# Fontconfig Developers Reference, Version &version;

Keith Packard HP Cambridge Research Lab KRP Fontconfig &version;

Copyright © 2002 Keith Packard

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## DESCRIPTION

Fontconfig is a library designed to provide system-wide font configuration, customization and application access.

## FUNCTIONAL OVERVIEW

Fontconfig contains two essential modules, the configuration module which builds an internal configuration from XML files and the matching module which accepts font patterns and returns the nearest matching font.

### FONT CONFIGURATION

The configuration module consists of the FcConfig datatype, libexpat and FcConfigParse which walks over an XML tree and 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.

### 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 application's rendering mechanism.

                     Property Definitions

        Property       C Preprocessor Symbol  Type    Description
        ----------------------------------------------------
        family         FC_FAMILY              String  Font family names
        familylang     FC_FAMILYLANG          String  Language corresponding to
                                                      each family name
        style          FC_STYLE               String  Font style. Overrides weight
                                                      and slant
        stylelang      FC_STYLELANG           String  Language corresponding to
                                                      each style name
        fullname       FC_FULLNAME            String  Font face full name where
                                                      different from family and
                                                      family + style
        fullnamelang   FC_FULLNAMELANG        String  Language corresponding to
                                                      each fullname
        slant          FC_SLANT               Int     Italic, oblique or roman
        weight         FC_WEIGHT              Int     Light, medium, demibold,
                                                      bold or black
        width          FC_WIDTH               Int     Condensed, normal or expanded
        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, dual-width,
                                                      monospace or charcell
        foundry        FC_FOUNDRY             String  Font foundry name
        antialias      FC_ANTIALIAS           Bool    Whether glyphs can be
                                                      antialiased
        hintstyle      FC_HINT_STYLE          Int     Automatic hinting style
        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 (deprecated)
        file           FC_FILE                String  The filename holding the font
                                                      relative to the config's sysroot
        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 (deprecated)
        outline        FC_OUTLINE             Bool    Whether the glyphs are outlines
        scalable       FC_SCALABLE            Bool    Whether the glyphs are outlines or have color
        dpi            FC_DPI                 Double  Target dots per inch
        rgba           FC_RGBA                Int     unknown, rgb, bgr, vrgb,
                                                      vbgr, none - subpixel geometry
        scale          FC_SCALE               Double  Scale factor for point->pixel
                                                      conversions (deprecated)
        minspace       FC_MINSPACE            Bool    Eliminate leading from line
                                                      spacing
        matrix         FC_MATRIX              Matrix  Hold an affine transformation
        charset        FC_CHARSET             CharSet Unicode chars encoded by
                                                      the font
        lang           FC_LANG                LangSet Set of RFC-3066-style
                                                      languages this font supports
        fontversion    FC_FONTVERSION         Int     Version number of the font
        capability     FC_CAPABILITY          String  List of layout capabilities in
                                                      the font
        fontformat     FC_FONTFORMAT          String  String name of the font format
        embolden       FC_EMBOLDEN            Bool    Rasterizer should
                                                      synthetically embolden the font
        embeddedbitmap FC_EMBEDDED_BITMAP     Bool    Use the embedded bitmap instead
                                                      of the outline
        decorative     FC_DECORATIVE          Bool    Whether the style is a decorative
                                                      variant
        lcdfilter      FC_LCD_FILTER          Int     Type of LCD filter
        namelang       FC_NAMELANG            String  Language name to be used for the
                                                      default value of familylang,
                                                      stylelang and fullnamelang
        fontfeatures   FC_FONT_FEATURES       String  List of extra feature tags in
                                                      OpenType to be enabled
        prgname        FC_PRGNAME             String  Name of the running program
        hash           FC_HASH                String  SHA256 hash value of the font data
                                                      with "sha256:" prefix (deprecated)
        postscriptname FC_POSTSCRIPT_NAME     String  Font name in PostScript
        color          FC_COLOR               Bool    Whether any glyphs have color
        symbol         FC_SYMBOL              Bool    Whether font uses MS symbol-font encoding
        fontvariations FC_FONT_VARIATIONS     String  comma-separated string of axes in variable font
        variable       FC_VARIABLE            Bool    Whether font is Variable Font
        fonthashint    FC_FONT_HAS_HINT       Bool    Whether font has hinting
        order          FC_ORDER               Int     Order number of the font
        desktop        FC_DESKTOP_NAME        String  Current desktop name
        namedinstance  FC_NAMED_INSTANCE      Bool    Whether font is a named instance
        fontwarapper   FC_FONT_WRAPPER        String  The font wrapper format

## Datatypes

Fontconfig uses abstract data types to hide internal implementation details for most data structures. A few structures are exposed where appropriate.

### FcChar8, FcChar16, FcChar32, FcBool

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

### FcMatrix

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;

### FcCharSet

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.

### FcLangSet

An FcLangSet is an abstract type that holds the set of languages supported by a font. Operations to build and compare these sets are provided. These are computed for a font based on orthographic information built into the fontconfig library. Fontconfig has orthographies for all of the ISO 639-1 languages except for MS, NA, PA, PS, QU, RN, RW, SD, SG, SN, SU and ZA. If you have orthographic information for any of these languages, please submit them.

### FcLangResult

An FcLangResult is an enumeration used to return the results of comparing two language strings or FcLangSet objects. FcLangEqual means the objects match language and territory. FcLangDifferentTerritory means the objects match in language but differ in territory. FcLangDifferentLang means the objects differ in language.

### FcType

Tags the kind of data stored in an FcValue.

### 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;
                            void *f;
                            const FcLangSet *l;
                            const FcRange   *r;
                    } u;
            } FcValue;

                      FcValue Members

            Type            Union member    Datatype
            --------------------------------
            FcTypeVoid      (none)          (none)
            FcTypeInteger   i               int
            FcTypeDouble    d               double
            FcTypeString    s               FcChar8 *
            FcTypeBool      b               b
            FcTypeMatrix    m               FcMatrix *
            FcTypeCharSet   c               FcCharSet *
            FcTypeFTFace    f               void * (FT_Face)
            FcTypeLangSet   l               FcLangSet *
            FcTypeRange     r               FcRange *

### FcPattern, FcPatternIter

An FcPattern 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. An FcPatternIter is used during iteration to access properties in FcPattern.

### FcFontSet

            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.

### FcStrSet, 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.

### FcObjectSet

            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.

### FcObjectType

            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.

### FcConstant

            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'.

### FcBlanks

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.

FcBlanks is deprecated and should not be used in newly written code. It is still accepted by some functions for compatibility with older code but will be removed in the future.

### FcFileCache

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.

### FcConfig

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 particular set use one of the FcSetName enumerated values.

### FcSetName

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.

### FcResult

Used as a return type for functions manipulating FcPattern objects.

          FcResult Values
            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
            FcResultOutOfMemory     malloc failed

### FcAtomic

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

### FcCache

Holds information about the fonts contained in a single directory. Normal applications need not worry about this as caches for font access are automatically managed by the library. Applications dealing with cache management may want to use some of these objects in their work, however the included 'fc-cache' program generally suffices for all of that.

## FUNCTIONS

These are grouped by functionality, often using the main data type being manipulated.

### Initialization

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

&fcinit;

### FcPattern

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; &fcformat;

### FcFontSet

An FcFontSet simply holds a list of patterns; these are used to return the results of listing available fonts.

&fcfontset;

### FcObjectSet

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

&fcobjectset;

### FreeType specific functions

While the fontconfig library doesn't insist that FreeType be used as the rasterization mechanism for fonts, it does provide some convenience functions.

&fcfreetype;

### Fontations specific functions

For font indexing, an alternative backend based on the Fontations set of font libraries is in development. The indexing functions are exposed as Fontations specific functions.

&fcfontations;

### FcValue

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.

&fcvalue;

### FcCharSet

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;

### FcLangSet

An FcLangSet is a set of language names (each of which include language and an optional territory). They are used when selecting fonts to indicate which languages the fonts need to support. Each font is marked, using language orthography information built into fontconfig, with the set of supported languages.

&fclangset;

### FcMatrix

FcMatrix structures hold an affine transformation in matrix form.

&fcmatrix;

### FcRange

An FcRange holds two variables to indicate a range in between.

&fcrange;

### FcConfig

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;

### FcObjectType

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

&fcobjecttype;

### FcConstant

Provides for application-specified symbolic constants for font names.

&fcconstant;

### FcWeight

Maps weights to and from OpenType weights.

&fcweight;

### FcBlanks

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 is deprecated and should not be used in newly written code. It is still accepted by some functions for compatibility with older code but will be removed in the future.

&fcblanks;

### FcAtomic

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

&fcatomic;

### File and Directory routines

These routines work with font files and directories, including font directory cache files.

&fcfile; &fcdircache;

### FcCache routines

These routines work with font directory caches, accessing their contents in limited ways. It is not expected that normal applications will need to use these functions.

&fccache;

### FcStrSet and FcStrList

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

&fcstrset;

### String utilities

Fontconfig manipulates many UTF-8 strings represented with the FcChar8 type. These functions are exposed to help applications deal with these UTF-8 strings in a locale-insensitive manner.

&fcstring;