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# 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
        size           FC_SIZE                Double  Point size
        width          FC_WIDTH               Int     Condensed, normal or expanded
        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
        hinting        FC_HINTING             Bool    Whether the rasterizer should
                                                      use hinting
        hintstyle      FC_HINT_STYLE          Int     Automatic hinting style
        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
        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 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
        lcdfilter      FC_LCD_FILTER          Int     Type of LCD filter
        minspace       FC_MINSPACE            Bool    Eliminate leading from line
                                                      spacing
        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
        embolden       FC_EMBOLDEN            Bool    Rasterizer should
                                                      synthetically embolden the font
        fontfeatures   FC_FONT_FEATURES       String  List of extra feature tags in
                                                      OpenType to be enabled
        namelang       FC_NAMELANG            String  Language name to be used for the
                                                      default value of familylang,
                                                      stylelang and fullnamelang
        prgname        FC_PRGNAME             String  Name of the running program
        hash           FC_HASH                String  SHA256 hash value of the font data
                                                      with "sha256:" prefix.
        postscriptname FC_POSTSCRIPT_NAME     String  Font name in PostScript

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