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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
180 color FC_COLOR Bool Whether any glyphs have color
181 dpi FC_DPI Double Target dots per inch
182 rgba FC_RGBA Int unknown, rgb, bgr, vrgb,
183 vbgr, none - subpixel geometry
184 lcdfilter FC_LCD_FILTER Int Type of LCD filter
185 minspace FC_MINSPACE Bool Eliminate leading from line
187 charset FC_CHARSET CharSet Unicode chars encoded by
189 lang FC_LANG LangSet Set of RFC-3066-style
190 languages this font supports
191 fontversion FC_FONTVERSION Int Version number of the font
192 capability FC_CAPABILITY String List of layout capabilities in
194 fontformat FC_FONTFORMAT String String name of the font format
195 embolden FC_EMBOLDEN Bool Rasterizer should
196 synthetically embolden the font
197 embeddedbitmap FC_EMBEDDED_BITMAP Bool Use the embedded bitmap instead
199 decorative FC_DECORATIVE Bool Whether the style is a decorative
201 fontfeatures FC_FONT_FEATURES String List of extra feature tags in
202 OpenType to be enabled
203 namelang FC_NAMELANG String Language name to be used for the
204 default value of familylang,
205 stylelang and fullnamelang
206 prgname FC_PRGNAME String Name of the running program
207 hash FC_HASH String SHA256 hash value of the font data
208 with "sha256:" prefix (deprecated)
209 postscriptname FC_POSTSCRIPT_NAME String Font name in PostScript
213 <sect1><title>Datatypes</title>
215 Fontconfig uses abstract data types to hide internal implementation details
216 for most data structures. A few structures are exposed where appropriate.
218 <sect2><title>FcChar8, FcChar16, FcChar32, FcBool</title>
220 These are primitive data types; the FcChar* types hold precisely the number
221 of bits stated (if supported by the C implementation). FcBool holds
222 one of two C preprocessor symbols: FcFalse or FcTrue.
225 <sect2><title>FcMatrix</title>
227 An FcMatrix holds an affine transformation, usually used to reshape glyphs.
228 A small set of matrix operations are provided to manipulate these.
230 typedef struct _FcMatrix {
231 double xx, xy, yx, yy;
236 <sect2><title>FcCharSet</title>
238 An FcCharSet is an abstract type that holds the set of encoded Unicode chars
239 in a font. Operations to build and compare these sets are provided.
242 <sect2><title>FcLangSet</title>
244 An FcLangSet is an abstract type that holds the set of languages supported
245 by a font. Operations to build and compare these sets are provided. These
246 are computed for a font based on orthographic information built into the
247 fontconfig library. Fontconfig has orthographies for all of the ISO 639-1
248 languages except for MS, NA, PA, PS, QU, RN, RW, SD, SG, SN, SU and ZA. If
249 you have orthographic information for any of these languages, please submit
253 <sect2><title>FcLangResult</title>
255 An FcLangResult is an enumeration used to return the results of comparing
256 two language strings or FcLangSet objects. FcLangEqual means the
257 objects match language and territory. FcLangDifferentTerritory means
258 the objects match in language but differ in territory.
259 FcLangDifferentLang means the objects differ in language.
262 <sect2><title>FcType</title>
264 Tags the kind of data stored in an FcValue.
267 <sect2><title>FcValue</title>
269 An FcValue object holds a single value with one of a number of different
270 types. The 'type' tag indicates which member is valid.
272 typedef struct _FcValue {
289 Type Union member Datatype
290 --------------------------------
291 FcTypeVoid (none) (none)
293 FcTypeDouble d double
294 FcTypeString s FcChar8 *
296 FcTypeMatrix m FcMatrix *
297 FcTypeCharSet c FcCharSet *
298 FcTypeFTFace f void * (FT_Face)
299 FcTypeLangSet l FcLangSet *
303 <sect2><title>FcPattern</title>
305 holds a set of names with associated value lists; each name refers to a
306 property of a font. FcPatterns are used as inputs to the matching code as
307 well as holding information about specific fonts. Each property can hold
308 one or more values; conventionally all of the same type, although the
309 interface doesn't demand that.
312 <sect2><title>FcFontSet</title>
315 typedef struct _FcFontSet {
321 An FcFontSet contains a list of FcPatterns. Internally fontconfig uses this
322 data structure to hold sets of fonts. Externally, fontconfig returns the
323 results of listing fonts in this format. 'nfont' holds the number of
324 patterns in the 'fonts' array; 'sfont' is used to indicate the size of that
328 <sect2><title>FcStrSet, FcStrList</title>
330 FcStrSet holds a list of strings that can be appended to and enumerated.
331 Its unique characteristic is that the enumeration works even while strings
332 are appended during enumeration. FcStrList is used during enumeration to
333 safely and correctly walk the list of strings even while that list is edited
334 in the middle of enumeration.
337 <sect2><title>FcObjectSet</title>
340 typedef struct _FcObjectSet {
343 const char **objects;
346 holds a set of names and is used to specify which fields from fonts are
347 placed in the the list of returned patterns when listing fonts.
350 <sect2><title>FcObjectType</title>
353 typedef struct _FcObjectType {
358 marks the type of a pattern element generated when parsing font names.
359 Applications can add new object types so that font names may contain the new
363 <sect2><title>FcConstant</title>
366 typedef struct _FcConstant {
372 Provides for symbolic constants for new pattern elements. When 'name' is
373 seen in a font name, an 'object' element is created with value 'value'.
376 <sect2><title>FcBlanks</title>
378 holds a list of Unicode chars which are expected to be blank; unexpectedly
379 blank chars are assumed to be invalid and are elided from the charset
380 associated with the font.
383 <sect2><title>FcFileCache</title>
385 holds the per-user cache information for use while loading the font
386 database. This is built automatically for the current configuration when
387 that is loaded. Applications must always pass '0' when one is requested.
390 <sect2><title>FcConfig</title>
392 holds a complete configuration of the library; there is one default
393 configuration, other can be constructed from XML data structures. All
394 public entry points that need global data can take an optional FcConfig*
395 argument; passing 0 uses the default configuration. FcConfig objects hold two
396 sets of fonts, the first contains those specified by the configuration, the
397 second set holds those added by the application at run-time. Interfaces
398 that need to reference a particular set use one of the FcSetName enumerated
402 <sect2><title>FcSetName</title>
404 Specifies one of the two sets of fonts available in a configuration;
405 FcSetSystem for those fonts specified in the configuration and
406 FcSetApplication which holds fonts provided by the application.
409 <sect2><title>FcResult</title>
411 Used as a return type for functions manipulating FcPattern objects.
415 -----------------------------------------------------------
416 FcResultMatch Object exists with the specified ID
417 FcResultNoMatch Object doesn't exist at all
418 FcResultTypeMismatch Object exists, but the type doesn't match
419 FcResultNoId Object exists, but has fewer values
421 FcResultOutOfMemory malloc failed
425 <sect2><title>FcAtomic</title>
427 Used for locking access to configuration files. Provides a safe way to update
431 <sect2><title>FcCache</title>
433 Holds information about the fonts contained in a single directory. Normal
434 applications need not worry about this as caches for font access are
435 automatically managed by the library. Applications dealing with cache
436 management may want to use some of these objects in their work, however the
437 included 'fc-cache' program generally suffices for all of that.
441 <sect1><title>FUNCTIONS</title>
443 These are grouped by functionality, often using the main data type being
446 <sect2><title>Initialization</title>
448 These functions provide some control over how the library is initialized.
452 <sect2><title>FcPattern</title>
454 An FcPattern is an opaque type that holds both patterns to match against the
455 available fonts, as well as the information about each font.
460 <sect2><title>FcFontSet</title>
462 An FcFontSet simply holds a list of patterns; these are used to return the
463 results of listing available fonts.
467 <sect2><title>FcObjectSet</title>
469 An FcObjectSet holds a list of pattern property names; it is used to
470 indicate which properties are to be returned in the patterns from
475 <sect2><title>FreeType specific functions</title>
477 While the fontconfig library doesn't insist that FreeType be used as the
478 rasterization mechanism for fonts, it does provide some convenience
483 <sect2><title>FcValue</title>
485 FcValue is a structure containing a type tag and a union of all possible
486 datatypes. The tag is an enum of type
487 <emphasis>FcType</emphasis>
488 and is intended to provide a measure of run-time
489 typechecking, although that depends on careful programming.
493 <sect2><title>FcCharSet</title>
495 An FcCharSet is a boolean array indicating a set of Unicode chars. Those
496 associated with a font are marked constant and cannot be edited.
497 FcCharSets may be reference counted internally to reduce memory consumption;
498 this may be visible to applications as the result of FcCharSetCopy may
499 return it's argument, and that CharSet may remain unmodifiable.
503 <sect2><title>FcLangSet</title>
505 An FcLangSet is a set of language names (each of which include language and
506 an optional territory). They are used when selecting fonts to indicate which
507 languages the fonts need to support. Each font is marked, using language
508 orthography information built into fontconfig, with the set of supported
513 <sect2><title>FcMatrix</title>
515 FcMatrix structures hold an affine transformation in matrix form.
519 <sect2><title>FcRange</title>
521 An FcRange holds two variables to indicate a range in between.
525 <sect2><title>FcConfig</title>
527 An FcConfig object holds the internal representation of a configuration.
528 There is a default configuration which applications may use by passing 0 to
529 any function using the data within an FcConfig.
533 <sect2><title>FcObjectType</title>
535 Provides for application-specified font name object types so that new
536 pattern elements can be generated from font names.
540 <sect2><title>FcConstant</title>
542 Provides for application-specified symbolic constants for font names.
546 <sect2><title>FcWeight</title>
548 Maps weights to and from OpenType weights.
552 <sect2><title>FcBlanks</title>
554 An FcBlanks object holds a list of Unicode chars which are expected to
555 be blank when drawn. When scanning new fonts, any glyphs which are
556 empty and not in this list will be assumed to be broken and not placed in
557 the FcCharSet associated with the font. This provides a significantly more
558 accurate CharSet for applications.
562 <sect2><title>FcAtomic</title>
564 These functions provide a safe way to update configuration files, allowing ongoing
565 reading of the old configuration file while locked for writing and ensuring that a
566 consistent and complete version of the configuration file is always available.
570 <sect2><title>File and Directory routines</title>
572 These routines work with font files and directories, including font
573 directory cache files.
578 <sect2><title>FcCache routines</title>
580 These routines work with font directory caches, accessing their contents in
581 limited ways. It is not expected that normal applications will need to use
586 <sect2><title>FcStrSet and FcStrList</title>
588 A data structure for enumerating strings, used to list directories while
589 scanning the configuration as directories are added while scanning.
593 <sect2><title>String utilities</title>
595 Fontconfig manipulates many UTF-8 strings represented with the FcChar8 type.
596 These functions are exposed to help applications deal with these UTF-8
597 strings in a locale-insensitive manner.