ref: 47b1a541cb1943d85da3976b93f9a5ed490288e2
dir: /include/freetype/ftincrem.h/
/****************************************************************************
*
* ftincrem.h
*
* FreeType incremental loading (specification).
*
* Copyright (C) 2002-2021 by
* David Turner, Robert Wilhelm, and Werner Lemberg.
*
* This file is part of the FreeType project, and may only be used,
* modified, and distributed under the terms of the FreeType project
* license, LICENSE.TXT. By continuing to use, modify, or distribute
* this file you indicate that you have read the license and
* understand and accept it fully.
*
*/
#ifndef FTINCREM_H_
#define FTINCREM_H_
#include <freetype/freetype.h>
#include <freetype/ftparams.h>
#ifdef FREETYPE_H
#error "freetype.h of FreeType 1 has been loaded!"
#error "Please fix the directory search order for header files"
#error "so that freetype.h of FreeType 2 is found first."
#endif
FT_BEGIN_HEADER
/**************************************************************************
*
* @section:
* incremental
*
* @title:
* Incremental Loading
*
* @abstract:
* Custom Glyph Loading.
*
* @description:
* This section contains various functions used to perform so-called
* 'incremental' glyph loading. This is a mode where all glyphs loaded
* from a given @FT_Face are provided by the client application.
*
* Apart from that, all other tables are loaded normally from the font
* file. This mode is useful when FreeType is used within another
* engine, e.g., a PostScript Imaging Processor.
*
* To enable this mode, you must use @FT_Open_Face, passing an
* @FT_Parameter with the @FT_PARAM_TAG_INCREMENTAL tag and an
* @FT_Incremental_Interface value. See the comments for
* @FT_Incremental_InterfaceRec for an example.
*
*/
/**************************************************************************
*
* @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
* overridden by different values.
*
* @note:
* 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_IncrementalRec_* FT_Incremental;
/**************************************************************************
*
* @struct:
* FT_Incremental_MetricsRec
*
* @description:
* A small structure used to contain the basic glyph metrics returned by
* the @FT_Incremental_GetGlyphMetricsFunc method.
*
* @fields:
* bearing_x ::
* Left bearing, in font units.
*
* bearing_y ::
* Top bearing, in font units.
*
* advance ::
* Horizontal component of glyph advance, in font units.
*
* advance_v ::
* Vertical component of glyph advance, in font units.
*
* @note:
* These correspond to horizontal or vertical metrics depending on the
* value of the `vertical` argument to the function
* @FT_Incremental_GetGlyphMetricsFunc.
*
*/
typedef struct FT_Incremental_MetricsRec_
{
FT_Long bearing_x;
FT_Long bearing_y;
FT_Long advance;
FT_Long advance_v; /* since 2.3.12 */
} FT_Incremental_MetricsRec;
/**************************************************************************
*
* @struct:
* FT_Incremental_Metrics
*
* @description:
* A handle to an @FT_Incremental_MetricsRec structure.
*
*/
typedef struct 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 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 @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 successfully 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 FT_Error
(*FT_Incremental_GetGlyphDataFunc)( FT_Incremental incremental,
FT_UInt glyph_index,
FT_Data* 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 ::
* A handle to an opaque @FT_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).
*
*/
typedef void
(*FT_Incremental_FreeGlyphDataFunc)( FT_Incremental incremental,
FT_Data* data );
/**************************************************************************
*
* @type:
* FT_Incremental_GetGlyphMetricsFunc
*
* @description:
* A function used to retrieve the basic metrics of a given glyph index
* before accessing its data. This allows for handling font types such
* as PCL~XL Format~1, Class~2 downloaded TrueType fonts, where the glyph
* metrics (`hmtx` and `vmtx` tables) are permitted to be omitted from
* the font, and the relevant metrics included in the header of the glyph
* outline data. Importantly, this is not intended to allow custom glyph
* metrics (for example, Postscript Metrics dictionaries), because that
* conflicts with the requirements of outline hinting. Such custom
* metrics must be handled separately, by the calling application.
*
* @input:
* incremental ::
* A handle to an opaque @FT_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 glyph metrics in font units.
*
*/
typedef FT_Error
(*FT_Incremental_GetGlyphMetricsFunc)
( FT_Incremental incremental,
FT_UInt glyph_index,
FT_Bool vertical,
FT_Incremental_MetricsRec *ametrics );
/**************************************************************************
*
* @struct:
* FT_Incremental_FuncsRec
*
* @description:
* A table of functions for accessing fonts that load data incrementally.
* Used in @FT_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
* require it.
*
*/
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;
/**************************************************************************
*
* @struct:
* FT_Incremental_InterfaceRec
*
* @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_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 = ¶meter; // we use one optional argument
*
* // open the font
* error = FT_Open_Face( library, &open_args, index, &face );
* ...
* ```
*
*/
typedef struct FT_Incremental_InterfaceRec_
{
const FT_Incremental_FuncsRec* funcs;
FT_Incremental object;
} FT_Incremental_InterfaceRec;
/**************************************************************************
*
* @type:
* FT_Incremental_Interface
*
* @description:
* A pointer to an @FT_Incremental_InterfaceRec structure.
*
*/
typedef FT_Incremental_InterfaceRec* FT_Incremental_Interface;
/* */
FT_END_HEADER
#endif /* FTINCREM_H_ */
/* END */