x19.htmlPrev x93.htmlNext 3. Datatypes 
Fontconfig uses abstract datatypes to hide internal implementation details
for most data structures.  A few structures are exposed where appropriate.
  
3.1. FcChar8, FcChar16, FcChar32, FcBool 
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.
    
3.2. 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;
    
    
3.3. 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.
    
3.4. FcType 
Tags the kind of data stored in an FcValue.
    
3.5. 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;
    
    
                  FcValue Members
        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 *
    
    
3.6. 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.
    
3.7. 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.
    
3.8. 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.
    
3.9. 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.
    
3.10. 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.
    
3.11. 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'.
    
3.12. 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.
    
3.13. 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.
    
3.14. 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 particulat set use one of the FcSetName enumerated
values.
    
3.15. 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.
    
3.16. 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
    
    
3.17. FcAtomic 
Used for locking access to config files.  Provides a safe way to update
configuration files.
    
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