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27 fontconfig/doc/local-fontconfig-devel.sgml
29 Copyright © 2003 Keith Packard
31 Permission to use, copy, modify, distribute, and sell this software and its
32 documentation for any purpose is hereby granted without fee, provided that
33 the above copyright notice appear in all copies and that both that
34 copyright notice and this permission notice appear in supporting
35 documentation, and that the name of the author(s) not be used in
36 advertising or publicity pertaining to distribution of the software without
37 specific, written prior permission. The authors make no
38 representations about the suitability of this software for any purpose. It
39 is provided "as is" without express or implied warranty.
41 THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
42 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
43 EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR
44 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
45 DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
46 TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
47 PERFORMANCE OF THIS SOFTWARE.
50 <title>Fontconfig Developers Reference, Version &version; </title>
53 <firstname>Keith</firstname>
54 <surname>Packard</surname>
55 <affiliation><orgname>
56 HP Cambridge Research Lab
57 </orgname></affiliation>
59 <authorinitials>KRP</authorinitials>
60 <productname>Fontconfig</productname>
61 <productnumber>&version;</productnumber>
64 Copyright © 2002 Keith Packard
66 Permission to use, copy, modify, distribute, and sell this software and its
67 documentation for any purpose is hereby granted without fee, provided that
68 the above copyright notice appear in all copies and that both that
69 copyright notice and this permission notice appear in supporting
70 documentation, and that the name of the author(s) not be used in
71 advertising or publicity pertaining to distribution of the software without
72 specific, written prior permission. The authors make no
73 representations about the suitability of this software for any purpose. It
74 is provided "as is" without express or implied warranty.
76 THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
77 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
78 EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR
79 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
80 DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
81 TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
82 PERFORMANCE OF THIS SOFTWARE.
86 <sect1><title>DESCRIPTION</title>
88 Fontconfig is a library designed to provide system-wide font configuration,
89 customization and application access.
92 <sect1><title>FUNCTIONAL OVERVIEW</title>
94 Fontconfig contains two essential modules, the configuration module which
95 builds an internal configuration from XML files and the matching module
96 which accepts font patterns and returns the nearest matching font.
98 <sect2><title>FONT CONFIGURATION</title>
100 The configuration module consists of the FcConfig datatype, libexpat and
101 FcConfigParse which walks over an XML tree and amends a configuration with
102 data found within. From an external perspective, configuration of the
103 library consists of generating a valid XML tree and feeding that to
104 FcConfigParse. The only other mechanism provided to applications for
105 changing the running configuration is to add fonts and directories to the
106 list of application-provided font files.
108 The intent is to make font configurations relatively static, and shared by
109 as many applications as possible. It is hoped that this will lead to more
110 stable font selection when passing names from one application to another.
111 XML was chosen as a configuration file format because it provides a format
112 which is easy for external agents to edit while retaining the correct
113 structure and syntax.
115 Font configuration is separate from font matching; applications needing to
116 do their own matching can access the available fonts from the library and
117 perform private matching. The intent is to permit applications to pick and
118 choose appropriate functionality from the library instead of forcing them to
119 choose between this library and a private configuration mechanism. The hope
120 is that this will ensure that configuration of fonts for all applications
121 can be centralized in one place. Centralizing font configuration will
122 simplify and regularize font installation and customization.
126 <title>FONT PROPERTIES</title>
128 While font patterns may contain essentially any properties, there are some
129 well known properties with associated types. Fontconfig uses some of these
130 properties for font matching and font completion. Others are provided as a
131 convenience for the application's rendering mechanism.
136 Property C Preprocessor Symbol Type Description
137 ----------------------------------------------------
138 family FC_FAMILY String Font family names
139 familylang FC_FAMILYLANG String Language corresponding to
141 style FC_STYLE String Font style. Overrides weight
143 stylelang FC_STYLELANG String Language corresponding to
145 fullname FC_FULLNAME String Font face full name where
146 different from family and
148 fullnamelang FC_FULLNAMELANG String Language corresponding to
150 slant FC_SLANT Int Italic, oblique or roman
151 weight FC_WEIGHT Int Light, medium, demibold,
153 size FC_SIZE Double Point size
154 width FC_WIDTH Int Condensed, normal or expanded
155 aspect FC_ASPECT Double Stretches glyphs horizontally
157 pixelsize FC_PIXEL_SIZE Double Pixel size
158 spacing FC_SPACING Int Proportional, dual-width,
159 monospace or charcell
160 foundry FC_FOUNDRY String Font foundry name
161 antialias FC_ANTIALIAS Bool Whether glyphs can be
163 hinting FC_HINTING Bool Whether the rasterizer should
165 hintstyle FC_HINT_STYLE Int Automatic hinting style
166 verticallayout FC_VERTICAL_LAYOUT Bool Use vertical layout
167 autohint FC_AUTOHINT Bool Use autohinter instead of
169 globaladvance FC_GLOBAL_ADVANCE Bool Use font global advance data (deprecated)
170 file FC_FILE String The filename holding the font
171 index FC_INDEX Int The index of the font within
173 ftface FC_FT_FACE FT_Face Use the specified FreeType
175 rasterizer FC_RASTERIZER String Which rasterizer is in use (deprecated)
176 outline FC_OUTLINE Bool Whether the glyphs are outlines
177 scalable FC_SCALABLE Bool Whether glyphs can be scaled
178 scale FC_SCALE Double Scale factor for point->pixel
179 conversions (deprecated)
180 symbol FC_SYMBOL Bool Whether font uses MS symbol-font encoding
181 color FC_COLOR Bool Whether any glyphs have color
182 dpi FC_DPI Double Target dots per inch
183 rgba FC_RGBA Int unknown, rgb, bgr, vrgb,
184 vbgr, none - subpixel geometry
185 lcdfilter FC_LCD_FILTER Int Type of LCD filter
186 minspace FC_MINSPACE Bool Eliminate leading from line
188 charset FC_CHARSET CharSet Unicode chars encoded by
190 lang FC_LANG LangSet Set of RFC-3066-style
191 languages this font supports
192 fontversion FC_FONTVERSION Int Version number of the font
193 capability FC_CAPABILITY String List of layout capabilities in
195 fontformat FC_FONTFORMAT String String name of the font format
196 embolden FC_EMBOLDEN Bool Rasterizer should
197 synthetically embolden the font
198 embeddedbitmap FC_EMBEDDED_BITMAP Bool Use the embedded bitmap instead
200 decorative FC_DECORATIVE Bool Whether the style is a decorative
202 fontfeatures FC_FONT_FEATURES String List of extra feature tags in
203 OpenType to be enabled
204 namelang FC_NAMELANG String Language name to be used for the
205 default value of familylang,
206 stylelang and fullnamelang
207 prgname FC_PRGNAME String Name of the running program
208 hash FC_HASH String SHA256 hash value of the font data
209 with "sha256:" prefix (deprecated)
210 postscriptname FC_POSTSCRIPT_NAME String Font name in PostScript
214 <sect1><title>Datatypes</title>
216 Fontconfig uses abstract data types to hide internal implementation details
217 for most data structures. A few structures are exposed where appropriate.
219 <sect2><title>FcChar8, FcChar16, FcChar32, FcBool</title>
221 These are primitive data types; the FcChar* types hold precisely the number
222 of bits stated (if supported by the C implementation). FcBool holds
223 one of two C preprocessor symbols: FcFalse or FcTrue.
226 <sect2><title>FcMatrix</title>
228 An FcMatrix holds an affine transformation, usually used to reshape glyphs.
229 A small set of matrix operations are provided to manipulate these.
231 typedef struct _FcMatrix {
232 double xx, xy, yx, yy;
237 <sect2><title>FcCharSet</title>
239 An FcCharSet is an abstract type that holds the set of encoded Unicode chars
240 in a font. Operations to build and compare these sets are provided.
243 <sect2><title>FcLangSet</title>
245 An FcLangSet is an abstract type that holds the set of languages supported
246 by a font. Operations to build and compare these sets are provided. These
247 are computed for a font based on orthographic information built into the
248 fontconfig library. Fontconfig has orthographies for all of the ISO 639-1
249 languages except for MS, NA, PA, PS, QU, RN, RW, SD, SG, SN, SU and ZA. If
250 you have orthographic information for any of these languages, please submit
254 <sect2><title>FcLangResult</title>
256 An FcLangResult is an enumeration used to return the results of comparing
257 two language strings or FcLangSet objects. FcLangEqual means the
258 objects match language and territory. FcLangDifferentTerritory means
259 the objects match in language but differ in territory.
260 FcLangDifferentLang means the objects differ in language.
263 <sect2><title>FcType</title>
265 Tags the kind of data stored in an FcValue.
268 <sect2><title>FcValue</title>
270 An FcValue object holds a single value with one of a number of different
271 types. The 'type' tag indicates which member is valid.
273 typedef struct _FcValue {
290 Type Union member Datatype
291 --------------------------------
292 FcTypeVoid (none) (none)
294 FcTypeDouble d double
295 FcTypeString s FcChar8 *
297 FcTypeMatrix m FcMatrix *
298 FcTypeCharSet c FcCharSet *
299 FcTypeFTFace f void * (FT_Face)
300 FcTypeLangSet l FcLangSet *
304 <sect2><title>FcPattern</title>
306 holds a set of names with associated value lists; each name refers to a
307 property of a font. FcPatterns are used as inputs to the matching code as
308 well as holding information about specific fonts. Each property can hold
309 one or more values; conventionally all of the same type, although the
310 interface doesn't demand that.
313 <sect2><title>FcFontSet</title>
316 typedef struct _FcFontSet {
322 An FcFontSet contains a list of FcPatterns. Internally fontconfig uses this
323 data structure to hold sets of fonts. Externally, fontconfig returns the
324 results of listing fonts in this format. 'nfont' holds the number of
325 patterns in the 'fonts' array; 'sfont' is used to indicate the size of that
329 <sect2><title>FcStrSet, FcStrList</title>
331 FcStrSet holds a list of strings that can be appended to and enumerated.
332 Its unique characteristic is that the enumeration works even while strings
333 are appended during enumeration. FcStrList is used during enumeration to
334 safely and correctly walk the list of strings even while that list is edited
335 in the middle of enumeration.
338 <sect2><title>FcObjectSet</title>
341 typedef struct _FcObjectSet {
344 const char **objects;
347 holds a set of names and is used to specify which fields from fonts are
348 placed in the the list of returned patterns when listing fonts.
351 <sect2><title>FcObjectType</title>
354 typedef struct _FcObjectType {
359 marks the type of a pattern element generated when parsing font names.
360 Applications can add new object types so that font names may contain the new
364 <sect2><title>FcConstant</title>
367 typedef struct _FcConstant {
373 Provides for symbolic constants for new pattern elements. When 'name' is
374 seen in a font name, an 'object' element is created with value 'value'.
377 <sect2><title>FcBlanks</title>
379 holds a list of Unicode chars which are expected to be blank; unexpectedly
380 blank chars are assumed to be invalid and are elided from the charset
381 associated with the font.
384 <sect2><title>FcFileCache</title>
386 holds the per-user cache information for use while loading the font
387 database. This is built automatically for the current configuration when
388 that is loaded. Applications must always pass '0' when one is requested.
391 <sect2><title>FcConfig</title>
393 holds a complete configuration of the library; there is one default
394 configuration, other can be constructed from XML data structures. All
395 public entry points that need global data can take an optional FcConfig*
396 argument; passing 0 uses the default configuration. FcConfig objects hold two
397 sets of fonts, the first contains those specified by the configuration, the
398 second set holds those added by the application at run-time. Interfaces
399 that need to reference a particular set use one of the FcSetName enumerated
403 <sect2><title>FcSetName</title>
405 Specifies one of the two sets of fonts available in a configuration;
406 FcSetSystem for those fonts specified in the configuration and
407 FcSetApplication which holds fonts provided by the application.
410 <sect2><title>FcResult</title>
412 Used as a return type for functions manipulating FcPattern objects.
416 -----------------------------------------------------------
417 FcResultMatch Object exists with the specified ID
418 FcResultNoMatch Object doesn't exist at all
419 FcResultTypeMismatch Object exists, but the type doesn't match
420 FcResultNoId Object exists, but has fewer values
422 FcResultOutOfMemory malloc failed
426 <sect2><title>FcAtomic</title>
428 Used for locking access to configuration files. Provides a safe way to update
432 <sect2><title>FcCache</title>
434 Holds information about the fonts contained in a single directory. Normal
435 applications need not worry about this as caches for font access are
436 automatically managed by the library. Applications dealing with cache
437 management may want to use some of these objects in their work, however the
438 included 'fc-cache' program generally suffices for all of that.
442 <sect1><title>FUNCTIONS</title>
444 These are grouped by functionality, often using the main data type being
447 <sect2><title>Initialization</title>
449 These functions provide some control over how the library is initialized.
453 <sect2><title>FcPattern</title>
455 An FcPattern is an opaque type that holds both patterns to match against the
456 available fonts, as well as the information about each font.
461 <sect2><title>FcFontSet</title>
463 An FcFontSet simply holds a list of patterns; these are used to return the
464 results of listing available fonts.
468 <sect2><title>FcObjectSet</title>
470 An FcObjectSet holds a list of pattern property names; it is used to
471 indicate which properties are to be returned in the patterns from
476 <sect2><title>FreeType specific functions</title>
478 While the fontconfig library doesn't insist that FreeType be used as the
479 rasterization mechanism for fonts, it does provide some convenience
484 <sect2><title>FcValue</title>
486 FcValue is a structure containing a type tag and a union of all possible
487 datatypes. The tag is an enum of type
488 <emphasis>FcType</emphasis>
489 and is intended to provide a measure of run-time
490 typechecking, although that depends on careful programming.
494 <sect2><title>FcCharSet</title>
496 An FcCharSet is a boolean array indicating a set of Unicode chars. Those
497 associated with a font are marked constant and cannot be edited.
498 FcCharSets may be reference counted internally to reduce memory consumption;
499 this may be visible to applications as the result of FcCharSetCopy may
500 return it's argument, and that CharSet may remain unmodifiable.
504 <sect2><title>FcLangSet</title>
506 An FcLangSet is a set of language names (each of which include language and
507 an optional territory). They are used when selecting fonts to indicate which
508 languages the fonts need to support. Each font is marked, using language
509 orthography information built into fontconfig, with the set of supported
514 <sect2><title>FcMatrix</title>
516 FcMatrix structures hold an affine transformation in matrix form.
520 <sect2><title>FcRange</title>
522 An FcRange holds two variables to indicate a range in between.
526 <sect2><title>FcConfig</title>
528 An FcConfig object holds the internal representation of a configuration.
529 There is a default configuration which applications may use by passing 0 to
530 any function using the data within an FcConfig.
534 <sect2><title>FcObjectType</title>
536 Provides for application-specified font name object types so that new
537 pattern elements can be generated from font names.
541 <sect2><title>FcConstant</title>
543 Provides for application-specified symbolic constants for font names.
547 <sect2><title>FcWeight</title>
549 Maps weights to and from OpenType weights.
553 <sect2><title>FcBlanks</title>
555 An FcBlanks object holds a list of Unicode chars which are expected to
556 be blank when drawn. When scanning new fonts, any glyphs which are
557 empty and not in this list will be assumed to be broken and not placed in
558 the FcCharSet associated with the font. This provides a significantly more
559 accurate CharSet for applications.
563 <sect2><title>FcAtomic</title>
565 These functions provide a safe way to update configuration files, allowing ongoing
566 reading of the old configuration file while locked for writing and ensuring that a
567 consistent and complete version of the configuration file is always available.
571 <sect2><title>File and Directory routines</title>
573 These routines work with font files and directories, including font
574 directory cache files.
579 <sect2><title>FcCache routines</title>
581 These routines work with font directory caches, accessing their contents in
582 limited ways. It is not expected that normal applications will need to use
587 <sect2><title>FcStrSet and FcStrList</title>
589 A data structure for enumerating strings, used to list directories while
590 scanning the configuration as directories are added while scanning.
594 <sect2><title>String utilities</title>
596 Fontconfig manipulates many UTF-8 strings represented with the FcChar8 type.
597 These functions are exposed to help applications deal with these UTF-8
598 strings in a locale-insensitive manner.