FreeType-2.1.10 API Reference
Scanline Converter
Synopsis
#FT_RasterFT_Raster #FT_Raster_RenderFuncFT_Raster_RenderFunc #FT_SpanFT_Span #FT_Raster_FuncsFT_Raster_Funcs #FT_SpanFuncFT_SpanFunc #FT_IncrementalFT_Incremental #FT_Raster_BitTest_FuncFT_Raster_BitTest_Func #FT_Incremental_MetricsFT_Incremental_Metrics #FT_Raster_BitSet_FuncFT_Raster_BitSet_Func #FT_Incremental_GetGlyphDataFuncFT_Incremental_GetGlyphDataFunc #FT_RASTER_FLAG_XXXFT_RASTER_FLAG_XXX #FT_Incremental_FreeGlyphDataFuncFT_Incremental_FreeGlyphDataFunc #FT_Raster_ParamsFT_Raster_Params #FT_Incremental_GetGlyphMetricsFuncFT_Incremental_GetGlyphMetricsFunc #FT_Raster_NewFuncFT_Raster_NewFunc #FT_Incremental_FuncsRecFT_Incremental_FuncsRec #FT_Raster_DoneFuncFT_Raster_DoneFunc #FT_Incremental_InterfaceRecFT_Incremental_InterfaceRec #FT_Raster_ResetFuncFT_Raster_ResetFunc #FT_PARAM_TAG_INCREMENTALFT_PARAM_TAG_INCREMENTAL #FT_Raster_SetModeFuncFT_Raster_SetModeFunc This section contains technical definitions.
FT_Raster 
  
typedef struct FT_RasterRec_*  FT_Raster;
A handle (pointer) to a raster object. Each object can be used independently to convert an outline into a bitmap or pixmap.
FT_Span 
  
typedef struct  FT_Span_
  {
    
short           x;
    
unsigned short  len;
    
unsigned char   coverage;
  } 
FT_Span;
A structure used to model a single span of gray (or black) pixels when rendering a monochrome or anti-aliased bitmap.
fields x The span's horizontal start position.
len The span's length in pixels.
coverage The span color/coverage, ranging from 0 (background) to 255 (foreground). Only used for anti-aliased rendering.
note This structure is used by the span drawing callback type named FT_SpanFunc which takes the y-coordinate of the span as a a parameter.
The coverage value is always between 0 and 255, even if the number of gray levels have been set through FT_Set_Gray_Levels().
FT_SpanFunc 
  
typedef void  (*
FT_SpanFunc)( int       y,
                  
int       count,
                  
ft2-raster.html#FT_SpanFT_Span *  spans,
                  
void*     user );
#define FT_Raster_Span_Func   
FT_SpanFunc A function used as a call-back by the anti-aliased renderer in order to let client applications draw themselves the gray pixel spans on each scan line.
input y The scanline's y-coordinate.
count The number of spans to draw on this scanline.
spans A table of `count' spans to draw on the scanline.
user User-supplied data that is passed to the callback.
note This callback allows client applications to directly render the gray spans of the anti-aliased bitmap to any kind of surfaces.
This can be used to write anti-aliased outlines directly to a given background bitmap, and even perform translucency.
Note that the `count' field cannot be greater than a fixed value defined by the FT_MAX_GRAY_SPANS configuration macro in ftoption.h. By default, this value is set to 32, which means that if there are more than 32 spans on a given scanline, the callback will be called several times with the same `y' parameter in order to draw all callbacks.
Otherwise, the callback is only called once per scan-line, and only for those scanlines that do have `gray' pixels on them.
FT_Raster_BitTest_Func 
  
typedef int  (*
FT_Raster_BitTest_Func)( int    y,
                             
int    x,
                             
void*  user );
THIS TYPE IS DEPRECATED. DO NOT USE IT.
A function used as a call-back by the monochrome scan-converter to test whether a given target pixel is already set to the drawing `color'. These tests are crucial to implement drop-out control per-se the TrueType spec.
input y The pixel's y-coordinate.
x The pixel's x-coordinate.
user User-supplied data that is passed to the callback.
return 1 if the pixel is `set', 0 otherwise.
FT_Raster_BitSet_Func 
  
typedef void  (*
FT_Raster_BitSet_Func)( int    y,
                            
int    x,
                            
void*  user );
THIS TYPE IS DEPRECATED. DO NOT USE IT.
A function used as a call-back by the monochrome scan-converter to set an individual target pixel. This is crucial to implement drop-out control according to the TrueType specification.
input y The pixel's y-coordinate.
x The pixel's x-coordinate.
user User-supplied data that is passed to the callback.
return 1 if the pixel is `set', 0 otherwise.
FT_RASTER_FLAG_XXX 
#define 
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_DEFAULT   0x0
#define 
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_AA        0x1
#define 
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_DIRECT    0x2
#define 
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_CLIP      0x4
  /* deprecated */
#define ft_raster_flag_default  
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_DEFAULT #define ft_raster_flag_aa       
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_AA #define ft_raster_flag_direct   
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_DIRECT #define ft_raster_flag_clip     
ft2-raster.html#FT_RASTER_FLAG_XXXFT_RASTER_FLAG_CLIP A list of bit flag constants as used in the `flags' field of a ft2-raster.html#FT_Raster_ParamsFT_Raster_Params  structure.
values FT_RASTER_FLAG_DEFAULT This value is 0.
FT_RASTER_FLAG_AA This flag is set to indicate that an anti-aliased glyph image should be generated. Otherwise, it will be monochrome (1-bit).
FT_RASTER_FLAG_DIRECT This flag is set to indicate direct rendering. In this mode, client applications must provide their own span callback. This lets them directly draw or compose over an existing bitmap. If this bit is not set, the target pixmap's buffer must be zeroed before rendering.
Note that for now, direct rendering is only possible with anti-aliased glyphs.
FT_RASTER_FLAG_CLIP This flag is only used in direct rendering mode. If set, the output will be clipped to a box specified in the "clip_box" field of the FT_Raster_Params structure.
Note that by default, the glyph bitmap is clipped to the target pixmap, except in direct rendering mode where all spans are generated if no clipping box is set.
FT_Raster_Params 
  
typedef struct  FT_Raster_Params_
  {
    
const ft2-basic_types.html#FT_BitmapFT_Bitmap *        target;
    
const void*             source;
    
int                     flags;
    
ft2-raster.html#FT_SpanFuncFT_SpanFunc              gray_spans;
    
ft2-raster.html#FT_SpanFuncFT_SpanFunc              black_spans;
    
ft2-raster.html#FT_Raster_BitTest_FuncFT_Raster_BitTest_Func   bit_test;     /* doesn't work! */
    
ft2-raster.html#FT_Raster_BitSet_FuncFT_Raster_BitSet_Func    bit_set;      /* doesn't work! */
    
void*                   user;
    
ft2-basic_types.html#FT_BBoxFT_BBox                  clip_box;
  } 
FT_Raster_Params;
A structure to hold the arguments used by a raster's render function.
fields target The target bitmap.
source A pointer to the source glyph image (e.g. an FT_Outline).
flags The rendering flags.
gray_spans The gray span drawing callback.
black_spans The black span drawing callback.
bit_test The bit test callback. UNIMPLEMENTED!
bit_set The bit set callback. UNIMPLEMENTED!
user User-supplied data that is passed to each drawing callback.
clip_box An optional clipping box. It is only used in direct rendering mode. Note that coordinates here should be expressed in integer pixels (and not in 26.6 fixed-point units).
note An anti-aliased glyph bitmap is drawn if the FT_RASTER_FLAG_AA bit flag is set in the `flags' field, otherwise a monochrome bitmap will be generated.
If the FT_RASTER_FLAG_DIRECT bit flag is set in `flags', the raster will call the `gray_spans' callback to draw gray pixel spans, in the case of an aa glyph bitmap, it will call `black_spans', and `bit_test' and `bit_set' in the case of a monochrome bitmap. This allows direct composition over a pre-existing bitmap through user-provided callbacks to perform the span drawing/composition.
Note that the `bit_test' and `bit_set' callbacks are required when rendering a monochrome bitmap, as they are crucial to implement correct drop-out control as defined in the TrueType specification.
FT_Raster_NewFunc 
  
typedef int  (*
FT_Raster_NewFunc)( void*       memory,
                        
ft2-raster.html#FT_RasterFT_Raster *  raster );
#define  FT_Raster_New_Func    
FT_Raster_NewFunc A function used to create a new raster object.
input memory A handle to the memory allocator.
output raster A handle to the new raster object.
return Error code. 0 means success.
note The `memory' parameter is a typeless pointer in order to avoid un-wanted dependencies on the rest of the FreeType code. In practice, it is a FT_Memory, i.e., a handle to the standard FreeType memory allocator. However, this field can be completely ignored by a given raster implementation.
FT_Raster_DoneFunc 
  
typedef void  (*
FT_Raster_DoneFunc)( ft2-raster.html#FT_RasterFT_Raster   raster );
#define  FT_Raster_Done_Func   
FT_Raster_DoneFunc A function used to destroy a given raster object.
input raster A handle to the raster object.
FT_Raster_ResetFunc 
  
typedef void  (*
FT_Raster_ResetFunc)( ft2-raster.html#FT_RasterFT_Raster        raster,
                          
unsigned char*  pool_base,
                          
unsigned long   pool_size );
#define  FT_Raster_Reset_Func   
FT_Raster_ResetFunc FreeType provides an area of memory called the `render pool', available to all registered rasters. This pool can be freely used during a given scan-conversion but is shared by all rasters. Its content is thus transient.
This function is called each time the render pool changes, or just after a new raster object is created.
input raster A handle to the new raster object.
pool_base The address in memory of the render pool.
pool_size The size in bytes of the render pool.
note Rasters can ignore the render pool and rely on dynamic memory allocation if they want to (a handle to the memory allocator is passed to the raster constructor). However, this is not recommended for efficiency purposes.
FT_Raster_SetModeFunc 
  
typedef int  (*
FT_Raster_SetModeFunc)( ft2-raster.html#FT_RasterFT_Raster       raster,
                            
unsigned long  mode,
                            
void*          args );
#define  FT_Raster_Set_Mode_Func  
FT_Raster_SetModeFunc This function is a generic facility to change modes or attributes in a given raster. This can be used for debugging purposes, or simply to allow implementation-specific `features' in a given raster module.
input raster A handle to the new raster object.
mode A 4-byte tag used to name the mode or property.
args A pointer to the new mode/property to use.
FT_Raster_RenderFunc 
  
typedef int  (*
FT_Raster_RenderFunc)( ft2-raster.html#FT_RasterFT_Raster           raster,
                           
ft2-raster.html#FT_Raster_ParamsFT_Raster_Params *  params );
#define  FT_Raster_Render_Func    
FT_Raster_RenderFunc Invokes a given raster to scan-convert a given glyph image into a target bitmap.
input raster A handle to the raster object.
params A pointer to a FT_Raster_Params structure used to store the rendering parameters.
return Error code. 0 means success.
note The exact format of the source image depends on the raster's glyph format defined in its FT_Raster_Funcs structure. It can be an FT_Outline or anything else in order to support a large array of glyph formats.
Note also that the render function can fail and return a FT_Err_Unimplemented_Feature error code if the raster used does not support direct composition.
XXX: For now, the standard raster doesn't support direct composition but this should change for the final release (see the files demos/src/ftgrays.c and demos/src/ftgrays2.c for examples of distinct implementations which support direct composition).
FT_Raster_Funcs 
  
typedef struct  FT_Raster_Funcs_
  {
    
ft2-basic_types.html#FT_Glyph_FormatFT_Glyph_Format          glyph_format;
    
ft2-raster.html#FT_Raster_NewFuncFT_Raster_NewFunc        raster_new;
    
ft2-raster.html#FT_Raster_ResetFuncFT_Raster_ResetFunc      raster_reset;
    
ft2-raster.html#FT_Raster_SetModeFuncFT_Raster_SetModeFunc    raster_set_mode;
    
ft2-raster.html#FT_Raster_RenderFuncFT_Raster_RenderFunc     raster_render;
    
ft2-raster.html#FT_Raster_DoneFuncFT_Raster_DoneFunc       raster_done;
  } 
FT_Raster_Funcs;
A structure used to describe a given raster class to the library.
fields glyph_format The supported glyph format for this raster.
raster_new The raster constructor.
raster_reset Used to reset the render pool within the raster.
raster_render A function to render a glyph into a given bitmap.
raster_done The raster destructor.
FT_Incremental 
  
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.
note It is up to client applications to create and implement ft2-raster.html#FT_IncrementalFT_Incremental  objects, as long as they provide implementations for the methods ft2-raster.html#FT_Incremental_GetGlyphDataFuncFT_Incremental_GetGlyphDataFunc , ft2-raster.html#FT_Incremental_FreeGlyphDataFuncFT_Incremental_FreeGlyphDataFunc  and ft2-raster.html#FT_Incremental_GetGlyphMetricsFuncFT_Incremental_GetGlyphMetricsFunc .
See the description of ft2-raster.html#FT_Incremental_InterfaceRecFT_Incremental_InterfaceRec  to understand how to use incremental objects with FreeType.
FT_Incremental_Metrics 
  
typedef struct  FT_Incremental_MetricsRec_
  {
    
ft2-basic_types.html#FT_LongFT_Long   bearing_x;
    
ft2-basic_types.html#FT_LongFT_Long   bearing_y;
    
ft2-basic_types.html#FT_LongFT_Long   advance;
  } FT_Incremental_MetricsRec, *
FT_Incremental_Metrics;
A small structure used to contain the basic glyph metrics returned by the ft2-raster.html#FT_Incremental_GetGlyphMetricsFuncFT_Incremental_GetGlyphMetricsFunc  method.
fields bearing_x Left bearing, in font units.
bearing_y Top bearing, in font units.
advance Glyph advance, in font units.
note These correspond to horizontal or vertical metrics depending on the value of the 'vertical' argument to the function ft2-raster.html#FT_Incremental_GetGlyphMetricsFuncFT_Incremental_GetGlyphMetricsFunc .
FT_Incremental_GetGlyphDataFunc 
  
typedef ft2-basic_types.html#FT_ErrorFT_Error   (*
FT_Incremental_GetGlyphDataFunc)( ft2-raster.html#FT_IncrementalFT_Incremental   incremental,
                                      
ft2-basic_types.html#FT_UIntFT_UInt          glyph_index,
                                      
ft2-basic_types.html#FT_DataFT_Data *        adata );
A function called by FreeType to access a given glyph's data bytes during ft2-base_interface.html#FT_Load_GlyphFT_Load_Glyph  or ft2-base_interface.html#FT_Load_CharFT_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.
input incremental Handle to an opaque ft2-raster.html#FT_IncrementalFT_Incremental  handle provided by the client application.
glyph_index Index of relevant glyph.
output adata A structure describing the returned glyph data bytes (which will be accessed as a read-only byte block).
return FreeType error code. 0 means success.
note If this function returns succesfully the method ft2-raster.html#FT_Incremental_FreeGlyphDataFuncFT_Incremental_FreeGlyphDataFunc  will be called later to release the data bytes.
Nested calls to ft2-raster.html#FT_Incremental_GetGlyphDataFuncFT_Incremental_GetGlyphDataFunc  can happen for compound glyphs.
FT_Incremental_FreeGlyphDataFunc 
  
typedef void  (*
FT_Incremental_FreeGlyphDataFunc)( ft2-raster.html#FT_IncrementalFT_Incremental   incremental,
                                       
ft2-basic_types.html#FT_DataFT_Data *        data );
A function used to release the glyph data bytes returned by a successful call to ft2-raster.html#FT_Incremental_GetGlyphDataFuncFT_Incremental_GetGlyphDataFunc .
input incremental A handle to an opaque ft2-raster.html#FT_IncrementalFT_Incremental  handle provided by the client application.
data A structure describing the glyph data bytes (which will be accessed as a read-only byte block).
FT_Incremental_GetGlyphMetricsFunc 
  
typedef ft2-basic_types.html#FT_ErrorFT_Error   (*
FT_Incremental_GetGlyphMetricsFunc)
                      ( 
ft2-raster.html#FT_IncrementalFT_Incremental               incremental,
                        
ft2-basic_types.html#FT_UIntFT_UInt                      glyph_index,
                        
ft2-basic_types.html#FT_BoolFT_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.
input incremental A handle to an opaque ft2-raster.html#FT_IncrementalFT_Incremental  handle provided by the client application.
glyph_index Index of relevant glyph.
vertical If true, return vertical metrics.
ametrics This parameter is used for both input and output. The original glyph metrics, if any, in font units. If metrics are not available all the values must be set to zero.
output ametrics The replacement glyph metrics in font units.
FT_Incremental_FuncsRec 
  
typedef struct  FT_Incremental_FuncsRec_
  {
    
ft2-raster.html#FT_Incremental_GetGlyphDataFuncFT_Incremental_GetGlyphDataFunc      get_glyph_data;
    
ft2-raster.html#FT_Incremental_FreeGlyphDataFuncFT_Incremental_FreeGlyphDataFunc     free_glyph_data;
    
ft2-raster.html#FT_Incremental_GetGlyphMetricsFuncFT_Incremental_GetGlyphMetricsFunc   get_glyph_metrics;
  } 
FT_Incremental_FuncsRec;
A table of functions for accessing fonts that load data incrementally. Used in ft2-raster.html#FT_Incremental_InterfaceRecFT_Incremental_InterfaceRec .
fields get_glyph_data The function to get glyph data. Must not be null.
free_glyph_data The function to release glyph data. Must not be null.
get_glyph_metrics The function to get glyph metrics. May be null if the font does not provide overriding glyph metrics.
FT_Incremental_InterfaceRec 
  
typedef struct  FT_Incremental_InterfaceRec_
  {
    
const ft2-raster.html#FT_Incremental_FuncsRecFT_Incremental_FuncsRec *  funcs;
    
ft2-raster.html#FT_IncrementalFT_Incremental                   object;
  
  } 
FT_Incremental_InterfaceRec;
A structure to be used with ft2-base_interface.html#FT_Open_FaceFT_Open_Face  to indicate that the user wants to support incremental glyph loading. You should use it with ft2-raster.html#FT_PARAM_TAG_INCREMENTALFT_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 );
  ...
FT_PARAM_TAG_INCREMENTAL 
#define 
FT_PARAM_TAG_INCREMENTAL  ft2-basic_types.html#FT_MAKE_TAGFT_MAKE_TAG ( 'i', 'n', 'c', 'r' )
A constant used as the tag of ft2-base_interface.html#FT_ParameterFT_Parameter  structures to indicate an incremental loading object to be used by FreeType.
