* include/freetype/ftincrem.h: adding new experimental header file
to demonstrate a "cleaner" API to support incremental font loading.
comments appreciated...
This commit is contained in:
David Turner
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2002-07-30 David Turner <david@freetype.org>
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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.
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comments appreciated...
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2002-07-28 Werner Lemberg <wl@gnu.org>
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s/ft_memset/FT_MEM_SET/.
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@ -0,0 +1,203 @@
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#ifndef __FT_INCREMENTAL_H__
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#define __FT_INCREMENTAL_H__
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#include <ft2build.h>
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#include FT_FREETYPE_H
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FT_BEGIN_HEADER
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/*************************************************************************
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*
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* @type: FT_Incremental
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*
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* @description:
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* an opaque type describing a user-provided object used to implement
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* "incremental" glyph loading within FreeType. This is used to support
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* embedded fonts in certain environments (e.g. Postscript interpreters),
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* where the glyph data isn't in the font file, or must be over-ridden by
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* different values.
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*
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* @note:
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* it's up to client applications to create and implement @FT_Incremental
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* objects, as long as they provide implementations for the methods
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* @FT_Incremental_GetGlyphDataFunc, @FT_Incremental_FreeGlyphDataFunc
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* and @FT_Incremental_GetGlyphMetricsFunc
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*
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* see the description of @FT_Incremental_ServiceRec to understand how to
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* use incremental objects with FreeType.
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*/
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typedef struct FT_IncrementalRec_* FT_Incremental;
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/*************************************************************************
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*
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* @struct: FT_Incremental_Metrics
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*
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* @description:
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* a small structure used to model the basic glyph metrics returned
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* by the @FT_Incremental_GetGlyphMetricsFunc method
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*
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* @fields:
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* bearing_x :: left-most bearing, in font units.
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* bearing_y :: top-most bearing, in font units.
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* advance :: glyph advance, in font units
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*
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* @note:
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* these correspond to horizontal or vertical metrics depending on the
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* value of the 'vertical' parameter of the method
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* @FT_Incremental_GetGlyphMetricsFunc
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*/
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typedef struct FT_Incremental_MetricsRec_
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{
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FT_Long bearing_x;
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FT_Long bearing_y;
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FT_Long advance;
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} FT_Incremental_MetricsRec, *FT_Incremental_Metrics;
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/**************************************************************************
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*
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* @type: FT_Incremental_GetGlyphDataFunc
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*
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* @description:
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* a function called by FreeType to access a given glyph's data bytes
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* during @FT_Load_Glyph or @FT_Load_Char, when incremental loading is
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* enable.
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*
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* note that the format of the glyph's data bytes depends on the font
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* file format. For TrueType, it must correspond to the raw bytes within
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* the 'glyf' table. For Postscript formats, it must correspond to the
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* *unencrypted* charstrings bytes, without any 'lenIV' header. It is
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* undefined for any other format.
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*
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* @input:
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* incremental :: handle to an opaque @FT_Incremental handle provided
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* by the client application
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*
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* glyph_index :: index of relevant glyph
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*
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* @output:
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* adata :: a structure describing the returned glyph data bytes
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* (which will be accessed as a read-only byte block)
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*
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* @return:
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* FreeType error code. 0 means success
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*
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* @note:
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* if this function returns succesfully, the method
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* @FT_Incremental_FreeGlyphDataFunc will be called later to "release"
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* the se bytes.
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*
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* nested @FT_Incremental_GetGlyphDataFunc can happen, in the case of
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* compound glyphs !!
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*/
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typedef FT_Error (*FT_Incremental_GetGlyphDataFunc)
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( FT_Incremental incremental,
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FT_UInt glyph_index,
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FT_DataRec *adata );
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/**************************************************************************
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*
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* @type: FT_Incremental_FreeGlyphDataFunc
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*
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* @description:
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* a function used to "release" the glyph data bytes returned by a
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* successful call to @FT_Incremental_GetGlyphDataFunc.
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*
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* @input:
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* incremental :: handle to an opaque @FT_Incremental handle provided
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* by the client application
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*
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* data :: glyph_index :: index of relevant glyph
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*/
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typedef void (*FT_Incremental_FreeGlyphDataFunc)
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( FT_Incremental incremental,
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FT_DataRec* data );
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/**************************************************************************
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*
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* @type: FT_Incremental_GetGlyphMetricsFunc
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*
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* @description:
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* a function used to retrieve the basic metrics of a given glyph index
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* before accessing its data. This is necessary because, in certain formats
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* like TrueType, the metrics are stored in a different place than the
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* glyph images proper.
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*
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* @input:
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* incremental :: handle to an opaque @FT_Incremental handle provided
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* by the client application
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*
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*/
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typedef FT_Error (*FT_Incremental_GetGlyphMetricsFunc)
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( FT_Incremental incremental,
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FT_UInt glyph_index,
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FT_Bool vertical,
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FT_Incremental_MetricsRec *ametrics,
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FT_Bool *afound );
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/**************************************************************************
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*
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* @struct: FT_Incremental_ServiceRec
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*
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* @description:
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* a structure to be used with @FT_Open_Face to indicate that the user
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* wants to support "incremental" glyph loading. You should use it with
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* @FT_PARAM_TAG_INCREMENTAL as in the following example:
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*
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* {
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* FT_Incremental_ServiceRec incr_service;
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* FT_Parameter parameter;
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* FT_Open_Args open_args;
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*
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* // set up incremental descriptor
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* incr_service.incremental = my_object;
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* incr_service.get_glyph_metrics = my_get_glyph_metrics;
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* incr_service.get_glyph_data = my_get_glyph_data;
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* incr_service.free_glyph_data = my_free_glyph_data;
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*
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* // set up optional parameter
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* parameter.tag = FT_PARAM_TAG_INCREMENTAL;
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* parameter.data = &incr_service;
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*
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* // set up FT_Open_Args structure
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* open_args.flags = ft_open_flag_pathname;
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* open_args.pathname = my_font_pathname;
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* open_args.num_params = 1;
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* open_args.params = ¶meter; // we use one optional argument
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*
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* // open the
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* error = FT_Open_Face( library, &open_args, index, &face );
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* ....
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* }
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*/
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typedef struct FT_IncrementalParamsRec_
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{
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FT_Incremental incremental;
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FT_Incremental_GetGlyphMetricsFunc get_glyph_metrics;
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FT_Incremental_GetGlyphDataFunc get_glyph_data;
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FT_Incremental_FreeGlyphDataFunc free_glyph_data;
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} FT_IncrementalParamsRec, *FT_IncrementalParams;
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/**************************************************************************
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*
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* @constant: FT_PARAM_TAG_INCREMENTAL
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*
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* @description:
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* a constant used as the tag of @FT_Parameter structures to indicate
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* an incremental loading object to be used by FreeType
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*
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* see the node for @FT_IncrementalParamsRec
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*/
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#define FT_PARAM_TAG_INCREMENTAL FT_MAKE_TAG('i','n','c','r')
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/* */
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FT_END_HEADER
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#endif /* __FT_INCREMENTAL_H__ */
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