
                                  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, dual-width, 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
  dual            spacing         90
  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 2.2.92
