345 lines
10 KiB
C
345 lines
10 KiB
C
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/****************************************************************************
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*
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* ftincrem.h
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*
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* FreeType incremental loading (specification).
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*
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* Copyright (C) 2002-2020 by
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* David Turner, Robert Wilhelm, and Werner Lemberg.
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*
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* This file is part of the FreeType project, and may only be used,
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* modified, and distributed under the terms of the FreeType project
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* license, LICENSE.TXT. By continuing to use, modify, or distribute
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* this file you indicate that you have read the license and
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* understand and accept it fully.
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*
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*/
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#ifndef FTINCREM_H_
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#define FTINCREM_H_
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#include FT_PARAMETER_TAGS_H
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#ifdef FREETYPE_H
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#error "freetype.h of FreeType 1 has been loaded!"
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#error "Please fix the directory search order for header files"
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#error "so that freetype.h of FreeType 2 is found first."
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#endif
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* incremental
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*
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* @title:
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* Incremental Loading
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*
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* @abstract:
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* Custom Glyph Loading.
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*
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* @description:
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* This section contains various functions used to perform so-called
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* 'incremental' glyph loading. This is a mode where all glyphs loaded
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* from a given @FT_Face are provided by the client application.
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*
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* Apart from that, all other tables are loaded normally from the font
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* file. This mode is useful when FreeType is used within another
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* engine, e.g., a PostScript Imaging Processor.
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*
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* To enable this mode, you must use @FT_Open_Face, passing an
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* @FT_Parameter with the @FT_PARAM_TAG_INCREMENTAL tag and an
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* @FT_Incremental_Interface value. See the comments for
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* @FT_Incremental_InterfaceRec for an example.
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*
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*/
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/**************************************************************************
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*
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* @type:
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* 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
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* interpreters), where the glyph data isn't in the font file, or must be
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* overridden by different values.
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*
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* @note:
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* It is up to client applications to create and implement
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* @FT_Incremental objects, as long as they provide implementations for
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* the methods @FT_Incremental_GetGlyphDataFunc,
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* @FT_Incremental_FreeGlyphDataFunc and
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* @FT_Incremental_GetGlyphMetricsFunc.
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*
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* See the description of @FT_Incremental_InterfaceRec to understand how
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* to use incremental objects with FreeType.
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*
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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:
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* FT_Incremental_MetricsRec
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*
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* @description:
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* A small structure used to contain the basic glyph metrics returned by
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* the @FT_Incremental_GetGlyphMetricsFunc method.
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*
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* @fields:
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* bearing_x ::
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* Left bearing, in font units.
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*
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* bearing_y ::
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* Top bearing, in font units.
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*
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* advance ::
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* Horizontal component of glyph advance, in font units.
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*
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* advance_v ::
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* Vertical component of 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` argument to the function
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* @FT_Incremental_GetGlyphMetricsFunc.
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*
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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_Long advance_v; /* since 2.3.12 */
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} FT_Incremental_MetricsRec;
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/**************************************************************************
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*
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* @struct:
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* FT_Incremental_Metrics
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*
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* @description:
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* A handle to an @FT_Incremental_MetricsRec structure.
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*
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*/
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typedef struct FT_Incremental_MetricsRec_* FT_Incremental_Metrics;
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/**************************************************************************
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*
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* @type:
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* 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 if incremental loading is
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* enabled.
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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** charstring 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 ::
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* Handle to an opaque @FT_Incremental handle provided by the client
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* application.
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*
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* glyph_index ::
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* Index of relevant glyph.
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*
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* @output:
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* adata ::
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* A structure describing the returned glyph data bytes (which will be
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* 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 successfully the method
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* @FT_Incremental_FreeGlyphDataFunc will be called later to release the
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* data bytes.
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*
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* Nested calls to @FT_Incremental_GetGlyphDataFunc can happen for
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* compound glyphs.
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*
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*/
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typedef FT_Error
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(*FT_Incremental_GetGlyphDataFunc)( FT_Incremental incremental,
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FT_UInt glyph_index,
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FT_Data* adata );
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/**************************************************************************
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*
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* @type:
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* 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 ::
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* A handle to an opaque @FT_Incremental handle provided by the client
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* application.
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*
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* data ::
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* A structure describing the glyph data bytes (which will be accessed
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* as a read-only byte block).
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*
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*/
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typedef void
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(*FT_Incremental_FreeGlyphDataFunc)( FT_Incremental incremental,
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FT_Data* data );
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/**************************************************************************
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*
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* @type:
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* 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
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* formats like TrueType, the metrics are stored in a different place
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* from the glyph images proper.
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*
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* @input:
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* incremental ::
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* A handle to an opaque @FT_Incremental handle provided by the client
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* application.
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*
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* glyph_index ::
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* Index of relevant glyph.
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*
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* vertical ::
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* If true, return vertical metrics.
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*
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* ametrics ::
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* This parameter is used for both input and output. The original
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* glyph metrics, if any, in font units. If metrics are not available
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* all the values must be set to zero.
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*
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* @output:
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* ametrics ::
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* The replacement glyph metrics in font units.
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*
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*/
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typedef FT_Error
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(*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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/**************************************************************************
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*
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* @struct:
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* FT_Incremental_FuncsRec
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*
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* @description:
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* A table of functions for accessing fonts that load data incrementally.
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* Used in @FT_Incremental_InterfaceRec.
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*
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* @fields:
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* get_glyph_data ::
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* The function to get glyph data. Must not be null.
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*
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* free_glyph_data ::
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* The function to release glyph data. Must not be null.
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*
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* get_glyph_metrics ::
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* The function to get glyph metrics. May be null if the font does not
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* provide overriding glyph metrics.
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*
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*/
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typedef struct FT_Incremental_FuncsRec_
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{
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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_Incremental_GetGlyphMetricsFunc get_glyph_metrics;
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} FT_Incremental_FuncsRec;
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/**************************************************************************
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*
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* @struct:
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* FT_Incremental_InterfaceRec
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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_InterfaceRec inc_int;
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* FT_Parameter parameter;
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* FT_Open_Args open_args;
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*
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*
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* // set up incremental descriptor
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* inc_int.funcs = my_funcs;
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* inc_int.object = my_object;
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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 = &inc_int;
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*
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* // set up FT_Open_Args structure
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* open_args.flags = FT_OPEN_PATHNAME | FT_OPEN_PARAMS;
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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 font
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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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*/
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typedef struct FT_Incremental_InterfaceRec_
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{
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const FT_Incremental_FuncsRec* funcs;
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FT_Incremental object;
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} FT_Incremental_InterfaceRec;
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/**************************************************************************
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*
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* @type:
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* FT_Incremental_Interface
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*
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* @description:
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* A pointer to an @FT_Incremental_InterfaceRec structure.
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*
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*/
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typedef FT_Incremental_InterfaceRec* FT_Incremental_Interface;
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/* */
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FT_END_HEADER
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#endif /* FTINCREM_H_ */
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/* END */
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