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 amends 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 pro-
vides a format which is easy for external agents to edit while retain-
ing 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 config-
uration 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
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
hintstyle Int Automatic hinting style
verticallayout Bool Use vertical layout
autohint Bool Use autohinter instead of normal hinter
globaladvance Bool Use font global advance data (deprecated)
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 (deprecated)
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
lcdfilter Int Type of LCD filter
minspace Bool Eliminate leading from line spacing
charset CharSet Unicode chars encoded by the font
lang String List of RFC-3066-style languages this
fontversion Int Version number of the font
capability String List of layout capabilities in the font
embolden Bool Rasterizer should synthetically embolden the font
fontfeatures String List of the feature tags in OpenType to be enabled
prgname String String Name of the running program
Fontconfig performs matching by measuring the distance from a provided
pattern to all of the available fonts in the system. The closest match-
ing 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 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.
to drive font selection when any document specified font is unavail-
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
The '\', '-', ':' and ',' characters in family names must be preceded
by a '\' character to avoid having them misinterpreted. Similarly, val-
ues containing '\', '=', '_', ':' and ',' must also have them preceded
by a '\' character. The '\' characters are stripped out of the family
name and values as the font name is read.
FONTSET 8 Track loading of font information at startup
CACHE 16 Watch cache files being written
CACHEV 32 Extensive cache file writing information
PARSE 64 (no longer in use)
SCAN 128 Watch font files being scanned to build caches
SCANV 256 Verbose font file scanning information
MEMORY 512 Monitor fontconfig memory usage
CONFIG 1024 Monitor which config files are loaded
LANGSET 2048 Dump char sets used to construct lang values
OBJTYPES 4096 Display message when value typechecks fail
Add the value of the desired debug levels together and assign that (in
base 10) to the FC_DEBUG environment variable before running the appli-
cation. Output from these statements is sent to stdout.
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 ISO 639 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. Languages
with both two and three letter codes are provided with only the two
For languages used in multiple territories with radically different
character sets, fontconfig includes per-territory orthographies. This
includes Azerbaijani, Kurdish, Pashto, Tigrinya and Chinese.
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 fol-
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
added as the path prefix. please see XDG Base Directory Specification
for more details.
This element contains a directory name that is supposed to be stored or
read the cache of font information. If multiple elements are specified
in the configuration file, the directory that can be accessed first in
the list will be used to store the cache files. If it starts with '~',
it refers to a directory in the users home directory. If 'prefix' is
set to "xdg", the value in the XDG_CACHE_HOME environment variable will
be added as the path prefix. please see XDG Base Directory Specifica-
tion for more details. The default directory is
``$XDG_CACHE_HOME/fontconfig'' and it contains the cache files named
``<hash value>-<architecture>.cache-<version'', where <version> is the
font configureation file version number (currently 3).
<INCLUDE IGNORE_MISSING="NO" PREFIX="DEFAULT">
This element contains the name of an additional configuration file or
directory. If a directory, every file within that directory starting
with an ASCII digit (U+0030 - U+0039) and ending with the string
``.conf'' will be processed in sorted order. When the XML datatype is
traversed by FcConfigParse, the contents of the file(s) will also be
incorporated into the configuration by passing the filename(s) to
FcConfigLoadAndParse. If 'ignore_missing' is set to "yes" instead of
the default "no", a missing file or directory will elicit no warning
message from the library. If 'prefix' is set to "xdg", the value in the
XDG_CONFIG_HOME environment variable will be added as the path prefix.
please see XDG Base Directory Specification for more details.
This element provides a place to consolidate 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-
This element is used to black/white list fonts from being listed or
matched against. It holds acceptfont and rejectfont elements.
Fonts matched by an acceptfont element are "whitelisted"; such fonts
Glob elements hold shell-style filename matching patterns (including ?
and *) which match fonts based on their complete pathnames. This can be
used to exclude a set of directories (/usr/share/fonts/uglyfont*), or
particular font file types (*.pcf.gz), but the latter mechanism relies
rather heavily on filenaming conventions which can't be relied upon.
Note that globs only apply to directories, not to individual fonts.
Pattern elements perform list-style matching on incoming fonts; that
is, they hold a list of elements and associated values. If all of those
elements have a matching value, then the pattern matches the font. This
can be used to select fonts based on attributes of the font (scalable,
bold, etc), which is a more reliable mechanism than using file exten-
sions. Pattern elements include patelt elements.
Patelt elements hold a single pattern element and list of values. They
must have a 'name' attribute which indicates the pattern element name.
Patelt elements include int, double, string, matrix, bool, charset and
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. If 'target' is set to "scan", then this element applies when
the font is scanned to build the fontconfig database.
<TEST QUAL="ANY" NAME="PROPERTY" TARGET="DEFAULT" COMPARE="EQ">
This element contains a single value which is compared with the target
('pattern', 'font', 'scan' or 'default') property "property" (substi-
tute any of the property names seen above). 'compare' can be one of
"eq", "not_eq", "less", "less_eq", "more", "more_eq", "contains" or
"not_contains". '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. 'ignore-blanks' takes a
boolean value. if 'ignore-blanks' is set "true", any blanks in the
string will be ignored on its comparison. this takes effects only when
compare="eq" or compare="not_eq". When used in a <match target="font">
element, the target= attribute in the <test> element selects between
matching the original pattern or the font. "default" selects whichever
target the outer <match> element has selected.
<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> ele-
ments, if so, the modification may affect the first matched value. Any
values inserted into the property are given the indicated binding
("strong", "weak" or "same") with "same" binding using the value from
<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 four numerical expressions of an affine transforma-
tion. At their simplest these will be four <double> elements but they
can also be more involved expressions.
This element holds the two <int> elements of a range representation.
This element holds at least one <int> element of an Unicode code point
This element holds at least one <string> element of a RFC-3066-style
languages or more.
Holds a property name. Evaluates to the first value from the property
of the pattern. If the 'target' attribute is not present, it will
default to 'default', in which case the property is returned from the
font pattern during a target="font" match, and to the pattern during a
target="pattern" match. The attribute can also take the values 'font'
or 'pattern' to explicitly choose which pattern to use. It is an error
to use a target of 'font' in a match that has target="pattern".
Holds the name of a constant; these are always integers and serve as
symbolic names for common font values:
Constant Property Value
thin weight 0
extralight weight 40
ultralight weight 40
light weight 50
book weight 75
regular weight 80
normal weight 80
medium weight 100
demibold weight 180
semibold weight 180
bold weight 200
extrabold weight 205
extraexpanded width 150
ultraexpanded width 200
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
lcdnone lcdfilter 0
lcddefault lcdfilter 1
lcdlight lcdfilter 2
lcdlegacy lcdfilter 3
hintnone hintstyle 0
hintslight hintstyle 1
hintmedium hintstyle 2
hintfull hintstyle 3
<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>, <CONTAINS>, <NOT_CON-
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 <prefer>ed families before the matching <family>,
append the <accept>able families 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> ele-
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-serif'
<test qual="all" name="family" mode="not_eq"><string>sans-serif</string></test>
<test qual="all" name="family" mode="not_eq"><string>serif</string></test>
<test qual="all" name="family" mode="not_eq"><string>monospace</string></test>
<edit name="family" mode="append_last"><string>sans-serif</string></edit>
Load per-user customization file, but don't complain
if it doesn't exist
<include ignore_missing="yes" prefix="xdg">fontconfig/fonts.conf</include>
Load local customization files, but don't complain
if there aren't any
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>
The example of the requirements of OR operator;
If the 'family' contains 'Courier New' OR 'Courier'
add 'monospace' as the alternative
<test name="family" mode="eq">
<edit name="family" mode="prepend">
<test name="family" mode="eq">
<edit name="family" mode="prepend">
USER CONFIGURATION FILE
This is an example of a per-user configuration file that lives in
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- $XDG_CONFIG_HOME/fontconfig/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>
<test name="lang" compare="contains">
<edit name="family" mode="prepend">
<string>WenQuanYi Zen Hei</string>
use VL Gothic font when sans-serif is requested for Japanese
<test name="lang" compare="contains">
<edit name="family" mode="prepend">
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.
conf.d is the conventional name for a directory of additional configu-
ration files managed by external applications or the local administra-
tor. The filenames starting with decimal digits are sorted in lexico-
graphic order and used as additional configuration files. All of these
files are in XML format. The master fonts.conf file references this
directory in an <include> directive.
fonts.dtd is a DTD that describes the format of the configuration
$XDG_CONFIG_HOME/fontconfig/conf.d and ~/.fonts.conf.d is the conven-
tional name for a per-user directory of (typically auto-generated) con-
figuration files, although the actual location is specified in the
global fonts.conf file. please note that ~/.fonts.conf.d is deprecated
now. it will not be read by default in the future version.
$XDG_CONFIG_HOME/fontconfig/fonts.conf and ~/.fonts.conf is the conven-
tional location for per-user font configuration, although the actual
location is specified in the global fonts.conf file. please note that
~/.fonts.conf is deprecated now. it will not be read by default in the
FC_DEBUG is used to output the detailed debugging messages. see Debug-
ging Applications section for more details.
FONTCONFIG_USE_MMAP is used to control the use of mmap(2) for the cache
files if available. this take a boolean value. fontconfig will checks
if the cache files are stored on the filesystem that is safe to use
mmap(2). explicitly setting this environment variable will causes skip-
ping this check and enforce to use or not use mmap(2) anyway.
fc-cat(1), fc-cache(1), fc-list(1), fc-match(1), fc-query(1)
Fontconfig version 2.11.0
11 10 2013 FONTS-CONF(5)
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