1 /****************************************************************************
5 * High-level 'autohint' module-specific interface (specification).
7 * Copyright (C) 1996-2020 by
8 * David Turner, Robert Wilhelm, and Werner Lemberg.
10 * This file is part of the FreeType project, and may only be used,
11 * modified, and distributed under the terms of the FreeType project
12 * license, LICENSE.TXT. By continuing to use, modify, or distribute
13 * this file you indicate that you have read the license and
14 * understand and accept it fully.
19 /**************************************************************************
21 * The auto-hinter is used to load and automatically hint glyphs if a
22 * format-specific hinter isn't available.
31 /**************************************************************************
33 * A small technical note regarding automatic hinting in order to clarify
34 * this module interface.
36 * An automatic hinter might compute two kinds of data for a given face:
38 * - global hints: Usually some metrics that describe global properties
39 * of the face. It is computed by scanning more or less
40 * aggressively the glyphs in the face, and thus can be
41 * very slow to compute (even if the size of global hints
44 * - glyph hints: These describe some important features of the glyph
45 * outline, as well as how to align them. They are
46 * generally much faster to compute than global hints.
48 * The current FreeType auto-hinter does a pretty good job while performing
49 * fast computations for both global and glyph hints. However, we might be
50 * interested in introducing more complex and powerful algorithms in the
51 * future, like the one described in the John D. Hobby paper, which
52 * unfortunately requires a lot more horsepower.
54 * Because a sufficiently sophisticated font management system would
55 * typically implement an LRU cache of opened face objects to reduce memory
56 * usage, it is a good idea to be able to avoid recomputing global hints
57 * every time the same face is re-opened.
59 * We thus provide the ability to cache global hints outside of the face
60 * object, in order to speed up font re-opening time. Of course, this
61 * feature is purely optional, so most client programs won't even notice
64 * I initially thought that it would be a good idea to cache the glyph
65 * hints too. However, my general idea now is that if you really need to
66 * cache these too, you are simply in need of a new font format, where all
67 * this information could be stored within the font file and decoded on the
73 #include <freetype/freetype.h>
79 typedef struct FT_AutoHinterRec_ *FT_AutoHinter;
82 /**************************************************************************
85 * FT_AutoHinter_GlobalGetFunc
88 * Retrieve the global hints computed for a given face object. The
89 * resulting data is dissociated from the face and will survive a call to
90 * FT_Done_Face(). It must be discarded through the API
91 * FT_AutoHinter_GlobalDoneFunc().
95 * A handle to the source auto-hinter.
98 * A handle to the source face object.
102 * A typeless pointer to the global hints.
105 * The size in bytes of the global hints.
108 (*FT_AutoHinter_GlobalGetFunc)( FT_AutoHinter hinter,
114 /**************************************************************************
117 * FT_AutoHinter_GlobalDoneFunc
120 * Discard the global hints retrieved through
121 * FT_AutoHinter_GlobalGetFunc(). This is the only way these hints are
126 * A handle to the auto-hinter module.
129 * A pointer to retrieved global hints to discard.
132 (*FT_AutoHinter_GlobalDoneFunc)( FT_AutoHinter hinter,
136 /**************************************************************************
139 * FT_AutoHinter_GlobalResetFunc
142 * This function is used to recompute the global metrics in a given font.
143 * This is useful when global font data changes (e.g. Multiple Masters
144 * fonts where blend coordinates change).
148 * A handle to the source auto-hinter.
151 * A handle to the face.
154 (*FT_AutoHinter_GlobalResetFunc)( FT_AutoHinter hinter,
158 /**************************************************************************
161 * FT_AutoHinter_GlyphLoadFunc
164 * This function is used to load, scale, and automatically hint a glyph
169 * A handle to the face.
178 * This function is capable of loading composite glyphs by hinting each
179 * sub-glyph independently (which improves quality).
181 * It will call the font driver with @FT_Load_Glyph, with
182 * @FT_LOAD_NO_SCALE set.
185 (*FT_AutoHinter_GlyphLoadFunc)( FT_AutoHinter hinter,
189 FT_Int32 load_flags );
192 /**************************************************************************
195 * FT_AutoHinter_InterfaceRec
198 * The auto-hinter module's interface.
200 typedef struct FT_AutoHinter_InterfaceRec_
202 FT_AutoHinter_GlobalResetFunc reset_face;
203 FT_AutoHinter_GlobalGetFunc get_global_hints;
204 FT_AutoHinter_GlobalDoneFunc done_global_hints;
205 FT_AutoHinter_GlyphLoadFunc load_glyph;
207 } FT_AutoHinter_InterfaceRec, *FT_AutoHinter_Interface;
210 #define FT_DECLARE_AUTOHINTER_INTERFACE( class_ ) \
211 FT_CALLBACK_TABLE const FT_AutoHinter_InterfaceRec class_;
213 #define FT_DEFINE_AUTOHINTER_INTERFACE( \
217 done_global_hints_, \
219 FT_CALLBACK_TABLE_DEF \
220 const FT_AutoHinter_InterfaceRec class_ = \
224 done_global_hints_, \
231 #endif /* AUTOHINT_H_ */