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 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
    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
    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
    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