Table of Contents


fontconfig - Font configuration and customization



#include <fontconfig/fontconfig.h>
#include <fontconfig/fcfreetype.h>


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 make 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    CPP symbol    Type    Description

family    FC_FAMILY    String    Font family name
style    FC_STYLE    String    Font style. Overrides weight and slant
slant    FC_SLANT    Int    Italic, oblique or roman
weight    FC_WEIGHT    Int    Light, medium, demibold, bold or black
size    FC_SIZE    Double    Point size
aspect    FC_ASPECT    Double    Stretches glyphs horizontally before hinting
pixelsize    FC_PIXEL_SIZE    Double    Pixel size
spacing    FC_SPACING    Int    Proportional, monospace or charcell
foundry    FC_FOUNDRY    String    Font foundry name
antialias    FC_ANTIALIAS    Bool    Whether glyphs can be antialiased
hinting    FC_HINTING    Bool    Whether the rasterizer should use hinting
verticallayout    FC_VERTICAL_LAYOUT    Bool    Use vertical layout
autohint    FC_AUTOHINT    Bool    Use autohinter instead of normal hinter
globaladvance    FC_GLOBAL_ADVANCE    Bool    Use font global advance data
file    FC_FILE    String    The filename holding the font
index    FC_INDEX    Int    The index of the font within the file
ftface    FC_FT_FACE    FT_Face    Use the specified FreeType face object
rasterizer    FC_RASTERIZER    String    Which rasterizer is in use
outline    FC_OUTLINE    Bool    Whether the glyphs are outlines
scalable    FC_SCALABLE    Bool    Whether glyphs can be scaled
scale    FC_SCALE    Double    Scale factor for point->pixel conversions
dpi    FC_DPI    Double    Target dots per inch
rgba    FC_RGBA    Int    unknown, rgb, bgr, vrgb, vbgr, none - subpixel geometry
minspace    FC_MINSPACE    Bool    Eliminate leading from line spacing
charset    FC_CHARSET    CharSet    Unicode chars encoded by the font
lang    FC_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 an FcPattern object. 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 List Matching

While many applications want to locate a single font best matching their search criteria, other applications need to build a set of fonts which can be used to present any Unicode data. Fontconfig provides an API to generate a list sorted by the nearness of each font to the pattern. Every font in the system is considered, the best matching fonts are placed first. The application then can select whether the remaining fonts are unconditionally included in the list, or whether they are included only if they cover portions of Unicode not covered by any of the preceeding fonts.

The list resulting from this match is represented by references to the original font patterns and so consumes very little memory. Using a list entry involves creating a pattern which combines the information from the font with the information from the original pattern and executing the font substitutions.

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:

    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.





These are primitive datatypes; the FcChar* types hold precisely the number of bits stated (if supported by the C implementation). FcBool holds one of two CPP symbols: FcFalse or FcTrue.

An FcMatrix holds an affine transformation, usually used to reshape glyphs. A small set of matrix operations are provided to manipulate these.

    typedef struct _FcMatrix {
        double xx, xy, yx, yy;
    } FcMatrix;

An FcCharSet is an abstract type that holds the set of encoded unicode chars in a font. Operations to build and compare these sets are provided.

Tags the kind of data stored in an FcValue.

An FcValue object holds a single value with one of a number of different types. The 'type' tag indicates which member is valid.

    typedef struct _FcValue {
        FcType type;
        union {
            const FcChar8 *s;
            int i;
            FcBool b;
            double d;
            const FcMatrix *m;
            const FcCharSet *c;
        } u;
    } FcValue;

    type    Union member    Datatype
    FcTypeVoid    (none)    (none)
    FcTypeInteger    i    int
    FcTypeDouble    d    double
    FcTypeString    s    char *
    FcTypeBool    b    b
    FcTypeMatrix    m    FcMatrix *
    FcTypeCharSet    c    FcCharSet *
holds a set of names with associated value lists; each name refers to a property of a font. FcPatterns are used as inputs to the matching code as well as holding information about specific fonts. Each property can hold one or more values; conventionally all of the same type, although the interface doesn't demand that.


    typedef struct _FcFontSet {
        int nfont;
        int sfont;
        FcPattern **fonts;
    } FcFontSet;
An FcFontSet contains a list of FcPatterns. Internally fontconfig uses this data structure to hold sets of fonts. Externally, fontconfig returns the results of listing fonts in this format. 'nfont' holds the number of patterns in the 'fonts' array; 'sfont' is used to indicate the size of that array.

FcStrList FcStrSet holds a list of strings that can be appended to and enumerated. Its unique characteristic is that the enumeration works even while strings are appended during enumeration. FcStrList is used during enumeration to safely and correctly walk the list of strings even while that list is edited in the middle of enumeration.


    typedef struct _FcObjectSet {
        int nobject;
        int sobject;
        const char **objects;
    } FcObjectSet;

holds a set of names and is used to specify which fields from fonts are placed in the the list of returned patterns when listing fonts.


    typedef struct _FcObjectType {
        const char *object;
        FcType type;
    } FcObjectType;
marks the type of a pattern element generated when parsing font names. Applications can add new object types so that font names may contain the new elements.


    typedef struct _FcConstant {
     const FcChar8 *name;
     const char *object;
     int value;
    } FcConstant;
Provides for symbolic constants for new pattern elements. When 'name' is seen in a font name, an 'object' element is created with value 'value'.

holds a list of Unicode chars which are expected to be blank; unexpectedly blank chars are assumed to be invalid and are elided from the charset associated with the font.

holds the per-user cache information for use while loading the font database. This is built automatically for the current configuration when that is loaded. Applications must always pass '0' when one is requested.

holds a complete configuration of the library; there is one default configuration, other can be constructed from XML data structures. All public entry points that need global data can take an optional FcConfig* argument; passing 0 uses the default configuration. FcConfig objects hold two sets of fonts, the first contains those specified by the configuration, the second set holds those added by the application at run-time. Interfaces that need to reference a particulat set use one of the FcSetName enumerated values.

Specifies one of the two sets of fonts available in a configuration; FcSetSystem for those fonts specified in the configuration and FcSetApplication which holds fonts provided by the application.

Used as a return type for functions manipulating FcPattern objects.

    Result code    Meaning


    FcResultMatch    Object exists with the specified ID

    FcResultNoMatch    Object doesn't exist at all

    FcResultTypeMismatch    Object exists, but the type doesn't match

    FcResultNoId    Object exists, but has fewer values than specified

Used for locking access to config files. Provides a safe way to update configuration files.



FcMatrix structures hold an affine transformation in matrix form.

Initializes a matrix to the identify transformation.

FcMatrix *FcMatrixCopy (const FcMatrix *mat)
Allocates a new FcMatrix and copies 'mat' into it.

FcBool FcMatrixEqual (const FcMatrix *mat1, const FcMatrix *mat2)
Returns FcTrue if 'mat1' and 'mat2' are equal, else FcFalse.

void FcMatrixMultiply (FcMatrix *result, const FcMatrix *a, const FcMatrix *b)
Multiplies 'a' and 'b' together, placing the result in 'result'. 'result' may refer to the sam matrix as either 'a' or 'b'.

void FcMatrixRotate (FcMatrix *m, double c, double s)
If 'c' is cos(angle) and 's' is sin(angle), FcMatrixRotate rotates the matrix by 'angle'.

void FcMatrixScale (FcMatrix *m, double sx, double sy)
Scales 'm' by 'sx' in the horizontal dimension and 'sy' in the vertical dimension.

void FcMatrixShear (FcMatrix *m, double sh, double sv)
Shears 'm' by 'sh' in the horizontal direction and 'sv' in the vertical direction.


An FcCharSet is a boolean array indicating a set of unicode chars. Those associated with a font are marked constant and cannot be edited. FcCharSets may be reference counted internally to reduce memory consumption; this may be visible to applications as the result of FcCharSetCopy may return it's argument, and that CharSet may remain unmodifiable.

FcCharSet *FcCharSetCreate (void)
Creates an empty FcCharSet object.

void FcCharSetDestroy (FcCharSet *fcs)
Frees an FcCharSet object.

FcBool FcCharSetAddChar (FcCharSet *fcs, FcChar32 ucs4)
Adds a single unicode char to the set, returning FcFalse on failure, either as a result of a constant set or from running out of memory.

FcCharSet *FcCharSetCopy (FcCharSet *src)
Makes a copy of 'src'; note that this may not actually do anything more than increment the reference count on 'src'.

FcBool FcCharSetEqual (const FcCharSet *a, const FcCharSet *b)
Returns whether 'a' and 'b' contain the same set of unicode chars.

FcCharSet *FcCharSetIntersect (const FcCharSet *a, const FcCharSet *b)
Returns a set including only those chars found in both 'a' and 'b'.

FcCharSet *FcCharSetUnion (const FcCharSet *a, const FcCharSet *b);
Returns a set including only those chars found in either 'a' or 'b'.

FcCharSet *FcCharSetSubtract (const FcCharSet *a, const FcCharSet *b)
Returns a set including only those chars found in 'a' but not 'b'.

FcBool FcCharSetHasChar (const FcCharSet *fcs, FcChar32 ucs4)
Returns whether 'fcs' contains the char 'ucs4'.

FcChar32 FcCharSetCount (const FcCharSet *a)
Returns the total number of unicode chars in 'a'.

FcChar32 FcCharSetIntersectCount (const FcCharSet *a, const FcCharSet *b)
Returns the number of chars that are in both 'a' and 'b'.

FcChar32 FcCharSetSubtractCount (const FcCharSet *a, const FcCharSet *b)
Returns the number of chars that are in 'a' but not in 'b'.

FcBool FcCharSetIsSubset (const FcCharSet *a, const FcCharSet *b)
Returns whether 'a' is a subset of 'b'.

FcChar32 FcCharSetFirstPage (const FcCharSet *a, FcChar32 [FC_CHARSET_MAP_SIZE], FcChar32 *next)
Builds an array of bits marking the first page of Unicode coverage of 'a'. Returns the base of the array. 'next' contains the next page in the font.

FcChar32 FcCharSetNextPage (const FcCharSet *a, FcChar32 [FC_CHARSET_MAP_SIZE], FcChar32 *next)
Builds an array of bits marking the Unicode coverage of 'a' for page '*next'. Returns the base of the array. 'next' contains the next page in the font.


FcValue is a structure containing a type tag and a union of all possible datatypes. The tag is an enum of type FcType and is intended to provide a measure of run-time typechecking, although that depends on careful programming.

void FcValueDestroy (FcValue v)
Frees any memory referenced by `v'. Values of type FcTypeString, FcTypeMatrix and FcTypeCharSet reference memory, the other types do not.

FcValue FcValueSave (FcValue v)
Returns a copy of `v' duplicating any object referenced by it so that `v' may be safely destroyed without harming the new value.


An FcPattern is an opaque type that holds both patterns to match against the available fonts, as well as the information about each font.

FcPattern *FcPatternCreate (void)
Creates a pattern with no properties; used to build patterns from scratch.

void FcPatternDestroy (FcPattern *p)
Destroys a pattern, in the process destroying all related values.

FcBool FcPatternEqual (const FcPattern *pa, const FcPattern *pb);
Returns whether 'pa' and 'pb' are exactly alike.

FcBool FcPatternEqualSubset (const FcPattern *pa, const FcPattern *pb, const FcObjectSet *os)
Returns whether 'pa' and 'pb' have exactly the same values for all of the objects in 'os'.

FcChar32 FcPatternHash (const FcPattern *p)
Returns a 32-bit number which is the same for any two patterns which are exactly alike.

FcBool FcPatternAdd (FcPattern *p, const char *object, FcValue value, FcBool append)
Adds a single value to the list of values associated with the property named `object'. If `append' is FcTrue, the value is added at the end of any existing list, otherwise it is inserted at the begining. `value' is saved (with FcValueSave) when inserted into the pattern so that the library retains no reference to any application-supplied data structure.

FcBool FcPatternAddWeak (FcPattern *p, const char *object, FcValue value, FcBool append)
FcPatternAddWeak is essentially the same as FcPatternAdd except that any values added to the list have binding 'weak' instead of 'strong'.

FcBool FcPatternAddInteger (FcPattern *p, const char *object, int i)

FcBool FcPatternAddDouble (FcPattern *p, const char *object, double d)

FcBool FcPatternAddString (FcPattern *p, const char *object, const char *s)

FcBool FcPatternAddMatrix (FcPattern *p, const char *object, const FcMatrix *s)

FcBool FcPatternAddCharSet (FcPattern *p, const char *object, const FcCharSet *c)

FcBool FcPatternAddBool (FcPattern *p, const char *object, FcBool b)
These are all convenience functions that insert objects of the specified type into the pattern. Use these in preference to FcPatternAdd as they will provide compile-time typechecking. These all append values to any existing list of values.

FcResult FcPatternGet (FcPattern *p, const char *object, int id, FcValue *v)
Returns in `v' the `id'th value associated with the property `object'. The value returned is not a copy, but rather refers to the data stored within the pattern directly. Applications must not free this value.

FcResult FcPatternGetInteger (FcPattern *p, const char *object, int n, int *i);

FcResult FcPatternGetDouble (FcPattern *p, const char *object, int n, double *d);

FcResult FcPatternGetString (FcPattern *p, const char *object, int n, char **const s);

FcResult FcPatternGetMatrix (FcPattern *p, const char *object, int n, FcMatrix **s);

FcResult FcPatternGetCharSet (FcPattern *p, const char *object, int n, FcCharSet **c);

FcResult FcPatternGetBool (FcPattern *p, const char *object, int n, FcBool *b);
These are convenience functions that call FcPatternGet and verify that the returned data is of the expected type. They return FcResultTypeMismatch if this is not the case. Note that these (like FcPatternGet) do not make a copy of any data structure referenced by the return value. Use these in preference to FcPatternGet to provide compile-time typechecking.

FcPattern *FcPatternBuild (FcPattern *orig, ...);

FcPattern *FcPatternVaBuild (FcPattern *orig, va_list va)
Builds a pattern using a list of objects, types and values. Each value to be entered in the pattern is specified with three arguments:

1. Object name, a string describing the property to be added.

2. Object type, one of the FcType enumerated values

3. Value, not an FcValue, but the raw type as passed to any of the FcPatternAdd<type> functions. Must match the type of the second argument.

The argument list is terminated by a null object name, no object type nor value need be passed for this. The values are added to `pattern', if `pattern' is null, a new pattern is created. In either case, the pattern is returned. Example:

pattern = FcPatternBuild (0, FC_FAMILY, FtTypeString, "Times", (char *) 0);

FcPatternVaBuild is used when the arguments are already in the form of a varargs value.

FcBool FcPatternDel (FcPattern *p, const char *object)
Deletes all values associated with the property `object', returning whether the property existed or not.

void FcPatternPrint (const FcPattern *p)
Prints an easily readable version of the pattern to stdout. There is no provision for reparsing data in this format, it's just for diagnostics and debugging.

void FcDefaultSubstitute (FcPattern *pattern)
Supplies default values for underspecified font patterns:

Patterns without a specified style or weight are set to Medium

Patterns without a specified style or slant are set to Roman

Patterns without a specified pixel size are given one computed from any specified point size (default 12), dpi (default 75) and scale (default 1).

FcPattern *FcNameParse (const char *name)
Converts 'name' from the standard text format described above into a pattern.

FcChar8 *FcNameUnparse (FcPattern *pat)
Converts the given pattern into the standard text format described above. The return value is not static, but instead refers to newly allocated memory which should be freed by the caller.


An FcFontSet simply holds a list of patterns; these are used to return the results of listing available fonts.
FcFontSet *FcFontSetCreate (void)
Creates an empty font set.

void FcFontSetDestroy (FcFontSet *s);
Destroys a font set. Note that this destroys any referenced patterns as well.

FcBool FcFontSetAdd (FcFontSet *s, FcPattern *font)
Adds a pattern to a font set. Note that the pattern is not copied before being inserted into the set.


An FcObjectSet holds a list of pattern property names; it is used to indiciate which properties are to be returned in the patterns from FcFontList.

FcObjectSet *FcObjectSetCreate (void)
Creates an empty set.

FcBool FcObjectSetAdd (FcObjectSet *os, const char *object)
Adds a proprety name to the set.

void FcObjectSetDestroy (FcObjectSet *os)
Destroys an object set.

FcObjectSet *FcObjectSetBuild (const char *first, ...)

FcObjectSet *FcObjectSetVaBuild (const char *first, va_list va)
These build an object set from a null-terminated list of property names.


Provides for applcation-specified font name object types so that new pattern elements can be generated from font names.

FcBool FcNameRegisterObjectTypes (const FcObjectType *types, int ntype)
Register 'ntype' new object types.

FcBool FcNameUnregisterObjectTypes (const FcObjectType *types, int ntype)
Unregister 'ntype' object types.
const FcObjectType *FcNameGetObjectType (const char *object)
Return the object type for the pattern element named 'object'.


Provides for application-specified symbolic constants for font names.

FcBool FcNameRegisterConstants (const FcConstant *consts, int nconsts)
Register 'nconsts' new symbolic constants.

FcBool FcNameUnregisterConstants (const FcConstant *consts, int nconsts)
Unregister 'nconsts' symbolic constants.
const FcConstant *FcNameGetConstant (FcChar8 *string)
Return the FcConstant structure related to symbolic constant 'string'.

FcBool FcNameConstant (FcChar8 *string, int *result);
Returns whether a symbolic constant with name 'string' is registered, placing the value of the constant in 'result' if present.


An FcBlanks object holds a list of Unicode chars which are expected to be blank when drawn. When scanning new fonts, any glyphs which are empty and not in this list will be assumed to be broken and not placed in the FcCharSet associated with the font. This provides a significantly more accurate CharSet for applications.

FcBlanks *FcBlanksCreate (void)
Creates an empty FcBlanks object.

void FcBlanksDestroy (FcBlanks *b)
Destroys an FcBlanks object, freeing any associated memory.

FcBool FcBlanksAdd (FcBlanks *b, FcChar32 ucs4)
Adds a single character to an FcBlanks object, returning FcFalse if this process ran out of memory.

FcBool FcBlanksIsMember (FcBlanks *b, FcChar32 ucs4)
Returns whether the specified FcBlanks object contains the indicated Unicode value.


An FcConfig object holds the internal representation of a configuration. There is a default configuration which applications may use by passing 0 to any function using the data within an FcConfig.

FcConfig *FcConfigCreate (void)
Creates an empty configuration.

void FcConfigDestroy (FcConfig *config)
Destroys a configuration and any data associated with it. Note that calling this function with the return from FcConfigGetCurrent will place the library in an indeterminate state.

FcBool FcConfigSetCurrent (FcConfig *config)
Sets the current default configuration to 'config'. Implicitly calls FcConfigBuildFonts if necessary, returning FcFalse if that call fails.

FcConfig *FcConfigGetCurrent (void)
Returns the current default configuration.

FcBool FcConfigUptoDate (FcConfig *config)
Checks all of the files related to 'config' and returns whether the in-memory version is in sync with the disk version.

FcBool FcConfigBuildFonts (FcConfig *config)
Builds the set of available fonts for the given configuration. Note that any changes to the configuration after this call have indeterminate effects. Returns FcFalse if this operation runs out of memory.

FcStrList *FcConfigGetConfigDirs (FcConfig *config)
Returns the list of font directories specified in the configuration files for 'config'. Does not include any subdirectories.

FcStrList *FcConfigGetFontDirs (FcConfig *config)
Returns the list of font directories in 'config'. This includes the configured font directories along with any directories below those in the filesystem.

FcStrList *FcConfigGetConfigFiles (FcConfig *config)
Returns the list of known configuration files used to generate 'config'. Note that this will not include any configuration done with FcConfigParse.

char *FcConfigGetCache (FcConfig *config)
Returns the name of the file used to store per-user font information.

FcFontSet *FcConfigGetFonts (FcConfig *config, FcSetName set)
Returns one of the two sets of fonts from the configuration as specified by 'set'.

FcBlanks *FcConfigGetBlanks (FcConfig *config)
Returns the FcBlanks object associated with the given configuration, if no blanks were present in the configuration, this function will return 0.

int FcConfigGetRescanInverval (FcConfig *config)
Returns the interval between automatic checks of the configuration (in seconds) specified in 'config'. The configuration is checked during a call to FcFontList when this interval has passed since the last check.

FcBool FcConfigSetRescanInverval (FcConfig *config, int rescanInterval)
Sets the rescan interval; returns FcFalse if an error occurred.

FcBool FcConfigAppFontAddFile (FcConfig *config, const char *file)
Adds an application-specific font to the configuration.

FcBool FcConfigAppFontAddDir (FcConfig *config, const char *dir)
Scans the specified directory for fonts, adding each one found to the application-specific set of fonts.

void FcConfigAppFontClear (FcConfig *config)
Clears the set of application-specific fonts.

FcBool FcConfigSubstituteWithPat (FcConfig *config, FcPattern *p, FcPattern *p_pat FcMatchKind kind)
Performs the sequence of pattern modification operations, if 'kind' is FcMatchPattern, then those tagged as pattern operations are applied, else if 'kind' is FcMatchFont, those tagged as font operations are applied and p_pat is used for <test> elements with target=pattern.

FcBool FcConfigSubstitute (FcConfig *config, FcPattern *p, FcMatchKind kind)
Calls FcConfigSubstituteWithPat setting p_pat to NULL.

FcPattern *FcFontMatch (FcConfig *config, FcPattern *p, FcResult *result)
Returns the font in 'config' most close matching 'p'. This function should be called only after FcConfigSubstitute and FcDefaultSubstitute have been called for 'p'; otherwise the results will not be correct.

FcFontSet *FcFontSort (FcConfig *config, FcPattern *p, FcBool trim, FcCharSet **csp, FcResult *result) Returns the list of fonts sorted by
closeness to 'p'. If 'trim' is FcTrue, elements in the list which don't include Unicode coverage not provided by earlier elements in the list are elided. The union of Unicode coverage of all of the fonts is returned in 'csp', if 'csp' is not NULL. This function should be called only after FcConfigSubstitute and FcDefaultSubstitute have been called for 'p'; otherwise the results will not be correct.

The returned FcFontSet references FcPattern structures which may be shared by the return value from multiple FcFontSort calls, applications must not modify these patterns. Instead, they should be passed, along with 'p' to FcFontRenderPrepare which combines them into a complete pattern.

The FcFontSet returned by FcFontSort is destroyed by caling FcFontSetDestroy.

FcPattern *FcFontRenderPrepare (FcConfig *config, FcPattern *pat, FcPattern *font)
Creates a new pattern consisting of elements of 'font' not appearing in 'pat', elements of 'pat' not appearing in 'font' and the best matching value from 'pat' for elements appearing in both. The result is passed to FcConfigSubstitute with 'kind' FcMatchFont and then returned.

FcFontSet *FcFontList (FcConfig *config, FcPattern *p, FcObjectSet *os)
Selects fonts matching 'p', creates patterns from those fonts containing only the objects in 'os' and returns the set of unique such patterns.

char *FcConfigFilename (const char *name)
Given the specified external entity name, return the associated filename. This provides applications a way to convert various configuration file references into filename form.

A null or empty 'name' indicates that the default configuration file should be used; which file this references can be overridden with the FC_CONFIG_FILE environment variable. Next, if the name starts with '~', it refers to a file in the current users home directory. Otherwise if the name doesn't start with '/', it refers to a file in the default configuration directory; the built-in default directory can be overridden with the FC_CONFIG_DIR environment variable.


These functions provide some control over how the library is initialized.

FcConfig *FcInitLoadConfig (void)
Loads the default configuration file and returns the resulting configuration. Does not load any font information.

FcConfig *FcInitLoadConfigAndFonts (void)
Loads the default configuration file and builds information about the available fonts. Returns the resulting configuration.

FcBool FcInit (void)
Loads the default configuration file and the fonts referenced therein and sets the default configuration to that result. Returns whether this process succeeded or not. If the default configuration has already been loaded, this routine does nothing and returns FcTrue.

int FcGetVersion (void)
Returns the version number of the library.

FcBool FcInitReinitialize (void)
Forces the default configuration file to be reloaded and resets the default configuration.

FcBool FcInitBringUptoDate (void)
Checks the rescan interval in the default configuration, checking the configuration if the interval has passed and reloading the configuration if when any changes are detected.


These functions provide a safe way to update config files, allowing ongoing reading of the old config file while locked for writing and ensuring that a consistent and complete version of the config file is always available.

FcAtomic * FcAtomicCreate (const FcChar8 *file)
Creates a data structure containing data needed to control access to 'file'. Writing is done to a separate file. Once that file is complete, the original configuration file is atomically replaced so that reading process always see a consistent and complete file without the need to lock for reading.

FcBool FcAtomicLock (FcAtomic *atomic)
Attempts to lock the file referenced by 'atomic'. Returns FcFalse if the file is locked by another process, else returns FcTrue and leaves the file locked.

FcChar8 *FcAtomicNewFile (FcAtomic *atomic)
Returns the filename for writing a new version of the file referenced by 'atomic'.

FcChar8 *FcAtomicOrigFile (FcAtomic *atomic)
Returns the file refernced by 'atomic'.

FcBool FcAtomicReplaceOrig (FcAtomic *atomic)
Replaces the original file referenced by 'atomic' with the new file.

void FcAtomicDeleteNew (FcAtomic *atomic)
Deletes the new file.

void FcAtomicUnlock (FcAtomic *atomic)
Unlocks the file.

void FcAtomicDestroy (FcAtomic *atomic)
Destroys 'atomic'.

FreeType specific functions

#include <fontconfig/fcfreetype.h>
While the fontconfig library doesn't insist that FreeType be used as the rasterization mechanism for fonts, it does provide some convenience functions.

FT_UInt FcFreeTypeCharIndex (FT_Face face, FcChar32 ucs4)
Maps a Unicode char to a glyph index. This function uses information from several possible underlying encoding tables to work around broken fonts. As a result, this function isn't designed to be used in performance sensitive areas; results from this function are intended to be cached by higher level functions.

FcCharSet *FcFreeTypeCharSet (FT_Face face, FcBlanks *blanks) Scans a
FreeType face and returns the set of encoded Unicode chars. This scans several encoding tables to build as complete a list as possible. If 'blanks' is not 0, the glyphs in the font are examined and any blank glyphs not in 'blanks' are not placed in the returned FcCharSet.

FcPattern *FcFreeTypeQuery (const char *file, int id, FcBlanks *blanks, int *count)
Constructs a pattern representing the 'id'th font in 'file'. The number of fonts in 'file' is returned in 'count'.

XML specific functions

FcBool FcConfigParseAndLoad (FcConfig *config, const FcChar8 *file, FcBool complain)
Walks the configuration in 'file' and constructs the internal representation in 'config'. Any include files referenced from within 'file' will be loaded with FcConfigLoad and also parsed. If 'complain' is FcFalse, no warning will be displayed if 'file' does not exist.

File and Directory routines

FcBool FcFileScan (FcFontSet *set, FcStrSet *dirs, FcFileCache *cache, FcBlanks *blanks, const char *file, FcBool force)
Scans a single file and adds all fonts found to 'set'. If 'force' is FcTrue, then the file is scanned even if associated information is found in 'cache'. If 'file' is a directory, it is added to 'dirs'.

FcBool FcDirScan (FcFontSet *set, FcStrSet *dirs, FcFileCache *cache, FcBlanks *blanks, const char *dir, FcBool force)
Scans an entire directory and adds all fonts found to 'set'. If 'force' is FcTrue, then the directory and all files within it are scanned even if information is present in the per-directory cache file or 'cache'. Any subdirectories found are added to 'dirs'.

FcBool FcDirSave (FcFontSet *set, FcStrSet *dirs, const char *dir)
Creates the per-directory cache file for 'dir' and populates it with the fonts in 'set' and subdirectories in 'dirs'.

FcBool FcDirCacheValid (const FcChar8 *cache_file)
Returns FcTrue if 'cache_file' is no older than the directory containing it, else FcFalse.

FcStrSet and FcStrList

A data structure for enumerating strings, used to list directories while scanning the configuration as directories are added while scanning.

FcStrSet *FcStrSetCreate (void)
Create an empty set.

FcBool FcStrSetMember (FcStrSet *set, const FcChar8 *s)
Returns whether 's' is a member of 'set'.

FcBool FcStrSetAdd (FcStrSet *set, const FcChar8 *s)
Adds a copy of 's' to 'set'.

FcBool FcStrSetAddFilename (FcStrSet *set, const FcChar8 *s)
Adds a copy 's' to 'set', The copy is created with FcStrCopyFilename so that leading '~' values are replaced with the value of the HOME environment variable.

FcBool FcStrSetDel (FcStrSet *set, const FcChar8 *s)
Removes 's' from 'set', returning FcTrue if 's' was a member else FcFalse.

void FcStrSetDestroy (FcStrSet *set)
Destroys 'set'.

FcStrList *FcStrListCreate (FcStrSet *set)
Creates an enumerator to list the strings in 'set'.

FcChar8 *FcStrListNext (FcStrList *list)
Returns the next string in 'set'.

void FcStrListDone (FcStrList *list)
Destroys the enumerator 'list'.

String utilities

int FcUtf8ToUcs4 (FcChar8 *src, FcChar32 *dst, int len)
Converts the next Unicode char from 'src' into 'dst' and returns the number of bytes containing the char. 'src' nust be at least 'len' bytes long.

int FcUcs4ToUtf8 (FcChar32 src, FcChar8 dst[FC_UTF8_MAX_LEN])
Converts the Unicode char from 'src' into 'dst' and returns the number of bytes needed to encode the char.

FcBool FcUtf8Len (FcChar8 *src, int len, int *nchar, int *wchar)
Counts the number of Unicode chars in 'len' bytes of 'src'. Places that count in 'nchar'. 'wchar' contains 1, 2 or 4 depending on the number of bytes needed to hold the largest unicode char counted. The return value indicates whether 'src' is a well-formed UTF8 string.

int FcUtf16ToUcs4 (FcChar8 *src, FcEndian endian, FcChar32 *dst, int len)
Converts the next Unicode char from 'src' into 'dst' and returns the number of bytes containing the char. 'src' must be at least 'len' bytes long. Bytes of 'src' are combined into 16-bit units according to 'endian'.

FcBool FcUtf16Len (FcChar8 *src, FcEndian endian, int len, int *nchar, int *wchar)
Counts the number of Unicode chars in 'len' bytes of 'src'. Bytes of 'src' are combined into 16-bit units according to 'endian'. Places that count in 'nchar'. 'wchar' contains 1, 2 or 4 depending on the number of bytes needed to hold the largest unicode char counted. The return value indicates whether 'string' is a well-formed UTF16 string.

FcChar8 *FcStrCopy (const FcChar8 *s)
Allocates memory, copies 's' and returns the resulting buffer. Yes, this is 'strdup', but that function isn't available on every platform.

FcChar8 *FcStrCopyFilename (const FcChar8 *s)
Just like FcStrCopy except that it converts any leading '~' characters in 's' to the value of the HOME environment variable.
int FcStrCmpIgnoreCase (const char *s1, const char *s2)
Returns the usual <0, 0, >0 result of comparing 's1' and 's2'. This test is case-insensitive in the ASCII range and will operate properly with UTF8 encoded strings, although it does not check for well formed strings.

FcChar8 *FcStrDirname (const FcChar8 *file)
Returns the directory containing 'file'.

FcChar8 *FcStrBasename (const FcChar8 *file)
Returns the filename of 'file' stripped of any leading directory names.

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">


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 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.


This element provides a place to consolodate 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. <b


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    Operation with match    Operation without match

"assign"    Replace matching value    Replace all values
"assign_replace"    Replace all values    Replace all values
"prepend"    Insert before matching value    Insert at head of list
"prepend_first"    Insert at head of list    Insert at head of list
"append"    Append after matching value    Append at end of list
"append_last"    Append at end of list    Append at end of list





These elements hold a single value of the indicated type. <bool> elements hold either true or false.


This element holds the four <double> elements of an affine transformation.


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    CPP symbol

light    weight    FC_WEIGHT_LIGHT
medium    weight    FC_WEIGHT_MEDIUM
demibold    weight    FC_WEIGHT_DEMIBOLD
bold    weight    FC_WEIGHT_BOLD
black    weight    FC_WEIGHT_BLACK
roman    slant    FC_SLANT_ROMAN
italic    slant    FC_SLANT_ITALIC
oblique    slant    FC_SLANT_OBLIQUE
proportional    spacing    FC_PROPORTIONAL
mono    spacing    FC_MONO
charcell    spacing    FC_CHARCELL
unknown    rgba    FC_RGBA_UNKNOWN
rgb    rgba    FC_RGBA_RGB
bgr    rgba    FC_RGBA_BGR
vrgb    rgba    FC_RGBA_VRGB
vbgr    rgba    FC_RGBA_VBGR
none    rgba    FC_RGBA_NONE







These elements perform the specified operation on a list of expression elements. <or> and <and> are boolean, not bitwise.







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 contain 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 familys after the matching <family> and append the <default> families to the end of the family list.


Holds a single font family name




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

<?xml version="1.0"?>
<!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'
<match target="pattern">
    <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'
<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>
    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.
    <prefer><family>Times New Roman</family></prefer>
    <prefer><family>Courier New</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>
    <prefer><family>Andale Mono</family></prefer>

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 -->
    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".
<match 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 files.

local.conf is sourced by the default system-wide fonts.conf file. Note that the normal 'make install' procedure for XFree86 is to replace any existing fonts.conf file with the new version. Place any local customizations in local.conf which this file references.

~/.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.


Keith Packard, member of the XFree86 Project, Inc.

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