/etc/fonts/fonts.conf /etc/fonts/fonts.dtd /etc/fonts/conf.d $XDG_CONFIG_HOME/fontconfig/conf.d $XDG_CONFIG_HOME/fontconfig/fonts.conf ~/.fonts.conf.d ~/.fonts.conf |
Fontconfig is a library designed to provide system-wide font configuration, 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 font.
The configuration module consists of the FcConfig datatype, libexpat and FcConfigParse which walks over an XML tree and amends 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.
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 names
familylang String Languages corresponding to each family
style String Font style. Overrides weight and slant
stylelang String Languages corresponding to each style
fullname String Font full names (often includes style)
fullnamelang String Languages corresponding to each fullname
slant Int Italic, oblique or roman
weight Int Light, medium, demibold, bold or black
size Double Point size
width Int Condensed, normal or expanded
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
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
color Bool Whether any glyphs have color
scale Double Scale factor for point->pixel conversions (deprecated)
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
font supports
fontversion Int Version number of the font
capability String List of layout capabilities in the font
fontformat String String name of the font format
embolden Bool Rasterizer should synthetically embolden the font
embeddedbitmap Bool Use the embedded bitmap instead of the outline
decorative Bool Whether the style is a decorative variant
fontfeatures String List of the feature tags in OpenType to be enabled
namelang String Language name to be used for the default value of
familylang, stylelang, and fullnamelang
prgname String String Name of the running program
postscriptname String Font family name in PostScript
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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.
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>...
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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
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The '\', '-', ':' and ',' characters in family names must be preceded by a '\' character to avoid having them misinterpreted. Similarly, values 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.
To help diagnose font and applications problems, fontconfig is built with a large amount of internal debugging left enabled. It is controlled by means of the FC_DEBUG environment variable. The value of this variable is interpreted as a number, and each bit within that value controls different debugging messages.
Name Value Meaning --------------------------------------------------------- MATCH 1 Brief information about font matching MATCHV 2 Extensive font matching information EDIT 4 Monitor match/test/edit execution 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 application. 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 letter code.
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 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>
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This is the top level element for a font configuration and can contain <dir>, <cachedir>, <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. If 'prefix' is set to "xdg", the value in the XDG_DATA_HOME environment variable will be 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 Specification 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 configuration file version number (currently 5).
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 order.
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.
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.
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 are explicitly included in the set of fonts used to resolve list and match requests; including them in this list protects them from being "blacklisted" by a rejectfont element. Acceptfont elements include glob and pattern elements which are used to match fonts.
Fonts matched by an rejectfont element are "blacklisted"; such fonts are excluded from the set of fonts used to resolve list and match requests as if they didn't exist in the system. Rejectfont elements include glob and pattern elements which are used to match 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 extensions. 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 const elements.
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.
This element contains a single value which is compared with the target ('pattern', 'font', 'scan' or 'default') property "property" (substitute 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.
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 ("strong", "weak" or "same") with "same" binding using the value from the matched pattern element. '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
"delete" Delete matching value Delete all values
"delete_all" Delete all values Delete all values
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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).
This element holds four numerical expressions of an affine transformation. At their simplest these will be four <double> elements but they can also be more involved expressions.
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 demilight weight 55 semilight weight 55 book weight 75 regular weight 80 normal weight 80 medium weight 100 demibold weight 180 semibold weight 1 |