typedef struct FT_IncrementalRec_*  FT_Incremental;

An opaque type describing a user-provided object used to implement ‘incremental’ glyph loading within FreeType. This is used to support embedded fonts in certain environments (e.g., Postscript interpreters), where the glyph data isn't in the font file, or must be overridden by different values.

It is up to client applications to create and implement FT_Incremental objects, as long as they provide implementations for the methods FT_Incremental_GetGlyphDataFunc, FT_Incremental_FreeGlyphDataFunc and FT_Incremental_GetGlyphMetricsFunc.

See the description of FT_Incremental_InterfaceRec to understand how to use incremental objects with FreeType.

  typedef struct  FT_Incremental_MetricsRec_
  {
    FT_Long  bearing_x;
    FT_Long  bearing_y;
    FT_Long  advance;

  } FT_Incremental_MetricsRec, *FT_Incremental_Metrics;

A small structure used to contain the basic glyph metrics returned by the FT_Incremental_GetGlyphMetricsFunc method.

These correspond to horizontal or vertical metrics depending on the value of the ‘vertical’ argument to the function FT_Incremental_GetGlyphMetricsFunc.

  typedef FT_Error
  (*FT_Incremental_GetGlyphDataFunc)( FT_Incremental  incremental,
                                      FT_UInt         glyph_index,
                                      FT_Data*        adata );

A function called by FreeType to access a given glyph's data bytes during FT_Load_Glyph or FT_Load_Char if incremental loading is enabled.

Note that the format of the glyph's data bytes depends on the font file format. For TrueType, it must correspond to the raw bytes within the ‘glyf’ table. For Postscript formats, it must correspond to the unencrypted charstring bytes, without any ‘lenIV’ header. It is undefined for any other format.

FreeType error code. 0 means success.

If this function returns succesfully the method FT_Incremental_FreeGlyphDataFunc will be called later to release the data bytes.

Nested calls to FT_Incremental_GetGlyphDataFunc can happen for compound glyphs.

  typedef void
  (*FT_Incremental_FreeGlyphDataFunc)( FT_Incremental  incremental,
                                       FT_Data*        data );

A function used to release the glyph data bytes returned by a successful call to FT_Incremental_GetGlyphDataFunc.

  typedef FT_Error
  (*FT_Incremental_GetGlyphMetricsFunc)
                      ( FT_Incremental              incremental,
                        FT_UInt                     glyph_index,
                        FT_Bool                     vertical,
                        FT_Incremental_MetricsRec  *ametrics );

A function used to retrieve the basic metrics of a given glyph index before accessing its data. This is necessary because, in certain formats like TrueType, the metrics are stored in a different place from the glyph images proper.

  typedef struct  FT_Incremental_FuncsRec_
  {
    FT_Incremental_GetGlyphDataFunc     get_glyph_data;
    FT_Incremental_FreeGlyphDataFunc    free_glyph_data;
    FT_Incremental_GetGlyphMetricsFunc  get_glyph_metrics;

  } FT_Incremental_FuncsRec;

A table of functions for accessing fonts that load data incrementally. Used in FT_Incremental_InterfaceRec.

  typedef struct  FT_Incremental_InterfaceRec_
  {
    const FT_Incremental_FuncsRec*  funcs;
    FT_Incremental                  object;
  
  } FT_Incremental_InterfaceRec;

A structure to be used with FT_Open_Face to indicate that the user wants to support incremental glyph loading. You should use it with FT_PARAM_TAG_INCREMENTAL as in the following example:

  FT_Incremental_InterfaceRec  inc_int;
  FT_Parameter                 parameter;
  FT_Open_Args                 open_args;


  // set up incremental descriptor
  inc_int.funcs  = my_funcs;
  inc_int.object = my_object;

  // set up optional parameter
  parameter.tag  = FT_PARAM_TAG_INCREMENTAL;
  parameter.data = &inc_int;

  // set up FT_Open_Args structure
  open_args.flags      = FT_OPEN_PATHNAME | FT_OPEN_PARAMS;
  open_args.pathname   = my_font_pathname;
  open_args.num_params = 1;
  open_args.params     = &parameter; // we use one optional argument

  // open the font
  error = FT_Open_Face( library, &open_args, index, &face );
  ...

  typedef FT_Incremental_InterfaceRec*   FT_Incremental_Interface;

A pointer to an FT_Incremental_InterfaceRec structure.

#define FT_PARAM_TAG_INCREMENTAL  FT_MAKE_TAG( 'i', 'n', 'c', 'r' )

A constant used as the tag of FT_Parameter structures to indicate an incremental loading object to be used by FreeType.