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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 width FC_WIDTH Int Condensed, normal or expanded
154 size FC_SIZE Double Point size
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 hintstyle FC_HINT_STYLE Int Automatic hinting style
164 hinting FC_HINTING Bool Whether the rasterizer should
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 relative to the config's sysroot
172 index FC_INDEX Int The index of the font within
174 ftface FC_FT_FACE FT_Face Use the specified FreeType
176 rasterizer FC_RASTERIZER String Which rasterizer is in use (deprecated)
177 outline FC_OUTLINE Bool Whether the glyphs are outlines
178 scalable FC_SCALABLE Bool Whether glyphs can be scaled
179 dpi FC_DPI Double Target dots per inch
180 rgba FC_RGBA Int unknown, rgb, bgr, vrgb,
181 vbgr, none - subpixel geometry
182 scale FC_SCALE Double Scale factor for point->pixel
183 conversions (deprecated)
184 minspace FC_MINSPACE Bool Eliminate leading from line
186 charset FC_CHARSET CharSet Unicode chars encoded by
188 lang FC_LANG LangSet Set of RFC-3066-style
189 languages this font supports
190 fontversion FC_FONTVERSION Int Version number of the font
191 capability FC_CAPABILITY String List of layout capabilities in
193 fontformat FC_FONTFORMAT String String name of the font format
194 embolden FC_EMBOLDEN Bool Rasterizer should
195 synthetically embolden the font
196 embeddedbitmap FC_EMBEDDED_BITMAP Bool Use the embedded bitmap instead
198 decorative FC_DECORATIVE Bool Whether the style is a decorative
200 lcdfilter FC_LCD_FILTER Int Type of LCD filter
201 namelang FC_NAMELANG String Language name to be used for the
202 default value of familylang,
203 stylelang and fullnamelang
204 fontfeatures FC_FONT_FEATURES String List of extra feature tags in
205 OpenType to be enabled
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
210 symbol FC_SYMBOL Bool Whether font uses MS symbol-font encoding
211 color FC_COLOR Bool Whether any glyphs have color
212 fontvariations FC_FONT_VARIATIONS String comma-separated string of axes in variable font
213 variable FC_VARIABLE Bool Whether font is Variable Font
214 fonthashint FC_FONT_HAS_HINT Bool Whether font has hinting
215 order FC_ORDER Int Order number of the font
219 <sect1><title>Datatypes</title>
221 Fontconfig uses abstract data types to hide internal implementation details
222 for most data structures. A few structures are exposed where appropriate.
224 <sect2><title>FcChar8, FcChar16, FcChar32, FcBool</title>
226 These are primitive data types; the FcChar* types hold precisely the number
227 of bits stated (if supported by the C implementation). FcBool holds
228 one of two C preprocessor symbols: FcFalse or FcTrue.
231 <sect2><title>FcMatrix</title>
233 An FcMatrix holds an affine transformation, usually used to reshape glyphs.
234 A small set of matrix operations are provided to manipulate these.
236 typedef struct _FcMatrix {
237 double xx, xy, yx, yy;
242 <sect2><title>FcCharSet</title>
244 An FcCharSet is an abstract type that holds the set of encoded Unicode chars
245 in a font. Operations to build and compare these sets are provided.
248 <sect2><title>FcLangSet</title>
250 An FcLangSet is an abstract type that holds the set of languages supported
251 by a font. Operations to build and compare these sets are provided. These
252 are computed for a font based on orthographic information built into the
253 fontconfig library. Fontconfig has orthographies for all of the ISO 639-1
254 languages except for MS, NA, PA, PS, QU, RN, RW, SD, SG, SN, SU and ZA. If
255 you have orthographic information for any of these languages, please submit
259 <sect2><title>FcLangResult</title>
261 An FcLangResult is an enumeration used to return the results of comparing
262 two language strings or FcLangSet objects. FcLangEqual means the
263 objects match language and territory. FcLangDifferentTerritory means
264 the objects match in language but differ in territory.
265 FcLangDifferentLang means the objects differ in language.
268 <sect2><title>FcType</title>
270 Tags the kind of data stored in an FcValue.
273 <sect2><title>FcValue</title>
275 An FcValue object holds a single value with one of a number of different
276 types. The 'type' tag indicates which member is valid.
278 typedef struct _FcValue {
296 Type Union member Datatype
297 --------------------------------
298 FcTypeVoid (none) (none)
300 FcTypeDouble d double
301 FcTypeString s FcChar8 *
303 FcTypeMatrix m FcMatrix *
304 FcTypeCharSet c FcCharSet *
305 FcTypeFTFace f void * (FT_Face)
306 FcTypeLangSet l FcLangSet *
307 FcTypeRange r FcRange *
311 <sect2><title>FcPattern, FcPatternIter</title>
313 An FcPattern holds a set of names with associated value lists; each name refers to a
314 property of a font. FcPatterns are used as inputs to the matching code as
315 well as holding information about specific fonts. Each property can hold
316 one or more values; conventionally all of the same type, although the
317 interface doesn't demand that. An FcPatternIter is used during iteration to
318 access properties in FcPattern.
321 <sect2><title>FcFontSet</title>
324 typedef struct _FcFontSet {
330 An FcFontSet contains a list of FcPatterns. Internally fontconfig uses this
331 data structure to hold sets of fonts. Externally, fontconfig returns the
332 results of listing fonts in this format. 'nfont' holds the number of
333 patterns in the 'fonts' array; 'sfont' is used to indicate the size of that
337 <sect2><title>FcStrSet, FcStrList</title>
339 FcStrSet holds a list of strings that can be appended to and enumerated.
340 Its unique characteristic is that the enumeration works even while strings
341 are appended during enumeration. FcStrList is used during enumeration to
342 safely and correctly walk the list of strings even while that list is edited
343 in the middle of enumeration.
346 <sect2><title>FcObjectSet</title>
349 typedef struct _FcObjectSet {
352 const char **objects;
355 holds a set of names and is used to specify which fields from fonts are
356 placed in the the list of returned patterns when listing fonts.
359 <sect2><title>FcObjectType</title>
362 typedef struct _FcObjectType {
367 marks the type of a pattern element generated when parsing font names.
368 Applications can add new object types so that font names may contain the new
372 <sect2><title>FcConstant</title>
375 typedef struct _FcConstant {
381 Provides for symbolic constants for new pattern elements. When 'name' is
382 seen in a font name, an 'object' element is created with value 'value'.
385 <sect2><title>FcBlanks</title>
387 holds a list of Unicode chars which are expected to be blank; unexpectedly
388 blank chars are assumed to be invalid and are elided from the charset
389 associated with the font.
392 FcBlanks is deprecated and should not be used in newly written code.
393 It is still accepted by some functions for compatibility with
394 older code but will be removed in the future.
397 <sect2><title>FcFileCache</title>
399 holds the per-user cache information for use while loading the font
400 database. This is built automatically for the current configuration when
401 that is loaded. Applications must always pass '0' when one is requested.
404 <sect2><title>FcConfig</title>
406 holds a complete configuration of the library; there is one default
407 configuration, other can be constructed from XML data structures. All
408 public entry points that need global data can take an optional FcConfig*
409 argument; passing 0 uses the default configuration. FcConfig objects hold two
410 sets of fonts, the first contains those specified by the configuration, the
411 second set holds those added by the application at run-time. Interfaces
412 that need to reference a particular set use one of the FcSetName enumerated
416 <sect2><title>FcSetName</title>
418 Specifies one of the two sets of fonts available in a configuration;
419 FcSetSystem for those fonts specified in the configuration and
420 FcSetApplication which holds fonts provided by the application.
423 <sect2><title>FcResult</title>
425 Used as a return type for functions manipulating FcPattern objects.
429 -----------------------------------------------------------
430 FcResultMatch Object exists with the specified ID
431 FcResultNoMatch Object doesn't exist at all
432 FcResultTypeMismatch Object exists, but the type doesn't match
433 FcResultNoId Object exists, but has fewer values
435 FcResultOutOfMemory malloc failed
439 <sect2><title>FcAtomic</title>
441 Used for locking access to configuration files. Provides a safe way to update
445 <sect2><title>FcCache</title>
447 Holds information about the fonts contained in a single directory. Normal
448 applications need not worry about this as caches for font access are
449 automatically managed by the library. Applications dealing with cache
450 management may want to use some of these objects in their work, however the
451 included 'fc-cache' program generally suffices for all of that.
455 <sect1><title>FUNCTIONS</title>
457 These are grouped by functionality, often using the main data type being
460 <sect2><title>Initialization</title>
462 These functions provide some control over how the library is initialized.
466 <sect2><title>FcPattern</title>
468 An FcPattern is an opaque type that holds both patterns to match against the
469 available fonts, as well as the information about each font.
474 <sect2><title>FcFontSet</title>
476 An FcFontSet simply holds a list of patterns; these are used to return the
477 results of listing available fonts.
481 <sect2><title>FcObjectSet</title>
483 An FcObjectSet holds a list of pattern property names; it is used to
484 indicate which properties are to be returned in the patterns from
489 <sect2><title>FreeType specific functions</title>
491 While the fontconfig library doesn't insist that FreeType be used as the
492 rasterization mechanism for fonts, it does provide some convenience
497 <sect2><title>FcValue</title>
499 FcValue is a structure containing a type tag and a union of all possible
500 datatypes. The tag is an enum of type
501 <emphasis>FcType</emphasis>
502 and is intended to provide a measure of run-time
503 typechecking, although that depends on careful programming.
507 <sect2><title>FcCharSet</title>
509 An FcCharSet is a boolean array indicating a set of Unicode chars. Those
510 associated with a font are marked constant and cannot be edited.
511 FcCharSets may be reference counted internally to reduce memory consumption;
512 this may be visible to applications as the result of FcCharSetCopy may
513 return it's argument, and that CharSet may remain unmodifiable.
517 <sect2><title>FcLangSet</title>
519 An FcLangSet is a set of language names (each of which include language and
520 an optional territory). They are used when selecting fonts to indicate which
521 languages the fonts need to support. Each font is marked, using language
522 orthography information built into fontconfig, with the set of supported
527 <sect2><title>FcMatrix</title>
529 FcMatrix structures hold an affine transformation in matrix form.
533 <sect2><title>FcRange</title>
535 An FcRange holds two variables to indicate a range in between.
539 <sect2><title>FcConfig</title>
541 An FcConfig object holds the internal representation of a configuration.
542 There is a default configuration which applications may use by passing 0 to
543 any function using the data within an FcConfig.
547 <sect2><title>FcObjectType</title>
549 Provides for application-specified font name object types so that new
550 pattern elements can be generated from font names.
554 <sect2><title>FcConstant</title>
556 Provides for application-specified symbolic constants for font names.
560 <sect2><title>FcWeight</title>
562 Maps weights to and from OpenType weights.
566 <sect2><title>FcBlanks</title>
568 An FcBlanks object holds a list of Unicode chars which are expected to
569 be blank when drawn. When scanning new fonts, any glyphs which are
570 empty and not in this list will be assumed to be broken and not placed in
571 the FcCharSet associated with the font. This provides a significantly more
572 accurate CharSet for applications.
575 FcBlanks is deprecated and should not be used in newly written code.
576 It is still accepted by some functions for compatibility with
577 older code but will be removed in the future.
581 <sect2><title>FcAtomic</title>
583 These functions provide a safe way to update configuration files, allowing ongoing
584 reading of the old configuration file while locked for writing and ensuring that a
585 consistent and complete version of the configuration file is always available.
589 <sect2><title>File and Directory routines</title>
591 These routines work with font files and directories, including font
592 directory cache files.
597 <sect2><title>FcCache routines</title>
599 These routines work with font directory caches, accessing their contents in
600 limited ways. It is not expected that normal applications will need to use
605 <sect2><title>FcStrSet and FcStrList</title>
607 A data structure for enumerating strings, used to list directories while
608 scanning the configuration as directories are added while scanning.
612 <sect2><title>String utilities</title>
614 Fontconfig manipulates many UTF-8 strings represented with the FcChar8 type.
615 These functions are exposed to help applications deal with these UTF-8
616 strings in a locale-insensitive manner.