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/****************************************************************************
*
* autohint.h
*
* High-level 'autohint' module-specific interface (specification).
*
* Copyright (C) 1996-2020 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.
*
*/
/**************************************************************************
*
* The auto-hinter is used to load and automatically hint glyphs if a
* format-specific hinter isn't available.
*
*/
#ifndef AUTOHINT_H_
#define AUTOHINT_H_
/**************************************************************************
*
* A small technical note regarding automatic hinting in order to clarify
* this module interface.
*
* An automatic hinter might compute two kinds of data for a given face:
*
* - global hints: Usually some metrics that describe global properties
* of the face. It is computed by scanning more or less
* aggressively the glyphs in the face, and thus can be
* very slow to compute (even if the size of global hints
* is really small).
*
* - glyph hints: These describe some important features of the glyph
* outline, as well as how to align them. They are
* generally much faster to compute than global hints.
*
* The current FreeType auto-hinter does a pretty good job while performing
* fast computations for both global and glyph hints. However, we might be
* interested in introducing more complex and powerful algorithms in the
* future, like the one described in the John D. Hobby paper, which
* unfortunately requires a lot more horsepower.
*
* Because a sufficiently sophisticated font management system would
* typically implement an LRU cache of opened face objects to reduce memory
* usage, it is a good idea to be able to avoid recomputing global hints
* every time the same face is re-opened.
*
* We thus provide the ability to cache global hints outside of the face
* object, in order to speed up font re-opening time. Of course, this
* feature is purely optional, so most client programs won't even notice
* it.
*
* I initially thought that it would be a good idea to cache the glyph
* hints too. However, my general idea now is that if you really need to
* cache these too, you are simply in need of a new font format, where all
* this information could be stored within the font file and decoded on the
* fly.
*
*/
#include <freetype/freetype.h>
FT_BEGIN_HEADER
typedef struct FT_AutoHinterRec_ *FT_AutoHinter;
/**************************************************************************
*
* @functype:
* FT_AutoHinter_GlobalGetFunc
*
* @description:
* Retrieve the global hints computed for a given face object. The
* resulting data is dissociated from the face and will survive a call to
* FT_Done_Face(). It must be discarded through the API
* FT_AutoHinter_GlobalDoneFunc().
*
* @input:
* hinter ::
* A handle to the source auto-hinter.
*
* face ::
* A handle to the source face object.
*
* @output:
* global_hints ::
* A typeless pointer to the global hints.
*
* global_len ::
* The size in bytes of the global hints.
*/
typedef void
(*FT_AutoHinter_GlobalGetFunc)( FT_AutoHinter hinter,
FT_Face face,
void** global_hints,
long* global_len );
/**************************************************************************
*
* @functype:
* FT_AutoHinter_GlobalDoneFunc
*
* @description:
* Discard the global hints retrieved through
* FT_AutoHinter_GlobalGetFunc(). This is the only way these hints are
* freed from memory.
*
* @input:
* hinter ::
* A handle to the auto-hinter module.
*
* global ::
* A pointer to retrieved global hints to discard.
*/
typedef void
(*FT_AutoHinter_GlobalDoneFunc)( FT_AutoHinter hinter,
void* global );
/**************************************************************************
*
* @functype:
* FT_AutoHinter_GlobalResetFunc
*
* @description:
* This function is used to recompute the global metrics in a given font.
* This is useful when global font data changes (e.g. Multiple Masters
* fonts where blend coordinates change).
*
* @input:
* hinter ::
* A handle to the source auto-hinter.
*
* face ::
* A handle to the face.
*/
typedef void
(*FT_AutoHinter_GlobalResetFunc)( FT_AutoHinter hinter,
FT_Face face );
/**************************************************************************
*
* @functype:
* FT_AutoHinter_GlyphLoadFunc
*
* @description:
* This function is used to load, scale, and automatically hint a glyph
* from a given face.
*
* @input:
* face ::
* A handle to the face.
*
* glyph_index ::
* The glyph index.
*
* load_flags ::
* The load flags.
*
* @note:
* This function is capable of loading composite glyphs by hinting each
* sub-glyph independently (which improves quality).
*
* It will call the font driver with @FT_Load_Glyph, with
* @FT_LOAD_NO_SCALE set.
*/
typedef FT_Error
(*FT_AutoHinter_GlyphLoadFunc)( FT_AutoHinter hinter,
FT_GlyphSlot slot,
FT_Size size,
FT_UInt glyph_index,
FT_Int32 load_flags );
/**************************************************************************
*
* @struct:
* FT_AutoHinter_InterfaceRec
*
* @description:
* The auto-hinter module's interface.
*/
typedef struct FT_AutoHinter_InterfaceRec_
{
FT_AutoHinter_GlobalResetFunc reset_face;
FT_AutoHinter_GlobalGetFunc get_global_hints;
FT_AutoHinter_GlobalDoneFunc done_global_hints;
FT_AutoHinter_GlyphLoadFunc load_glyph;
} FT_AutoHinter_InterfaceRec, *FT_AutoHinter_Interface;
#define FT_DECLARE_AUTOHINTER_INTERFACE( class_ ) \
FT_CALLBACK_TABLE const FT_AutoHinter_InterfaceRec class_;
#define FT_DEFINE_AUTOHINTER_INTERFACE( \
class_, \
reset_face_, \
get_global_hints_, \
done_global_hints_, \
load_glyph_ ) \
FT_CALLBACK_TABLE_DEF \
const FT_AutoHinter_InterfaceRec class_ = \
{ \
reset_face_, \
get_global_hints_, \
done_global_hints_, \
load_glyph_ \
};
FT_END_HEADER
#endif /* AUTOHINT_H_ */
/* END */
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