dfn{overlays} to alter the appearance of a buffer's text on | |
bfe721d1 KH |
707 | the screen, for the sake of presentation features. An overlay is an |
708 | object that belongs to a particular buffer, and has a specified | |
709 | beginning and end. It also has properties that you can examine and set; | |
710 | these affect the display of the text within the overlay. | |
42b85554 RS |
711 | |
712 | @menu | |
713 | * Overlay Properties:: How to read and set properties. | |
714 | What properties do to the screen display. | |
715 | * Managing Overlays:: Creating, moving, finding overlays. | |
716 | @end menu | |
717 | ||
718 | @node Overlay Properties | |
719 | @subsection Overlay Properties | |
720 | ||
8241495d | 721 | Overlay properties are like text properties in that the properties that |
a9f0a989 RS |
722 | alter how a character is displayed can come from either source. But in |
723 | most respects they are different. Text properties are considered a part | |
724 | of the text; overlays are specifically considered not to be part of the | |
725 | text. Thus, copying text between various buffers and strings preserves | |
726 | text properties, but does not try to preserve overlays. Changing a | |
727 | buffer's text properties marks the buffer as modified, while moving an | |
728 | overlay or changing its properties does not. Unlike text property | |
729 | changes, overlay changes are not recorded in the buffer's undo list. | |
730 | @xref{Text Properties}, for comparison. | |
42b85554 | 731 | |
8241495d RS |
732 | These functions are used for reading and writing the properties of an |
733 | overlay: | |
734 | ||
735 | @defun overlay-get overlay prop | |
736 | This function returns the value of property @var{prop} recorded in | |
737 | @var{overlay}, if any. If @var{overlay} does not record any value for | |
738 | that property, but it does have a @code{category} property which is a | |
739 | symbol, that symbol's @var{prop} property is used. Otherwise, the value | |
740 | is @code{nil}. | |
741 | @end defun | |
742 | ||
743 | @defun overlay-put overlay prop value | |
744 | This function sets the value of property @var{prop} recorded in | |
745 | @var{overlay} to @var{value}. It returns @var{value}. | |
746 | @end defun | |
747 | ||
748 | See also the function @code{get-char-property} which checks both | |
749 | overlay properties and text properties for a given character. | |
750 | @xref{Examining Properties}. | |
751 | ||
752 | Many overlay properties have special meanings; here is a table | |
753 | of them: | |
754 | ||
42b85554 RS |
755 | @table @code |
756 | @item priority | |
757 | @kindex priority @r{(overlay property)} | |
758 | This property's value (which should be a nonnegative number) determines | |
759 | the priority of the overlay. The priority matters when two or more | |
760 | overlays cover the same character and both specify a face for display; | |
761 | the one whose @code{priority} value is larger takes priority over the | |
762 | other, and its face attributes override the face attributes of the lower | |
763 | priority overlay. | |
764 | ||
765 | Currently, all overlays take priority over text properties. Please | |
766 | avoid using negative priority values, as we have not yet decided just | |
767 | what they should mean. | |
768 | ||
769 | @item window | |
770 | @kindex window @r{(overlay property)} | |
771 | If the @code{window} property is non-@code{nil}, then the overlay | |
772 | applies only on that window. | |
773 | ||
22697dac KH |
774 | @item category |
775 | @kindex category @r{(overlay property)} | |
776 | If an overlay has a @code{category} property, we call it the | |
bfe721d1 | 777 | @dfn{category} of the overlay. It should be a symbol. The properties |
22697dac KH |
778 | of the symbol serve as defaults for the properties of the overlay. |
779 | ||
42b85554 RS |
780 | @item face |
781 | @kindex face @r{(overlay property)} | |
f9f59935 | 782 | This property controls the way text is displayed---for example, which |
8241495d | 783 | font and which colors. @xref{Faces}, for more information. |
f9f59935 | 784 | |
8241495d | 785 | In the simplest case, the value is a face name. It can also be a list; |
a40d4712 | 786 | then each element can be any of these possibilities: |
8241495d RS |
787 | |
788 | @itemize @bullet | |
789 | @item | |
790 | A face name (a symbol or string). | |
791 | ||
792 | @item | |
793 | Starting in Emacs 21, a property list of face attributes. This has the | |
794 | form (@var{keyword} @var{value} @dots{}), where each @var{keyword} is a | |
795 | face attribute name and @var{value} is a meaningful value for that | |
796 | attribute. With this feature, you do not need to create a face each | |
797 | time you want to specify a particular attribute for certain text. | |
798 | @xref{Face Attributes}. | |
799 | ||
800 | @item | |
801 | A cons cell of the form @code{(foreground-color . @var{color-name})} or | |
802 | @code{(background-color . @var{color-name})}. These elements specify | |
803 | just the foreground color or just the background color. | |
804 | ||
805 | @code{(foreground-color . @var{color-name})} is equivalent to | |
806 | @code{(:foreground @var{color-name})}, and likewise for the background. | |
807 | @end itemize | |
42b85554 RS |
808 | |
809 | @item mouse-face | |
810 | @kindex mouse-face @r{(overlay property)} | |
811 | This property is used instead of @code{face} when the mouse is within | |
f9f59935 | 812 | the range of the overlay. |
42b85554 | 813 | |
8241495d RS |
814 | @item display |
815 | @kindex display @r{(overlay property)} | |
816 | This property activates various features that change the | |
817 | way text is displayed. For example, it can make text appear taller | |
818 | or shorter, higher or lower, wider or narror, or replaced with an image. | |
819 | @xref{Display Property}. | |
820 | ||
821 | @item help-echo | |
822 | @kindex help-echo @r{(text property)} | |
823 | If an overlay has a string as its @code{help-echo} property, then when | |
824 | you move the mouse onto the text in the overlay, Emacs displays that | |
a40d4712 PR |
825 | string in the echo area, or in the tooltip window. This feature is |
826 | available starting in Emacs 21. | |
8241495d | 827 | |
42b85554 RS |
828 | @item modification-hooks |
829 | @kindex modification-hooks @r{(overlay property)} | |
830 | This property's value is a list of functions to be called if any | |
831 | character within the overlay is changed or if text is inserted strictly | |
22697dac KH |
832 | within the overlay. |
833 | ||
834 | The hook functions are called both before and after each change. | |
835 | If the functions save the information they receive, and compare notes | |
836 | between calls, they can determine exactly what change has been made | |
837 | in the buffer text. | |
838 | ||
839 | When called before a change, each function receives four arguments: the | |
840 | overlay, @code{nil}, and the beginning and end of the text range to be | |
a890e1b0 | 841 | modified. |
42b85554 | 842 | |
22697dac KH |
843 | When called after a change, each function receives five arguments: the |
844 | overlay, @code{t}, the beginning and end of the text range just | |
845 | modified, and the length of the pre-change text replaced by that range. | |
846 | (For an insertion, the pre-change length is zero; for a deletion, that | |
847 | length is the number of characters deleted, and the post-change | |
bfe721d1 | 848 | beginning and end are equal.) |
22697dac | 849 | |
42b85554 RS |
850 | @item insert-in-front-hooks |
851 | @kindex insert-in-front-hooks @r{(overlay property)} | |
22697dac KH |
852 | This property's value is a list of functions to be called before and |
853 | after inserting text right at the beginning of the overlay. The calling | |
854 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
855 | |
856 | @item insert-behind-hooks | |
857 | @kindex insert-behind-hooks @r{(overlay property)} | |
22697dac KH |
858 | This property's value is a list of functions to be called before and |
859 | after inserting text right at the end of the overlay. The calling | |
860 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
861 | |
862 | @item invisible | |
863 | @kindex invisible @r{(overlay property)} | |
22697dac KH |
864 | The @code{invisible} property can make the text in the overlay |
865 | invisible, which means that it does not appear on the screen. | |
866 | @xref{Invisible Text}, for details. | |
867 | ||
868 | @item intangible | |
869 | @kindex intangible @r{(overlay property)} | |
870 | The @code{intangible} property on an overlay works just like the | |
bfe721d1 | 871 | @code{intangible} text property. @xref{Special Properties}, for details. |
f9f59935 RS |
872 | |
873 | @item isearch-open-invisible | |
a9f0a989 RS |
874 | This property tells incremental search how to make an invisible overlay |
875 | visible, permanently, if the final match overlaps it. @xref{Invisible | |
f9f59935 | 876 | Text}. |
42b85554 | 877 | |
a9f0a989 RS |
878 | @item isearch-open-invisible-temporary |
879 | This property tells incremental search how to make an invisible overlay | |
880 | visible, temporarily, during the search. @xref{Invisible Text}. | |
881 | ||
42b85554 RS |
882 | @item before-string |
883 | @kindex before-string @r{(overlay property)} | |
884 | This property's value is a string to add to the display at the beginning | |
885 | of the overlay. The string does not appear in the buffer in any | |
a40d4712 | 886 | sense---only on the screen. |
42b85554 RS |
887 | |
888 | @item after-string | |
889 | @kindex after-string @r{(overlay property)} | |
890 | This property's value is a string to add to the display at the end of | |
891 | the overlay. The string does not appear in the buffer in any | |
a40d4712 | 892 | sense---only on the screen. |
22697dac KH |
893 | |
894 | @item evaporate | |
895 | @kindex evaporate @r{(overlay property)} | |
896 | If this property is non-@code{nil}, the overlay is deleted automatically | |
897 | if it ever becomes empty (i.e., if it spans no characters). | |
d2609065 RS |
898 | |
899 | @item local-map | |
969fe9b5 RS |
900 | @cindex keymap of character (and overlays) |
901 | @kindex local-map @r{(overlay property)} | |
d2609065 RS |
902 | If this property is non-@code{nil}, it specifies a keymap for a portion |
903 | of the text. The property's value replaces the buffer's local map, when | |
904 | the character after point is within the overlay. @xref{Active Keymaps}. | |
42b85554 RS |
905 | @end table |
906 | ||
42b85554 RS |
907 | @node Managing Overlays |
908 | @subsection Managing Overlays | |
909 | ||
910 | This section describes the functions to create, delete and move | |
911 | overlays, and to examine their contents. | |
912 | ||
f9f59935 | 913 | @defun make-overlay start end &optional buffer front-advance rear-advance |
78608595 | 914 | This function creates and returns an overlay that belongs to |
42b85554 RS |
915 | @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start} |
916 | and @var{end} must specify buffer positions; they may be integers or | |
917 | markers. If @var{buffer} is omitted, the overlay is created in the | |
918 | current buffer. | |
f9f59935 RS |
919 | |
920 | The arguments @var{front-advance} and @var{rear-advance} specify the | |
921 | insertion type for the start of the overlay and for the end of the | |
2468d0c0 | 922 | overlay, respectively. @xref{Marker Insertion Types}. |
42b85554 RS |
923 | @end defun |
924 | ||
925 | @defun overlay-start overlay | |
f9f59935 RS |
926 | This function returns the position at which @var{overlay} starts, |
927 | as an integer. | |
42b85554 RS |
928 | @end defun |
929 | ||
930 | @defun overlay-end overlay | |
f9f59935 RS |
931 | This function returns the position at which @var{overlay} ends, |
932 | as an integer. | |
42b85554 RS |
933 | @end defun |
934 | ||
935 | @defun overlay-buffer overlay | |
936 | This function returns the buffer that @var{overlay} belongs to. | |
937 | @end defun | |
938 | ||
939 | @defun delete-overlay overlay | |
940 | This function deletes @var{overlay}. The overlay continues to exist as | |
2468d0c0 DL |
941 | a Lisp object, and its property list is unchanged, but it ceases to be |
942 | attached to the buffer it belonged to, and ceases to have any effect on | |
943 | display. | |
a9f0a989 | 944 | |
2468d0c0 DL |
945 | A deleted overlay is not permanently disconnected. You can give it a |
946 | position in a buffer again by calling @code{move-overlay}. | |
42b85554 RS |
947 | @end defun |
948 | ||
949 | @defun move-overlay overlay start end &optional buffer | |
950 | This function moves @var{overlay} to @var{buffer}, and places its bounds | |
951 | at @var{start} and @var{end}. Both arguments @var{start} and @var{end} | |
2468d0c0 DL |
952 | must specify buffer positions; they may be integers or markers. |
953 | ||
954 | If @var{buffer} is omitted, @var{overlay} stays in the same buffer it | |
955 | was already associated with; if @var{overlay} was deleted, it goes into | |
956 | the current buffer. | |
42b85554 RS |
957 | |
958 | The return value is @var{overlay}. | |
959 | ||
960 | This is the only valid way to change the endpoints of an overlay. Do | |
961 | not try modifying the markers in the overlay by hand, as that fails to | |
962 | update other vital data structures and can cause some overlays to be | |
963 | ``lost''. | |
964 | @end defun | |
965 | ||
2468d0c0 DL |
966 | Here are some examples: |
967 | ||
968 | @example | |
969 | ;; @r{Create an overlay.} | |
970 | (setq foo (make-overlay 1 10)) | |
971 | @result{} #<overlay from 1 to 10 in display.texi> | |
972 | (overlay-start foo) | |
973 | @result{} 1 | |
974 | (overlay-end foo) | |
975 | @result{} 10 | |
976 | (overlay-buffer foo) | |
977 | @result{} #<buffer display.texi> | |
978 | ;; @r{Give it a property we can check later.} | |
979 | (overlay-put foo 'happy t) | |
980 | @result{} t | |
981 | ;; @r{Verify the property is present.} | |
982 | (overlay-get foo 'happy) | |
983 | @result{} t | |
984 | ;; @r{Move the overlay.} | |
985 | (move-overlay foo 5 20) | |
986 | @result{} #<overlay from 5 to 20 in display.texi> | |
987 | (overlay-start foo) | |
988 | @result{} 5 | |
989 | (overlay-end foo) | |
990 | @result{} 20 | |
991 | ;; @r{Delete the overlay.} | |
992 | (delete-overlay foo) | |
993 | @result{} nil | |
994 | ;; @r{Verify it is deleted.} | |
995 | foo | |
996 | @result{} #<overlay in no buffer> | |
997 | ;; @r{A deleted overlay has no position.} | |
998 | (overlay-start foo) | |
999 | @result{} nil | |
1000 | (overlay-end foo) | |
1001 | @result{} nil | |
1002 | (overlay-buffer foo) | |
1003 | @result{} nil | |
1004 | ;; @r{Undelete the overlay.} | |
1005 | (move-overlay foo 1 20) | |
1006 | @result{} #<overlay from 1 to 20 in display.texi> | |
1007 | ;; @r{Verify the results.} | |
1008 | (overlay-start foo) | |
1009 | @result{} 1 | |
1010 | (overlay-end foo) | |
1011 | @result{} 20 | |
1012 | (overlay-buffer foo) | |
1013 | @result{} #<buffer display.texi> | |
1014 | ;; @r{Moving and deleting the overlay don't change its properties.} | |
1015 | (overlay-get foo 'happy) | |
1016 | @result{} t | |
1017 | @end example | |
1018 | ||
1019 | @node Finding Overlays | |
1020 | @subsection Searching for Overlays | |
1021 | ||
42b85554 | 1022 | @defun overlays-at pos |
2468d0c0 DL |
1023 | This function returns a list of all the overlays that cover the |
1024 | character at position @var{pos} in the current buffer. The list is in | |
1025 | no particular order. An overlay contains position @var{pos} if it | |
1026 | begins at or before @var{pos}, and ends after @var{pos}. | |
1027 | ||
1028 | To illustrate usage, here is a Lisp function that returns a list of the | |
1029 | overlays that specify property @var{prop} for the character at point: | |
1030 | ||
1031 | @smallexample | |
1032 | (defun find-overlays-specifying (prop) | |
1033 | (let ((overlays (overlays-at (point))) | |
1034 | found) | |
1035 | (while overlays | |
1036 | (let ((overlay (cdr overlays))) | |
1037 | (if (overlay-get overlay prop) | |
1038 | (setq found (cons overlay found)))) | |
1039 | (setq overlays (cdr overlays))) | |
1040 | found)) | |
1041 | @end smallexample | |
42b85554 RS |
1042 | @end defun |
1043 | ||
f9f59935 | 1044 | @defun overlays-in beg end |
a9f0a989 | 1045 | @tindex overlays-in |
f9f59935 RS |
1046 | This function returns a list of the overlays that overlap the region |
1047 | @var{beg} through @var{end}. ``Overlap'' means that at least one | |
1048 | character is contained within the overlay and also contained within the | |
1049 | specified region; however, empty overlays are included in the result if | |
2468d0c0 | 1050 | they are located at @var{beg}, or strictly between @var{beg} and @var{end}. |
f9f59935 RS |
1051 | @end defun |
1052 | ||
42b85554 RS |
1053 | @defun next-overlay-change pos |
1054 | This function returns the buffer position of the next beginning or end | |
1055 | of an overlay, after @var{pos}. | |
1056 | @end defun | |
1057 | ||
22697dac KH |
1058 | @defun previous-overlay-change pos |
1059 | This function returns the buffer position of the previous beginning or | |
1060 | end of an overlay, before @var{pos}. | |
1061 | @end defun | |
1062 | ||
2468d0c0 DL |
1063 | Here's an easy way to use @code{next-overlay-change} to search for the |
1064 | next character which gets a non-@code{nil} @code{happy} property from | |
1065 | either its overlays or its text properties (@pxref{Property Search}): | |
1066 | ||
1067 | @smallexample | |
1068 | (defun find-overlay-prop (prop) | |
1069 | (save-excursion | |
1070 | (while (and (not (eobp)) | |
1071 | (not (get-char-property (point) 'happy))) | |
1072 | (goto-char (min (next-overlay-change (point)) | |
1073 | (next-single-property-change (point) 'happy)))) | |
1074 | (point))) | |
1075 | @end smallexample | |
1076 | ||
f9f59935 RS |
1077 | @node Width |
1078 | @section Width | |
1079 | ||
1080 | Since not all characters have the same width, these functions let you | |
969fe9b5 RS |
1081 | check the width of a character. @xref{Primitive Indent}, and |
1082 | @ref{Screen Lines}, for related functions. | |
f9f59935 | 1083 | |
f9f59935 | 1084 | @defun char-width char |
a9f0a989 | 1085 | @tindex char-width |
f9f59935 RS |
1086 | This function returns the width in columns of the character @var{char}, |
1087 | if it were displayed in the current buffer and the selected window. | |
1088 | @end defun | |
1089 | ||
f9f59935 | 1090 | @defun string-width string |
a9f0a989 | 1091 | @tindex string-width |
f9f59935 RS |
1092 | This function returns the width in columns of the string @var{string}, |
1093 | if it were displayed in the current buffer and the selected window. | |
1094 | @end defun | |
1095 | ||
f9f59935 | 1096 | @defun truncate-string-to-width string width &optional start-column padding |
a9f0a989 | 1097 | @tindex truncate-string-to-width |
f9f59935 RS |
1098 | This function returns the part of @var{string} that fits within |
1099 | @var{width} columns, as a new string. | |
1100 | ||
1101 | If @var{string} does not reach @var{width}, then the result ends where | |
1102 | @var{string} ends. If one multi-column character in @var{string} | |
1103 | extends across the column @var{width}, that character is not included in | |
1104 | the result. Thus, the result can fall short of @var{width} but cannot | |
1105 | go beyond it. | |
1106 | ||
1107 | The optional argument @var{start-column} specifies the starting column. | |
1108 | If this is non-@code{nil}, then the first @var{start-column} columns of | |
1109 | the string are omitted from the value. If one multi-column character in | |
1110 | @var{string} extends across the column @var{start-column}, that | |
1111 | character is not included. | |
1112 | ||
1113 | The optional argument @var{padding}, if non-@code{nil}, is a padding | |
1114 | character added at the beginning and end of the result string, to extend | |
1115 | it to exactly @var{width} columns. The padding character is used at the | |
1116 | end of the result if it falls short of @var{width}. It is also used at | |
1117 | the beginning of the result if one multi-column character in | |
1118 | @var{string} extends across the column @var{start-column}. | |
1119 | ||
1120 | @example | |
1121 | (truncate-string-to-width "\tab\t" 12 4) | |
1122 | @result{} "ab" | |
1123 | (truncate-string-to-width "\tab\t" 12 4 ?\ ) | |
1124 | @result{} " ab " | |
1125 | @end example | |
1126 | @end defun | |
1127 | ||
42b85554 RS |
1128 | @node Faces |
1129 | @section Faces | |
1130 | @cindex face | |
1131 | ||
8241495d RS |
1132 | A @dfn{face} is a named collection of graphical attributes: font |
1133 | family, foreground color, background color, optional underlining, and | |
1134 | many others. Faces are used in Emacs to control the style of display of | |
1135 | particular parts of the text or the frame. | |
42b85554 RS |
1136 | |
1137 | @cindex face id | |
969fe9b5 | 1138 | Each face has its own @dfn{face number}, which distinguishes faces at |
8241495d | 1139 | low levels within Emacs. However, for most purposes, you refer to |
42b85554 RS |
1140 | faces in Lisp programs by their names. |
1141 | ||
22697dac KH |
1142 | @defun facep object |
1143 | This function returns @code{t} if @var{object} is a face name symbol (or | |
1144 | if it is a vector of the kind used internally to record face data). It | |
1145 | returns @code{nil} otherwise. | |
1146 | @end defun | |
1147 | ||
42b85554 RS |
1148 | Each face name is meaningful for all frames, and by default it has the |
1149 | same meaning in all frames. But you can arrange to give a particular | |
1150 | face name a special meaning in one frame if you wish. | |
1151 | ||
1152 | @menu | |
1153 | * Standard Faces:: The faces Emacs normally comes with. | |
969fe9b5 | 1154 | * Defining Faces:: How to define a face with @code{defface}. |
8241495d RS |
1155 | * Face Attributes:: What is in a face? |
1156 | * Attribute Functions:: Functions to examine and set face attributes. | |
1157 | * Merging Faces:: How Emacs combines the faces specified for a character. | |
1158 | * Font Selection:: Finding the best available font for a face. | |
42b85554 | 1159 | * Face Functions:: How to define and examine faces. |
8241495d RS |
1160 | * Auto Faces:: Hook for automatic face assignment. |
1161 | * Font Lookup:: Looking up the names of available fonts | |
1162 | and information about them. | |
1163 | * Fontsets:: A fontset is a collection of fonts | |
1164 | that handle a range of character sets. | |
42b85554 RS |
1165 | @end menu |
1166 | ||
1167 | @node Standard Faces | |
1168 | @subsection Standard Faces | |
1169 | ||
8241495d RS |
1170 | This table lists all the standard faces and their uses. Most of them |
1171 | are used for displaying certain parts of the frames or certain kinds of | |
1172 | text; you can control how those places look by customizing these faces. | |
42b85554 RS |
1173 | |
1174 | @table @code | |
1175 | @item default | |
1176 | @kindex default @r{(face name)} | |
1177 | This face is used for ordinary text. | |
1178 | ||
8241495d RS |
1179 | @item mode-line |
1180 | @kindex mode-line @r{(face name)} | |
a40d4712 PR |
1181 | This face is used for mode lines, and for menu bars when toolkit menus |
1182 | are not used---but only if @code{mode-line-inverse-video} is | |
1183 | non-@code{nil}. | |
8241495d | 1184 | |
42b85554 RS |
1185 | @item modeline |
1186 | @kindex modeline @r{(face name)} | |
8241495d RS |
1187 | This is an alias for the @code{mode-line} face, for compatibility with |
1188 | old Emacs versions. | |
1189 | ||
1190 | @item header-line | |
1191 | @kindex header-line @r{(face name)} | |
1192 | This face is used for the header lines of windows that have them. | |
1193 | ||
a40d4712 PR |
1194 | @item menu |
1195 | This face controls the display of menus, both their colors and their | |
1196 | font. (This works only on certain systems.) | |
1197 | ||
8241495d RS |
1198 | @item fringe |
1199 | @kindex fringe @r{(face name)} | |
1200 | This face controls the colors of window fringes, the thin areas on | |
1201 | either side that are used to display continuation and truncation glyphs. | |
1202 | ||
1203 | @item scroll-bar | |
1204 | @kindex scroll-bar @r{(face name)} | |
1205 | This face controls the colors for display of scroll bars. | |
1206 | ||
1207 | @item tool-bar | |
1208 | @kindex tool-bar @r{(face name)} | |
1209 | This face is used for display of the tool bar, if any. | |
42b85554 RS |
1210 | |
1211 | @item region | |
1212 | @kindex region @r{(face name)} | |
1213 | This face is used for highlighting the region in Transient Mark mode. | |
1214 | ||
1215 | @item secondary-selection | |
1216 | @kindex secondary-selection @r{(face name)} | |
1217 | This face is used to show any secondary selection you have made. | |
1218 | ||
1219 | @item highlight | |
1220 | @kindex highlight @r{(face name)} | |
1221 | This face is meant to be used for highlighting for various purposes. | |
1222 | ||
8241495d RS |
1223 | @item trailing-whitespace |
1224 | @kindex trailing-whitespace @r{(face name)} | |
a40d4712 PR |
1225 | This face is used to display excess whitespace at the end of a line, |
1226 | if @code{show-trailing-whitespace} is non-@code{nil}. | |
8241495d | 1227 | @end table |
42b85554 | 1228 | |
8241495d RS |
1229 | In contrast, these faces are provided to change the appearance of text |
1230 | in specific ways. You can use them on specific text, when you want | |
1231 | the effects they produce. | |
1232 | ||
1233 | @table @code | |
42b85554 RS |
1234 | @item bold |
1235 | @kindex bold @r{(face name)} | |
1236 | This face uses a bold font, if possible. It uses the bold variant of | |
1237 | the frame's font, if it has one. It's up to you to choose a default | |
1238 | font that has a bold variant, if you want to use one. | |
1239 | ||
1240 | @item italic | |
1241 | @kindex italic @r{(face name)} | |
1242 | This face uses the italic variant of the frame's font, if it has one. | |
1243 | ||
1244 | @item bold-italic | |
1245 | @kindex bold-italic @r{(face name)} | |
1246 | This face uses the bold italic variant of the frame's font, if it has | |
1247 | one. | |
8241495d RS |
1248 | |
1249 | @item underline | |
1250 | @kindex underline @r{(face name)} | |
1251 | This face underlines text. | |
1252 | ||
1253 | @item fixed-patch | |
1254 | @kindex fixed-patch @r{(face name)} | |
1255 | This face forces use of a particular fixed-width font. | |
1256 | ||
1257 | @item variable-patch | |
1258 | @kindex variable-patch @r{(face name)} | |
1259 | This face forces use of a particular variable-width font. It's | |
a40d4712 | 1260 | reasonable to customize this to use a different variable-width font, if |
8241495d | 1261 | you like, but you should not make it a fixed-width font. |
42b85554 RS |
1262 | @end table |
1263 | ||
a40d4712 PR |
1264 | @defvar show-trailing-whitespace |
1265 | @tindex show-trailing-whitespace | |
1266 | If this variable is non-@code{nil}, Emacs uses the | |
1267 | @code{trailing-whitespace} face to display any spaces and tabs at the | |
1268 | end of a line. | |
1269 | @end defvar | |
1270 | ||
969fe9b5 | 1271 | @node Defining Faces |
a9f0a989 | 1272 | @subsection Defining Faces |
969fe9b5 RS |
1273 | |
1274 | The way to define a new face is with @code{defface}. This creates a | |
1275 | kind of customization item (@pxref{Customization}) which the user can | |
1276 | customize using the Customization buffer (@pxref{Easy Customization,,, | |
1277 | emacs, The GNU Emacs Manual}). | |
1278 | ||
969fe9b5 | 1279 | @defmac defface face spec doc [keyword value]... |
a9f0a989 | 1280 | @tindex defface |
a40d4712 PR |
1281 | This declares @var{face} as a customizable face that defaults according |
1282 | to @var{spec}. You should not quote the symbol @var{face}. The | |
1283 | argument @var{doc} specifies the face documentation. The keywords you | |
1284 | can use in @code{defface} are the same ones that are meaningful in both | |
1285 | @code{defgroup} and @code{defcustom} (@pxref{Common Keywords}). | |
969fe9b5 RS |
1286 | |
1287 | When @code{defface} executes, it defines the face according to | |
a9f0a989 | 1288 | @var{spec}, then uses any customizations that were read from the |
a40d4712 | 1289 | init file (@pxref{Init File}) to override that specification. |
969fe9b5 RS |
1290 | |
1291 | The purpose of @var{spec} is to specify how the face should appear on | |
1292 | different kinds of terminals. It should be an alist whose elements have | |
a40d4712 PR |
1293 | the form @code{(@var{display} @var{atts})}. Each element's @sc{car}, |
1294 | @var{display}, specifies a class of terminals. The element's second element, | |
969fe9b5 RS |
1295 | @var{atts}, is a list of face attributes and their values; it specifies |
1296 | what the face should look like on that kind of terminal. The possible | |
1297 | attributes are defined in the value of @code{custom-face-attributes}. | |
1298 | ||
1299 | The @var{display} part of an element of @var{spec} determines which | |
1300 | frames the element applies to. If more than one element of @var{spec} | |
1301 | matches a given frame, the first matching element is the only one used | |
1302 | for that frame. There are two possibilities for @var{display}: | |
1303 | ||
1304 | @table @asis | |
1305 | @item @code{t} | |
1306 | This element of @var{spec} matches all frames. Therefore, any | |
1307 | subsequent elements of @var{spec} are never used. Normally | |
1308 | @code{t} is used in the last (or only) element of @var{spec}. | |
1309 | ||
a9f0a989 | 1310 | @item a list |
1911e6e5 | 1311 | If @var{display} is a list, each element should have the form |
969fe9b5 RS |
1312 | @code{(@var{characteristic} @var{value}@dots{})}. Here |
1313 | @var{characteristic} specifies a way of classifying frames, and the | |
1314 | @var{value}s are possible classifications which @var{display} should | |
1315 | apply to. Here are the possible values of @var{characteristic}: | |
1316 | ||
1317 | @table @code | |
1318 | @item type | |
1319 | The kind of window system the frame uses---either @code{x}, @code{pc} | |
1320 | (for the MS-DOS console), @code{w32} (for MS Windows 9X/NT), or | |
1321 | @code{tty}. | |
1322 | ||
1323 | @item class | |
1324 | What kinds of colors the frame supports---either @code{color}, | |
1325 | @code{grayscale}, or @code{mono}. | |
1326 | ||
1327 | @item background | |
1911e6e5 | 1328 | The kind of background---either @code{light} or @code{dark}. |
969fe9b5 RS |
1329 | @end table |
1330 | ||
1331 | If an element of @var{display} specifies more than one @var{value} for a | |
1332 | given @var{characteristic}, any of those values is acceptable. If | |
1333 | @var{display} has more than one element, each element should specify a | |
1334 | different @var{characteristic}; then @emph{each} characteristic of the | |
1335 | frame must match one of the @var{value}s specified for it in | |
1336 | @var{display}. | |
1337 | @end table | |
1338 | @end defmac | |
1339 | ||
a40d4712 | 1340 | Here's how the standard face @code{region} is defined: |
969fe9b5 RS |
1341 | |
1342 | @example | |
a40d4712 | 1343 | @group |
969fe9b5 | 1344 | (defface region |
a40d4712 PR |
1345 | `((((type tty) (class color)) |
1346 | (:background "blue" :foreground "white")) | |
1347 | @end group | |
1348 | (((type tty) (class mono)) | |
1349 | (:inverse-video t)) | |
1350 | (((class color) (background dark)) | |
1351 | (:background "blue")) | |
1352 | (((class color) (background light)) | |
1353 | (:background "lightblue")) | |
1354 | (t (:background "gray"))) | |
1355 | @group | |
1356 | "Basic face for highlighting the region." | |
1357 | :group 'basic-faces) | |
1358 | @end group | |
969fe9b5 RS |
1359 | @end example |
1360 | ||
1361 | Internally, @code{defface} uses the symbol property | |
1362 | @code{face-defface-spec} to record the face attributes specified in | |
1363 | @code{defface}, @code{saved-face} for the attributes saved by the user | |
1364 | with the customization buffer, and @code{face-documentation} for the | |
1365 | documentation string. | |
1366 | ||
1911e6e5 RS |
1367 | @tindex frame-background-mode |
1368 | @defopt frame-background-mode | |
1369 | This option, if non-@code{nil}, specifies the background type to use for | |
1370 | interpreting face definitions. If it is @code{dark}, then Emacs treats | |
1371 | all frames as if they had a dark background, regardless of their actual | |
1372 | background colors. If it is @code{light}, then Emacs treats all frames | |
1373 | as if they had a light background. | |
1374 | @end defopt | |
1375 | ||
8241495d RS |
1376 | @node Face Attributes |
1377 | @subsection Face Attributes | |
1378 | @cindex face attributes | |
42b85554 | 1379 | |
8241495d RS |
1380 | The effect of using a face is determined by a fixed set of @dfn{face |
1381 | attributes}. This table lists all the face attributes, and what they | |
a40d4712 PR |
1382 | mean. Note that in general, more than one face can be specified for a |
1383 | given piece of text; when that happens, the attributes of all the faces | |
1384 | are merged to specify how to display the text. @xref{Merging Faces}. | |
42b85554 | 1385 | |
8241495d RS |
1386 | In Emacs 21, any attribute in a face can have the value |
1387 | @code{unspecified}. This means the face doesn't specify that attribute. | |
1388 | In face merging, when the first face fails to specify a particular | |
1389 | attribute, that means the next face gets a chance. However, the | |
1390 | @code{default} face must specify all attributes. | |
42b85554 | 1391 | |
a40d4712 PR |
1392 | Some of these font attributes are meaningful only on certain kinds of |
1393 | displays---if your display cannot handle a certain attribute, the | |
1394 | attribute is ignored. (The attributes @code{:family}, @code{:width}, | |
1395 | @code{:height}, @code{:weight}, and @code{:slant} correspond to parts of | |
1396 | an X Logical Font Descriptor.) | |
42b85554 | 1397 | |
8241495d RS |
1398 | @table @code |
1399 | @item :family | |
1400 | Font family name, or fontset name (@pxref{Fontsets}). If you specify a | |
a40d4712 PR |
1401 | font family name, the wild-card characters @samp{*} and @samp{?} are |
1402 | allowed. | |
8241495d RS |
1403 | |
1404 | @item :width | |
1405 | Relative proportionate width, also known as the character set width or | |
1406 | set width. This should be one of the symbols @code{ultra-condensed}, | |
1407 | @code{extra-condensed}, @code{condensed}, @code{semi-condensed}, | |
1408 | @code{normal}, @code{semi-expanded}, @code{expanded}, | |
1409 | @code{extra-expanded}, or @code{ultra-expanded}. | |
1410 | ||
1411 | @item :height | |
a40d4712 | 1412 | Font height, an integer in units of 1/10 point. |
8241495d RS |
1413 | |
1414 | @item :weight | |
1415 | Font weight---a symbol from this series (from most dense to most faint): | |
1416 | @code{ultra-bold}, @code{extra-bold}, @code{bold}, @code{semi-bold}, | |
1417 | @code{normal}, @code{semi-light}, @code{light}, @code{extra-light}, | |
a40d4712 | 1418 | or @code{ultra-light}. |
66f54605 PR |
1419 | |
1420 | On a text-only terminal, any weight greater than normal is displayed as | |
1421 | extra bright, and any weight less than normal is displayed as | |
1422 | half-bright (This is provided the terminal supports the feature.) | |
1423 | ||
a40d4712 PR |
1424 | On a text-only terminal, any weight greater than normal is displayed as |
1425 | extra bright, and any weight less than normal is displayed as | |
1426 | half-bright (provided the terminal supports the feature). | |
1427 | ||
8241495d RS |
1428 | @item :slant |
1429 | Font slant---one of the symbols @code{italic}, @code{oblique}, @code{normal}, | |
1430 | @code{reverse-italic}, or @code{reverse-oblique}. | |
66f54605 PR |
1431 | |
1432 | On a text-only terminal, slanted text is displayed as half-bright, if | |
1433 | the terminal supports the feature. | |
1434 | ||
8241495d RS |
1435 | @item :foreground |
1436 | Foreground color, a string. | |
1437 | ||
1438 | @item :background | |
1439 | Background color, a string. | |
1440 | ||
1441 | @item :inverse-video | |
1442 | Whether or not characters should be displayed in inverse video. The | |
1443 | value should be @code{t} (yes) or @code{nil} (no). | |
1444 | ||
1445 | @item :stipple | |
a40d4712 | 1446 | The background stipple, a bitmap. |
8241495d | 1447 | |
a40d4712 PR |
1448 | The value can be a string; that should be the name of a file containing |
1449 | external-format X bitmap data. The file is found in the directories | |
1450 | listed in the variable @code{x-bitmap-file-path}. | |
8241495d | 1451 | |
a40d4712 PR |
1452 | Alternatively, the value can specify the bitmap directly, with a list of |
1453 | the form @code{(@var{width} @var{height} @var{data})}. Here, | |
1454 | @var{width} and @var{height} specify the size in pixels, and @var{data} | |
1455 | is a string containing the raw bits of the bitmap, row by row. Each row | |
1456 | occupies @math{(@var{width} + 7) / 8} consecutie bytes in the string | |
1457 | (which should be a unibyte string for best results). | |
8241495d RS |
1458 | |
1459 | If the value is @code{nil}, that means use no stipple pattern. | |
1460 | ||
1461 | Normally you do not need to set the stipple attribute, because it is | |
1462 | used automatically to handle certain shades of gray. | |
1463 | ||
1464 | @item :underline | |
1465 | Whether or not characters should be underlined, and in what color. If | |
1466 | the value is @code{t}, underlining uses the foreground color of the | |
1467 | face. If the value is a string, underlining uses that color. The | |
1468 | value @code{nil} means do not underline. | |
1469 | ||
1470 | @item :overline | |
1471 | Whether or not characters should be overlined, and in what color. | |
1472 | The value is used like that of @code{:underline}. | |
1473 | ||
1474 | @item :strike-through | |
1475 | Whether or not characters should be strike-through, and in what | |
1476 | color. The value is used like that of @code{:underline}. | |
1477 | ||
1478 | @item :box | |
1479 | Whether or not a box should be drawn around characters, its color, the | |
a40d4712 | 1480 | width of the box lines, and 3D appearance. |
8241495d | 1481 | @end table |
42b85554 | 1482 | |
8241495d RS |
1483 | Here are the possible values of the @code{:box} attribute, and what |
1484 | they mean: | |
42b85554 | 1485 | |
8241495d RS |
1486 | @table @asis |
1487 | @item @code{nil} | |
1488 | Don't draw a box. | |
bfe721d1 | 1489 | |
8241495d RS |
1490 | @item @code{t} |
1491 | Draw a box with lines of width 1, in the foreground color. | |
42b85554 | 1492 | |
8241495d RS |
1493 | @item @var{color} |
1494 | Draw a box with lines of width 1, in color @var{color}. | |
42b85554 | 1495 | |
8241495d RS |
1496 | @item @code{(:line-width @var{width} :color @var{color} :style @var{style})} |
1497 | This way you can explicitly specify all aspects of the box. The value | |
1498 | @var{width} specifies the width of the lines to draw; it defaults to 1. | |
42b85554 | 1499 | |
8241495d RS |
1500 | The value @var{color} specifies the color to draw with. The default is |
1501 | the foreground color of the face for simple boxes, and the background | |
1502 | color of the face for 3D boxes. | |
42b85554 | 1503 | |
8241495d RS |
1504 | The value @var{style} specifies whether to draw a 3D box. If it is |
1505 | @code{released-button}, the box looks like a 3D button that is not being | |
1506 | pressed. If it is @code{pressed-button}, the box looks like a 3D button | |
1507 | that is being pressed. If it is @code{nil} or omitted, a plain 2D box | |
1508 | is used. | |
1509 | @end table | |
42b85554 | 1510 | |
8241495d RS |
1511 | The attributes @code{:overline}, @code{:strike-through} and |
1512 | @code{:box} are new in Emacs 21. The attributes @code{:family}, | |
1513 | @code{:height}, @code{:width}, @code{:weight}, @code{:slant} are also | |
a40d4712 PR |
1514 | new; previous versions used the following attributes, now semi-obsolete, |
1515 | to specify some of the same information: | |
42b85554 | 1516 | |
8241495d RS |
1517 | @table @code |
1518 | @item :font | |
a40d4712 | 1519 | This attribute specifies the font name. |
42b85554 | 1520 | |
8241495d RS |
1521 | @item :bold |
1522 | A non-@code{nil} value specifies a bold font. | |
42b85554 | 1523 | |
8241495d RS |
1524 | @item :italic |
1525 | A non-@code{nil} value specifies an italic font. | |
1526 | @end table | |
42b85554 | 1527 | |
8241495d RS |
1528 | For compatibility, you can still set these ``attributes'' in Emacs 21, |
1529 | even though they are not real face attributes. Here is what that does: | |
42b85554 | 1530 | |
8241495d RS |
1531 | @table @code |
1532 | @item :font | |
a40d4712 PR |
1533 | You can specify an X font name as the ``value'' of this ``attribute''; |
1534 | that sets the @code{:family}, @code{:width}, @code{:height}, | |
1535 | @code{:weight}, and @code{:slant} attributes according to the font name. | |
8241495d RS |
1536 | |
1537 | If the value is a pattern with wildcards, the first font that matches | |
1538 | the pattern is used to set these attributes. | |
1539 | ||
1540 | @item :bold | |
1541 | A non-@code{nil} makes the face bold; @code{nil} makes it normal. | |
1542 | This actually works by setting the @code{:weight} attribute. | |
1543 | ||
1544 | @item :italic | |
1545 | A non-@code{nil} makes the face italic; @code{nil} makes it normal. | |
1546 | This actually works by setting the @code{:slant} attribute. | |
1547 | @end table | |
42b85554 | 1548 | |
8241495d RS |
1549 | @defvar x-bitmap-file-path |
1550 | This variable specifies a list of directories for searching | |
1551 | for bitmap files, for the @code{:stipple} attribute. | |
1552 | @end defvar | |
1553 | ||
ea7220f8 | 1554 | @defun bitmap-spec-p object |
a40d4712 PR |
1555 | This returns @code{t} if @var{object} is a valid bitmap |
1556 | specification, suitable for use with @code{:stipple}. | |
1557 | It returns @code{nil} otherwise. | |
1558 | @end defun | |
1559 | ||
8241495d RS |
1560 | @node Attribute Functions |
1561 | @subsection Face Attribute Functions | |
42b85554 RS |
1562 | |
1563 | You can modify the attributes of an existing face with the following | |
1564 | functions. If you specify @var{frame}, they affect just that frame; | |
1565 | otherwise, they affect all frames as well as the defaults that apply to | |
1566 | new frames. | |
1567 | ||
8241495d RS |
1568 | @tindex set-face-attribute |
1569 | @defun set-face-attribute face frame &rest arguments | |
1570 | This function sets one or more attributes of face @var{face} | |
1571 | for frame @var{frame}. If @var{frame} is @code{nil}, it sets | |
1572 | the attribute for all frames, and the defaults for new frames. | |
1573 | ||
1574 | The extra arguments @var{arguments} specify the attributes to set, and | |
1575 | the values for them. They should consist of alternating attribute names | |
a40d4712 | 1576 | (such as @code{:family} or @code{:underline}) and corresponding values. |
8241495d RS |
1577 | Thus, |
1578 | ||
1579 | @example | |
1580 | (set-face-attribute 'foo nil | |
1581 | :width :extended | |
1582 | :weight :bold | |
1583 | :underline "red") | |
1584 | @end example | |
1585 | ||
1586 | @noindent | |
1587 | sets the attributes @code{:width}, @code{:weight} and @code{:underline} | |
1588 | to the corresponding values. | |
1589 | @end defun | |
1590 | ||
1591 | @tindex face-attribute | |
1592 | @defun face-attribute face attribute &optional frame | |
1593 | This returns the value of the @var{attribute} attribute of face | |
1594 | @var{face} on @var{frame}. If @var{frame} is @code{nil}, | |
1595 | that means the selected frame. | |
1596 | ||
1597 | If @var{frame} is @code{t}, the value is the default for | |
1598 | @var{face} for new frames. | |
1599 | ||
1600 | For example, | |
1601 | ||
1602 | @example | |
1603 | (face-attribute 'bold :weight) | |
1604 | @result{} bold | |
1605 | @end example | |
1606 | @end defun | |
1607 | ||
a40d4712 PR |
1608 | The functions above did not exist before Emacs 21. For compatibility |
1609 | with older Emacs versions, you can use the following functions to set | |
8241495d RS |
1610 | and examine the face attributes which existed in those versions. |
1611 | ||
42b85554 RS |
1612 | @defun set-face-foreground face color &optional frame |
1613 | @defunx set-face-background face color &optional frame | |
78608595 RS |
1614 | These functions set the foreground (or background, respectively) color |
1615 | of face @var{face} to @var{color}. The argument @var{color} should be a | |
42b85554 | 1616 | string, the name of a color. |
bfe721d1 KH |
1617 | |
1618 | Certain shades of gray are implemented by stipple patterns on | |
1619 | black-and-white screens. | |
1620 | @end defun | |
1621 | ||
1622 | @defun set-face-stipple face pattern &optional frame | |
1623 | This function sets the background stipple pattern of face @var{face} to | |
1624 | @var{pattern}. The argument @var{pattern} should be the name of a | |
1625 | stipple pattern defined by the X server, or @code{nil} meaning don't use | |
1626 | stipple. | |
1627 | ||
1628 | Normally there is no need to pay attention to stipple patterns, because | |
1629 | they are used automatically to handle certain shades of gray. | |
42b85554 RS |
1630 | @end defun |
1631 | ||
1632 | @defun set-face-font face font &optional frame | |
8241495d RS |
1633 | This function sets the font of face @var{face}. |
1634 | ||
1635 | In Emacs 21, this actually sets the attributes @code{:family}, | |
1636 | @code{:width}, @code{:height}, @code{:weight}, and @code{:slant} | |
1637 | according to the font name @var{font}. | |
1638 | ||
1639 | In Emacs 20, this sets the font attribute. Once you set the font | |
a9f0a989 | 1640 | explicitly, the bold and italic attributes cease to have any effect, |
8241495d | 1641 | because the precise font that you specified is used. |
21cffb83 RS |
1642 | @end defun |
1643 | ||
f9f59935 | 1644 | @defun set-face-bold-p face bold-p &optional frame |
a9f0a989 | 1645 | @tindex set-face-bold-p |
8241495d RS |
1646 | This function specifies whether @var{face} should be bold. If |
1647 | @var{bold-p} is non-@code{nil}, that means yes; @code{nil} means no. | |
1648 | ||
1649 | In Emacs 21, this sets the @code{:weight} attribute. | |
1650 | In Emacs 20, it sets the @code{:bold} attribute. | |
21cffb83 RS |
1651 | @end defun |
1652 | ||
f9f59935 | 1653 | @defun set-face-italic-p face italic-p &optional frame |
a9f0a989 | 1654 | @tindex set-face-italic-p |
8241495d RS |
1655 | This function specifies whether @var{face} should be italic. If |
1656 | @var{italic-p} is non-@code{nil}, that means yes; @code{nil} means no. | |
1657 | ||
1658 | In Emacs 21, this sets the @code{:slant} attribute. | |
1659 | In Emacs 20, it sets the @code{:italic} attribute. | |
42b85554 RS |
1660 | @end defun |
1661 | ||
969fe9b5 RS |
1662 | @defun set-face-underline-p face underline-p &optional frame |
1663 | This function sets the underline attribute of face @var{face}. | |
1664 | Non-@code{nil} means do underline; @code{nil} means don't. | |
1665 | @end defun | |
1666 | ||
42b85554 | 1667 | @defun invert-face face &optional frame |
8241495d RS |
1668 | This function inverts the @code{:inverse-video} attribute of face |
1669 | @var{face}. If the attribute is @code{nil}, this function sets it to | |
1670 | @code{t}, and vice versa. | |
42b85554 RS |
1671 | @end defun |
1672 | ||
1673 | These functions examine the attributes of a face. If you don't | |
1674 | specify @var{frame}, they refer to the default data for new frames. | |
a40d4712 PR |
1675 | They return the symbol @code{unspecified} if the face doesn't define any |
1676 | value for that attribute. | |
42b85554 RS |
1677 | |
1678 | @defun face-foreground face &optional frame | |
1679 | @defunx face-background face &optional frame | |
78608595 RS |
1680 | These functions return the foreground color (or background color, |
1681 | respectively) of face @var{face}, as a string. | |
42b85554 RS |
1682 | @end defun |
1683 | ||
bfe721d1 KH |
1684 | @defun face-stipple face &optional frame |
1685 | This function returns the name of the background stipple pattern of face | |
1686 | @var{face}, or @code{nil} if it doesn't have one. | |
1687 | @end defun | |
1688 | ||
42b85554 RS |
1689 | @defun face-font face &optional frame |
1690 | This function returns the name of the font of face @var{face}. | |
1691 | @end defun | |
1692 | ||
f9f59935 | 1693 | @defun face-bold-p face &optional frame |
a9f0a989 | 1694 | @tindex face-bold-p |
8241495d RS |
1695 | This function returns @code{t} if @var{face} is bold---that is, if it is |
1696 | bolder than normal. It returns @code{nil} otherwise. | |
f9f59935 RS |
1697 | @end defun |
1698 | ||
f9f59935 | 1699 | @defun face-italic-p face &optional frame |
a9f0a989 | 1700 | @tindex face-italic-p |
8241495d RS |
1701 | This function returns @code{t} if @var{face} is italic or oblique, |
1702 | @code{nil} otherwise. | |
f9f59935 RS |
1703 | @end defun |
1704 | ||
969fe9b5 | 1705 | @defun face-underline-p face &optional frame |
8241495d RS |
1706 | This function returns the @code{:underline} attribute of face @var{face}. |
1707 | @end defun | |
1708 | ||
1709 | @defun face-inverse-video-p face &optional frame | |
1710 | This function returns the @code{:inverse-video} attribute of face @var{face}. | |
1711 | @end defun | |
1712 | ||
1713 | @node Merging Faces | |
1714 | @subsection Merging Faces for Display | |
1715 | ||
1716 | Here are the ways to specify which faces to use for display of text: | |
1717 | ||
1718 | @itemize @bullet | |
1719 | @item | |
1720 | With defaults. The @code{default} face is used as the ultimate | |
1721 | default for all text. (In Emacs 19 and 20, the @code{default} | |
1722 | face is used only when no other face is specified.) | |
1723 | ||
1724 | For a mode line or header line, the face @code{modeline} or | |
1725 | @code{header-line} is used just before @code{default}. | |
1726 | ||
1727 | @item | |
1728 | With text properties. A character can have a @code{face} property; if | |
1729 | so, the faces and face attributes specified there apply. @xref{Special | |
1730 | Properties}. | |
1731 | ||
1732 | If the character has a @code{mouse-face} property, that is used instead | |
1733 | of the @code{face} property when the mouse is ``near enough'' to the | |
1734 | character. | |
1735 | ||
1736 | @item | |
1737 | With overlays. An overlay can have @code{face} and @code{mouse-face} | |
1738 | properties too; they apply to all the text covered by the overlay. | |
1739 | ||
1740 | @item | |
1741 | With a region that is active. In Transient Mark mode, the region is | |
1742 | highlighted with the face @code{region} (@pxref{Standard Faces}). | |
1743 | ||
1744 | @item | |
1745 | With special glyphs. Each glyph can specify a particular face | |
1746 | number. @xref{Glyphs}. | |
1747 | @end itemize | |
1748 | ||
1749 | If these various sources together specify more than one face for a | |
1750 | particular character, Emacs merges the attributes of the various faces | |
1751 | specified. The attributes of the faces of special glyphs come first; | |
1752 | then comes the face for region highlighting, if appropriate; | |
1753 | then come attributes of faces from overlays, followed by those from text | |
1754 | properties, and last the default face. | |
1755 | ||
1756 | When multiple overlays cover one character, an overlay with higher | |
1757 | priority overrides those with lower priority. @xref{Overlays}. | |
1758 | ||
1759 | In Emacs 20, if an attribute such as the font or a color is not | |
1760 | specified in any of the above ways, the frame's own font or color is | |
1761 | used. In newer Emacs versions, this cannot happen, because the | |
1762 | @code{default} face specifies all attributes---in fact, the frame's own | |
1763 | font and colors are synonymous with those of the default face. | |
1764 | ||
1765 | @node Font Selection | |
1766 | @subsection Font Selection | |
1767 | ||
1768 | @dfn{Selecting a font} means mapping the specified face attributes for | |
1769 | a character to a font that is available on a particular display. The | |
1770 | face attributes, as determined by face merging, specify most of the | |
1771 | font choice, but not all. Part of the choice depends on what character | |
1772 | it is. | |
1773 | ||
1774 | For multibyte characters, typically each font covers only one | |
1775 | character set. So each character set (@pxref{Character Sets}) specifies | |
1776 | a registry and encoding to use, with the character set's | |
1777 | @code{x-charset-registry} property. Its value is a string containing | |
1778 | the registry and the encoding, with a dash between them: | |
1779 | ||
1780 | @example | |
1781 | (plist-get (charset-plist 'latin-iso8859-1) | |
1782 | 'x-charset-registry) | |
1783 | @result{} "ISO8859-1" | |
1784 | @end example | |
1785 | ||
1786 | Unibyte text does not have character sets, so displaying a unibyte | |
1787 | character takes the registry and encoding from the variable | |
1788 | @code{face-default-registry}. | |
1789 | ||
1790 | @defvar face-default-registry | |
1791 | This variable specifies which registry and encoding to use in choosing | |
1792 | fonts for unibyte characters. The value is initialized at Emacs startup | |
1793 | time from the font the user specified for Emacs. | |
1794 | @end defvar | |
1795 | ||
1796 | If the face specifies a fontset name, that fontset determines a | |
1797 | pattern for fonts of the given charset. If the face specifies a font | |
1798 | family, a font pattern is constructed. | |
1799 | ||
1800 | Emacs tries to find an available font for the given face attributes | |
1801 | and character's registry and encoding. If there is a font that matches | |
1802 | exactly, it is used, of course. The hard case is when no available font | |
1803 | exactly fits the specification. Then Emacs looks for one that is | |
1804 | ``close''---one attribute at a time. You can specify the order | |
1805 | to consider the attributes. | |
1806 | ||
1807 | @defvar face-font-selection-order | |
1808 | @tindex face-font-selection-order | |
1809 | This variable specifies the order of importance of the face attributes | |
1810 | @code{:width}, @code{:height}, @code{:weight}, and @code{:slant}. The | |
1811 | value should be a list containing those four symbols, in order of | |
1812 | decreasing importance. | |
1813 | ||
1814 | Font selection first finds the best available matches for the first | |
1815 | attribute listed; then, among the fonts which are best in that way, it | |
1816 | searches for the best matches in the second attribute, and so on. | |
1817 | ||
1818 | The attributes @code{:weight} and @code{:width} have symbolic values in | |
1819 | a range centered around @code{normal}. Matches that are more extreme | |
1820 | (farther from @code{normal}) are somewhat preferred to matches that are | |
1821 | less extreme (closer to @code{normal}); this is designed to ensure that | |
1822 | non-normal faces contrast with normal ones, whenever possible. | |
1823 | ||
1824 | The default is @code{(:width :height :weight :slant)}, which means first | |
1825 | find the fonts closest to the specified @code{:width}, then---among the | |
1826 | fonts with that width---find a best match for the specified font height, | |
1827 | and so on. | |
1828 | ||
1829 | One example of a case where this variable makes a difference is when the | |
1830 | default font has no italic equivalent. With the default ordering, the | |
1831 | @code{italic} face will use a non-italic font that is similar to the | |
1832 | default one. But if you put @code{:slant} before @code{:height}, the | |
1833 | @code{italic} face will use an italic font, even if its height is not | |
1834 | quite right. | |
1835 | @end defvar | |
1836 | ||
1837 | @defvar face-alternative-font-family-alist | |
1838 | @tindex face-alternative-font-family-alist | |
1839 | This variable lets you specify alternative font families to try, if a | |
1840 | given family is specified and doesn't exist. Each element should have | |
1841 | this form: | |
1842 | ||
1843 | @example | |
1844 | (@var{family} @var{alternate-families}@dots{}) | |
1845 | @end example | |
1846 | ||
1847 | If @var{family} is specified but not available, Emacs will try the other | |
1848 | families given in @var{alternate-families}, one by one, until it finds a | |
1849 | family that does exist. | |
1850 | @end defvar | |
1851 | ||
1852 | Emacs can make use of scalable fonts, but by default it does not use | |
1853 | them, since the use of too many or too big scalable fonts can crash | |
1854 | XFree86 servers. | |
1855 | ||
1856 | @defvar scalable-fonts-allowed | |
1857 | @tindex scalable-fonts-allowed | |
1858 | This variable controls which scalable fonts to use. A value of | |
1859 | @code{nil}, the default, means do not use scalable fonts. @code{t} | |
1860 | means to use any scalable font that seems appropriate for the text. | |
1861 | ||
1862 | Otherwise, the value must be a list of regular expressions. Then a | |
1863 | scalable font is enabled for use if its name matches any regular | |
1864 | expression in the list. For example, | |
1865 | ||
1866 | @example | |
1867 | (setq scalable-fonts-allowed '("muleindian-2$")) | |
1868 | @end example | |
1869 | ||
1870 | @noindent | |
1871 | allows the use of scalable fonts with registry @code{muleindian-2}. | |
1872 | @end example | |
1873 | ||
1874 | @defun clear-face-cache &optional unload-p | |
1875 | @tindex clear-face-cache | |
1876 | This function clears the face cache for all frames. | |
1877 | If @var{unload-p} is non-@code{nil}, that means to unload | |
1878 | all unused fonts as well. | |
1879 | @end defun | |
1880 | ||
1881 | @node Face Functions | |
1882 | @subsection Functions for Working with Faces | |
1883 | ||
1884 | Here are additional functions for creating and working with faces. | |
1885 | ||
1886 | @defun make-face name | |
1887 | This function defines a new face named @var{name}, initially with all | |
1888 | attributes @code{nil}. It does nothing if there is already a face named | |
1889 | @var{name}. | |
1890 | @end defun | |
1891 | ||
1892 | @defun face-list | |
1893 | This function returns a list of all defined face names. | |
1894 | @end defun | |
1895 | ||
1896 | @defun copy-face old-face new-name &optional frame new-frame | |
1897 | This function defines the face @var{new-name} as a copy of the existing | |
1898 | face named @var{old-face}. It creates the face @var{new-name} if that | |
1899 | doesn't already exist. | |
1900 | ||
1901 | If the optional argument @var{frame} is given, this function applies | |
1902 | only to that frame. Otherwise it applies to each frame individually, | |
1903 | copying attributes from @var{old-face} in each frame to @var{new-face} | |
1904 | in the same frame. | |
1905 | ||
1906 | If the optional argument @var{new-frame} is given, then @code{copy-face} | |
1907 | copies the attributes of @var{old-face} in @var{frame} to @var{new-name} | |
1908 | in @var{new-frame}. | |
969fe9b5 RS |
1909 | @end defun |
1910 | ||
bfe721d1 | 1911 | @defun face-id face |
969fe9b5 | 1912 | This function returns the face number of face @var{face}. |
42b85554 RS |
1913 | @end defun |
1914 | ||
f9f59935 | 1915 | @defun face-documentation face |
a9f0a989 | 1916 | @tindex face-documentation |
f9f59935 RS |
1917 | This function returns the documentation string of face @var{face}, or |
1918 | @code{nil} if none was specified for it. | |
1919 | @end defun | |
1920 | ||
42b85554 RS |
1921 | @defun face-equal face1 face2 &optional frame |
1922 | This returns @code{t} if the faces @var{face1} and @var{face2} have the | |
1923 | same attributes for display. | |
1924 | @end defun | |
1925 | ||
1926 | @defun face-differs-from-default-p face &optional frame | |
1927 | This returns @code{t} if the face @var{face} displays differently from | |
a40d4712 PR |
1928 | the default face. A face is considered to be ``the same'' as the |
1929 | default face if each attribute is either the same as that of the default | |
1930 | face, or unspecified (meaning to inherit from the default). | |
1911e6e5 RS |
1931 | @end defun |
1932 | ||
8241495d RS |
1933 | @node Auto Faces |
1934 | @subsection Automatic Face Assignment | |
1935 | @cindex automatic face assignment | |
1936 | @cindex faces, automatic choice | |
1937 | ||
1938 | @cindex Font-Lock mode | |
1939 | Starting with Emacs 21, a hook is available for automatically | |
1940 | assigning faces to text in the buffer. This hook is used for part of | |
1941 | the implementation of Font-Lock mode. | |
1942 | ||
1943 | @tindex fontification-functions | |
1944 | @defvar fontification-functions | |
1945 | This variable holds a list of functions that are called by Emacs | |
1946 | redisplay as needed to assign faces automatically to text in the buffer. | |
1947 | ||
1948 | The functions are called in the order listed, with one argument, a | |
1949 | buffer position @var{pos}. Each function should attempt to assign faces | |
1950 | to the text in the current buffer starting at @var{pos}. | |
1951 | ||
1952 | Each function should record the faces they assign by setting the | |
1953 | @code{face} property. It should also add a non-@code{nil} | |
1954 | @code{fontified} property for all the text it has assigned faces to. | |
1955 | That property tells redisplay that faces have been assigned to that text | |
1956 | already. | |
1957 | ||
1958 | It is probably a good idea for each function to do nothing if the | |
1959 | character after @var{pos} already has a non-@code{nil} @code{fontified} | |
1960 | property, but this is not required. If one function overrides the | |
1961 | assignments made by a previous one, the properties as they are | |
1962 | after the last function finishes are the ones that really matter. | |
1963 | ||
1964 | For efficiency, we recommend writing these functions so that they | |
1965 | usually assign faces to around 400 to 600 characters at each call. | |
1966 | @end defvar | |
1967 | ||
1968 | @node Font Lookup | |
1969 | @subsection Looking Up Fonts | |
1970 | ||
1971 | @defun x-list-fonts pattern &optional face frame maximum | |
1972 | This function returns a list of available font names that match | |
1973 | @var{pattern}. If the optional arguments @var{face} and @var{frame} are | |
1974 | specified, then the list is limited to fonts that are the same size as | |
1975 | @var{face} currently is on @var{frame}. | |
1976 | ||
1977 | The argument @var{pattern} should be a string, perhaps with wildcard | |
1978 | characters: the @samp{*} character matches any substring, and the | |
1979 | @samp{?} character matches any single character. Pattern matching | |
1980 | of font names ignores case. | |
1981 | ||
1982 | If you specify @var{face} and @var{frame}, @var{face} should be a face name | |
1983 | (a symbol) and @var{frame} should be a frame. | |
1984 | ||
1985 | The optional argument @var{maximum} sets a limit on how many fonts to | |
1986 | return. If this is non-@code{nil}, then the return value is truncated | |
1987 | after the first @var{maximum} matching fonts. Specifying a small value | |
1988 | for @var{maximum} can make this function much faster, in cases where | |
1989 | many fonts match the pattern. | |
1990 | @end defun | |
1991 | ||
1992 | These additional functions are available starting in Emacs 21. | |
1993 | ||
1994 | @defun x-family-fonts &optional family frame | |
1995 | @tindex x-family-fonts | |
1996 | This function returns a list describing the available fonts for family | |
1997 | @var{family} on @var{frame}. If @var{family} is omitted or @code{nil}, | |
1998 | this list applies to all families, and therefore, it contains all | |
1999 | available fonts. Otherwise, @var{family} must be a string; it may | |
2000 | contain the wildcards @samp{?} and @samp{*}. | |
2001 | ||
2002 | The list describes the display that @var{frame} is on; if @var{frame} is | |
2003 | omitted or @code{nil}, it applies to the selected frame's display. | |
2004 | ||
2005 | The list contains a vector of the following form for each font: | |
2006 | ||
2007 | @example | |
2008 | [@var{family} @var{width} @var{point-size} @var{weight} @var{slant} | |
2009 | @var{fixed-p} @var{full} @var{registry-and-encoding}] | |
2010 | @end example | |
2011 | ||
2012 | The first five elements correspond to face attributes; if you | |
2013 | specify these attributes for a face, it will use this font. | |
2014 | ||
2015 | The last three elements give additional information about the font. | |
2016 | @var{fixed-p} is non-nil if the font is fixed-pitch. @var{full} is the | |
2017 | full name of the font, and @var{registry-and-encoding} is a string | |
2018 | giving the registry and encoding of the font. | |
2019 | ||
2020 | The result list is sorted according to the current face font sort order. | |
2021 | @end defun | |
2022 | ||
2023 | @defun x-font-family-list &optional frame | |
2024 | @tindex x-font-family-list | |
2025 | This function returns a list of the font families available for | |
2026 | @var{frame}'s display. If @var{frame} is omitted or @code{nil}, it | |
2027 | describes the selected frame's display. | |
2028 | ||
2029 | The value is a list of elements of this form: | |
2030 | ||
2031 | @example | |
2032 | (@var{family} . @var{fixed-p}) | |
2033 | @end example | |
2034 | ||
2035 | @noindent | |
2036 | Here @var{family} is a font family, and @var{fixed-p} is | |
2037 | non-@code{nil} if fonts of that family are fixed-pitch. | |
2038 | @end defun | |
2039 | ||
2040 | @defvar font-list-limit | |
2041 | @tindex font-list-limit | |
2042 | This variable specifies maximum number of fonts to consider in font | |
2043 | matching. The function @code{x-family-fonts} will not return more than | |
2044 | that many fonts, and font selection will consider only that many fonts | |
2045 | when searching a matching font for face attributes. The default is | |
2046 | currently 100. | |
2047 | @end defvar | |
2048 | ||
2049 | @node Fontsets | |
2050 | @subsection Fontsets | |
2051 | ||
2052 | A @dfn{fontset} is a list of fonts, each assigned to a range of | |
2053 | character codes. An individual font cannot display the whole range of | |
2054 | characters that Emacs supports, but a fontset can. Fontsets have names, | |
2055 | just as fonts do, and you can use a fontset name in place of a font name | |
2056 | when you specify the ``font'' for a frame or a face. Here is | |
2057 | information about defining a fontset under Lisp program control. | |
2058 | ||
2059 | @defun create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror | |
2060 | This function defines a new fontset according to the specification | |
2061 | string @var{fontset-spec}. The string should have this format: | |
2062 | ||
2063 | @smallexample | |
2064 | @var{fontpattern}, @r{[}@var{charsetname}:@var{fontname}@r{]@dots{}} | |
2065 | @end smallexample | |
2066 | ||
2067 | @noindent | |
2068 | Whitespace characters before and after the commas are ignored. | |
2069 | ||
2070 | The first part of the string, @var{fontpattern}, should have the form of | |
2071 | a standard X font name, except that the last two fields should be | |
2072 | @samp{fontset-@var{alias}}. | |
2073 | ||
2074 | The new fontset has two names, one long and one short. The long name is | |
2075 | @var{fontpattern} in its entirety. The short name is | |
2076 | @samp{fontset-@var{alias}}. You can refer to the fontset by either | |
2077 | name. If a fontset with the same name already exists, an error is | |
2078 | signaled, unless @var{noerror} is non-@code{nil}, in which case this | |
2079 | function does nothing. | |
2080 | ||
2081 | If optional argument @var{style-variant-p} is non-@code{nil}, that says | |
2082 | to create bold, italic and bold-italic variants of the fontset as well. | |
2083 | These variant fontsets do not have a short name, only a long one, which | |
2084 | is made by altering @var{fontpattern} to indicate the bold or italic | |
2085 | status. | |
2086 | ||
2087 | The specification string also says which fonts to use in the fontset. | |
2088 | See below for the details. | |
2089 | @end defun | |
2090 | ||
2091 | The construct @samp{@var{charset}:@var{font}} specifies which font to | |
2092 | use (in this fontset) for one particular character set. Here, | |
2093 | @var{charset} is the name of a character set, and @var{font} is the font | |
2094 | to use for that character set. You can use this construct any number of | |
2095 | times in the specification string. | |
2096 | ||
2097 | For the remaining character sets, those that you don't specify | |
2098 | explicitly, Emacs chooses a font based on @var{fontpattern}: it replaces | |
2099 | @samp{fontset-@var{alias}} with a value that names one character set. | |
2100 | For the @sc{ascii} character set, @samp{fontset-@var{alias}} is replaced | |
2101 | with @samp{ISO8859-1}. | |
2102 | ||
2103 | In addition, when several consecutive fields are wildcards, Emacs | |
2104 | collapses them into a single wildcard. This is to prevent use of | |
2105 | auto-scaled fonts. Fonts made by scaling larger fonts are not usable | |
2106 | for editing, and scaling a smaller font is not useful because it is | |
2107 | better to use the smaller font in its own size, which Emacs does. | |
2108 | ||
2109 | Thus if @var{fontpattern} is this, | |
2110 | ||
2111 | @example | |
2112 | -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24 | |
2113 | @end example | |
2114 | ||
2115 | @noindent | |
2116 | the font specification for ASCII characters would be this: | |
2117 | ||
2118 | @example | |
2119 | -*-fixed-medium-r-normal-*-24-*-ISO8859-1 | |
2120 | @end example | |
2121 | ||
2122 | @noindent | |
2123 | and the font specification for Chinese GB2312 characters would be this: | |
2124 | ||
2125 | @example | |
2126 | -*-fixed-medium-r-normal-*-24-*-gb2312*-* | |
2127 | @end example | |
2128 | ||
2129 | You may not have any Chinese font matching the above font | |
2130 | specification. Most X distributions include only Chinese fonts that | |
2131 | have @samp{song ti} or @samp{fangsong ti} in the @var{family} field. In | |
2132 | such a case, @samp{Fontset-@var{n}} can be specified as below: | |
2133 | ||
2134 | @smallexample | |
2135 | Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\ | |
2136 | chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-* | |
2137 | @end smallexample | |
2138 | ||
2139 | @noindent | |
2140 | Then, the font specifications for all but Chinese GB2312 characters have | |
2141 | @samp{fixed} in the @var{family} field, and the font specification for | |
2142 | Chinese GB2312 characters has a wild card @samp{*} in the @var{family} | |
2143 | field. | |
2144 | ||
2145 | @node Display Property | |
2146 | @section The @code{display} Property | |
2147 | @cindex display specification | |
2148 | @kindex display @r{(text property)} | |
2149 | ||
a40d4712 PR |
2150 | The @code{display} text property (or overlay property) is used to |
2151 | insert images into text, and also control other aspects of how text | |
2152 | displays. These features are available starting in Emacs 21. The value | |
2153 | of the @code{display} property should be a display specification, or a | |
2154 | list or vector containing several display specifications. The rest of | |
2155 | this section describes several kinds of display specifications and what | |
2156 | they mean. | |
8241495d RS |
2157 | |
2158 | @menu | |
a40d4712 PR |
2159 | * Specified Space:: Displaying one space with a specified width. |
2160 | * Other Display Specs:: Displaying an image; magnifying text; moving it | |
2161 | up or down on the page; adjusting the width | |
2162 | of spaces within text. | |
2163 | * Display Margins:: Displaying text or images to the side of the main text. | |
2164 | * Conditional Display:: Making any of the above features conditional | |
2165 | depending on some Lisp expression. | |
8241495d RS |
2166 | @end menu |
2167 | ||
2168 | @node Specified Space | |
2169 | @subsection Specified Spaces | |
2170 | @cindex spaces, specified height or width | |
2171 | @cindex specified spaces | |
2172 | @cindex variable-width spaces | |
2173 | ||
2174 | To display a space of specified width and/or height, use a display | |
a40d4712 PR |
2175 | specification of the form @code{(space . @var{props})}, where |
2176 | @var{props} is a property list (a list of alternating properties and | |
2177 | values). You can put this property on one or more consecutive | |
2178 | characters; a space of the specified height and width is displayed in | |
2179 | place of @emph{all} of those characters. These are the properties you | |
2180 | can use to specify the weight of the space: | |
8241495d RS |
2181 | |
2182 | @table @code | |
2183 | @item :width @var{width} | |
2184 | Specifies that the space width should be @var{width} times the normal | |
2185 | character width. @var{width} can be an integer or floating point | |
2186 | number. | |
2187 | ||
2188 | @item :relative-width @var{factor} | |
2189 | Specifies that the width of the stretch should be computed from the | |
2190 | first character in the group of consecutive characters that have the | |
2191 | same @code{display} property. The space width is the width of that | |
2192 | character, multiplied by @var{factor}. | |
2193 | ||
2194 | @item :align-to @var{hpos} | |
2195 | Specifies that the space should be wide enough to reach @var{hpos}. The | |
a40d4712 PR |
2196 | value @var{hpos} is measured in units of the normal character width. It |
2197 | may be an interer or a floating point number. | |
8241495d RS |
2198 | @end table |
2199 | ||
2200 | Exactly one of the above properties should be used. You can also | |
2201 | specify the height of the space, with other properties: | |
2202 | ||
2203 | @table @code | |
2204 | @item :height @var{height} | |
2205 | Specifies the height of the space, as @var{height}, | |
2206 | measured in terms of the normal line height. | |
2207 | ||
2208 | @item :relative-height @var{factor} | |
2209 | Specifies the height of the space, multiplying the ordinary height | |
2210 | of the text having this display specification by @var{factor}. | |
2211 | ||
2212 | @item :ascent @var{ascent} | |
2213 | Specifies that @var{ascent} percent of the height of the space should be | |
a40d4712 PR |
2214 | considered as the ascent of the space---that is, the part above the |
2215 | baseline. The value of @var{ascent} must be a non-negative number no | |
2216 | greater than 100. | |
8241495d RS |
2217 | @end table |
2218 | ||
2219 | You should not use both @code{:height} and @code{:relative-height} | |
2220 | together. | |
2221 | ||
2222 | @node Other Display Specs | |
2223 | @subsection Other Display Specifications | |
2224 | ||
2225 | @table @code | |
2226 | @item (image . @var{image-props}) | |
2227 | This is in fact an image descriptor (@pxref{Images}). When used as a | |
2228 | display specification, it means to display the image instead of the text | |
2229 | that has the display specification. | |
2230 | ||
2231 | @item (space-width @var{factor}) | |
a40d4712 PR |
2232 | This display specification affects all the space characters within the |
2233 | text that has the specification. It displays all of these spaces | |
2234 | @var{factor} times as wide as normal. The element @var{factor} should | |
2235 | be an integer or float. Characters other than spaces are not affected | |
2236 | at all; in particular, this has no effect on tab characters. | |
8241495d RS |
2237 | |
2238 | @item (height @var{height}) | |
2239 | This display specification makes the text taller or shorter. | |
2240 | Here are the possibilities for @var{height}: | |
2241 | ||
2242 | @table @asis | |
2243 | @item @code{(+ @var{n})} | |
2244 | This means to use a font that is @var{n} steps larger. A ``step'' is | |
a40d4712 PR |
2245 | defined by the set of available fonts---specifically, those that match |
2246 | what was otherwise specified for this text, in all attributes except | |
2247 | height. Each size for which a suitable font is available counts as | |
2248 | another step. @var{n} should be an integer. | |
8241495d RS |
2249 | |
2250 | @item @code{(- @var{n})} | |
2251 | This means to use a font that is @var{n} steps smaller. | |
2252 | ||
2253 | @item a number, @var{factor} | |
2254 | A number, @var{factor}, means to use a font that is @var{factor} times | |
2255 | as tall as the default font. | |
2256 | ||
2257 | @item a symbol, @var{function} | |
2258 | A symbol is a function to compute the height. It is called with the | |
2259 | current height as argument, and should return the new height to use. | |
2260 | ||
2261 | @item anything else, @var{form} | |
2262 | If the @var{height} value doesn't fit the previous possibilities, it is | |
2263 | a form. Emacs evaluates it to get the new height, with the symbol | |
2264 | @code{height} bound to the current specified font height. | |
2265 | @end table | |
2266 | ||
2267 | @item (raise @var{factor}) | |
2268 | This kind of display specification raises or lowers the text | |
2269 | it applies to, relative to the baseline of the line. | |
2270 | ||
2271 | @var{factor} must be a number, which is interpreted as a multiple of the | |
2272 | height of the affected text. If it is positive, that means to display | |
2273 | the characters raised. If it is negative, that means to display them | |
2274 | lower down. | |
2275 | ||
2276 | If the text also has a @code{height} display specification, that does | |
2277 | not affect the amount of raising or lowering, which is based on the | |
2278 | faces used for the text. | |
2279 | @end table | |
2280 | ||
2281 | @node Display Margins | |
2282 | @subsection Displaying in the Margins | |
2283 | @cindex display margins | |
2284 | @cindex margins, display | |
2285 | ||
2286 | A buffer can have blank areas called @dfn{display margins} on the left | |
2287 | and on the right. Ordinary text never appears in these areas, but you | |
2288 | can put things into the display margins using the @code{display} | |
2289 | property. | |
2290 | ||
2291 | To put text in the left or right display margin of the window, use a | |
2292 | display specification of the form @code{(margin right-margin)} or | |
2293 | @code{(margin left-margin)} on it. To put an image in a display margin, | |
2294 | use that display specification along with the display specification for | |
2295 | the image. | |
2296 | ||
2297 | Before the display margins can display anything, you must give | |
2298 | them a nonzero width. The usual way to do that is to set these | |
2299 | variables: | |
2300 | ||
2301 | @defvar left-margin-width | |
2302 | @tindex left-margin-width | |
2303 | This variable specifies the width of the left margin. | |
2304 | It is buffer-local in all buffers. | |
2305 | @end defvar | |
2306 | ||
2307 | @defvar right-margin-width | |
2308 | @tindex right-margin-width | |
2309 | This variable specifies the width of the right margin. | |
2310 | It is buffer-local in all buffers. | |
2311 | @end defvar | |
2312 | ||
2313 | Setting these variables does not immediately affect the window. These | |
2314 | variables are checked when a new buffer is displayed in the window. | |
2315 | Thus, you can make changes take effect by calling | |
2316 | @code{set-window-buffer}. | |
2317 | ||
2318 | You can also set the margin widths immediately. | |
2319 | ||
2320 | @defun set-window-margins window left right | |
2321 | @tindex set-window-margins | |
2322 | This function specifies the margin widths for window @var{window}. | |
2323 | The argument @var{left} controls the left margin and | |
2324 | @var{right} controls the right margin. | |
2325 | @end defun | |
2326 | ||
2327 | @defun window-margins &optional window | |
2328 | @tindex window-margins | |
2329 | This function returns the left and right margins of @var{window} | |
2330 | as a cons cell of the form @code{(@var{left} . @var{right})}. | |
2331 | If @var{window} is @code{nil}, the selected window is used. | |
2332 | @end defun | |
2333 | ||
2334 | @node Conditional Display | |
2335 | @subsection Conditional Display Specifications | |
2336 | @cindex conditional display specifications | |
2337 | ||
2338 | You can make any display specification conditional. To do that, | |
2339 | package it in another list of the form @code{(when @var{condition} | |
2340 | @var{spec})}. Then the specification @var{spec} applies only when | |
2341 | @var{condition} evaluates to a non-@code{nil} value. During the | |
2342 | evaluation, point is temporarily set at the end position of the text | |
2343 | having this conditional display specification. | |
2344 | ||
2345 | @node Images | |
2346 | @section Images | |
2347 | @cindex images in buffers | |
2348 | ||
2349 | To display an image in an Emacs buffer, you must first create an image | |
2350 | descriptor, then use it as a display specifier in the @code{display} | |
2351 | property of text that is displayed (@pxref{Display Property}). Like the | |
2352 | @code{display} property, this feature is available starting in Emacs 21. | |
2353 | ||
2354 | Emacs can display a number of different image formats; some of them | |
2355 | are supported only if particular support libraries are installed on your | |
2356 | machine. The supported image formats include XBM, XPM (needing the | |
2357 | libraries @code{libXpm} version 3.4k and @code{libz}), GIF (needing | |
2358 | @code{libungif} 4.1.0), Postscript, PBM, JPEG (needing the | |
2359 | @code{libjpeg} library version v6a), TIFF (needing @code{libtiff} v3.4), | |
2360 | and PNG (needing @code{libpng} 1.0.2). | |
2361 | ||
2362 | You specify one of these formats with an image type symbol. The image | |
2363 | type symbols are @code{xbm}, @code{xpm}, @code{gif}, @code{postscript}, | |
2364 | @code{pbm}, @code{jpeg}, @code{tiff}, and @code{png}. | |
2365 | ||
2366 | @defvar image-types | |
2367 | This variable contains a list of those image type symbols that are | |
2368 | supported in the current configuration. | |
2369 | @end defvar | |
2370 | ||
2371 | @menu | |
a40d4712 PR |
2372 | * Image Descriptors:: How to specify an image for use in @code{:display}. |
2373 | * XBM Images:: Special features for XBM format. | |
2374 | * XPM Images:: Special features for XPM format. | |
2375 | * GIF Images:: Special features for GIF format. | |
2376 | * Postscript Images:: Special features for Postscript format. | |
2377 | * Other Image Types:: Various other formats are supported. | |
2378 | * Defining Images:: Convenient ways to define an image for later use. | |
2379 | * Showing Images:: Convenient ways to display an image once it is defined. | |
2380 | * Image Cache:: Internal mechanisms of image display. | |
8241495d RS |
2381 | @end menu |
2382 | ||
2383 | @node Image Descriptors | |
2384 | @subsection Image Descriptors | |
2385 | @cindex image descriptor | |
2386 | ||
2387 | An image description is a list of the form @code{(image | |
2388 | . @var{props})}, where @var{props} is a property list containing | |
2389 | alternating keyword symbols (symbols whose names start with a colon) and | |
14ac7224 GM |
2390 | their values. You can use any Lisp object as a property, but the only |
2391 | properties that have any special meaning are certain symbols, all of | |
2392 | them keywords. | |
2393 | ||
2394 | Every image descriptor must contain the property @code{:type | |
2395 | @var{type}} to specify the format of the image. The value of @var{type} | |
2396 | should be an image type symbol; for example, @code{xpm} for an image in | |
2397 | XPM format. | |
8241495d RS |
2398 | |
2399 | Here is a list of other properties that are meaningful for all image | |
2400 | types: | |
2401 | ||
2402 | @table @code | |
2403 | @item :ascent @var{ascent} | |
2404 | The @code{:ascent} property specifies the percentage of the image's | |
2405 | height to use for its ascent---that is, the part above the baseline. The | |
2406 | value, @var{ascent}, must be a number in the range 0 to 100. If this | |
2407 | property is omitted, it defaults to 50. | |
2408 | ||
2409 | @item :margin @var{margin} | |
2410 | The @code{:margin} property specifies how many pixels to add as an extra | |
2411 | margin around the image. The value, @var{margin}, must be a | |
2412 | non-negative number; if it is not specified, the default is zero. | |
2413 | ||
2414 | @item :relief @var{relief} | |
2415 | The @code{:relief} property, if non-@code{nil}, adds a shadow rectangle | |
2416 | around the image. The value, @var{relief}, specifies the width of the | |
2417 | shadow lines, in pixels. If @var{relief} is negative, shadows are drawn | |
2418 | so that the image appears as a pressed button; otherwise, it appears as | |
2419 | an unpressed button. | |
2420 | ||
2421 | @item :algorithm @var{algorithm} | |
2422 | The @code{:algorithm} property, if non-@code{nil}, specifies a | |
2423 | conversion algorithm that should be applied to the image before it is | |
2424 | displayed; the value, @var{algorithm}, specifies which algorithm. | |
2425 | ||
2426 | Currently, the only meaningful value for @var{algorithm} (aside from | |
2427 | @code{nil}) is @code{laplace}; this applies the Laplace edge detection | |
2428 | algorithm, which blurs out small differences in color while highlighting | |
2429 | larger differences. People sometimes consider this useful for | |
2430 | displaying the image for a ``disabled'' button. | |
2431 | ||
2432 | @item :heuristic-mask @var{transparent-color} | |
2433 | The @code{:heuristic-mask} property, if non-@code{nil}, specifies that a | |
2434 | certain color in the image should be transparent. Each pixel where this | |
2435 | color appears will actually allow the frame's background to show | |
2436 | through. | |
2437 | ||
2438 | If @var{transparent-color} is @code{t}, then determine the transparent | |
2439 | color by looking at the four corners of the image. This uses the color | |
2440 | that occurs most frequently near the corners as the transparent color. | |
2441 | ||
2442 | Otherwise, @var{heuristic-mask} should specify the transparent color | |
2443 | directly, as a list of three integers in the form @code{(@var{red} | |
2444 | @var{green} @var{blue})}. | |
2445 | ||
2446 | @item :file @var{file} | |
2447 | The @code{:file} property specifies to load the image from file | |
2448 | @var{file}. If @var{file} is not an absolute file name, it is expanded | |
2449 | in @code{data-directory}. | |
2450 | ||
2451 | @item :data @var{data} | |
2452 | The @code{:data} property specifies the actual contents of the image. | |
2453 | Each image must use either @code{:data} or @code{:file}, but not both. | |
2454 | However, only certain image types support @code{:data}; for other types, | |
2455 | you must use @code{:file}. | |
2456 | ||
2457 | The formats that support @code{:data} include XBM and XPM. | |
2458 | Before using @code{:data}, see the section describing the specific | |
2459 | format you wish to use for further information. | |
2460 | @end table | |
2461 | ||
2462 | @node XBM Images | |
2463 | @subsection XBM Images | |
2464 | @cindex XBM | |
2465 | ||
2466 | To use XBM format, specify @code{xbm} as the image type. This image | |
2467 | format doesn't require an external library, so images of this type are | |
2468 | always supported. | |
2469 | ||
2470 | Additional image properties supported for the @code{xbm} image type are: | |
2471 | ||
2472 | @table @code | |
2473 | @item :foreground @var{foreground} | |
2474 | The value, @var{foreground}, should be a string specifying the image | |
2475 | foreground color. This color is used for each pixel in the XBM that is | |
2476 | 1. The default is the frame's foreground color. | |
2477 | ||
2478 | @item :background @var{background} | |
2479 | The value, @var{background}, should be a string specifying the image | |
2480 | background color. This color is used for each pixel in the XBM that is | |
2481 | 0. The default is the frame's background color. | |
2482 | @end table | |
2483 | ||
2484 | You can specify an XBM image using data within Emacs instead | |
2485 | of an external file. To do this, don't use @code{:file}; instead, | |
2486 | use the following three properties (all of them): | |
2487 | ||
2488 | @table @code | |
2489 | @item :width @var{width} | |
2490 | The value, @var{width}, specifies the width the image in pixels. | |
2491 | ||
2492 | @item :height @var{height} | |
2493 | The value, @var{height}, specifies the height of the image in pixels. | |
2494 | ||
2495 | @item :data @var{data} | |
2496 | The value, @var{data}, is normally a string or a bool-vector. Either | |
2497 | way, it must contain enough bits for the area of the image: at least | |
2498 | @var{width} * @code{height}. | |
2499 | ||
2500 | Alternatively, @var{data} can be a vector of strings or bool-vectors, | |
2501 | each specifying one line of the image. | |
2502 | @end table | |
2503 | ||
2504 | @node XPM Images | |
2505 | @subsection XPM Images | |
2506 | @cindex XPM | |
2507 | ||
2508 | To use XPM format, specify @code{xpm} as the image type. These | |
2509 | additional image properties are meaningful with the @code{xpm} image | |
2510 | type: | |
2511 | ||
2512 | @table @code | |
2513 | @item :color-symbols @var{symbols} | |
2514 | The value, @var{symbols}, should be an alist whose elements have the | |
2515 | form @code{(@var{name} . @var{color})}. In each element, @var{name} is | |
2516 | the name of a color as it appears in the image file, and @var{color} | |
2517 | specifies the actual color to use for displaying that name. | |
2518 | ||
2519 | @item :data @var{data} | |
2520 | XPM images can be displayed from data instead of files. In that case, | |
2521 | use the @code{:data} property instead of the @code{:file} property. | |
2522 | ||
2523 | The value @var{data} must be a string containing an XPM image. The | |
2524 | contents of the string have same format as an external XPM file. | |
2525 | @end table | |
2526 | ||
2527 | @node GIF Images | |
2528 | @subsection GIF Images | |
2529 | @cindex GIF | |
2530 | ||
2531 | For GIF images, specify image type @code{gif}. Because of the patents | |
2532 | in the US covering the LZW algorithm, the continued use of GIF format is | |
2533 | a problem for the whole Internet; to end this problem, it is a good idea | |
2534 | for everyone, even outside the US, to stop using GIFS right away | |
2535 | (@uref{http://www.burnallgifs.org/}). But if you still want to use | |
2536 | them, Emacs can display them. | |
2537 | ||
2538 | @table @code | |
2539 | @item :index @var{index} | |
2540 | You can use @code{:index} to specify one image from a GIF file that | |
2541 | contains more than one image. This property specifies use of image | |
2542 | number @var{index} from the file. An error is signaled if the GIF file | |
2543 | doesn't contain an image with index @var{index}. | |
2544 | @end table | |
2545 | ||
2546 | @ignore | |
2547 | This could be used to implement limited support for animated GIFs. | |
2548 | For example, the following function displays a multi-image GIF file | |
2549 | at point-min in the current buffer, switching between sub-images | |
2550 | every 0.1 seconds. | |
2551 | ||
2552 | (defun show-anim (file max) | |
2553 | "Display multi-image GIF file FILE which contains MAX subimages." | |
2554 | (display-anim (current-buffer) file 0 max t)) | |
2555 | ||
2556 | (defun display-anim (buffer file idx max first-time) | |
2557 | (when (= idx max) | |
2558 | (setq idx 0)) | |
2559 | (let ((img (create-image file nil :image idx))) | |
2560 | (save-excursion | |
2561 | (set-buffer buffer) | |
2562 | (goto-char (point-min)) | |
2563 | (unless first-time (delete-char 1)) | |
2564 | (insert-image img)) | |
2565 | (run-with-timer 0.1 nil 'display-anim buffer file (1+ idx) max nil))) | |
2566 | @end ignore | |
2567 | ||
2568 | @node Postscript Images | |
2569 | @subsection Postscript Images | |
2570 | @cindex Postscript images | |
2571 | ||
2572 | To use Postscript for an image, specify image type @code{postscript}. | |
2573 | This works only if you have Ghostscript installed. You must always use | |
2574 | these three properties: | |
2575 | ||
2576 | @table @code | |
2577 | @item :pt-width @var{width} | |
2578 | The value, @var{width}, specifies the width of the image measured in | |
2579 | points (1/72 inch). @var{width} must be an integer. | |
2580 | ||
2581 | @item :pt-height @var{height} | |
2582 | The value, @var{height}, specifies the height of the image in points | |
2583 | (1/72 inch). @var{height} must be an integer. | |
2584 | ||
2585 | @item :bounding-box @var{box} | |
2586 | The value, @var{box}, must be a list or vector of four integers, which | |
2587 | specifying the bounding box of the Postscript image, analogous to the | |
2588 | @samp{BoundingBox} comment found in Postscript files. | |
2589 | ||
2590 | @example | |
2591 | %%BoundingBox: 22 171 567 738 | |
2592 | @end example | |
2593 | @end table | |
2594 | ||
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 | ||
2602 | For JPEG images, specify image type @code{jpeg}. There are no | |
2603 | additional image properties defined. | |
2604 | ||
2605 | For TIFF images, specify image type @code{tiff}. | |
2606 | ||
2607 | For PNG images, specify image type @code{png}. | |
2608 | ||
2609 | @node Defining Images | |
2610 | @subsection Defining Images | |
2611 | ||
2612 | The functions @code{create-image} and @code{defimage} provide | |
2613 | convenient ways to create image descriptors. | |
2614 | ||
2615 | @defun create-image file &optional type &rest props | |
2616 | @tindex create-image | |
2617 | This function creates and returns an image descriptor which uses the | |
2618 | data in @var{file}. | |
2619 | ||
2620 | The optional argument @var{type} is a symbol specifying the image type. | |
2621 | If @var{type} is omitted or @code{nil}, @code{create-image} tries to | |
2622 | determine the image type from the file's first few bytes, or else | |
2623 | from the file's name. | |
2624 | ||
2625 | The remaining arguments, @var{props}, specify additional image | |
2626 | properties---for example, | |
2627 | ||
2628 | @example | |
2629 | (create-image "foo.xpm" 'xpm :heuristic-mask t) | |
2630 | @end example | |
2631 | ||
2632 | The function returns @code{nil} if images of this type are not | |
2633 | supported. Otherwise it returns an image descriptor. | |
2634 | @end defun | |
2635 | ||
2636 | @defmac defimage variable doc &rest specs | |
2637 | @tindex defimage | |
2638 | This macro defines @var{variable} as an image name. The second argument, | |
2639 | @var{doc}, is an optional documentation string. The remaining | |
2640 | arguments, @var{specs}, specify alternative ways to display the image. | |
2641 | ||
2642 | Each argument in @var{specs} has the form of a property list, and each | |
2643 | one should specify at least the @code{:type} property and the | |
2644 | @code{:file} property. Here is an example: | |
2645 | ||
a40d4712 PR |
2646 | @example |
2647 | (defimage test-image | |
2648 | '((:type xpm :file "~/test1.xpm") | |
2649 | (:type xbm :file "~/test1.xbm"))) | |
2650 | @end example | |
8241495d RS |
2651 | |
2652 | @code{defimage} tests each argument, one by one, to see if it is | |
2653 | usable---that is, if the type is supported and the file exists. The | |
2654 | first usable argument is used to make an image descriptor which is | |
2655 | stored in the variable @var{variable}. | |
2656 | ||
2657 | If none of the alternatives will work, then @var{variable} is defined | |
2658 | as @code{nil}. | |
2659 | @end defmac | |
2660 | ||
2661 | @node Showing Images | |
2662 | @subsection Showing Images | |
2663 | ||
2664 | You can use an image descriptor by setting up the @code{display} | |
2665 | property yourself, but it is easier to use the functions in this | |
2666 | section. | |
2667 | ||
a40d4712 | 2668 | @defun insert-image image string &optional area |
8241495d RS |
2669 | This function inserts @var{image} in the current buffer at point. The |
2670 | value @var{image} should be an image descriptor; it could be a value | |
2671 | returned by @code{create-image}, or the value of a symbol defined with | |
a40d4712 PR |
2672 | @code{defimage}. The argument @var{string} specifies the text to put in |
2673 | the buffer to hold the image. | |
8241495d RS |
2674 | |
2675 | The argument @var{area} specifies whether to put the image in a margin. | |
2676 | If it is @code{left-margin}, the image appears in the left margin; | |
2677 | @code{right-margin} specifies the right margin. If @var{area} is | |
2678 | @code{nil} or omitted, the image is displayed at point within the | |
2679 | buffer's text. | |
2680 | ||
a40d4712 PR |
2681 | Internally, this function inserts @var{string} in the buffer, and gives |
2682 | it a @code{display} property which specifies @var{image}. @xref{Display | |
8241495d RS |
2683 | Property}. |
2684 | @end defun | |
2685 | ||
a40d4712 | 2686 | @defun put-image image pos string &optional area |
8241495d RS |
2687 | This function puts image @var{image} in front of @var{pos} in the |
2688 | current buffer. The argument @var{pos} should be an integer or a | |
2689 | marker. It specifies the buffer position where the image should appear. | |
a40d4712 | 2690 | The argument @var{string} specifies the text that should hold the image. |
8241495d RS |
2691 | |
2692 | The argument @var{image} must be an image descriptor, perhaps returned | |
2693 | by @code{create-image} or stored by @code{defimage}. | |
2694 | ||
2695 | The argument @var{area} specifies whether to put the image in a margin. | |
2696 | If it is @code{left-margin}, the image appears in the left margin; | |
2697 | @code{right-margin} specifies the right margin. If @var{area} is | |
2698 | @code{nil} or omitted, the image is displayed at point within the | |
2699 | buffer's text. | |
2700 | ||
2701 | Internally, this function creates an overlay, and gives it a | |
2702 | @code{before-string} property containing text that has a @code{display} | |
2703 | property whose value is the image. (Whew!) | |
2704 | @end defun | |
2705 | ||
2706 | @defun remove-images start end &optional buffer | |
2707 | This function removes images in @var{buffer} between positions | |
2708 | @var{start} and @var{end}. If @var{buffer} is omitted or @code{nil}, | |
2709 | images are removed from the current buffer. | |
2710 | ||
2711 | This remove only images that were put into @var{buffer} the way | |
2712 | @code{put-image} does it, not images that were inserted with | |
2713 | @code{insert-image} or in other ways. | |
2714 | @end defun | |
2715 | ||
2716 | @node Image Cache | |
2717 | @subsection Image Cache | |
2718 | ||
2719 | Emacs stores images in an image cache when it displays them, so it can | |
2720 | display them again more efficiently. It removes an image from the cache | |
2721 | when it hasn't been displayed for a specified period of time. | |
2722 | ||
2723 | @defvar image-cache-eviction-delay | |
2724 | @tindex image-cache-eviction-delay | |
2725 | This variable specifies the number of seconds an image can remain in the | |
2726 | cache without being displayed. When an image is not displayed for this | |
2727 | length of time, Emacs removes it from the image cache. | |
2728 | ||
2729 | If the value is @code{nil}, Emacs does not remove images from the cache | |
2730 | except when you explicitly clear it. This mode can be useful for | |
2731 | debugging. | |
2732 | @end defvar | |
2733 | ||
2734 | @defun clear-image-cache &optional frame | |
2735 | @tindex clear-image-cache | |
2736 | This function clears the image cache. If @var{frame} is non-@code{nil}, | |
2737 | only the cache for that frame is cleared. Otherwise all frames' caches | |
2738 | are cleared. | |
2739 | @end defun | |
42b85554 RS |
2740 | @node Blinking |
2741 | @section Blinking Parentheses | |
2742 | @cindex parenthesis matching | |
2743 | @cindex blinking | |
2744 | @cindex balancing parentheses | |
2745 | @cindex close parenthesis | |
2746 | ||
2747 | This section describes the mechanism by which Emacs shows a matching | |
2748 | open parenthesis when the user inserts a close parenthesis. | |
2749 | ||
42b85554 RS |
2750 | @defvar blink-paren-function |
2751 | The value of this variable should be a function (of no arguments) to | |
2752 | be called whenever a character with close parenthesis syntax is inserted. | |
2753 | The value of @code{blink-paren-function} may be @code{nil}, in which | |
2754 | case nothing is done. | |
42b85554 RS |
2755 | @end defvar |
2756 | ||
1911e6e5 | 2757 | @defopt blink-matching-paren |
42b85554 RS |
2758 | If this variable is @code{nil}, then @code{blink-matching-open} does |
2759 | nothing. | |
1911e6e5 | 2760 | @end defopt |
42b85554 | 2761 | |
1911e6e5 | 2762 | @defopt blink-matching-paren-distance |
42b85554 RS |
2763 | This variable specifies the maximum distance to scan for a matching |
2764 | parenthesis before giving up. | |
1911e6e5 | 2765 | @end defopt |
42b85554 | 2766 | |
1911e6e5 | 2767 | @defopt blink-matching-delay |
bfe721d1 KH |
2768 | This variable specifies the number of seconds for the cursor to remain |
2769 | at the matching parenthesis. A fraction of a second often gives | |
2770 | good results, but the default is 1, which works on all systems. | |
1911e6e5 | 2771 | @end defopt |
bfe721d1 | 2772 | |
1911e6e5 | 2773 | @deffn Command blink-matching-open |
42b85554 RS |
2774 | This function is the default value of @code{blink-paren-function}. It |
2775 | assumes that point follows a character with close parenthesis syntax and | |
2776 | moves the cursor momentarily to the matching opening character. If that | |
2777 | character is not already on the screen, it displays the character's | |
2778 | context in the echo area. To avoid long delays, this function does not | |
2779 | search farther than @code{blink-matching-paren-distance} characters. | |
2780 | ||
2781 | Here is an example of calling this function explicitly. | |
2782 | ||
2783 | @smallexample | |
2784 | @group | |
2785 | (defun interactive-blink-matching-open () | |
2786 | @c Do not break this line! -- rms. | |
2787 | @c The first line of a doc string | |
2788 | @c must stand alone. | |
2789 | "Indicate momentarily the start of sexp before point." | |
2790 | (interactive) | |
2791 | @end group | |
2792 | @group | |
2793 | (let ((blink-matching-paren-distance | |
2794 | (buffer-size)) | |
2795 | (blink-matching-paren t)) | |
2796 | (blink-matching-open))) | |
2797 | @end group | |
2798 | @end smallexample | |
1911e6e5 | 2799 | @end deffn |
42b85554 RS |
2800 | |
2801 | @node Inverse Video | |
2802 | @section Inverse Video | |
2803 | @cindex Inverse Video | |
2804 | ||
2805 | @defopt inverse-video | |
2806 | @cindex highlighting | |
2807 | This variable controls whether Emacs uses inverse video for all text | |
2808 | on the screen. Non-@code{nil} means yes, @code{nil} means no. The | |
2809 | default is @code{nil}. | |
2810 | @end defopt | |
2811 | ||
2812 | @defopt mode-line-inverse-video | |
a40d4712 PR |
2813 | This variable controls the use of inverse video for mode lines and menu |
2814 | bars. If it is non-@code{nil}, then these lines are displayed in | |
2815 | inverse video. Otherwise, they lines are displayed normally, just like | |
2816 | other text. The default is @code{t}. | |
2817 | ||
2818 | For window frames, this feature actually applies the face named | |
2819 | @code{mode-line}; that face is normally set up as the inverse of the | |
2820 | default face, unless you change it. | |
42b85554 RS |
2821 | @end defopt |
2822 | ||
2823 | @node Usual Display | |
2824 | @section Usual Display Conventions | |
2825 | ||
2826 | The usual display conventions define how to display each character | |
2827 | code. You can override these conventions by setting up a display table | |
2828 | (@pxref{Display Tables}). Here are the usual display conventions: | |
2829 | ||
2830 | @itemize @bullet | |
2831 | @item | |
2832 | Character codes 32 through 126 map to glyph codes 32 through 126. | |
2833 | Normally this means they display as themselves. | |
2834 | ||
2835 | @item | |
2836 | Character code 9 is a horizontal tab. It displays as whitespace | |
2837 | up to a position determined by @code{tab-width}. | |
2838 | ||
2839 | @item | |
2840 | Character code 10 is a newline. | |
2841 | ||
2842 | @item | |
2843 | All other codes in the range 0 through 31, and code 127, display in one | |
78608595 | 2844 | of two ways according to the value of @code{ctl-arrow}. If it is |
42b85554 | 2845 | non-@code{nil}, these codes map to sequences of two glyphs, where the |
8241495d | 2846 | first glyph is the @sc{ascii} code for @samp{^}. (A display table can |
42b85554 RS |
2847 | specify a glyph to use instead of @samp{^}.) Otherwise, these codes map |
2848 | just like the codes in the range 128 to 255. | |
2849 | ||
8241495d RS |
2850 | On MS-DOS terminals, Emacs arranges by default for the character code |
2851 | 127 to be mapped to the glyph code 127, which normally displays as an | |
2852 | empty polygon. This glyph is used to display non-@sc{ascii} characters | |
2853 | that the MS-DOS terminal doesn't support. @xref{MS-DOS and MULE,,, | |
2854 | emacs, The GNU Emacs Manual}. | |
2855 | ||
42b85554 RS |
2856 | @item |
2857 | Character codes 128 through 255 map to sequences of four glyphs, where | |
8241495d | 2858 | the first glyph is the @sc{ascii} code for @samp{\}, and the others are |
a9f0a989 | 2859 | digit characters representing the character code in octal. (A display |
969fe9b5 RS |
2860 | table can specify a glyph to use instead of @samp{\}.) |
2861 | ||
2862 | @item | |
2863 | Multibyte character codes above 256 are displayed as themselves, or as a | |
2864 | question mark or empty box if the terminal cannot display that | |
2865 | character. | |
42b85554 RS |
2866 | @end itemize |
2867 | ||
2868 | The usual display conventions apply even when there is a display | |
2869 | table, for any character whose entry in the active display table is | |
2870 | @code{nil}. Thus, when you set up a display table, you need only | |
969fe9b5 | 2871 | specify the characters for which you want special behavior. |
42b85554 | 2872 | |
b6954afd RS |
2873 | These display rules apply to carriage return (character code 13), when |
2874 | it appears in the buffer. But that character may not appear in the | |
2875 | buffer where you expect it, if it was eliminated as part of end-of-line | |
15da7853 | 2876 | conversion (@pxref{Coding System Basics}). |
b6954afd | 2877 | |
42b85554 RS |
2878 | These variables affect the way certain characters are displayed on the |
2879 | screen. Since they change the number of columns the characters occupy, | |
f9f59935 RS |
2880 | they also affect the indentation functions. These variables also affect |
2881 | how the mode line is displayed; if you want to force redisplay of the | |
2882 | mode line using the new values, call the function | |
2883 | @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
42b85554 RS |
2884 | |
2885 | @defopt ctl-arrow | |
2886 | @cindex control characters in display | |
2887 | This buffer-local variable controls how control characters are | |
2888 | displayed. If it is non-@code{nil}, they are displayed as a caret | |
2889 | followed by the character: @samp{^A}. If it is @code{nil}, they are | |
2890 | displayed as a backslash followed by three octal digits: @samp{\001}. | |
2891 | @end defopt | |
2892 | ||
2893 | @c Following may have overfull hbox. | |
2894 | @defvar default-ctl-arrow | |
2895 | The value of this variable is the default value for @code{ctl-arrow} in | |
2896 | buffers that do not override it. @xref{Default Value}. | |
2897 | @end defvar | |
2898 | ||
2468d0c0 DL |
2899 | @defopt indicate-empty-lines |
2900 | @tindex indicate-empty-lines | |
2901 | When this is non-@code{nil}, Emacs displays a special glyph in | |
2902 | each empty line at the end of the buffer, on terminals that | |
2903 | support it (window systems). | |
2904 | @end defopt | |
2905 | ||
42b85554 RS |
2906 | @defopt tab-width |
2907 | The value of this variable is the spacing between tab stops used for | |
a40d4712 PR |
2908 | displaying tab characters in Emacs buffers. The value is in units of |
2909 | columns, and the default is 8. Note that this feature is completely | |
2910 | independent of the user-settable tab stops used by the command | |
2911 | @code{tab-to-tab-stop}. @xref{Indent Tabs}. | |
42b85554 RS |
2912 | @end defopt |
2913 | ||
2914 | @node Display Tables | |
2915 | @section Display Tables | |
2916 | ||
2917 | @cindex display table | |
969fe9b5 RS |
2918 | You can use the @dfn{display table} feature to control how all possible |
2919 | character codes display on the screen. This is useful for displaying | |
8241495d | 2920 | European languages that have letters not in the @sc{ascii} character |
969fe9b5 | 2921 | set. |
42b85554 RS |
2922 | |
2923 | The display table maps each character code into a sequence of | |
8241495d | 2924 | @dfn{glyphs}, each glyph being a graphic that takes up one character |
42b85554 RS |
2925 | position on the screen. You can also define how to display each glyph |
2926 | on your terminal, using the @dfn{glyph table}. | |
2927 | ||
f9f59935 RS |
2928 | Display tables affect how the mode line is displayed; if you want to |
2929 | force redisplay of the mode line using a new display table, call | |
2930 | @code{force-mode-line-update} (@pxref{Mode Line Format}). | |
2931 | ||
42b85554 RS |
2932 | @menu |
2933 | * Display Table Format:: What a display table consists of. | |
2934 | * Active Display Table:: How Emacs selects a display table to use. | |
2935 | * Glyphs:: How to define a glyph, and what glyphs mean. | |
42b85554 RS |
2936 | @end menu |
2937 | ||
2938 | @node Display Table Format | |
2939 | @subsection Display Table Format | |
2940 | ||
a9f0a989 RS |
2941 | A display table is actually a char-table (@pxref{Char-Tables}) with |
2942 | @code{display-table} as its subtype. | |
42b85554 RS |
2943 | |
2944 | @defun make-display-table | |
2945 | This creates and returns a display table. The table initially has | |
2946 | @code{nil} in all elements. | |
2947 | @end defun | |
2948 | ||
f9f59935 RS |
2949 | The ordinary elements of the display table are indexed by character |
2950 | codes; the element at index @var{c} says how to display the character | |
2951 | code @var{c}. The value should be @code{nil} or a vector of glyph | |
2952 | values (@pxref{Glyphs}). If an element is @code{nil}, it says to | |
2953 | display that character according to the usual display conventions | |
2954 | (@pxref{Usual Display}). | |
22697dac KH |
2955 | |
2956 | If you use the display table to change the display of newline | |
2957 | characters, the whole buffer will be displayed as one long ``line.'' | |
42b85554 | 2958 | |
f9f59935 | 2959 | The display table also has six ``extra slots'' which serve special |
969fe9b5 RS |
2960 | purposes. Here is a table of their meanings; @code{nil} in any slot |
2961 | means to use the default for that slot, as stated below. | |
42b85554 RS |
2962 | |
2963 | @table @asis | |
f9f59935 | 2964 | @item 0 |
42b85554 | 2965 | The glyph for the end of a truncated screen line (the default for this |
8241495d RS |
2966 | is @samp{$}). @xref{Glyphs}. Newer Emacs versions, on some platforms, |
2967 | display arrows to indicate truncation---the display table has no effect | |
2968 | in these situations. | |
f9f59935 | 2969 | @item 1 |
42b85554 | 2970 | The glyph for the end of a continued line (the default is @samp{\}). |
8241495d RS |
2971 | Newer Emacs versions, on some platforms, display curved arrows to |
2972 | indicate truncation---the display table has no effect in these | |
2973 | situations. | |
f9f59935 | 2974 | @item 2 |
42b85554 RS |
2975 | The glyph for indicating a character displayed as an octal character |
2976 | code (the default is @samp{\}). | |
f9f59935 | 2977 | @item 3 |
42b85554 | 2978 | The glyph for indicating a control character (the default is @samp{^}). |
f9f59935 | 2979 | @item 4 |
42b85554 RS |
2980 | A vector of glyphs for indicating the presence of invisible lines (the |
2981 | default is @samp{...}). @xref{Selective Display}. | |
f9f59935 | 2982 | @item 5 |
50b04c36 | 2983 | The glyph used to draw the border between side-by-side windows (the |
8241495d RS |
2984 | default is @samp{|}). @xref{Splitting Windows}. This takes effect only |
2985 | when there are no scroll bars; if scroll bars are supported and in use, | |
2986 | a scroll bar separates the two windows. | |
42b85554 RS |
2987 | @end table |
2988 | ||
2989 | For example, here is how to construct a display table that mimics the | |
2990 | effect of setting @code{ctl-arrow} to a non-@code{nil} value: | |
2991 | ||
2992 | @example | |
2993 | (setq disptab (make-display-table)) | |
2994 | (let ((i 0)) | |
2995 | (while (< i 32) | |
2996 | (or (= i ?\t) (= i ?\n) | |
2997 | (aset disptab i (vector ?^ (+ i 64)))) | |
2998 | (setq i (1+ i))) | |
2999 | (aset disptab 127 (vector ?^ ??))) | |
3000 | @end example | |
3001 | ||
f9f59935 | 3002 | @defun display-table-slot display-table slot |
a9f0a989 | 3003 | @tindex display-table-slot |
f9f59935 RS |
3004 | This function returns the value of the extra slot @var{slot} of |
3005 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
3006 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
3007 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
3008 | @code{selective-display}, and @code{vertical-border}. | |
3009 | @end defun | |
3010 | ||
f9f59935 | 3011 | @defun set-display-table-slot display-table slot value |
a9f0a989 | 3012 | @tindex set-display-table-slot |
f9f59935 RS |
3013 | This function stores @var{value} in the extra slot @var{slot} of |
3014 | @var{display-table}. The argument @var{slot} may be a number from 0 to | |
3015 | 5 inclusive, or a slot name (symbol). Valid symbols are | |
3016 | @code{truncation}, @code{wrap}, @code{escape}, @code{control}, | |
3017 | @code{selective-display}, and @code{vertical-border}. | |
3018 | @end defun | |
3019 | ||
8241495d RS |
3020 | @defun describe-display-table display-table |
3021 | @tindex describe-display-table | |
3022 | This function displays a description of the display table | |
3023 | @var{display-table} in a help buffer. | |
3024 | @end defun | |
3025 | ||
3026 | @deffn Command describe-current-display-table | |
3027 | @tindex describe-current-display-table | |
3028 | This command displays a description of the current display table in a | |
3029 | help buffer. | |
3030 | @end deffn | |
3031 | ||
42b85554 RS |
3032 | @node Active Display Table |
3033 | @subsection Active Display Table | |
3034 | @cindex active display table | |
3035 | ||
3036 | Each window can specify a display table, and so can each buffer. When | |
3037 | a buffer @var{b} is displayed in window @var{w}, display uses the | |
3038 | display table for window @var{w} if it has one; otherwise, the display | |
3039 | table for buffer @var{b} if it has one; otherwise, the standard display | |
3040 | table if any. The display table chosen is called the @dfn{active} | |
3041 | display table. | |
3042 | ||
3043 | @defun window-display-table window | |
3044 | This function returns @var{window}'s display table, or @code{nil} | |
3045 | if @var{window} does not have an assigned display table. | |
3046 | @end defun | |
3047 | ||
3048 | @defun set-window-display-table window table | |
3049 | This function sets the display table of @var{window} to @var{table}. | |
3050 | The argument @var{table} should be either a display table or | |
3051 | @code{nil}. | |
3052 | @end defun | |
3053 | ||
3054 | @defvar buffer-display-table | |
969fe9b5 RS |
3055 | This variable is automatically buffer-local in all buffers; its value in |
3056 | a particular buffer specifies the display table for that buffer. If it | |
3057 | is @code{nil}, that means the buffer does not have an assigned display | |
3058 | table. | |
42b85554 RS |
3059 | @end defvar |
3060 | ||
3061 | @defvar standard-display-table | |
3062 | This variable's value is the default display table, used whenever a | |
3063 | window has no display table and neither does the buffer displayed in | |
3064 | that window. This variable is @code{nil} by default. | |
3065 | @end defvar | |
3066 | ||
3067 | If there is no display table to use for a particular window---that is, | |
f9f59935 RS |
3068 | if the window specifies none, its buffer specifies none, and |
3069 | @code{standard-display-table} is @code{nil}---then Emacs uses the usual | |
42b85554 RS |
3070 | display conventions for all character codes in that window. @xref{Usual |
3071 | Display}. | |
3072 | ||
8241495d RS |
3073 | A number of functions for changing the standard display table |
3074 | are defined in the library @file{disp-table}. | |
3075 | ||
42b85554 RS |
3076 | @node Glyphs |
3077 | @subsection Glyphs | |
3078 | ||
3079 | @cindex glyph | |
3080 | A @dfn{glyph} is a generalization of a character; it stands for an | |
3081 | image that takes up a single character position on the screen. Glyphs | |
3082 | are represented in Lisp as integers, just as characters are. | |
3083 | ||
3084 | @cindex glyph table | |
3085 | The meaning of each integer, as a glyph, is defined by the glyph | |
3086 | table, which is the value of the variable @code{glyph-table}. | |
3087 | ||
3088 | @defvar glyph-table | |
3089 | The value of this variable is the current glyph table. It should be a | |
3090 | vector; the @var{g}th element defines glyph code @var{g}. If the value | |
3091 | is @code{nil} instead of a vector, then all glyphs are simple (see | |
3092 | below). | |
3093 | @end defvar | |
3094 | ||
3095 | Here are the possible types of elements in the glyph table: | |
3096 | ||
1911e6e5 RS |
3097 | @table @asis |
3098 | @item @var{string} | |
42b85554 RS |
3099 | Send the characters in @var{string} to the terminal to output |
3100 | this glyph. This alternative is available on character terminals, | |
969fe9b5 | 3101 | but not under a window system. |
42b85554 | 3102 | |
1911e6e5 | 3103 | @item @var{integer} |
969fe9b5 RS |
3104 | Define this glyph code as an alias for glyph code @var{integer}. You |
3105 | can use an alias to specify a face code for the glyph; see below. | |
42b85554 RS |
3106 | |
3107 | @item @code{nil} | |
969fe9b5 RS |
3108 | This glyph is simple. On an ordinary terminal, the glyph code mod |
3109 | 524288 is the character to output. In a window system, the glyph code | |
3110 | mod 524288 is the character to output, and the glyph code divided by | |
3111 | 524288 specifies the face number (@pxref{Face Functions}) to use while | |
3112 | outputting it. (524288 is | |
f9f59935 | 3113 | @ifinfo |
969fe9b5 | 3114 | 2**19.) |
f9f59935 RS |
3115 | @end ifinfo |
3116 | @tex | |
969fe9b5 | 3117 | $2^{19}$.) |
f9f59935 RS |
3118 | @end tex |
3119 | @xref{Faces}. | |
42b85554 RS |
3120 | @end table |
3121 | ||
3122 | If a glyph code is greater than or equal to the length of the glyph | |
3123 | table, that code is automatically simple. | |
3124 | ||
8241495d RS |
3125 | @defun create-glyph string |
3126 | @tindex create-glyph | |
3127 | This function returns a newly-allocated glyph code which is set up to | |
3128 | display by sending @var{string} to the terminal. | |
3129 | @end defun | |
3130 | ||
42b85554 RS |
3131 | @node Beeping |
3132 | @section Beeping | |
3133 | @cindex beeping | |
3134 | @cindex bell | |
3135 | ||
f9f59935 RS |
3136 | This section describes how to make Emacs ring the bell (or blink the |
3137 | screen) to attract the user's attention. Be conservative about how | |
3138 | often you do this; frequent bells can become irritating. Also be | |
3139 | careful not to use just beeping when signaling an error is more | |
3140 | appropriate. (@xref{Errors}.) | |
42b85554 | 3141 | |
a9f0a989 | 3142 | @defun ding &optional do-not-terminate |
42b85554 RS |
3143 | @cindex keyboard macro termination |
3144 | This function beeps, or flashes the screen (see @code{visible-bell} below). | |
3145 | It also terminates any keyboard macro currently executing unless | |
a9f0a989 | 3146 | @var{do-not-terminate} is non-@code{nil}. |
42b85554 RS |
3147 | @end defun |
3148 | ||
a9f0a989 | 3149 | @defun beep &optional do-not-terminate |
42b85554 RS |
3150 | This is a synonym for @code{ding}. |
3151 | @end defun | |
3152 | ||
1911e6e5 | 3153 | @defopt visible-bell |
42b85554 RS |
3154 | This variable determines whether Emacs should flash the screen to |
3155 | represent a bell. Non-@code{nil} means yes, @code{nil} means no. This | |
969fe9b5 RS |
3156 | is effective on a window system, and on a character-only terminal |
3157 | provided the terminal's Termcap entry defines the visible bell | |
3158 | capability (@samp{vb}). | |
1911e6e5 | 3159 | @end defopt |
42b85554 | 3160 | |
f9f59935 | 3161 | @defvar ring-bell-function |
a9f0a989 | 3162 | @tindex ring-bell-function |
f9f59935 | 3163 | If this is non-@code{nil}, it specifies how Emacs should ``ring the |
a40d4712 PR |
3164 | bell.'' Its value should be a function of no arguments. If this is |
3165 | non-@code{nil}, it takes precedence over the @code{visible-bell} | |
3166 | variable. | |
f9f59935 RS |
3167 | @end defvar |
3168 | ||
42b85554 RS |
3169 | @node Window Systems |
3170 | @section Window Systems | |
3171 | ||
3172 | Emacs works with several window systems, most notably the X Window | |
3173 | System. Both Emacs and X use the term ``window'', but use it | |
3174 | differently. An Emacs frame is a single window as far as X is | |
3175 | concerned; the individual Emacs windows are not known to X at all. | |
3176 | ||
3177 | @defvar window-system | |
42b85554 | 3178 | This variable tells Lisp programs what window system Emacs is running |
1911e6e5 RS |
3179 | under. The possible values are |
3180 | ||
3181 | @table @code | |
3182 | @item x | |
3183 | @cindex X Window System | |
3184 | Emacs is displaying using X. | |
3185 | @item pc | |
8241495d | 3186 | Emacs is displaying using MS-DOS. |
1911e6e5 | 3187 | @item w32 |
8241495d RS |
3188 | Emacs is displaying using Windows NT or Windows 9x. |
3189 | @item mac | |
3190 | Emacs is displaying using a Macintosh. | |
1911e6e5 RS |
3191 | @item nil |
3192 | Emacs is using a character-based terminal. | |
3193 | @end table | |
42b85554 RS |
3194 | @end defvar |
3195 | ||
42b85554 | 3196 | @defvar window-setup-hook |
f9f59935 RS |
3197 | This variable is a normal hook which Emacs runs after handling the |
3198 | initialization files. Emacs runs this hook after it has completed | |
a40d4712 | 3199 | loading your init file, the default initialization file (if |
a9f0a989 | 3200 | any), and the terminal-specific Lisp code, and running the hook |
42b85554 RS |
3201 | @code{term-setup-hook}. |
3202 | ||
3203 | This hook is used for internal purposes: setting up communication with | |
3204 | the window system, and creating the initial window. Users should not | |
3205 | interfere with it. | |
3206 | @end defvar |