                                   fonts-conf

Name

   fonts.conf -- Font configuration files

Synopsis

      /etc/fonts/fonts.conf                                                   
      /etc/fonts/fonts.dtd                                                    
      ~/.fonts.conf                                                           

Description

   Fontconfig is a library designed to provide system-wide font
   configuration, customization and application access.

Functional Overview

   Fontconfig contains two essential modules, the configuration module which
   builds an internal configuration from XML files and the matching module
   which accepts font patterns and returns the nearest matching font.

  Font Configuration

   The configuration module consists of the FcConfig datatype, libexpat and
   FcConfigParse which walks over an XML tree and ammends a configuration
   with data found within. From an external perspective, configuration of the
   library consists of generating a valid XML tree and feeding that to
   FcConfigParse. The only other mechanism provided to applications for
   changing the running configuration is to add fonts and directories to the
   list of application-provided font files.

   The intent is to make font configurations relatively static, and shared by
   as many applications as possible. It is hoped that this will lead to more
   stable font selection when passing names from one application to another.
   XML was chosen as a configuration file format because it provides a format
   which is easy for external agents to edit while retaining the correct
   structure and syntax.

   Font configuration is separate from font matching; applications needing to
   do their own matching can access the available fonts from the library and
   perform private matching. The intent is to permit applications to pick and
   choose appropriate functionality from the library instead of forcing them
   to choose between this library and a private configuration mechanism. The
   hope is that this will ensure that configuration of fonts for all
   applications can be centralized in one place. Centralizing font
   configuration will simplify and regularize font installation and
   customization.

  Font Properties

   While font patterns may contain essentially any properties, there are some
   well known properties with associated types. Fontconfig uses some of these
   properties for font matching and font completion. Others are provided as a
   convenience for the applications rendering mechanism.

     Property        Type    Description                                      
     --------------------------------------------------------------           
     family          String  Font family name                                 
     style           String  Font style. Overrides weight and slant           
     slant           Int     Italic, oblique or roman                         
     weight          Int     Light, medium, demibold, bold or black           
     size            Double  Point size                                       
     aspect          Double  Stretches glyphs horizontally before hinting     
     pixelsize       Double  Pixel size                                       
     spacing         Int     Proportional, monospace or charcell              
     foundry         String  Font foundry name                                
     antialias       Bool    Whether glyphs can be antialiased                
     hinting         Bool    Whether the rasterizer should use hinting        
     verticallayout  Bool    Use vertical layout                              
     autohint        Bool    Use autohinter instead of normal hinter          
     globaladvance   Bool    Use font global advance data                     
     file            String  The filename holding the font                    
     index           Int     The index of the font within the file            
     ftface          FT_Face Use the specified FreeType face object           
     rasterizer      String  Which rasterizer is in use                       
     outline         Bool    Whether the glyphs are outlines                  
     scalable        Bool    Whether glyphs can be scaled                     
     scale           Double  Scale factor for point->pixel conversions        
     dpi             Double  Target dots per inch                             
     rgba            Int     unknown, rgb, bgr, vrgb, vbgr,                   
                             none - subpixel geometry                         
     minspace        Bool    Eliminate leading from line spacing              
     charset         CharSet Unicode chars encoded by the font                
     lang            String  List of RFC-3066-style languages this            
                             font supports                                    
                                                                              

  Font Matching

   Fontconfig performs matching by measuring the distance from a provided
   pattern to all of the available fonts in the system. The closest matching
   font is selected. This ensures that a font will always be returned, but
   doesn't ensure that it is anything like the requested pattern.

   Font matching starts with an application constructed pattern. The desired
   attributes of the resulting font are collected together in a pattern. Each
   property of the pattern can contain one or more values; these are listed
   in priority order; matches earlier in the list are considered "closer"
   than matches later in the list.

   The initial pattern is modified by applying the list of editing
   instructions specific to patterns found in the configuration; each
   consists of a match predicate and a set of editing operations. They are
   executed in the order they appeared in the configuration. Each match
   causes the associated sequence of editing operations to be applied.

   After the pattern has been edited, a sequence of default substitutions are
   performed to canonicalize the set of available properties; this avoids the
   need for the lower layers to constantly provide default values for various
   font properties during rendering.

   The canonical font pattern is finally matched against all available fonts.
   The distance from the pattern to the font is measured for each of several
   properties: foundry, charset, family, lang, spacing, pixelsize, style,
   slant, weight, antialias, rasterizer and outline. This list is in priority
   order -- results of comparing earlier elements of this list weigh more
   heavily than later elements.

   There is one special case to this rule; family names are split into two
   bindings; strong and weak. Strong family names are given greater
   precedence in the match than lang elements while weak family names are
   given lower precedence than lang elements. This permits the document
   language to drive font selection when any document specified font is
   unavailable.

   The pattern representing that font is augmented to include any properties
   found in the pattern but not found in the font itself; this permits the
   application to pass rendering instructions or any other data through the
   matching system. Finally, the list of editing instructions specific to
   fonts found in the configuration are applied to the pattern. This modified
   pattern is returned to the application.

   The return value contains sufficient information to locate and rasterize
   the font, including the file name, pixel size and other rendering data. As
   none of the information involved pertains to the FreeType library,
   applications are free to use any rasterization engine or even to take the
   identified font file and access it directly.

   The match/edit sequences in the configuration are performed in two passes
   because there are essentially two different operations necessary -- the
   first is to modify how fonts are selected; aliasing families and adding
   suitable defaults. The second is to modify how the selected fonts are
   rasterized. Those must apply to the selected font, not the original
   pattern as false matches will often occur.

  Font Names

   Fontconfig provides a textual representation for patterns that the library
   can both accept and generate. The representation is in three parts, first
   a list of family names, second a list of point sizes and finally a list of
   additional properties:

           <families>-<point sizes>:<name1>=<values1>:<name2>=<values2>...    
                                                                              

   Values in a list are separated with commas. The name needn't include
   either families or point sizes; they can be elided. In addition, there are
   symbolic constants that simultaneously indicate both a name and a value.
   Here are some examples:

     Name                            Meaning                                  
     ----------------------------------------------------------               
     Times-12                        12 point Times Roman                     
     Times-12:bold                   12 point Times Bold                      
     Courier:italic                  Courier Italic in the default size       
     Monospace:matrix=1 .1 0 1       The users preferred monospace font       
                                     with artificial obliquing                
                                                                              

Lang Tags

   Each font in the database contains a list of languages it supports. This
   is computed by comparing the Unicode coverage of the font with the
   orthography of each language. Languages are tagged using an RFC-3066
   compatible naming and occur in two parts -- the ISO639 language tag
   followed a hyphen and then by the ISO 3166 country code. The hyphen and
   country code may be elided.

   Fontconfig has orthographies for several languages built into the library.
   No provision has been made for adding new ones aside from rebuilding the
   library. It currently supports 122 of the 139 languages named in ISO
   639-1, 141 of the languages with two-letter codes from ISO 639-2 and
   another 30 languages with only three-letter codes.

Configuration File Format

   Configuration files for fontconfig are stored in XML format; this format
   makes external configuration tools easier to write and ensures that they
   will generate syntactically correct configuration files. As XML files are
   plain text, they can also be manipulated by the expert user using a text
   editor.

   The fontconfig document type definition resides in the external entity
   "fonts.dtd"; this is normally stored in the default font configuration
   directory (/etc/fonts). Each configuration file should contain the
   following structure:

           <?xml version="1.0"?>                                              
           <!DOCTYPE fontconfig SYSTEM "fonts.dtd">                           
           <fontconfig>                                                       
           ...                                                                
           </fontconfig>                                                      
                                                                              

  <fontconfig>

   This is the top level element for a font configuration and can contain
   dir, cache, include, match and alias elements in any order.

  dir

   This element contains a directory name which will be scanned for font
   files to include in the set of available fonts.

  cache

   This element contains a file name for the per-user cache of font
   information. If it starts with '~', it refers to a file in the users home
   directory. This file is used to hold information about fonts that isn't
   present in the per-directory cache files. It is automatically maintained
   by the fontconfig library. The default for this file is
   ``~/.fonts.cache-version'', where version is the font configuration file
   version number (currently 1).

  include ignore_missing="no"

   This element contains the name of an additional configuration file. When
   the XML datatype is traversed by FcConfigParse, the contents of the file
   will also be incorporated into the configuration by passing the filename
   to FcConfigLoadAndParse. If 'ignore_missing' is set to "yes" instead of
   the default "no", a missing file will elicit no warning message from the
   library.

  config

   This element provides a place to consolodate additional configuration
   information. config can contain blank and rescan elements in any order.

  blank

   Fonts often include "broken" glyphs which appear in the encoding but are
   drawn as blanks on the screen. Within the blank element, place each
   Unicode characters which is supposed to be blank in an int element.
   Characters outside of this set which are drawn as blank will be elided
   from the set of characters supported by the font.

  rescan

   The rescan element holds an int element which indicates the default
   interval between automatic checks for font configuration changes.
   Fontconfig will validate all of the configuration files and directories
   and automatically rebuild the internal datastructures when this interval
   passes.

  match target="pattern"

   This element holds first a (possibly empty) list of test elements and then
   a (possibly empty) list of edit elements. Patterns which match all of the
   tests are subjected to all the edits. If 'target' is set to "font" instead
   of the default "pattern", then this element applies to the font name
   resulting from a match rather than a font pattern to be matched.

  test qual="any" name="property" compare="eq"

   This element contains a single value which is compared with the pattern
   property "property" (substitute any of the property names seen above).
   'compare' can be one of "eq", "not_eq", "less", "less_eq", "more", or
   "more_eq". 'qual' may either be the default, "any", in which case the
   match succeeds if any value associated with the property matches the test
   value, or "all", in which case all of the values associated with the
   property must match the test value.

  edit name="property" mode="assign" binding="weak"

   This element contains a list of expression elements (any of the value or
   operator elements). The expression elements are evaluated at run-time and
   modify the property "property". The modification depends on whether
   "property" was matched by one of the associated test elements, if so, the
   modification may affect the first matched value. Any values inserted into
   the property are given the indicated binding. 'mode' is one of:

     Mode                    With Match              Without Match            
     ---------------------------------------------------------------------    
     "assign"                Replace matching value  Replace all values       
     "assign_replace"        Replace all values      Replace all values       
     "prepend"               Insert before matching  Insert at head of list   
     "prepend_first"         Insert at head of list  Insert at head of list   
     "append"                Append after matching   Append at end of list    
     "append_last"           Append at end of list   Append at end of list    
                                                                              

  int, double, string, bool

   These elements hold a single value of the indicated type. bool elements
   hold either true or false. An important limitation exists in the parsing
   of floating point numbers -- fontconfig requires that the mantissa start
   with a digit, not a decimal point, so insert a leading zero for purely
   fractional values (e.g. use 0.5 instead of .5 and -0.5 instead of -.5).

  matrix

   This element holds the four double elements of an affine transformation.

  name

   Holds a property name. Evaluates to the first value from the property of
   the font, not the pattern.

  const

   Holds the name of a constant; these are always integers and serve as
   symbolic names for common font values:

     Constant        Property        Value                                    
     -------------------------------------                                    
     light           weight          0                                        
     medium          weight          100                                      
     demibold        weight          180                                      
     bold            weight          200                                      
     black           weight          210                                      
     roman           slant           0                                        
     italic          slant           100                                      
     oblique         slant           110                                      
     proportional    spacing         0                                        
     mono            spacing         100                                      
     charcell        spacing         110                                      
     unknown         rgba            0                                        
     rgb             rgba            1                                        
     bgr             rgba            2                                        
     vrgb            rgba            3                                        
     vbgr            rgba            4                                        
     none            rgba            5                                        
                                                                              

  or, and, plus, minus, times, divide

   These elements perform the specified operation on a list of expression
   elements. or and and are boolean, not bitwise.

  eq, not_eq, less, less_eq, more, more_eq

   These elements compare two values, producing a boolean result.

  not

   Inverts the boolean sense of its one expression element

  if

   This element takes three expression elements; if the value of the first is
   true, it produces the value of the second, otherwise it produces the value
   of the third.

  alias

   Alias elements provide a shorthand notation for the set of common match
   operations needed to substitute one font family for another. They contain
   a family element followed by optional prefer, accept and default elements.
   Fonts matching the family element are edited to prepend the list of
   prefered families before the matching family, append the acceptable
   familys after the matching family and append the default families to the
   end of the family list.

  family

   Holds a single font family name

  prefer, accept, default

   These hold a list of family elements to be used by the alias element.
   /article

EXAMPLE CONFIGURATION FILE

  System configuration file

   This is an example of a system-wide configuration file

   <?xml version="1.0"?>                                                       
   <!DOCTYPE fontconfig SYSTEM "fonts.dtd">                                    
   <!-- /etc/fonts/fonts.conf file to configure system font access -->         
   <fontconfig>                                                                
   <!--                                                                        
           Find fonts in these directories                                     
   -->                                                                         
   <dir>/usr/X11R6/lib/X11/fonts/truetype</dir>                                
   <dir>/usr/X11R6/lib/X11/fonts/Type1</dir>                                   
                                                                               
   <!--                                                                        
           Accept deprecated 'mono' alias, replacing it with 'monospace'       
   -->                                                                         
   <match target="pattern">                                                    
           <test qual="any" name="family"><string>mono</string></test>         
           <edit name="family" mode="assign"><string>monospace</string></edit> 
   </match>                                                                    
                                                                               
   <!--                                                                        
           Names not including any well known alias are given 'sans'           
   -->                                                                         
   <match target="pattern">                                                    
           <test qual="all" name="family" mode="not_eq">sans</test>            
           <test qual="all" name="family" mode="not_eq">serif</test>           
           <test qual="all" name="family" mode="not_eq">monospace</test>       
           <edit name="family" mode="append_last"><string>sans</string></edit> 
   </match>                                                                    
                                                                               
   <!--                                                                        
           Load per-user customization file, but don't complain                
           if it doesn't exist                                                 
   -->                                                                         
   <include ignore_missing="yes">~/.fonts.conf</include>                       
                                                                               
   <!--                                                                        
           Alias well known font names to available TrueType fonts.            
           These substitute TrueType faces for similar Type1                   
           faces to improve screen appearance.                                 
   -->                                                                         
   <alias>                                                                     
           <family>Times</family>                                              
           <prefer><family>Times New Roman</family></prefer>                   
           <default><family>serif</family></default>                           
   </alias>                                                                    
   <alias>                                                                     
           <family>Helvetica</family>                                          
           <prefer><family>Verdana</family></prefer>                           
           <default><family>sans</family></default>                            
   </alias>                                                                    
   <alias>                                                                     
           <family>Courier</family>                                            
           <prefer><family>Courier New</family></prefer>                       
           <default><family>monospace</family></default>                       
   </alias>                                                                    
                                                                               
   <!--                                                                        
           Provide required aliases for standard names                         
           Do these after the users configuration file so that                 
           any aliases there are used preferentially                           
   -->                                                                         
   <alias>                                                                     
           <family>serif</family>                                              
           <prefer><family>Times New Roman</family></prefer>                   
   </alias>                                                                    
   <alias>                                                                     
           <family>sans</family>                                               
           <prefer><family>Verdana</family></prefer>                           
   </alias>                                                                    
   <alias>                                                                     
           <family>monospace</family>                                          
           <prefer><family>Andale Mono</family></prefer>                       
   </alias>                                                                    
   </fontconfig>                                                               
                                                                               

  User configuration file

   This is an example of a per-user configuration file that lives in
   ~/.fonts.conf

   <?xml version="1.0"?>                                                      
   <!DOCTYPE fontconfig SYSTEM "fonts.dtd">                                   
   <!-- ~/.fonts.conf for per-user font configuration -->                     
   <fontconfig>                                                               
                                                                              
   <!--                                                                       
           Private font directory                                             
   -->                                                                        
   <dir>~/misc/fonts</dir>                                                    
                                                                              
   <!--                                                                       
           use rgb sub-pixel ordering to improve glyph appearance on          
           LCD screens.  Changes affecting rendering, but not matching        
           should always use target="font".                                   
   -->                                                                        
   <match target="font">                                                      
           <edit name="rgba" mode="assign"><const>rgb</const></edit>          
   </match>                                                                   
   </fontconfig>                                                              
                                                                              

Files

   fonts.conf contains configuration information for the fontconfig library
   consisting of directories to look at for font information as well as
   instructions on editing program specified font patterns before attempting
   to match the available fonts. It is in xml format.

   fonts.dtd is a DTD that describes the format of the configuration files.

   ~/.fonts.conf is the conventional location for per-user font
   configuration, although the actual location is specified in the global
   fonts.conf file.

   ~/.fonts.cache-* is the conventional repository of font information that
   isn't found in the per-directory caches. This file is automatically
   maintained by fontconfig.

Version

   Fontconfig version 2.2.1
