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1 | @c -*-texinfo-*- |
2 | @c This is part of the GNU Emacs Lisp Reference Manual. | |
3 | @c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. | |
4 | @c See the file elisp.texi for copying conditions. | |
5 | @setfilename ../info/display | |
6 | @node Display, Calendar, System Interface, Top | |
7 | @chapter Emacs Display | |
8 | ||
9 | This chapter describes a number of features related to the display | |
10 | that Emacs presents to the user. | |
11 | ||
12 | @menu | |
13 | * Refresh Screen:: Clearing the screen and redrawing everything on it. | |
14 | * Screen Size:: How big is the Emacs screen. | |
15 | * Truncation:: Folding or wrapping long text lines. | |
16 | * The Echo Area:: Where messages are displayed. | |
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17 | * Invisible Text:: Hiding part of the buffer text. |
18 | * Selective Display:: Hiding part of the buffer text (the old way). | |
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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. | |
22 | * Faces:: A face defines a graphics appearance: font, color, etc. | |
23 | * Blinking:: How Emacs shows the matching open parenthesis. | |
24 | * Inverse Video:: Specifying how the screen looks. | |
25 | * Usual Display:: The usual conventions for displaying nonprinting chars. | |
26 | * Display Tables:: How to specify other conventions. | |
27 | * Beeping:: Audible signal to the user. | |
28 | * Window Systems:: Which window system is being used. | |
29 | @end menu | |
30 | ||
31 | @node Refresh Screen | |
32 | @section Refreshing the Screen | |
33 | ||
34 | The function @code{redraw-frame} redisplays the entire contents of a | |
35 | given frame. @xref{Frames}. | |
36 | ||
37 | @c Emacs 19 feature | |
38 | @defun redraw-frame frame | |
39 | This function clears and redisplays frame @var{frame}. | |
40 | @end defun | |
41 | ||
42 | Even more powerful is @code{redraw-display}: | |
43 | ||
44 | @deffn Command redraw-display | |
45 | This function clears and redisplays all visible frames. | |
46 | @end deffn | |
47 | ||
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48 | Processing user input takes absolute priority over redisplay. If you |
49 | call these functions when input is available, they do nothing | |
50 | immediately, but a full redisplay does happen eventually---after all the | |
51 | input has been processed. | |
52 | ||
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53 | Normally, suspending and resuming Emacs also refreshes the screen. |
54 | Some terminal emulators record separate contents for display-oriented | |
55 | programs such as Emacs and for ordinary sequential display. If you are | |
56 | using such a terminal, you might want to inhibit the redisplay on | |
78608595 | 57 | resumption. |
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58 | |
59 | @defvar no-redraw-on-reenter | |
60 | @cindex suspend (cf. @code{no-redraw-on-reenter}) | |
61 | @cindex resume (cf. @code{no-redraw-on-reenter}) | |
62 | This variable controls whether Emacs redraws the entire screen after it | |
63 | has been suspended and resumed. Non-@code{nil} means yes, @code{nil} | |
64 | means no. | |
65 | @end defvar | |
66 | ||
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67 | @node Screen Size |
68 | @section Screen Size | |
69 | @cindex size of screen | |
70 | @cindex screen size | |
71 | @cindex display lines | |
72 | @cindex display columns | |
73 | @cindex resize redisplay | |
74 | ||
78608595 | 75 | The screen size functions access or specify the height or width of |
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76 | the terminal. When you are using multiple frames, they apply to the |
77 | selected frame (@pxref{Frames}). | |
78 | ||
79 | @defun screen-height | |
80 | This function returns the number of lines on the screen that are | |
81 | available for display. | |
82 | ||
83 | @example | |
84 | @group | |
85 | (screen-height) | |
86 | @result{} 50 | |
87 | @end group | |
88 | @end example | |
89 | @end defun | |
90 | ||
91 | @defun screen-width | |
92 | This function returns the number of columns on the screen that are | |
93 | available for display. | |
94 | ||
95 | @example | |
96 | @group | |
97 | (screen-width) | |
98 | @result{} 80 | |
99 | @end group | |
100 | @end example | |
101 | @end defun | |
102 | ||
103 | @defun set-screen-height lines &optional not-actual-size | |
104 | This function declares that the terminal can display @var{lines} lines. | |
105 | The sizes of existing windows are altered proportionally to fit. | |
106 | ||
107 | If @var{not-actual-size} is non-@code{nil}, then Emacs displays | |
108 | @var{lines} lines of output, but does not change its value for the | |
109 | actual height of the screen. (Knowing the correct actual size may be | |
110 | necessary for correct cursor positioning.) Using a smaller height than | |
111 | the terminal actually implements may be useful to reproduce behavior | |
112 | observed on a smaller screen, or if the terminal malfunctions when using | |
113 | its whole screen. | |
114 | ||
115 | If @var{lines} is different from what it was previously, then the | |
116 | entire screen is cleared and redisplayed using the new size. | |
117 | ||
118 | This function returns @code{nil}. | |
119 | @end defun | |
120 | ||
121 | @defun set-screen-width columns &optional not-actual-size | |
122 | This function declares that the terminal can display @var{columns} | |
123 | columns. The details are as in @code{set-screen-height}. | |
124 | @end defun | |
125 | ||
126 | @node Truncation | |
127 | @section Truncation | |
128 | @cindex line wrapping | |
129 | @cindex continuation lines | |
130 | @cindex @samp{$} in display | |
131 | @cindex @samp{\} in display | |
132 | ||
133 | When a line of text extends beyond the right edge of a window, the | |
134 | line can either be continued on the next screen line, or truncated to | |
135 | one screen line. The additional screen lines used to display a long | |
136 | text line are called @dfn{continuation} lines. Normally, a @samp{$} in | |
137 | the rightmost column of the window indicates truncation; a @samp{\} on | |
138 | the rightmost column indicates a line that ``wraps'' or is continued | |
139 | onto the next line. (The display table can specify alternative | |
a890e1b0 | 140 | indicators; see @ref{Display Tables}.) |
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141 | |
142 | Note that continuation is different from filling; continuation happens | |
143 | on the screen only, not in the buffer contents, and it breaks a line | |
144 | precisely at the right margin, not at a word boundary. @xref{Filling}. | |
145 | ||
146 | @defopt truncate-lines | |
147 | This buffer-local variable controls how Emacs displays lines that extend | |
148 | beyond the right edge of the window. The default is @code{nil}, which | |
149 | specifies continuation. If the value is non-@code{nil}, then these | |
150 | lines are truncated. | |
151 | ||
152 | If the variable @code{truncate-partial-width-windows} is non-@code{nil}, | |
153 | then truncation is always used for side-by-side windows (within one | |
154 | frame) regardless of the value of @code{truncate-lines}. | |
155 | @end defopt | |
156 | ||
bfe721d1 | 157 | @defopt default-truncate-lines |
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158 | This variable is the default value for @code{truncate-lines}, for |
159 | buffers that do not have local values for it. | |
bfe721d1 | 160 | @end defopt |
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161 | |
162 | @defopt truncate-partial-width-windows | |
163 | This variable controls display of lines that extend beyond the right | |
164 | edge of the window, in side-by-side windows (@pxref{Splitting Windows}). | |
165 | If it is non-@code{nil}, these lines are truncated; otherwise, | |
166 | @code{truncate-lines} says what to do with them. | |
167 | @end defopt | |
168 | ||
169 | You can override the images that indicate continuation or truncation | |
170 | with the display table; see @ref{Display Tables}. | |
171 | ||
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172 | If your buffer contains @strong{very} long lines, and you use |
173 | continuation to display them, just thinking about them can make Emacs | |
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174 | redisplay slow. The column computation and indentation functions also |
175 | become slow. Then you might find it advisable to set | |
176 | @code{cache-long-line-scans} to @code{t}. | |
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177 | |
178 | @defvar cache-long-line-scans | |
179 | If this variable is non-@code{nil}, various indentation and motion | |
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180 | functions, and Emacs redisplay, cache the results of scanning the |
181 | buffer, and consult the cache to avoid rescanning regions of the buffer | |
182 | unless they are modified. | |
22697dac | 183 | |
bfe721d1 | 184 | Turning on the cache slows down processing of short lines somewhat. |
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185 | |
186 | This variable is automatically local in every buffer. | |
187 | @end defvar | |
188 | ||
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189 | @node The Echo Area |
190 | @section The Echo Area | |
191 | @cindex error display | |
192 | @cindex echo area | |
193 | ||
22697dac | 194 | The @dfn{echo area} is used for displaying messages made with the |
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195 | @code{message} primitive, and for echoing keystrokes. It is not the |
196 | same as the minibuffer, despite the fact that the minibuffer appears | |
197 | (when active) in the same place on the screen as the echo area. The | |
198 | @cite{GNU Emacs Manual} specifies the rules for resolving conflicts | |
199 | between the echo area and the minibuffer for use of that screen space | |
200 | (@pxref{Minibuffer,, The Minibuffer, emacs, The GNU Emacs Manual}). | |
201 | Error messages appear in the echo area; see @ref{Errors}. | |
202 | ||
203 | You can write output in the echo area by using the Lisp printing | |
204 | functions with @code{t} as the stream (@pxref{Output Functions}), or as | |
205 | follows: | |
206 | ||
207 | @defun message string &rest arguments | |
22697dac | 208 | This function displays a one-line message in the echo area. The |
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209 | argument @var{string} is similar to a C language @code{printf} control |
210 | string. See @code{format} in @ref{String Conversion}, for the details | |
211 | on the conversion specifications. @code{message} returns the | |
212 | constructed string. | |
213 | ||
b22f3a19 RS |
214 | In batch mode, @code{message} prints the message text on the standard |
215 | error stream, followed by a newline. | |
216 | ||
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217 | @c Emacs 19 feature |
218 | If @var{string} is @code{nil}, @code{message} clears the echo area. If | |
219 | the minibuffer is active, this brings the minibuffer contents back onto | |
220 | the screen immediately. | |
b22f3a19 | 221 | |
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222 | @example |
223 | @group | |
224 | (message "Minibuffer depth is %d." | |
225 | (minibuffer-depth)) | |
226 | @print{} Minibuffer depth is 0. | |
227 | @result{} "Minibuffer depth is 0." | |
228 | @end group | |
229 | ||
230 | @group | |
231 | ---------- Echo Area ---------- | |
232 | Minibuffer depth is 0. | |
233 | ---------- Echo Area ---------- | |
234 | @end group | |
235 | @end example | |
236 | @end defun | |
237 | ||
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238 | Almost all the messages displayed in the echo area are also recorded |
239 | in the @samp{*Messages*} buffer. | |
240 | ||
241 | @defopt message-log-max | |
242 | This variable specifies how many lines to keep in the @samp{*Messages*} | |
243 | buffer. The value @code{t} means there is no limit on how many lines to | |
244 | keep. The value @code{nil} disables message logging entirely. Here's | |
245 | how to display a message and prevent it from being logged: | |
246 | ||
247 | @example | |
248 | (let (message-log-max) | |
249 | (message @dots{})) | |
250 | @end example | |
251 | @end defopt | |
252 | ||
bfe721d1 KH |
253 | @defvar echo-keystrokes |
254 | This variable determines how much time should elapse before command | |
255 | characters echo. Its value must be an integer, which specifies the | |
256 | number of seconds to wait before echoing. If the user types a prefix | |
257 | key (such as @kbd{C-x}) and then delays this many seconds before | |
258 | continuing, the prefix key is echoed in the echo area. Any subsequent | |
259 | characters in the same command will be echoed as well. | |
260 | ||
261 | If the value is zero, then command input is not echoed. | |
262 | @end defvar | |
263 | ||
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264 | @defvar cursor-in-echo-area |
265 | This variable controls where the cursor appears when a message is | |
266 | displayed in the echo area. If it is non-@code{nil}, then the cursor | |
267 | appears at the end of the message. Otherwise, the cursor appears at | |
268 | point---not in the echo area at all. | |
269 | ||
270 | The value is normally @code{nil}; Lisp programs bind it to @code{t} | |
271 | for brief periods of time. | |
272 | @end defvar | |
273 | ||
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274 | @node Invisible Text |
275 | @section Invisible Text | |
276 | ||
277 | @cindex invisible text | |
278 | You can make characters @dfn{invisible}, so that they do not appear on | |
279 | the screen, with the @code{invisible} property. This can be either a | |
280 | text property or a property of an overlay. | |
281 | ||
282 | In the simplest case, any non-@code{nil} @code{invisible} property makes | |
283 | a character invisible. This is the default case---if you don't alter | |
284 | the default value of @code{buffer-invisibility-spec}, this is how the | |
285 | @code{invisibility} property works. This feature is much like selective | |
286 | display (@pxref{Selective Display}), but more general and cleaner. | |
287 | ||
288 | More generally, you can use the variable @code{buffer-invisibility-spec} | |
289 | to control which values of the @code{invisible} property make text | |
290 | invisible. This permits you to classify the text into different subsets | |
291 | in advance, by giving them different @code{invisible} values, and | |
292 | subsequently make various subsets visible or invisible by changing the | |
293 | value of @code{buffer-invisibility-spec}. | |
294 | ||
295 | Controlling visibility with @code{buffer-invisibility-spec} is | |
296 | especially useful in a program to display the list of entries in a data | |
297 | base. It permits the implementation of convenient filtering commands to | |
298 | view just a part of the entries in the data base. Setting this variable | |
299 | is very fast, much faster than scanning all the text in the buffer | |
bfe721d1 | 300 | looking for properties to change. |
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301 | |
302 | @defvar buffer-invisibility-spec | |
303 | This variable specifies which kinds of @code{invisible} properties | |
304 | actually make a character invisible. | |
305 | ||
306 | @table @asis | |
307 | @item @code{t} | |
308 | A character is invisible if its @code{invisible} property is | |
309 | non-@code{nil}. This is the default. | |
310 | ||
311 | @item a list | |
312 | Each element of the list makes certain characters invisible. | |
313 | Ultimately, a character is invisible if any of the elements of this list | |
314 | applies to it. The list can have two kinds of elements: | |
315 | ||
316 | @table @code | |
317 | @item @var{atom} | |
318 | A character is invisible if its @code{invisible} propery value | |
319 | is @var{atom} or if it is a list with @var{atom} as a member. | |
320 | ||
321 | @item (@var{atom} . t) | |
322 | A character is invisible if its @code{invisible} propery value | |
323 | is @var{atom} or if it is a list with @var{atom} as a member. | |
324 | Moreover, if this character is at the end of a line and is followed | |
325 | by a visible newline, it displays an ellipsis. | |
326 | @end table | |
327 | @end table | |
328 | @end defvar | |
329 | ||
5e8ae792 | 330 | @vindex line-move-ignore-invisible |
bfe721d1 | 331 | Ordinarily, commands that operate on text or move point do not care |
5e8ae792 RS |
332 | whether the text is invisible. The user-level line motion commands |
333 | explicitly ignore invisible newlines if | |
334 | @code{line-move-ignore-invisible} is non-@code{nil}, but only because | |
335 | they are explicitly programmed to do so. | |
bfe721d1 | 336 | |
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337 | @node Selective Display |
338 | @section Selective Display | |
339 | @cindex selective display | |
340 | ||
bfe721d1 KH |
341 | @dfn{Selective display} is a pair of features that hide certain |
342 | lines on the screen. | |
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343 | |
344 | The first variant, explicit selective display, is designed for use in | |
345 | a Lisp program. The program controls which lines are hidden by altering | |
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346 | the text. Outline mode has traditionally used this variant. It has |
347 | been partially replaced by the invisible text feature (@pxref{Invisible | |
348 | Text}); there is a new version of Outline mode which uses that instead. | |
349 | ||
350 | In the second variant, the choice of lines to hide is made | |
bfe721d1 | 351 | automatically based on indentation. This variant is designed to be a |
22697dac | 352 | user-level feature. |
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353 | |
354 | The way you control explicit selective display is by replacing a | |
78608595 | 355 | newline (control-j) with a carriage return (control-m). The text that |
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356 | was formerly a line following that newline is now invisible. Strictly |
357 | speaking, it is temporarily no longer a line at all, since only newlines | |
358 | can separate lines; it is now part of the previous line. | |
359 | ||
360 | Selective display does not directly affect editing commands. For | |
361 | example, @kbd{C-f} (@code{forward-char}) moves point unhesitatingly into | |
362 | invisible text. However, the replacement of newline characters with | |
363 | carriage return characters affects some editing commands. For example, | |
364 | @code{next-line} skips invisible lines, since it searches only for | |
365 | newlines. Modes that use selective display can also define commands | |
366 | that take account of the newlines, or that make parts of the text | |
367 | visible or invisible. | |
368 | ||
369 | When you write a selectively displayed buffer into a file, all the | |
370 | control-m's are output as newlines. This means that when you next read | |
371 | in the file, it looks OK, with nothing invisible. The selective display | |
372 | effect is seen only within Emacs. | |
373 | ||
374 | @defvar selective-display | |
375 | This buffer-local variable enables selective display. This means that | |
376 | lines, or portions of lines, may be made invisible. | |
377 | ||
378 | @itemize @bullet | |
379 | @item | |
380 | If the value of @code{selective-display} is @code{t}, then any portion | |
381 | of a line that follows a control-m is not displayed. | |
382 | ||
383 | @item | |
384 | If the value of @code{selective-display} is a positive integer, then | |
385 | lines that start with more than that many columns of indentation are not | |
386 | displayed. | |
387 | @end itemize | |
388 | ||
389 | When some portion of a buffer is invisible, the vertical movement | |
390 | commands operate as if that portion did not exist, allowing a single | |
391 | @code{next-line} command to skip any number of invisible lines. | |
392 | However, character movement commands (such as @code{forward-char}) do | |
393 | not skip the invisible portion, and it is possible (if tricky) to insert | |
394 | or delete text in an invisible portion. | |
395 | ||
396 | In the examples below, we show the @emph{display appearance} of the | |
397 | buffer @code{foo}, which changes with the value of | |
398 | @code{selective-display}. The @emph{contents} of the buffer do not | |
399 | change. | |
400 | ||
401 | @example | |
402 | @group | |
403 | (setq selective-display nil) | |
404 | @result{} nil | |
405 | ||
406 | ---------- Buffer: foo ---------- | |
407 | 1 on this column | |
408 | 2on this column | |
409 | 3n this column | |
410 | 3n this column | |
411 | 2on this column | |
412 | 1 on this column | |
413 | ---------- Buffer: foo ---------- | |
414 | @end group | |
415 | ||
416 | @group | |
417 | (setq selective-display 2) | |
418 | @result{} 2 | |
419 | ||
420 | ---------- Buffer: foo ---------- | |
421 | 1 on this column | |
422 | 2on this column | |
423 | 2on this column | |
424 | 1 on this column | |
425 | ---------- Buffer: foo ---------- | |
426 | @end group | |
427 | @end example | |
428 | @end defvar | |
429 | ||
430 | @defvar selective-display-ellipses | |
431 | If this buffer-local variable is non-@code{nil}, then Emacs displays | |
432 | @samp{@dots{}} at the end of a line that is followed by invisible text. | |
433 | This example is a continuation of the previous one. | |
434 | ||
435 | @example | |
436 | @group | |
437 | (setq selective-display-ellipses t) | |
438 | @result{} t | |
439 | ||
440 | ---------- Buffer: foo ---------- | |
441 | 1 on this column | |
442 | 2on this column ... | |
443 | 2on this column | |
444 | 1 on this column | |
445 | ---------- Buffer: foo ---------- | |
446 | @end group | |
447 | @end example | |
448 | ||
449 | You can use a display table to substitute other text for the ellipsis | |
450 | (@samp{@dots{}}). @xref{Display Tables}. | |
451 | @end defvar | |
452 | ||
453 | @node Overlay Arrow | |
454 | @section The Overlay Arrow | |
455 | @cindex overlay arrow | |
456 | ||
457 | The @dfn{overlay arrow} is useful for directing the user's attention | |
458 | to a particular line in a buffer. For example, in the modes used for | |
459 | interface to debuggers, the overlay arrow indicates the line of code | |
460 | about to be executed. | |
461 | ||
462 | @defvar overlay-arrow-string | |
78608595 RS |
463 | This variable holds the string to display to call attention to a |
464 | particular line, or @code{nil} if the arrow feature is not in use. | |
42b85554 RS |
465 | @end defvar |
466 | ||
467 | @defvar overlay-arrow-position | |
78608595 RS |
468 | This variable holds a marker that indicates where to display the overlay |
469 | arrow. It should point at the beginning of a line. The arrow text | |
470 | appears at the beginning of that line, overlaying any text that would | |
471 | otherwise appear. Since the arrow is usually short, and the line | |
472 | usually begins with indentation, normally nothing significant is | |
473 | overwritten. | |
474 | ||
475 | The overlay string is displayed only in the buffer that this marker | |
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476 | points into. Thus, only one buffer can have an overlay arrow at any |
477 | given time. | |
478 | @c !!! overlay-arrow-position: but the overlay string may remain in the display | |
479 | @c of some other buffer until an update is required. This should be fixed | |
480 | @c now. Is it? | |
481 | @end defvar | |
482 | ||
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483 | You can do the same job by creating an overlay with a |
484 | @code{before-string} property. @xref{Overlay Properties}. | |
485 | ||
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486 | @node Temporary Displays |
487 | @section Temporary Displays | |
488 | ||
489 | Temporary displays are used by commands to put output into a buffer | |
490 | and then present it to the user for perusal rather than for editing. | |
bfe721d1 | 491 | Many of the help commands use this feature. |
42b85554 RS |
492 | |
493 | @defspec with-output-to-temp-buffer buffer-name forms@dots{} | |
494 | This function executes @var{forms} while arranging to insert any | |
495 | output they print into the buffer named @var{buffer-name}. The buffer | |
496 | is then shown in some window for viewing, displayed but not selected. | |
497 | ||
498 | The string @var{buffer-name} specifies the temporary buffer, which | |
499 | need not already exist. The argument must be a string, not a buffer. | |
500 | The buffer is erased initially (with no questions asked), and it is | |
501 | marked as unmodified after @code{with-output-to-temp-buffer} exits. | |
502 | ||
503 | @code{with-output-to-temp-buffer} binds @code{standard-output} to the | |
504 | temporary buffer, then it evaluates the forms in @var{forms}. Output | |
505 | using the Lisp output functions within @var{forms} goes by default to | |
506 | that buffer (but screen display and messages in the echo area, although | |
507 | they are ``output'' in the general sense of the word, are not affected). | |
508 | @xref{Output Functions}. | |
509 | ||
510 | The value of the last form in @var{forms} is returned. | |
511 | ||
512 | @example | |
513 | @group | |
514 | ---------- Buffer: foo ---------- | |
515 | This is the contents of foo. | |
516 | ---------- Buffer: foo ---------- | |
517 | @end group | |
518 | ||
519 | @group | |
520 | (with-output-to-temp-buffer "foo" | |
521 | (print 20) | |
522 | (print standard-output)) | |
523 | @result{} #<buffer foo> | |
524 | ||
525 | ---------- Buffer: foo ---------- | |
526 | 20 | |
527 | ||
528 | #<buffer foo> | |
529 | ||
530 | ---------- Buffer: foo ---------- | |
531 | @end group | |
532 | @end example | |
533 | @end defspec | |
534 | ||
535 | @defvar temp-buffer-show-function | |
78608595 | 536 | If this variable is non-@code{nil}, @code{with-output-to-temp-buffer} |
42b85554 RS |
537 | calls it as a function to do the job of displaying a help buffer. The |
538 | function gets one argument, which is the buffer it should display. | |
539 | ||
540 | In Emacs versions 18 and earlier, this variable was called | |
541 | @code{temp-buffer-show-hook}. | |
542 | @end defvar | |
543 | ||
544 | @defun momentary-string-display string position &optional char message | |
545 | This function momentarily displays @var{string} in the current buffer at | |
546 | @var{position}. It has no effect on the undo list or on the buffer's | |
547 | modification status. | |
548 | ||
549 | The momentary display remains until the next input event. If the next | |
550 | input event is @var{char}, @code{momentary-string-display} ignores it | |
551 | and returns. Otherwise, that event remains buffered for subsequent use | |
552 | as input. Thus, typing @var{char} will simply remove the string from | |
553 | the display, while typing (say) @kbd{C-f} will remove the string from | |
554 | the display and later (presumably) move point forward. The argument | |
555 | @var{char} is a space by default. | |
556 | ||
557 | The return value of @code{momentary-string-display} is not meaningful. | |
558 | ||
bfe721d1 KH |
559 | If the string @var{string} does not contain control characters, you can |
560 | do the same job in a more general way by creating an overlay with a | |
561 | @code{before-string} property. @xref{Overlay Properties}. | |
562 | ||
42b85554 RS |
563 | If @var{message} is non-@code{nil}, it is displayed in the echo area |
564 | while @var{string} is displayed in the buffer. If it is @code{nil}, a | |
565 | default message says to type @var{char} to continue. | |
566 | ||
567 | In this example, point is initially located at the beginning of the | |
568 | second line: | |
569 | ||
570 | @example | |
571 | @group | |
572 | ---------- Buffer: foo ---------- | |
573 | This is the contents of foo. | |
574 | @point{}Second line. | |
575 | ---------- Buffer: foo ---------- | |
576 | @end group | |
577 | ||
578 | @group | |
579 | (momentary-string-display | |
580 | "**** Important Message! ****" | |
581 | (point) ?\r | |
582 | "Type RET when done reading") | |
583 | @result{} t | |
584 | @end group | |
585 | ||
586 | @group | |
587 | ---------- Buffer: foo ---------- | |
588 | This is the contents of foo. | |
589 | **** Important Message! ****Second line. | |
590 | ---------- Buffer: foo ---------- | |
591 | ||
592 | ---------- Echo Area ---------- | |
593 | Type RET when done reading | |
594 | ---------- Echo Area ---------- | |
595 | @end group | |
596 | @end example | |
597 | @end defun | |
598 | ||
599 | @node Overlays | |
600 | @section Overlays | |
601 | @cindex overlays | |
602 | ||
603 | You can use @dfn{overlays} to alter the appearance of a buffer's text on | |
bfe721d1 KH |
604 | the screen, for the sake of presentation features. An overlay is an |
605 | object that belongs to a particular buffer, and has a specified | |
606 | beginning and end. It also has properties that you can examine and set; | |
607 | these affect the display of the text within the overlay. | |
42b85554 RS |
608 | |
609 | @menu | |
610 | * Overlay Properties:: How to read and set properties. | |
611 | What properties do to the screen display. | |
612 | * Managing Overlays:: Creating, moving, finding overlays. | |
613 | @end menu | |
614 | ||
615 | @node Overlay Properties | |
616 | @subsection Overlay Properties | |
617 | ||
618 | Overlay properties are like text properties in some respects, but the | |
619 | differences are more important than the similarities. Text properties | |
620 | are considered a part of the text; overlays are specifically considered | |
621 | not to be part of the text. Thus, copying text between various buffers | |
622 | and strings preserves text properties, but does not try to preserve | |
623 | overlays. Changing a buffer's text properties marks the buffer as | |
624 | modified, while moving an overlay or changing its properties does not. | |
625 | Unlike text propery changes, overlay changes are not recorded in the | |
626 | buffer's undo list. | |
627 | ||
628 | @table @code | |
629 | @item priority | |
630 | @kindex priority @r{(overlay property)} | |
631 | This property's value (which should be a nonnegative number) determines | |
632 | the priority of the overlay. The priority matters when two or more | |
633 | overlays cover the same character and both specify a face for display; | |
634 | the one whose @code{priority} value is larger takes priority over the | |
635 | other, and its face attributes override the face attributes of the lower | |
636 | priority overlay. | |
637 | ||
638 | Currently, all overlays take priority over text properties. Please | |
639 | avoid using negative priority values, as we have not yet decided just | |
640 | what they should mean. | |
641 | ||
642 | @item window | |
643 | @kindex window @r{(overlay property)} | |
644 | If the @code{window} property is non-@code{nil}, then the overlay | |
645 | applies only on that window. | |
646 | ||
22697dac KH |
647 | @item category |
648 | @kindex category @r{(overlay property)} | |
649 | If an overlay has a @code{category} property, we call it the | |
bfe721d1 | 650 | @dfn{category} of the overlay. It should be a symbol. The properties |
22697dac KH |
651 | of the symbol serve as defaults for the properties of the overlay. |
652 | ||
42b85554 RS |
653 | @item face |
654 | @kindex face @r{(overlay property)} | |
22697dac KH |
655 | This property controls the font and color of text. Its value is a face |
656 | name or a list of face names. @xref{Faces}, for more information. This | |
657 | feature may be temporary; in the future, we may replace it with other | |
658 | ways of specifying how to display text. | |
42b85554 RS |
659 | |
660 | @item mouse-face | |
661 | @kindex mouse-face @r{(overlay property)} | |
662 | This property is used instead of @code{face} when the mouse is within | |
663 | the range of the overlay. This feature may be temporary, like | |
664 | @code{face}. | |
665 | ||
666 | @item modification-hooks | |
667 | @kindex modification-hooks @r{(overlay property)} | |
668 | This property's value is a list of functions to be called if any | |
669 | character within the overlay is changed or if text is inserted strictly | |
22697dac KH |
670 | within the overlay. |
671 | ||
672 | The hook functions are called both before and after each change. | |
673 | If the functions save the information they receive, and compare notes | |
674 | between calls, they can determine exactly what change has been made | |
675 | in the buffer text. | |
676 | ||
677 | When called before a change, each function receives four arguments: the | |
678 | overlay, @code{nil}, and the beginning and end of the text range to be | |
a890e1b0 | 679 | modified. |
42b85554 | 680 | |
22697dac KH |
681 | When called after a change, each function receives five arguments: the |
682 | overlay, @code{t}, the beginning and end of the text range just | |
683 | modified, and the length of the pre-change text replaced by that range. | |
684 | (For an insertion, the pre-change length is zero; for a deletion, that | |
685 | length is the number of characters deleted, and the post-change | |
bfe721d1 | 686 | beginning and end are equal.) |
22697dac | 687 | |
42b85554 RS |
688 | @item insert-in-front-hooks |
689 | @kindex insert-in-front-hooks @r{(overlay property)} | |
22697dac KH |
690 | This property's value is a list of functions to be called before and |
691 | after inserting text right at the beginning of the overlay. The calling | |
692 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
693 | |
694 | @item insert-behind-hooks | |
695 | @kindex insert-behind-hooks @r{(overlay property)} | |
22697dac KH |
696 | This property's value is a list of functions to be called before and |
697 | after inserting text right at the end of the overlay. The calling | |
698 | conventions are the same as for the @code{modification-hooks} functions. | |
42b85554 RS |
699 | |
700 | @item invisible | |
701 | @kindex invisible @r{(overlay property)} | |
22697dac KH |
702 | The @code{invisible} property can make the text in the overlay |
703 | invisible, which means that it does not appear on the screen. | |
704 | @xref{Invisible Text}, for details. | |
705 | ||
2a8095d5 | 706 | @ignore This isn't implemented yet |
22697dac KH |
707 | @item intangible |
708 | @kindex intangible @r{(overlay property)} | |
709 | The @code{intangible} property on an overlay works just like the | |
bfe721d1 | 710 | @code{intangible} text property. @xref{Special Properties}, for details. |
2a8095d5 | 711 | @end ignore |
42b85554 RS |
712 | |
713 | @item before-string | |
714 | @kindex before-string @r{(overlay property)} | |
715 | This property's value is a string to add to the display at the beginning | |
716 | of the overlay. The string does not appear in the buffer in any | |
22697dac KH |
717 | sense---only on the screen. The string should contain only characters |
718 | that display as a single column---control characters, including tabs or | |
719 | newlines, will give strange results. | |
42b85554 RS |
720 | |
721 | @item after-string | |
722 | @kindex after-string @r{(overlay property)} | |
723 | This property's value is a string to add to the display at the end of | |
724 | the overlay. The string does not appear in the buffer in any | |
22697dac KH |
725 | sense---only on the screen. The string should contain only characters |
726 | that display as a single column---control characters, including tabs or | |
727 | newlines, will give strange results. | |
728 | ||
729 | @item evaporate | |
730 | @kindex evaporate @r{(overlay property)} | |
731 | If this property is non-@code{nil}, the overlay is deleted automatically | |
732 | if it ever becomes empty (i.e., if it spans no characters). | |
d2609065 RS |
733 | |
734 | @item local-map | |
735 | @cindex keymap of character | |
736 | @kindex local-map @r{(text property)} | |
737 | If this property is non-@code{nil}, it specifies a keymap for a portion | |
738 | of the text. The property's value replaces the buffer's local map, when | |
739 | the character after point is within the overlay. @xref{Active Keymaps}. | |
42b85554 RS |
740 | @end table |
741 | ||
742 | These are the functions for reading and writing the properties of an | |
743 | overlay. | |
744 | ||
745 | @defun overlay-get overlay prop | |
746 | This function returns the value of property @var{prop} recorded in | |
22697dac KH |
747 | @var{overlay}, if any. If @var{overlay} does not record any value for |
748 | that property, but it does have a @code{category} property which is a | |
749 | symbol, that symbol's @var{prop} property is used. Otherwise, the value | |
750 | is @code{nil}. | |
42b85554 RS |
751 | @end defun |
752 | ||
753 | @defun overlay-put overlay prop value | |
754 | This function sets the value of property @var{prop} recorded in | |
755 | @var{overlay} to @var{value}. It returns @var{value}. | |
756 | @end defun | |
757 | ||
758 | See also the function @code{get-char-property} which checks both | |
759 | overlay properties and text properties for a given character. | |
760 | @xref{Examining Properties}. | |
761 | ||
762 | @node Managing Overlays | |
763 | @subsection Managing Overlays | |
764 | ||
765 | This section describes the functions to create, delete and move | |
766 | overlays, and to examine their contents. | |
767 | ||
768 | @defun make-overlay start end &optional buffer | |
78608595 | 769 | This function creates and returns an overlay that belongs to |
42b85554 RS |
770 | @var{buffer} and ranges from @var{start} to @var{end}. Both @var{start} |
771 | and @var{end} must specify buffer positions; they may be integers or | |
772 | markers. If @var{buffer} is omitted, the overlay is created in the | |
773 | current buffer. | |
774 | @end defun | |
775 | ||
776 | @defun overlay-start overlay | |
777 | This function returns the position at which @var{overlay} starts. | |
778 | @end defun | |
779 | ||
780 | @defun overlay-end overlay | |
781 | This function returns the position at which @var{overlay} ends. | |
782 | @end defun | |
783 | ||
784 | @defun overlay-buffer overlay | |
785 | This function returns the buffer that @var{overlay} belongs to. | |
786 | @end defun | |
787 | ||
788 | @defun delete-overlay overlay | |
789 | This function deletes @var{overlay}. The overlay continues to exist as | |
790 | a Lisp object, but ceases to be part of the buffer it belonged to, and | |
791 | ceases to have any effect on display. | |
792 | @end defun | |
793 | ||
794 | @defun move-overlay overlay start end &optional buffer | |
795 | This function moves @var{overlay} to @var{buffer}, and places its bounds | |
796 | at @var{start} and @var{end}. Both arguments @var{start} and @var{end} | |
797 | must specify buffer positions; they may be integers or markers. If | |
798 | @var{buffer} is omitted, the overlay stays in the same buffer. | |
799 | ||
800 | The return value is @var{overlay}. | |
801 | ||
802 | This is the only valid way to change the endpoints of an overlay. Do | |
803 | not try modifying the markers in the overlay by hand, as that fails to | |
804 | update other vital data structures and can cause some overlays to be | |
805 | ``lost''. | |
806 | @end defun | |
807 | ||
808 | @defun overlays-at pos | |
809 | This function returns a list of all the overlays that contain position | |
810 | @var{pos} in the current buffer. The list is in no particular order. | |
811 | An overlay contains position @var{pos} if it begins at or before | |
812 | @var{pos}, and ends after @var{pos}. | |
813 | @end defun | |
814 | ||
815 | @defun next-overlay-change pos | |
816 | This function returns the buffer position of the next beginning or end | |
817 | of an overlay, after @var{pos}. | |
818 | @end defun | |
819 | ||
22697dac KH |
820 | @defun previous-overlay-change pos |
821 | This function returns the buffer position of the previous beginning or | |
822 | end of an overlay, before @var{pos}. | |
823 | @end defun | |
824 | ||
42b85554 RS |
825 | @node Faces |
826 | @section Faces | |
827 | @cindex face | |
828 | ||
829 | A @dfn{face} is a named collection of graphical attributes: font, | |
830 | foreground color, background color and optional underlining. Faces | |
831 | control the display of text on the screen. | |
832 | ||
833 | @cindex face id | |
834 | Each face has its own @dfn{face id number} which distinguishes faces at | |
835 | low levels within Emacs. However, for most purposes, you can refer to | |
836 | faces in Lisp programs by their names. | |
837 | ||
22697dac KH |
838 | @defun facep object |
839 | This function returns @code{t} if @var{object} is a face name symbol (or | |
840 | if it is a vector of the kind used internally to record face data). It | |
841 | returns @code{nil} otherwise. | |
842 | @end defun | |
843 | ||
42b85554 RS |
844 | Each face name is meaningful for all frames, and by default it has the |
845 | same meaning in all frames. But you can arrange to give a particular | |
846 | face name a special meaning in one frame if you wish. | |
847 | ||
848 | @menu | |
849 | * Standard Faces:: The faces Emacs normally comes with. | |
850 | * Merging Faces:: How Emacs decides which face to use for a character. | |
851 | * Face Functions:: How to define and examine faces. | |
852 | @end menu | |
853 | ||
854 | @node Standard Faces | |
855 | @subsection Standard Faces | |
856 | ||
857 | This table lists all the standard faces and their uses. | |
858 | ||
859 | @table @code | |
860 | @item default | |
861 | @kindex default @r{(face name)} | |
862 | This face is used for ordinary text. | |
863 | ||
864 | @item modeline | |
865 | @kindex modeline @r{(face name)} | |
866 | This face is used for mode lines and menu bars. | |
867 | ||
868 | @item region | |
869 | @kindex region @r{(face name)} | |
870 | This face is used for highlighting the region in Transient Mark mode. | |
871 | ||
872 | @item secondary-selection | |
873 | @kindex secondary-selection @r{(face name)} | |
874 | This face is used to show any secondary selection you have made. | |
875 | ||
876 | @item highlight | |
877 | @kindex highlight @r{(face name)} | |
878 | This face is meant to be used for highlighting for various purposes. | |
879 | ||
880 | @item underline | |
881 | @kindex underline @r{(face name)} | |
882 | This face underlines text. | |
883 | ||
884 | @item bold | |
885 | @kindex bold @r{(face name)} | |
886 | This face uses a bold font, if possible. It uses the bold variant of | |
887 | the frame's font, if it has one. It's up to you to choose a default | |
888 | font that has a bold variant, if you want to use one. | |
889 | ||
890 | @item italic | |
891 | @kindex italic @r{(face name)} | |
892 | This face uses the italic variant of the frame's font, if it has one. | |
893 | ||
894 | @item bold-italic | |
895 | @kindex bold-italic @r{(face name)} | |
896 | This face uses the bold italic variant of the frame's font, if it has | |
897 | one. | |
898 | @end table | |
899 | ||
900 | @node Merging Faces | |
901 | @subsection Merging Faces for Display | |
902 | ||
903 | Here are all the ways to specify which face to use for display of text: | |
904 | ||
905 | @itemize @bullet | |
906 | @item | |
907 | With defaults. Each frame has a @dfn{default face}, whose id number is | |
908 | zero, which is used for all text that doesn't somehow specify another | |
909 | face. | |
910 | ||
911 | @item | |
912 | With text properties. A character may have a @code{face} property; if so, | |
78608595 | 913 | it is displayed with that face. @xref{Special Properties}. |
42b85554 RS |
914 | |
915 | If the character has a @code{mouse-face} property, that is used instead | |
916 | of the @code{face} property when the mouse is ``near enough'' to the | |
917 | character. | |
918 | ||
919 | @item | |
920 | With overlays. An overlay may have @code{face} and @code{mouse-face} | |
921 | properties too; they apply to all the text covered by the overlay. | |
922 | ||
bfe721d1 KH |
923 | @item |
924 | With a region that is active. In Transient Mark mode, the region is | |
925 | highlighted with a particular face (see @code{region-face}, below). | |
926 | ||
42b85554 RS |
927 | @item |
928 | With special glyphs. Each glyph can specify a particular face id | |
929 | number. @xref{Glyphs}. | |
930 | @end itemize | |
931 | ||
932 | If these various sources together specify more than one face for a | |
933 | particular character, Emacs merges the attributes of the various faces | |
934 | specified. The attributes of the faces of special glyphs come first; | |
bfe721d1 | 935 | then comes the face for region highlighting, if appropriate; |
42b85554 RS |
936 | then come attributes of faces from overlays, followed by those from text |
937 | properties, and last the default face. | |
938 | ||
939 | When multiple overlays cover one character, an overlay with higher | |
940 | priority overrides those with lower priority. @xref{Overlays}. | |
941 | ||
942 | If an attribute such as the font or a color is not specified in any of | |
943 | the above ways, the frame's own font or color is used. | |
944 | ||
945 | @node Face Functions | |
946 | @subsection Functions for Working with Faces | |
947 | ||
948 | The attributes a face can specify include the font, the foreground | |
949 | color, the background color, and underlining. The face can also leave | |
950 | these unspecified by giving the value @code{nil} for them. | |
951 | ||
952 | Here are the primitives for creating and changing faces. | |
953 | ||
954 | @defun make-face name | |
955 | This function defines a new face named @var{name}, initially with all | |
956 | attributes @code{nil}. It does nothing if there is already a face named | |
957 | @var{name}. | |
958 | @end defun | |
959 | ||
960 | @defun face-list | |
961 | This function returns a list of all defined face names. | |
962 | @end defun | |
963 | ||
964 | @defun copy-face old-face new-name &optional frame new-frame | |
965 | This function defines the face @var{new-name} as a copy of the existing | |
966 | face named @var{old-face}. It creates the face @var{new-name} if that | |
967 | doesn't already exist. | |
968 | ||
969 | If the optional argument @var{frame} is given, this function applies | |
970 | only to that frame. Otherwise it applies to each frame individually, | |
971 | copying attributes from @var{old-face} in each frame to @var{new-face} | |
972 | in the same frame. | |
973 | ||
974 | If the optional argument @var{new-frame} is given, then @code{copy-face} | |
975 | copies the attributes of @var{old-face} in @var{frame} to @var{new-name} | |
976 | in @var{new-frame}. | |
977 | @end defun | |
978 | ||
979 | You can modify the attributes of an existing face with the following | |
980 | functions. If you specify @var{frame}, they affect just that frame; | |
981 | otherwise, they affect all frames as well as the defaults that apply to | |
982 | new frames. | |
983 | ||
984 | @defun set-face-foreground face color &optional frame | |
985 | @defunx set-face-background face color &optional frame | |
78608595 RS |
986 | These functions set the foreground (or background, respectively) color |
987 | of face @var{face} to @var{color}. The argument @var{color} should be a | |
42b85554 | 988 | string, the name of a color. |
bfe721d1 KH |
989 | |
990 | Certain shades of gray are implemented by stipple patterns on | |
991 | black-and-white screens. | |
992 | @end defun | |
993 | ||
994 | @defun set-face-stipple face pattern &optional frame | |
995 | This function sets the background stipple pattern of face @var{face} to | |
996 | @var{pattern}. The argument @var{pattern} should be the name of a | |
997 | stipple pattern defined by the X server, or @code{nil} meaning don't use | |
998 | stipple. | |
999 | ||
1000 | Normally there is no need to pay attention to stipple patterns, because | |
1001 | they are used automatically to handle certain shades of gray. | |
42b85554 RS |
1002 | @end defun |
1003 | ||
1004 | @defun set-face-font face font &optional frame | |
1005 | This function sets the font of face @var{face}. The argument @var{font} | |
1006 | should be a string. | |
1007 | @end defun | |
1008 | ||
1009 | @defun set-face-underline-p face underline-p &optional frame | |
1010 | This function sets the underline attribute of face @var{face}. | |
1011 | Non-@code{nil} means do underline; @code{nil} means don't. | |
1012 | @end defun | |
1013 | ||
1014 | @defun invert-face face &optional frame | |
1015 | Swap the foreground and background colors of face @var{face}. If the | |
1016 | face doesn't specify both foreground and background, then its foreground | |
78608595 RS |
1017 | and background are set to the default background and foreground, |
1018 | respectively. | |
42b85554 RS |
1019 | @end defun |
1020 | ||
1021 | These functions examine the attributes of a face. If you don't | |
1022 | specify @var{frame}, they refer to the default data for new frames. | |
1023 | ||
1024 | @defun face-foreground face &optional frame | |
1025 | @defunx face-background face &optional frame | |
78608595 RS |
1026 | These functions return the foreground color (or background color, |
1027 | respectively) of face @var{face}, as a string. | |
42b85554 RS |
1028 | @end defun |
1029 | ||
bfe721d1 KH |
1030 | @defun face-stipple face &optional frame |
1031 | This function returns the name of the background stipple pattern of face | |
1032 | @var{face}, or @code{nil} if it doesn't have one. | |
1033 | @end defun | |
1034 | ||
42b85554 RS |
1035 | @defun face-font face &optional frame |
1036 | This function returns the name of the font of face @var{face}. | |
1037 | @end defun | |
1038 | ||
1039 | @defun face-underline-p face &optional frame | |
1040 | This function returns the underline attribute of face @var{face}. | |
1041 | @end defun | |
1042 | ||
bfe721d1 | 1043 | @defun face-id face |
42b85554 RS |
1044 | This function returns the face id number of face @var{face}. |
1045 | @end defun | |
1046 | ||
1047 | @defun face-equal face1 face2 &optional frame | |
1048 | This returns @code{t} if the faces @var{face1} and @var{face2} have the | |
1049 | same attributes for display. | |
1050 | @end defun | |
1051 | ||
1052 | @defun face-differs-from-default-p face &optional frame | |
1053 | This returns @code{t} if the face @var{face} displays differently from | |
1054 | the default face. A face is considered to be ``the same'' as the normal | |
1055 | face if each attribute is either the same as that of the default face or | |
1056 | @code{nil} (meaning to inherit from the default). | |
1057 | @end defun | |
1058 | ||
1059 | @defvar region-face | |
1060 | This variable's value specifies the face id to use to display characters | |
1061 | in the region when it is active (in Transient Mark mode only). The face | |
1062 | thus specified takes precedence over all faces that come from text | |
1063 | properties and overlays, for characters in the region. @xref{The Mark}, | |
1064 | for more information about Transient Mark mode. | |
1065 | ||
1066 | Normally, the value is the id number of the face named @code{region}. | |
1067 | @end defvar | |
1068 | ||
1069 | @node Blinking | |
1070 | @section Blinking Parentheses | |
1071 | @cindex parenthesis matching | |
1072 | @cindex blinking | |
1073 | @cindex balancing parentheses | |
1074 | @cindex close parenthesis | |
1075 | ||
1076 | This section describes the mechanism by which Emacs shows a matching | |
1077 | open parenthesis when the user inserts a close parenthesis. | |
1078 | ||
1079 | @vindex blink-paren-hook | |
1080 | @defvar blink-paren-function | |
1081 | The value of this variable should be a function (of no arguments) to | |
1082 | be called whenever a character with close parenthesis syntax is inserted. | |
1083 | The value of @code{blink-paren-function} may be @code{nil}, in which | |
1084 | case nothing is done. | |
1085 | ||
1086 | @quotation | |
b22f3a19 | 1087 | @strong{Please note:} This variable was named @code{blink-paren-hook} in |
42b85554 RS |
1088 | older Emacs versions, but since it is not called with the standard |
1089 | convention for hooks, it was renamed to @code{blink-paren-function} in | |
1090 | version 19. | |
1091 | @end quotation | |
1092 | @end defvar | |
1093 | ||
1094 | @defvar blink-matching-paren | |
1095 | If this variable is @code{nil}, then @code{blink-matching-open} does | |
1096 | nothing. | |
1097 | @end defvar | |
1098 | ||
1099 | @defvar blink-matching-paren-distance | |
1100 | This variable specifies the maximum distance to scan for a matching | |
1101 | parenthesis before giving up. | |
1102 | @end defvar | |
1103 | ||
bfe721d1 KH |
1104 | @defvar blink-matching-paren-delay |
1105 | This variable specifies the number of seconds for the cursor to remain | |
1106 | at the matching parenthesis. A fraction of a second often gives | |
1107 | good results, but the default is 1, which works on all systems. | |
1108 | @end defvar | |
1109 | ||
42b85554 RS |
1110 | @defun blink-matching-open |
1111 | This function is the default value of @code{blink-paren-function}. It | |
1112 | assumes that point follows a character with close parenthesis syntax and | |
1113 | moves the cursor momentarily to the matching opening character. If that | |
1114 | character is not already on the screen, it displays the character's | |
1115 | context in the echo area. To avoid long delays, this function does not | |
1116 | search farther than @code{blink-matching-paren-distance} characters. | |
1117 | ||
1118 | Here is an example of calling this function explicitly. | |
1119 | ||
1120 | @smallexample | |
1121 | @group | |
1122 | (defun interactive-blink-matching-open () | |
1123 | @c Do not break this line! -- rms. | |
1124 | @c The first line of a doc string | |
1125 | @c must stand alone. | |
1126 | "Indicate momentarily the start of sexp before point." | |
1127 | (interactive) | |
1128 | @end group | |
1129 | @group | |
1130 | (let ((blink-matching-paren-distance | |
1131 | (buffer-size)) | |
1132 | (blink-matching-paren t)) | |
1133 | (blink-matching-open))) | |
1134 | @end group | |
1135 | @end smallexample | |
1136 | @end defun | |
1137 | ||
1138 | @node Inverse Video | |
1139 | @section Inverse Video | |
1140 | @cindex Inverse Video | |
1141 | ||
1142 | @defopt inverse-video | |
1143 | @cindex highlighting | |
1144 | This variable controls whether Emacs uses inverse video for all text | |
1145 | on the screen. Non-@code{nil} means yes, @code{nil} means no. The | |
1146 | default is @code{nil}. | |
1147 | @end defopt | |
1148 | ||
1149 | @defopt mode-line-inverse-video | |
1150 | This variable controls the use of inverse video for mode lines. If it | |
bfe721d1 KH |
1151 | is non-@code{nil}, then mode lines are displayed in inverse video. |
1152 | Otherwise, mode lines are displayed normally, just like text. The | |
1153 | default is @code{t}. | |
1154 | ||
1155 | For X window frames, this displays mode lines using the face named | |
1156 | @code{modeline}, which is normally the inverse of the default face | |
1157 | unless you change it. | |
42b85554 RS |
1158 | @end defopt |
1159 | ||
1160 | @node Usual Display | |
1161 | @section Usual Display Conventions | |
1162 | ||
1163 | The usual display conventions define how to display each character | |
1164 | code. You can override these conventions by setting up a display table | |
1165 | (@pxref{Display Tables}). Here are the usual display conventions: | |
1166 | ||
1167 | @itemize @bullet | |
1168 | @item | |
1169 | Character codes 32 through 126 map to glyph codes 32 through 126. | |
1170 | Normally this means they display as themselves. | |
1171 | ||
1172 | @item | |
1173 | Character code 9 is a horizontal tab. It displays as whitespace | |
1174 | up to a position determined by @code{tab-width}. | |
1175 | ||
1176 | @item | |
1177 | Character code 10 is a newline. | |
1178 | ||
1179 | @item | |
1180 | All other codes in the range 0 through 31, and code 127, display in one | |
78608595 | 1181 | of two ways according to the value of @code{ctl-arrow}. If it is |
42b85554 RS |
1182 | non-@code{nil}, these codes map to sequences of two glyphs, where the |
1183 | first glyph is the @sc{ASCII} code for @samp{^}. (A display table can | |
1184 | specify a glyph to use instead of @samp{^}.) Otherwise, these codes map | |
1185 | just like the codes in the range 128 to 255. | |
1186 | ||
1187 | @item | |
1188 | Character codes 128 through 255 map to sequences of four glyphs, where | |
1189 | the first glyph is the @sc{ASCII} code for @samp{\}, and the others are | |
1190 | digit characters representing the code in octal. (A display table can | |
1191 | specify a glyph to use instead of @samp{\}.) | |
1192 | @end itemize | |
1193 | ||
1194 | The usual display conventions apply even when there is a display | |
1195 | table, for any character whose entry in the active display table is | |
1196 | @code{nil}. Thus, when you set up a display table, you need only | |
bfe721d1 | 1197 | specify the characters for which you want unusual behavior. |
42b85554 RS |
1198 | |
1199 | These variables affect the way certain characters are displayed on the | |
1200 | screen. Since they change the number of columns the characters occupy, | |
1201 | they also affect the indentation functions. | |
1202 | ||
1203 | @defopt ctl-arrow | |
1204 | @cindex control characters in display | |
1205 | This buffer-local variable controls how control characters are | |
1206 | displayed. If it is non-@code{nil}, they are displayed as a caret | |
1207 | followed by the character: @samp{^A}. If it is @code{nil}, they are | |
1208 | displayed as a backslash followed by three octal digits: @samp{\001}. | |
1209 | @end defopt | |
1210 | ||
1211 | @c Following may have overfull hbox. | |
1212 | @defvar default-ctl-arrow | |
1213 | The value of this variable is the default value for @code{ctl-arrow} in | |
1214 | buffers that do not override it. @xref{Default Value}. | |
1215 | @end defvar | |
1216 | ||
1217 | @defopt tab-width | |
1218 | The value of this variable is the spacing between tab stops used for | |
1219 | displaying tab characters in Emacs buffers. The default is 8. Note | |
1220 | that this feature is completely independent from the user-settable tab | |
1221 | stops used by the command @code{tab-to-tab-stop}. @xref{Indent Tabs}. | |
1222 | @end defopt | |
1223 | ||
1224 | @node Display Tables | |
1225 | @section Display Tables | |
1226 | ||
1227 | @cindex display table | |
1228 | You can use the @dfn{display table} feature to control how all 256 | |
1229 | possible character codes display on the screen. This is useful for | |
1230 | displaying European languages that have letters not in the @sc{ASCII} | |
1231 | character set. | |
1232 | ||
1233 | The display table maps each character code into a sequence of | |
1234 | @dfn{glyphs}, each glyph being an image that takes up one character | |
1235 | position on the screen. You can also define how to display each glyph | |
1236 | on your terminal, using the @dfn{glyph table}. | |
1237 | ||
1238 | @menu | |
1239 | * Display Table Format:: What a display table consists of. | |
1240 | * Active Display Table:: How Emacs selects a display table to use. | |
1241 | * Glyphs:: How to define a glyph, and what glyphs mean. | |
1242 | * ISO Latin 1:: How to use display tables | |
1243 | to support the ISO Latin 1 character set. | |
1244 | @end menu | |
1245 | ||
1246 | @node Display Table Format | |
1247 | @subsection Display Table Format | |
1248 | ||
50b04c36 | 1249 | A display table is actually an array of 262 elements. |
42b85554 RS |
1250 | |
1251 | @defun make-display-table | |
1252 | This creates and returns a display table. The table initially has | |
1253 | @code{nil} in all elements. | |
1254 | @end defun | |
1255 | ||
1256 | The first 256 elements correspond to character codes; the @var{n}th | |
1257 | element says how to display the character code @var{n}. The value | |
1258 | should be @code{nil} or a vector of glyph values (@pxref{Glyphs}). If | |
1259 | an element is @code{nil}, it says to display that character according to | |
22697dac KH |
1260 | the usual display conventions (@pxref{Usual Display}). |
1261 | ||
1262 | If you use the display table to change the display of newline | |
1263 | characters, the whole buffer will be displayed as one long ``line.'' | |
42b85554 | 1264 | |
50b04c36 | 1265 | The remaining six elements of a display table serve special purposes, |
42b85554 RS |
1266 | and @code{nil} means use the default stated below. |
1267 | ||
1268 | @table @asis | |
1269 | @item 256 | |
1270 | The glyph for the end of a truncated screen line (the default for this | |
1271 | is @samp{$}). @xref{Glyphs}. | |
1272 | @item 257 | |
1273 | The glyph for the end of a continued line (the default is @samp{\}). | |
1274 | @item 258 | |
1275 | The glyph for indicating a character displayed as an octal character | |
1276 | code (the default is @samp{\}). | |
1277 | @item 259 | |
1278 | The glyph for indicating a control character (the default is @samp{^}). | |
1279 | @item 260 | |
1280 | A vector of glyphs for indicating the presence of invisible lines (the | |
1281 | default is @samp{...}). @xref{Selective Display}. | |
50b04c36 JB |
1282 | @item 261 |
1283 | The glyph used to draw the border between side-by-side windows (the | |
1284 | default is @samp{|}). @xref{Splitting Windows}. | |
42b85554 RS |
1285 | @end table |
1286 | ||
1287 | For example, here is how to construct a display table that mimics the | |
1288 | effect of setting @code{ctl-arrow} to a non-@code{nil} value: | |
1289 | ||
1290 | @example | |
1291 | (setq disptab (make-display-table)) | |
1292 | (let ((i 0)) | |
1293 | (while (< i 32) | |
1294 | (or (= i ?\t) (= i ?\n) | |
1295 | (aset disptab i (vector ?^ (+ i 64)))) | |
1296 | (setq i (1+ i))) | |
1297 | (aset disptab 127 (vector ?^ ??))) | |
1298 | @end example | |
1299 | ||
1300 | @node Active Display Table | |
1301 | @subsection Active Display Table | |
1302 | @cindex active display table | |
1303 | ||
1304 | Each window can specify a display table, and so can each buffer. When | |
1305 | a buffer @var{b} is displayed in window @var{w}, display uses the | |
1306 | display table for window @var{w} if it has one; otherwise, the display | |
1307 | table for buffer @var{b} if it has one; otherwise, the standard display | |
1308 | table if any. The display table chosen is called the @dfn{active} | |
1309 | display table. | |
1310 | ||
1311 | @defun window-display-table window | |
1312 | This function returns @var{window}'s display table, or @code{nil} | |
1313 | if @var{window} does not have an assigned display table. | |
1314 | @end defun | |
1315 | ||
1316 | @defun set-window-display-table window table | |
1317 | This function sets the display table of @var{window} to @var{table}. | |
1318 | The argument @var{table} should be either a display table or | |
1319 | @code{nil}. | |
1320 | @end defun | |
1321 | ||
1322 | @defvar buffer-display-table | |
1323 | This variable is automatically local in all buffers; its value in a | |
1324 | particular buffer is the display table for that buffer, or @code{nil} if | |
1325 | the buffer does not have an assigned display table. | |
1326 | @end defvar | |
1327 | ||
1328 | @defvar standard-display-table | |
1329 | This variable's value is the default display table, used whenever a | |
1330 | window has no display table and neither does the buffer displayed in | |
1331 | that window. This variable is @code{nil} by default. | |
1332 | @end defvar | |
1333 | ||
1334 | If there is no display table to use for a particular window---that is, | |
1335 | if the window has none, its buffer has none, and | |
1336 | @code{standard-display-table} has none---then Emacs uses the usual | |
1337 | display conventions for all character codes in that window. @xref{Usual | |
1338 | Display}. | |
1339 | ||
1340 | @node Glyphs | |
1341 | @subsection Glyphs | |
1342 | ||
1343 | @cindex glyph | |
1344 | A @dfn{glyph} is a generalization of a character; it stands for an | |
1345 | image that takes up a single character position on the screen. Glyphs | |
1346 | are represented in Lisp as integers, just as characters are. | |
1347 | ||
1348 | @cindex glyph table | |
1349 | The meaning of each integer, as a glyph, is defined by the glyph | |
1350 | table, which is the value of the variable @code{glyph-table}. | |
1351 | ||
1352 | @defvar glyph-table | |
1353 | The value of this variable is the current glyph table. It should be a | |
1354 | vector; the @var{g}th element defines glyph code @var{g}. If the value | |
1355 | is @code{nil} instead of a vector, then all glyphs are simple (see | |
1356 | below). | |
1357 | @end defvar | |
1358 | ||
1359 | Here are the possible types of elements in the glyph table: | |
1360 | ||
1361 | @table @var | |
1362 | @item string | |
1363 | Send the characters in @var{string} to the terminal to output | |
1364 | this glyph. This alternative is available on character terminals, | |
1365 | but not under X. | |
1366 | ||
1367 | @item integer | |
1368 | Define this glyph code as an alias for code @var{integer}. You can use | |
1369 | an alias to specify a face code for the glyph; see below. | |
1370 | ||
1371 | @item @code{nil} | |
1372 | This glyph is simple. On an ordinary terminal, the glyph code mod 256 | |
1373 | is the character to output. With X, the glyph code mod 256 is the | |
1374 | character to output, and the glyph code divided by 256 specifies the | |
1375 | @dfn{face id number} to use while outputting it. @xref{Faces}. | |
1376 | @end table | |
1377 | ||
1378 | If a glyph code is greater than or equal to the length of the glyph | |
1379 | table, that code is automatically simple. | |
1380 | ||
1381 | @node ISO Latin 1 | |
1382 | @subsection ISO Latin 1 | |
1383 | ||
1384 | If you have a terminal that can handle the entire ISO Latin 1 character | |
1385 | set, you can arrange to use that character set as follows: | |
1386 | ||
1387 | @example | |
1388 | (require 'disp-table) | |
1389 | ;; @r{Set char codes 160--255 to display as themselves.} | |
1390 | ;; @r{(Codes 128--159 are the additional control characters.)} | |
1391 | (standard-display-8bit 160 255) | |
1392 | @end example | |
1393 | ||
1394 | If you are editing buffers written in the ISO Latin 1 character set and | |
78608595 RS |
1395 | your terminal doesn't handle anything but @sc{ASCII}, you can load the |
1396 | file @file{iso-ascii} to set up a display table that displays the other | |
1397 | ISO characters as explanatory sequences of @sc{ASCII} characters. For | |
1398 | example, the character ``o with umlaut'' displays as @samp{@{"o@}}. | |
42b85554 RS |
1399 | |
1400 | Some European countries have terminals that don't support ISO Latin 1 | |
1401 | but do support the special characters for that country's language. You | |
1402 | can define a display table to work one language using such terminals. | |
1403 | For an example, see @file{lisp/iso-swed.el}, which handles certain | |
1404 | Swedish terminals. | |
1405 | ||
1406 | You can load the appropriate display table for your terminal | |
1407 | automatically by writing a terminal-specific Lisp file for the terminal | |
1408 | type. | |
1409 | ||
1410 | @node Beeping | |
1411 | @section Beeping | |
1412 | @cindex beeping | |
1413 | @cindex bell | |
1414 | ||
1415 | You can make Emacs ring a bell (or blink the screen) to attract the | |
1416 | user's attention. Be conservative about how often you do this; frequent | |
1417 | bells can become irritating. Also be careful not to use beeping alone | |
1418 | when signaling an error is appropriate. (@xref{Errors}.) | |
1419 | ||
1420 | @defun ding &optional dont-terminate | |
1421 | @cindex keyboard macro termination | |
1422 | This function beeps, or flashes the screen (see @code{visible-bell} below). | |
1423 | It also terminates any keyboard macro currently executing unless | |
1424 | @var{dont-terminate} is non-@code{nil}. | |
1425 | @end defun | |
1426 | ||
1427 | @defun beep &optional dont-terminate | |
1428 | This is a synonym for @code{ding}. | |
1429 | @end defun | |
1430 | ||
1431 | @defvar visible-bell | |
1432 | This variable determines whether Emacs should flash the screen to | |
1433 | represent a bell. Non-@code{nil} means yes, @code{nil} means no. This | |
2b1e7b27 RS |
1434 | is effective under X windows, and on a character-only terminal provided |
1435 | the terminal's Termcap entry defines the visible bell capability | |
1436 | (@samp{vb}). | |
42b85554 RS |
1437 | @end defvar |
1438 | ||
1439 | @node Window Systems | |
1440 | @section Window Systems | |
1441 | ||
1442 | Emacs works with several window systems, most notably the X Window | |
1443 | System. Both Emacs and X use the term ``window'', but use it | |
1444 | differently. An Emacs frame is a single window as far as X is | |
1445 | concerned; the individual Emacs windows are not known to X at all. | |
1446 | ||
1447 | @defvar window-system | |
1448 | @cindex X Window System | |
1449 | This variable tells Lisp programs what window system Emacs is running | |
1450 | under. Its value should be a symbol such as @code{x} (if Emacs is | |
1451 | running under X) or @code{nil} (if Emacs is running on an ordinary | |
1452 | terminal). | |
1453 | @end defvar | |
1454 | ||
42b85554 RS |
1455 | @defvar window-setup-hook |
1456 | This variable is a normal hook which Emacs runs after loading your | |
1457 | @file{.emacs} file and the default initialization file (if any), after | |
1458 | loading terminal-specific Lisp code, and after running the hook | |
1459 | @code{term-setup-hook}. | |
1460 | ||
1461 | This hook is used for internal purposes: setting up communication with | |
1462 | the window system, and creating the initial window. Users should not | |
1463 | interfere with it. | |
1464 | @end defvar |