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