fontconfig-devel.sgml revision 6fc018e4
1<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [ 2<!ENTITY fcatomic SYSTEM "fcatomic.sgml"> 3<!ENTITY fcblanks SYSTEM "fcblanks.sgml"> 4<!ENTITY fccache SYSTEM "fccache.sgml"> 5<!ENTITY fccharset SYSTEM "fccharset.sgml"> 6<!ENTITY fcconfig SYSTEM "fcconfig.sgml"> 7<!ENTITY fcconstant SYSTEM "fcconstant.sgml"> 8<!ENTITY fcdircache SYSTEM "fcdircache.sgml"> 9<!ENTITY fcfile SYSTEM "fcfile.sgml"> 10<!ENTITY fcfontset SYSTEM "fcfontset.sgml"> 11<!ENTITY fcformat SYSTEM "fcformat.sgml"> 12<!ENTITY fcfreetype SYSTEM "fcfreetype.sgml"> 13<!ENTITY fcinit SYSTEM "fcinit.sgml"> 14<!ENTITY fclangset SYSTEM "fclangset.sgml"> 15<!ENTITY fcmatrix SYSTEM "fcmatrix.sgml"> 16<!ENTITY fcobjectset SYSTEM "fcobjectset.sgml"> 17<!ENTITY fcobjecttype SYSTEM "fcobjecttype.sgml"> 18<!ENTITY fcpattern SYSTEM "fcpattern.sgml"> 19<!ENTITY fcstring SYSTEM "fcstring.sgml"> 20<!ENTITY fcstrset SYSTEM "fcstrset.sgml"> 21<!ENTITY fcvalue SYSTEM "fcvalue.sgml"> 22<!ENTITY version SYSTEM "version.sgml"> 23]> 24<!-- 25 fontconfig/doc/local-fontconfig-devel.sgml 26 27 Copyright © 2003 Keith Packard 28 29 Permission to use, copy, modify, distribute, and sell this software and its 30 documentation for any purpose is hereby granted without fee, provided that 31 the above copyright notice appear in all copies and that both that 32 copyright notice and this permission notice appear in supporting 33 documentation, and that the name of the author(s) not be used in 34 advertising or publicity pertaining to distribution of the software without 35 specific, written prior permission. The authors make no 36 representations about the suitability of this software for any purpose. It 37 is provided "as is" without express or implied warranty. 38 39 THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, 40 INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO 41 EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR 42 CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, 43 DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER 44 TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 45 PERFORMANCE OF THIS SOFTWARE. 46--> 47<article> 48 <title>Fontconfig Developers Reference, Version &version; </title> 49 <artheader> 50 <author> 51 <firstname>Keith</firstname> 52 <surname>Packard</surname> 53 <affiliation><orgname> 54 HP Cambridge Research Lab 55 </orgname></affiliation> 56 </author> 57 <authorinitials>KRP</authorinitials> 58 <productname>Fontconfig</productname> 59 <productnumber>&version;</productnumber> 60 <LegalNotice> 61 <simpara> 62Copyright © 2002 Keith Packard 63 </simpara><simpara> 64Permission to use, copy, modify, distribute, and sell this software and its 65documentation for any purpose is hereby granted without fee, provided that 66the above copyright notice appear in all copies and that both that 67copyright notice and this permission notice appear in supporting 68documentation, and that the name of the author(s) not be used in 69advertising or publicity pertaining to distribution of the software without 70specific, written prior permission. The authors make no 71representations about the suitability of this software for any purpose. It 72is provided "as is" without express or implied warranty. 73 </simpara><simpara> 74THE AUTHOR(S) DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, 75INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO 76EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY SPECIAL, INDIRECT OR 77CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, 78DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER 79TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR 80PERFORMANCE OF THIS SOFTWARE. 81 </simpara> 82 </LegalNotice> 83 </artheader> 84<sect1><title>DESCRIPTION</title> 85 <para> 86Fontconfig is a library designed to provide system-wide font configuration, 87customization and application access. 88 </para> 89</sect1> 90<sect1><title>FUNCTIONAL OVERVIEW</title> 91 <para> 92Fontconfig contains two essential modules, the configuration module which 93builds an internal configuration from XML files and the matching module 94which accepts font patterns and returns the nearest matching font. 95 </para> 96 <sect2><title>FONT CONFIGURATION</title> 97 <para> 98The configuration module consists of the FcConfig datatype, libexpat and 99FcConfigParse which walks over an XML tree and amends a configuration with 100data found within. From an external perspective, configuration of the 101library consists of generating a valid XML tree and feeding that to 102FcConfigParse. The only other mechanism provided to applications for 103changing the running configuration is to add fonts and directories to the 104list of application-provided font files. 105 </para><para> 106The intent is to make font configurations relatively static, and shared by 107as many applications as possible. It is hoped that this will lead to more 108stable font selection when passing names from one application to another. 109XML was chosen as a configuration file format because it provides a format 110which is easy for external agents to edit while retaining the correct 111structure and syntax. 112 </para><para> 113Font configuration is separate from font matching; applications needing to 114do their own matching can access the available fonts from the library and 115perform private matching. The intent is to permit applications to pick and 116choose appropriate functionality from the library instead of forcing them to 117choose between this library and a private configuration mechanism. The hope 118is that this will ensure that configuration of fonts for all applications 119can be centralized in one place. Centralizing font configuration will 120simplify and regularize font installation and customization. 121 </para> 122 </sect2> 123 <sect2> 124 <title>FONT PROPERTIES</title> 125 <para> 126While font patterns may contain essentially any properties, there are some 127well known properties with associated types. Fontconfig uses some of these 128properties for font matching and font completion. Others are provided as a 129convenience for the application's rendering mechanism. 130 </para> 131 <programlisting> 132 Property Definitions 133 134 Property C Preprocessor Symbol Type Description 135 ---------------------------------------------------- 136 family FC_FAMILY String Font family names 137 familylang FC_FAMILYLANG String Language corresponding to 138 each family name 139 style FC_STYLE String Font style. Overrides weight 140 and slant 141 stylelang FC_STYLELANG String Language corresponding to 142 each style name 143 fullname FC_FULLNAME String Font face full name where 144 different from family and 145 family + style 146 fullnamelang FC_FULLNAMELANG String Language corresponding to 147 each fullname 148 slant FC_SLANT Int Italic, oblique or roman 149 weight FC_WEIGHT Int Light, medium, demibold, 150 bold or black 151 size FC_SIZE Double Point size 152 width FC_WIDTH Int Condensed, normal or expanded 153 aspect FC_ASPECT Double Stretches glyphs horizontally 154 before hinting 155 pixelsize FC_PIXEL_SIZE Double Pixel size 156 spacing FC_SPACING Int Proportional, dual-width, 157 monospace or charcell 158 foundry FC_FOUNDRY String Font foundry name 159 antialias FC_ANTIALIAS Bool Whether glyphs can be 160 antialiased 161 hinting FC_HINTING Bool Whether the rasterizer should 162 use hinting 163 hintstyle FC_HINT_STYLE Int Automatic hinting style 164 verticallayout FC_VERTICAL_LAYOUT Bool Use vertical layout 165 autohint FC_AUTOHINT Bool Use autohinter instead of 166 normal hinter 167 globaladvance FC_GLOBAL_ADVANCE Bool Use font global advance data (deprecated) 168 file FC_FILE String The filename holding the font 169 index FC_INDEX Int The index of the font within 170 the file 171 ftface FC_FT_FACE FT_Face Use the specified FreeType 172 face object 173 rasterizer FC_RASTERIZER String Which rasterizer is in use (deprecated) 174 outline FC_OUTLINE Bool Whether the glyphs are outlines 175 scalable FC_SCALABLE Bool Whether glyphs can be scaled 176 scale FC_SCALE Double Scale factor for point->pixel 177 conversions 178 dpi FC_DPI Double Target dots per inch 179 rgba FC_RGBA Int unknown, rgb, bgr, vrgb, 180 vbgr, none - subpixel geometry 181 lcdfilter FC_LCD_FILTER Int Type of LCD filter 182 minspace FC_MINSPACE Bool Eliminate leading from line 183 spacing 184 charset FC_CHARSET CharSet Unicode chars encoded by 185 the font 186 lang FC_LANG LangSet Set of RFC-3066-style 187 languages this font supports 188 fontversion FC_FONTVERSION Int Version number of the font 189 capability FC_CAPABILITY String List of layout capabilities in 190 the font 191 embolden FC_EMBOLDEN Bool Rasterizer should 192 synthetically embolden the font 193 fontfeatures FC_FONT_FEATURES String List of extra feature tags in 194 OpenType to be enabled 195 namelang FC_NAMELANG String Language name to be used for the 196 default value of familylang, 197 stylelang and fullnamelang 198 prgname FC_PRGNAME String Name of the running program 199 hash FC_HASH String SHA256 hash value of the font data 200 with "sha256:" prefix. 201 postscriptname FC_POSTSCRIPT_NAME String Font name in PostScript 202 </programlisting> 203 </sect2> 204</sect1> 205<sect1><title>Datatypes</title> 206 <para> 207Fontconfig uses abstract data types to hide internal implementation details 208for most data structures. A few structures are exposed where appropriate. 209 </para> 210 <sect2><title>FcChar8, FcChar16, FcChar32, FcBool</title> 211 <para> 212These are primitive data types; the FcChar* types hold precisely the number 213of bits stated (if supported by the C implementation). FcBool holds 214one of two C preprocessor symbols: FcFalse or FcTrue. 215 </para> 216 </sect2> 217 <sect2><title>FcMatrix</title> 218 <para> 219An FcMatrix holds an affine transformation, usually used to reshape glyphs. 220A small set of matrix operations are provided to manipulate these. 221 <programlisting> 222 typedef struct _FcMatrix { 223 double xx, xy, yx, yy; 224 } FcMatrix; 225 </programlisting> 226 </para> 227 </sect2> 228 <sect2><title>FcCharSet</title> 229 <para> 230An FcCharSet is an abstract type that holds the set of encoded Unicode chars 231in a font. Operations to build and compare these sets are provided. 232 </para> 233 </sect2> 234 <sect2><title>FcLangSet</title> 235 <para> 236An FcLangSet is an abstract type that holds the set of languages supported 237by a font. Operations to build and compare these sets are provided. These 238are computed for a font based on orthographic information built into the 239fontconfig library. Fontconfig has orthographies for all of the ISO 639-1 240languages except for MS, NA, PA, PS, QU, RN, RW, SD, SG, SN, SU and ZA. If 241you have orthographic information for any of these languages, please submit 242them. 243 </para> 244 </sect2> 245 <sect2><title>FcLangResult</title> 246 <para> 247An FcLangResult is an enumeration used to return the results of comparing 248two language strings or FcLangSet objects. FcLangEqual means the 249objects match language and territory. FcLangDifferentTerritory means 250the objects match in language but differ in territory. 251FcLangDifferentLang means the objects differ in language. 252 </para> 253 </sect2> 254 <sect2><title>FcType</title> 255 <para> 256Tags the kind of data stored in an FcValue. 257 </para> 258 </sect2> 259 <sect2><title>FcValue</title> 260 <para> 261An FcValue object holds a single value with one of a number of different 262types. The 'type' tag indicates which member is valid. 263 <programlisting> 264 typedef struct _FcValue { 265 FcType type; 266 union { 267 const FcChar8 *s; 268 int i; 269 FcBool b; 270 double d; 271 const FcMatrix *m; 272 const FcCharSet *c; 273 void *f; 274 const FcLangSet *l; 275 } u; 276 } FcValue; 277 </programlisting> 278 <programlisting> 279 FcValue Members 280 281 Type Union member Datatype 282 -------------------------------- 283 FcTypeVoid (none) (none) 284 FcTypeInteger i int 285 FcTypeDouble d double 286 FcTypeString s FcChar8 * 287 FcTypeBool b b 288 FcTypeMatrix m FcMatrix * 289 FcTypeCharSet c FcCharSet * 290 FcTypeFTFace f void * (FT_Face) 291 FcTypeLangSet l FcLangSet * 292 </programlisting> 293 </para> 294 </sect2> 295 <sect2><title>FcPattern</title> 296 <para> 297holds a set of names with associated value lists; each name refers to a 298property of a font. FcPatterns are used as inputs to the matching code as 299well as holding information about specific fonts. Each property can hold 300one or more values; conventionally all of the same type, although the 301interface doesn't demand that. 302 </para> 303 </sect2> 304 <sect2><title>FcFontSet</title> 305 <para> 306 <programlisting> 307 typedef struct _FcFontSet { 308 int nfont; 309 int sfont; 310 FcPattern **fonts; 311 } FcFontSet; 312 </programlisting> 313An FcFontSet contains a list of FcPatterns. Internally fontconfig uses this 314data structure to hold sets of fonts. Externally, fontconfig returns the 315results of listing fonts in this format. 'nfont' holds the number of 316patterns in the 'fonts' array; 'sfont' is used to indicate the size of that 317array. 318 </para> 319 </sect2> 320 <sect2><title>FcStrSet, FcStrList</title> 321 <para> 322FcStrSet holds a list of strings that can be appended to and enumerated. 323Its unique characteristic is that the enumeration works even while strings 324are appended during enumeration. FcStrList is used during enumeration to 325safely and correctly walk the list of strings even while that list is edited 326in the middle of enumeration. 327 </para> 328 </sect2> 329 <sect2><title>FcObjectSet</title> 330 <para> 331 <programlisting> 332 typedef struct _FcObjectSet { 333 int nobject; 334 int sobject; 335 const char **objects; 336 } FcObjectSet; 337 </programlisting> 338holds a set of names and is used to specify which fields from fonts are 339placed in the the list of returned patterns when listing fonts. 340 </para> 341 </sect2> 342 <sect2><title>FcObjectType</title> 343 <para> 344 <programlisting> 345 typedef struct _FcObjectType { 346 const char *object; 347 FcType type; 348 } FcObjectType; 349 </programlisting> 350marks the type of a pattern element generated when parsing font names. 351Applications can add new object types so that font names may contain the new 352elements. 353 </para> 354 </sect2> 355 <sect2><title>FcConstant</title> 356 <para> 357 <programlisting> 358 typedef struct _FcConstant { 359 const FcChar8 *name; 360 const char *object; 361 int value; 362 } FcConstant; 363 </programlisting> 364Provides for symbolic constants for new pattern elements. When 'name' is 365seen in a font name, an 'object' element is created with value 'value'. 366 </para> 367 </sect2> 368 <sect2><title>FcBlanks</title> 369 <para> 370holds a list of Unicode chars which are expected to be blank; unexpectedly 371blank chars are assumed to be invalid and are elided from the charset 372associated with the font. 373 </para> 374 </sect2> 375 <sect2><title>FcFileCache</title> 376 <para> 377holds the per-user cache information for use while loading the font 378database. This is built automatically for the current configuration when 379that is loaded. Applications must always pass '0' when one is requested. 380 </para> 381 </sect2> 382 <sect2><title>FcConfig</title> 383 <para> 384holds a complete configuration of the library; there is one default 385configuration, other can be constructed from XML data structures. All 386public entry points that need global data can take an optional FcConfig* 387argument; passing 0 uses the default configuration. FcConfig objects hold two 388sets of fonts, the first contains those specified by the configuration, the 389second set holds those added by the application at run-time. Interfaces 390that need to reference a particular set use one of the FcSetName enumerated 391values. 392 </para> 393 </sect2> 394 <sect2><title>FcSetName</title> 395 <para> 396Specifies one of the two sets of fonts available in a configuration; 397FcSetSystem for those fonts specified in the configuration and 398FcSetApplication which holds fonts provided by the application. 399 </para> 400 </sect2> 401 <sect2><title>FcResult</title> 402 <para> 403Used as a return type for functions manipulating FcPattern objects. 404 <programlisting> 405 FcResult Values 406 Result Code Meaning 407 ----------------------------------------------------------- 408 FcResultMatch Object exists with the specified ID 409 FcResultNoMatch Object doesn't exist at all 410 FcResultTypeMismatch Object exists, but the type doesn't match 411 FcResultNoId Object exists, but has fewer values 412 than specified 413 FcResultOutOfMemory malloc failed 414 </programlisting> 415 </para> 416 </sect2> 417 <sect2><title>FcAtomic</title> 418 <para> 419Used for locking access to configuration files. Provides a safe way to update 420configuration files. 421 </para> 422 </sect2> 423 <sect2><title>FcCache</title> 424 <para> 425Holds information about the fonts contained in a single directory. Normal 426applications need not worry about this as caches for font access are 427automatically managed by the library. Applications dealing with cache 428management may want to use some of these objects in their work, however the 429included 'fc-cache' program generally suffices for all of that. 430 </para> 431 </sect2> 432</sect1> 433<sect1><title>FUNCTIONS</title> 434 <para> 435These are grouped by functionality, often using the main data type being 436manipulated. 437 </para> 438 <sect2><title>Initialization</title> 439 <para> 440These functions provide some control over how the library is initialized. 441 </para> 442 &fcinit; 443 </sect2> 444 <sect2><title>FcPattern</title> 445 <para> 446An FcPattern is an opaque type that holds both patterns to match against the 447available fonts, as well as the information about each font. 448 </para> 449 &fcpattern; 450 &fcformat; 451 </sect2> 452 <sect2><title>FcFontSet</title> 453 <para> 454An FcFontSet simply holds a list of patterns; these are used to return the 455results of listing available fonts. 456 </para> 457 &fcfontset; 458 </sect2> 459 <sect2><title>FcObjectSet</title> 460 <para> 461An FcObjectSet holds a list of pattern property names; it is used to 462indicate which properties are to be returned in the patterns from 463FcFontList. 464 </para> 465 &fcobjectset; 466 </sect2> 467 <sect2><title>FreeType specific functions</title> 468 <para> 469While the fontconfig library doesn't insist that FreeType be used as the 470rasterization mechanism for fonts, it does provide some convenience 471functions. 472 </para> 473 &fcfreetype; 474 </sect2> 475 <sect2><title>FcValue</title> 476 <para> 477FcValue is a structure containing a type tag and a union of all possible 478datatypes. The tag is an enum of type 479<emphasis>FcType</emphasis> 480and is intended to provide a measure of run-time 481typechecking, although that depends on careful programming. 482 </para> 483 &fcvalue; 484 </sect2> 485 <sect2><title>FcCharSet</title> 486 <para> 487An FcCharSet is a boolean array indicating a set of Unicode chars. Those 488associated with a font are marked constant and cannot be edited. 489FcCharSets may be reference counted internally to reduce memory consumption; 490this may be visible to applications as the result of FcCharSetCopy may 491return it's argument, and that CharSet may remain unmodifiable. 492 </para> 493 &fccharset; 494 </sect2> 495 <sect2><title>FcLangSet</title> 496 <para> 497An FcLangSet is a set of language names (each of which include language and 498an optional territory). They are used when selecting fonts to indicate which 499languages the fonts need to support. Each font is marked, using language 500orthography information built into fontconfig, with the set of supported 501languages. 502 </para> 503 &fclangset; 504 </sect2> 505 <sect2><title>FcMatrix</title> 506 <para> 507FcMatrix structures hold an affine transformation in matrix form. 508 </para> 509 &fcmatrix; 510 </sect2> 511 <sect2><title>FcConfig</title> 512 <para> 513An FcConfig object holds the internal representation of a configuration. 514There is a default configuration which applications may use by passing 0 to 515any function using the data within an FcConfig. 516 </para> 517 &fcconfig; 518 </sect2> 519 <sect2><title>FcObjectType</title> 520 <para> 521Provides for application-specified font name object types so that new 522pattern elements can be generated from font names. 523 </para> 524 &fcobjecttype; 525 </sect2> 526 <sect2><title>FcConstant</title> 527 <para> 528Provides for application-specified symbolic constants for font names. 529 </para> 530 &fcconstant; 531 </sect2> 532 <sect2><title>FcBlanks</title> 533 <para> 534An FcBlanks object holds a list of Unicode chars which are expected to 535be blank when drawn. When scanning new fonts, any glyphs which are 536empty and not in this list will be assumed to be broken and not placed in 537the FcCharSet associated with the font. This provides a significantly more 538accurate CharSet for applications. 539 </para> 540 &fcblanks; 541 </sect2> 542 <sect2><title>FcAtomic</title> 543 <para> 544These functions provide a safe way to update configuration files, allowing ongoing 545reading of the old configuration file while locked for writing and ensuring that a 546consistent and complete version of the configuration file is always available. 547 </para> 548 &fcatomic; 549 </sect2> 550 <sect2><title>File and Directory routines</title> 551 <para> 552These routines work with font files and directories, including font 553directory cache files. 554 </para> 555 &fcfile; 556 &fcdircache; 557 </sect2> 558 <sect2><title>FcCache routines</title> 559 <para> 560These routines work with font directory caches, accessing their contents in 561limited ways. It is not expected that normal applications will need to use 562these functions. 563 </para> 564 &fccache; 565 </sect2> 566 <sect2><title>FcStrSet and FcStrList</title> 567 <para> 568A data structure for enumerating strings, used to list directories while 569scanning the configuration as directories are added while scanning. 570 </para> 571 &fcstrset; 572 </sect2> 573 <sect2><title>String utilities</title> 574 <para> 575Fontconfig manipulates many UTF-8 strings represented with the FcChar8 type. 576These functions are exposed to help applications deal with these UTF-8 577strings in a locale-insensitive manner. 578 </para> 579 &fcstring; 580 </sect2> 581</sect1> 582</article> 583