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* include/freetype/ftincrem.h: adding new experimental header file

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to demonstrate a "cleaner" API to support incremental font loading.
        comments appreciated...
BRANCH-2-1-5
David Turner 23 years ago
parent 5e6cd65d5f
commit 1ff88d285d
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  1. 6
      ChangeLog
  2. 203
      include/freetype/ftincrem.h

6
ChangeLog
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@ -1,3 +1,9 @@
2002-07-30 David Turner <david@freetype.org>
* include/freetype/ftincrem.h: adding new experimental header file
to demonstrate a "cleaner" API to support incremental font loading.
comments appreciated...
2002-07-28 Werner Lemberg <wl@gnu.org>
s/ft_memset/FT_MEM_SET/.

203
include/freetype/ftincrem.h
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#ifndef __FT_INCREMENTAL_H__
#define __FT_INCREMENTAL_H__
#include <ft2build.h>
#include FT_FREETYPE_H
FT_BEGIN_HEADER
/*************************************************************************
*
* @type: FT_Incremental
*
* @description:
* 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 over-ridden by
* different values.
*
* @note:
* it's 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_ServiceRec to understand how to
* use incremental objects with FreeType.
*/
typedef struct FT_IncrementalRec_* FT_Incremental;
/*************************************************************************
*
* @struct: FT_Incremental_Metrics
*
* @description:
* a small structure used to model the basic glyph metrics returned
* by the @FT_Incremental_GetGlyphMetricsFunc method
*
* @fields:
* bearing_x :: left-most bearing, in font units.
* bearing_y :: top-most 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' parameter of the method
* @FT_Incremental_GetGlyphMetricsFunc
*/
typedef struct FT_Incremental_MetricsRec_
{
FT_Long bearing_x;
FT_Long bearing_y;
FT_Long advance;
} FT_Incremental_MetricsRec, *FT_Incremental_Metrics;
/**************************************************************************
*
* @type: FT_Incremental_GetGlyphDataFunc
*
* @description:
* a function called by FreeType to access a given glyph's data bytes
* during @FT_Load_Glyph or @FT_Load_Char, when incremental loading is
* enable.
*
* 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* charstrings bytes, without any 'lenIV' header. It is
* undefined for any other format.
*
* @input:
* incremental :: handle to an opaque @FT_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
* @FT_Incremental_FreeGlyphDataFunc will be called later to "release"
* the se bytes.
*
* nested @FT_Incremental_GetGlyphDataFunc can happen, in the case of
* compound glyphs !!
*/
typedef FT_Error (*FT_Incremental_GetGlyphDataFunc)
( FT_Incremental incremental,
FT_UInt glyph_index,
FT_DataRec *adata );
/**************************************************************************
*
* @type: FT_Incremental_FreeGlyphDataFunc
*
* @description:
* a function used to "release" the glyph data bytes returned by a
* successful call to @FT_Incremental_GetGlyphDataFunc.
*
* @input:
* incremental :: handle to an opaque @FT_Incremental handle provided
* by the client application
*
* data :: glyph_index :: index of relevant glyph
*/
typedef void (*FT_Incremental_FreeGlyphDataFunc)
( FT_Incremental incremental,
FT_DataRec* data );
/**************************************************************************
*
* @type: FT_Incremental_GetGlyphMetricsFunc
*
* @description:
* 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 than the
* glyph images proper.
*
* @input:
* incremental :: handle to an opaque @FT_Incremental handle provided
* by the client application
*
*/
typedef FT_Error (*FT_Incremental_GetGlyphMetricsFunc)
( FT_Incremental incremental,
FT_UInt glyph_index,
FT_Bool vertical,
FT_Incremental_MetricsRec *ametrics,
FT_Bool *afound );
/**************************************************************************
*
* @struct: FT_Incremental_ServiceRec
*
* @description:
* 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_ServiceRec incr_service;
* FT_Parameter parameter;
* FT_Open_Args open_args;
*
* // set up incremental descriptor
* incr_service.incremental = my_object;
* incr_service.get_glyph_metrics = my_get_glyph_metrics;
* incr_service.get_glyph_data = my_get_glyph_data;
* incr_service.free_glyph_data = my_free_glyph_data;
*
* // set up optional parameter
* parameter.tag = FT_PARAM_TAG_INCREMENTAL;
* parameter.data = &incr_service;
*
* // set up FT_Open_Args structure
* open_args.flags = ft_open_flag_pathname;
* open_args.pathname = my_font_pathname;
* open_args.num_params = 1;
* open_args.params = &parameter; // we use one optional argument
*
* // open the
* error = FT_Open_Face( library, &open_args, index, &face );
* ....
* }
*/
typedef struct FT_IncrementalParamsRec_
{
FT_Incremental incremental;
FT_Incremental_GetGlyphMetricsFunc get_glyph_metrics;
FT_Incremental_GetGlyphDataFunc get_glyph_data;
FT_Incremental_FreeGlyphDataFunc free_glyph_data;
} FT_IncrementalParamsRec, *FT_IncrementalParams;
/**************************************************************************
*
* @constant: FT_PARAM_TAG_INCREMENTAL
*
* @description:
* a constant used as the tag of @FT_Parameter structures to indicate
* an incremental loading object to be used by FreeType
*
* see the node for @FT_IncrementalParamsRec
*/
#define FT_PARAM_TAG_INCREMENTAL FT_MAKE_TAG('i','n','c','r')
/* */
FT_END_HEADER
#endif /* __FT_INCREMENTAL_H__ */
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