doc/fontconfig-devel.sgml

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