
                              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 lis
t
  "prepend_first"         Insert at head of list  Insert at head of lis
t
  "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></e
dit>
</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></e
dit>
</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 2.2.3
