fonts.conf - Font configuration files
Fontconfig is a library designed to provide system-wide font configura-
tion, customization and application access.
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
The configuration module consists of the FcConfig datatype, libexpat
and FcConfigParse which walks over an XML tree and ammends a configura-
tion with data found within. From an external perspective, configura-
tion of the library consists of generating a valid XML tree and feeding
that to FcConfigParse. The only other mechanism provided to applica-
tions for changing the running configuration is to add fonts and direc-
tories 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 applica-
tions 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 con-
figuration of fonts for all applications can be centralized in one
place. Centralizing font configuration will simplify and regularize
font installation and customization.
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
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
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 con-
sists 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 val-
ues 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, pixel-
size, 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
The pattern representing that font is augmented to include any proper-
ties found in the pattern but not found in the font itself; this per-
mits 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 pat-
tern. This modified pattern is returned to the application.
The return value contains sufficient information to locate and raster-
ize 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.
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:
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:
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
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 for-
mat 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
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
This is the top level element for a font configuration and can contain
dir, cache, include, match and alias elements in any order.
This element contains a directory name which will be scanned for font
files to include in the set of available fonts.
This element contains a file name for the per-user cache of font infor-
mation. 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 warn-
ing message from the library.
This element provides a place to consolodate additional configuration
information. config can contain blank and rescan elements in any
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 ele-
ment. Characters outside of this set which are drawn as blank will be
elided from the set of characters supported by the font.
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 inter-
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
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
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 ele-
ments hold either true or false. An important limitation exists in the
parsing of floating point numbers -- fontconfig requires that the man-
tissa 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).
This element holds the four double elements of an affine transforma-
Holds a property name. Evaluates to the first value from the property
of the font, not the pattern.
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.
Inverts the boolean sense of its one expression element
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 elements provide a shorthand notation for the set of common match
operations needed to substitute one font family for another. They con-
tain 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.
Holds a single font family name
PREFER, ACCEPT, DEFAULT
These hold a list of family elements to be used by the alias element.
EXAMPLE CONFIGURATION FILE
SYSTEM CONFIGURATION FILE
This is an example of a system-wide configuration file
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- /etc/fonts/fonts.conf file to configure system font access -->
Find fonts in these directories
Accept deprecated 'mono' alias, replacing it with 'monospace'
<test qual="any" name="family"><string>mono</string></test>
<edit name="family" mode="assign"><string>monospace</string></edit>
Names not including any well known alias are given 'sans'
<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>
Load per-user customization file, but don't complain
if it doesn't exist
Alias well known font names to available TrueType fonts.
These substitute TrueType faces for similar Type1
faces to improve screen appearance.
<prefer><family>Times New Roman</family></prefer>
Provide required aliases for standard names
Do these after the users configuration file so that
any aliases there are used preferentially
<prefer><family>Times New Roman</family></prefer>
USER CONFIGURATION FILE
This is an example of a per-user configuration file that lives in
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- ~/.fonts.conf for per-user font configuration -->
Private font directory
use rgb sub-pixel ordering to improve glyph appearance on
LCD screens. Changes affecting rendering, but not matching
should always use target="font".
<edit name="rgba" mode="assign"><const>rgb</const></edit>
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
~/.fonts.conf is the conventional location for per-user font configura-
tion, although the actual location is specified in the global
~/.fonts.cache-* is the conventional repository of font information
that isn't found in the per-directory caches. This file is automati-
cally maintained by fontconfig.
Fontconfig version 2.2.3
See attributes(5) for descriptions of the following attributes:
box; cbp-1 | cbp-1 l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE = Availabil-
ity SUNWfontconfig-root Interface Stability External
30 June 2004 fonts.conf(4)