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Improve redisplay docs in Internals a bit.
author Stephen J. Turnbull <stephen@xemacs.org>
date Tue, 28 Jul 2009 23:24:15 +0900
parents b93587f33338
children 1cecc3e9f0a0
comparison
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4667:cbe5d2169270 4668:8b2a8ecf91cd
18219 18219
18220 @node Redisplay Piece by Piece, Modules for the Redisplay Mechanism, Line Start Cache, The Redisplay Mechanism 18220 @node Redisplay Piece by Piece, Modules for the Redisplay Mechanism, Line Start Cache, The Redisplay Mechanism
18221 @section Redisplay Piece by Piece 18221 @section Redisplay Piece by Piece
18222 @cindex redisplay piece by piece 18222 @cindex redisplay piece by piece
18223 18223
18224 As you can begin to see redisplay is complex and also not well 18224 Redisplay is complex and not very well documented. Chuck Thompson no
18225 documented. Chuck no longer works on XEmacs so this section is my take 18225 longer works on XEmacs so this section is my [presumably Ben's] take on
18226 on the workings of redisplay. 18226 the workings of redisplay.
18227 18227
18228 Redisplay happens in three phases: 18228 Redisplay happens in three phases:
18229 18229
18230 @enumerate 18230 @enumerate
18231 @item 18231 @item
18232 Determine desired display in area that needs redisplay. 18232 Determine desired display in area that needs redisplay.
18233 Implemented by @code{redisplay.c} 18233
18234 Implemented in @code{redisplay.c}
18234 @item 18235 @item
18235 Compare desired display with current display 18236 Compare desired display with current display
18236 Implemented by @code{redisplay-output.c} 18237
18237 @item 18238 Implemented in @code{redisplay-output.c}
18238 Output changes Implemented by @code{redisplay-output.c}, 18239 @item
18240 Output changes
18241
18242 Implemented in @code{redisplay-output.c},
18239 @code{redisplay-x.c}, @code{redisplay-msw.c} and @code{redisplay-tty.c} 18243 @code{redisplay-x.c}, @code{redisplay-msw.c} and @code{redisplay-tty.c}
18240 @end enumerate 18244 @end enumerate
18241 18245
18242 Steps 1 and 2 are device-independent and relatively complex. Step 3 is 18246 Steps 1 and 2 are device-independent and relatively complex. Step 3 is
18243 mostly device-dependent. 18247 mostly device-dependent.
18253 The @code{display_line} structures are tightly tied to buffers which 18257 The @code{display_line} structures are tightly tied to buffers which
18254 presents a problem for redisplay as this connection is bogus for the 18258 presents a problem for redisplay as this connection is bogus for the
18255 modeline. Hence the @code{display_line} generation routines are 18259 modeline. Hence the @code{display_line} generation routines are
18256 duplicated for generating the modeline. This means that the modeline 18260 duplicated for generating the modeline. This means that the modeline
18257 display code has many bugs that the standard redisplay code does not. 18261 display code has many bugs that the standard redisplay code does not.
18262 Perhaps the modeline redisplay could be unified with gutter redisplay
18263 (see below).
18258 18264
18259 The guts of @code{display_line} generation are in 18265 The guts of @code{display_line} generation are in
18260 @code{create_text_block}, which creates a single display line for the 18266 @code{create_text_block}, which creates a single display line for the
18261 desired locale. This incrementally parses the characters on the current 18267 desired locale. This incrementally parses the characters on the current
18262 line and generates redisplay structures for each. 18268 line and generates redisplay structures for each.
18265 a string we cannot use @code{create_text_block}. Instead we use 18271 a string we cannot use @code{create_text_block}. Instead we use
18266 @code{create_text_string_block} which performs the same function as 18272 @code{create_text_string_block} which performs the same function as
18267 @code{create_text_block} but for strings. Many of the complexities of 18273 @code{create_text_block} but for strings. Many of the complexities of
18268 @code{create_text_block} to do with cursor handling and selective 18274 @code{create_text_block} to do with cursor handling and selective
18269 display have been removed. 18275 display have been removed.
18276
18277 In the following, @code{create_text_block} only will be described, so
18278 keep in mind in the fact that modeline and gutter redisplay are somewhat
18279 different.
18280
18281 @code{create_text_block} takes a @code{struct window *}, the index of a
18282 line in the text (a @code{Bytebpos}) and a @code{struct display_line *},
18283 as well as two arguments @code{prop} and @code{type} (as yet
18284 undocumented). Given the window, it can derive the relevant buffer, and
18285 use the @code{Bytebpos} to find the line of text. It then walks over
18286 the characters in the text and regenerates the display line information
18287 for each.
18288
18289 @code{create_text_block} calls out to @code{extent_fragment_update} to
18290 get information about faces (fonts and colors), which are represented as
18291 a @code{face_index}, an index into a table of merged faces. Faces must
18292 be merged because (1) a face may inherit properties from their parents
18293 and (2) faces may be only partially specified, in which case redisplay
18294 must fall back to faces associated with extents earlier in the extent
18295 order (@pxref{Extent Ordering}). Since getting complete information
18296 about a face involves instantantiating many specifiers, we keep a cache
18297 of this information, and a @code{face_index} is an index into the cache.
18298
18299 @code{extent_fragment_update} calls out to
18300 @code{get_extent_fragment_face_cache_index}, which in turn calls
18301 @code{merge_face_cachel_data} on each relevant face.
18302 @code{merge_face_cachel_data} is straightforward, except for font
18303 handling. In the case of fonts, the legacy XLFD model has a different
18304 font for each Mule charset (in fact, both the XLFD model of I18N and
18305 that of Mule are derived from the same root, ISO 2022, and so mesh
18306 well---or as well as anything based on ISO 2022 can). This means that
18307 @code{merge_face_cachel_data} has to iterate over the list of Mule
18308 charsets, and update the font for each one.
18309
18310 @code{create_text_block} is not responsible for creating face cachels.
18311 That is done by @code{redisplay_output_layout},
18312 @code{redisplay_text_width_string} or
18313 @code{redisplay_text_width_ichar_string}, via
18314 @code{ensure_face_cachel_complete}, with the actual work being done by
18315 @code{ensure_face_cachel_contains_charset}.
18270 18316
18271 @node Modules for the Redisplay Mechanism, Modules for other Display-Related Lisp Objects, Redisplay Piece by Piece, The Redisplay Mechanism 18317 @node Modules for the Redisplay Mechanism, Modules for other Display-Related Lisp Objects, Redisplay Piece by Piece, The Redisplay Mechanism
18272 @section Modules for the Redisplay Mechanism 18318 @section Modules for the Redisplay Mechanism
18273 @cindex modules for the redisplay mechanism 18319 @cindex modules for the redisplay mechanism
18274 @cindex redisplay mechanism, modules for the 18320 @cindex redisplay mechanism, modules for the