1 /****************************************************************************
2 *
3 * autohint.h
4 *
5 * High-level 'autohint' module-specific interface (specification).
6 *
7 * Copyright (C) 1996-2020 by
8 * David Turner, Robert Wilhelm, and Werner Lemberg.
9 *
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.
15 *
16 */
17
18
19 /**************************************************************************
20 *
21 * The auto-hinter is used to load and automatically hint glyphs if a
22 * format-specific hinter isn't available.
23 *
24 */
25
26
27 #ifndef AUTOHINT_H_
28 #define AUTOHINT_H_
29
30
31 /**************************************************************************
32 *
33 * A small technical note regarding automatic hinting in order to clarify
34 * this module interface.
35 *
36 * An automatic hinter might compute two kinds of data for a given face:
37 *
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
42 * is really small).
43 *
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.
47 *
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.
53 *
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.
58 *
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
62 * it.
63 *
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
68 * fly.
69 *
70 */
71
72
73 #include <ft2build.h>
74 #include FT_FREETYPE_H
75
76
77 FT_BEGIN_HEADER
78
79
80 typedef struct FT_AutoHinterRec_ *FT_AutoHinter;
81
82
83 /**************************************************************************
84 *
85 * @functype:
86 * FT_AutoHinter_GlobalGetFunc
87 *
88 * @description:
89 * Retrieve the global hints computed for a given face object. The
90 * resulting data is dissociated from the face and will survive a call to
91 * FT_Done_Face(). It must be discarded through the API
92 * FT_AutoHinter_GlobalDoneFunc().
93 *
94 * @input:
95 * hinter ::
96 * A handle to the source auto-hinter.
97 *
98 * face ::
99 * A handle to the source face object.
100 *
101 * @output:
102 * global_hints ::
103 * A typeless pointer to the global hints.
104 *
105 * global_len ::
106 * The size in bytes of the global hints.
107 */
108 typedef void
109 (*FT_AutoHinter_GlobalGetFunc)( FT_AutoHinter hinter,
110 FT_Face face,
111 void** global_hints,
112 long* global_len );
113
114
115 /**************************************************************************
116 *
117 * @functype:
118 * FT_AutoHinter_GlobalDoneFunc
119 *
120 * @description:
121 * Discard the global hints retrieved through
122 * FT_AutoHinter_GlobalGetFunc(). This is the only way these hints are
123 * freed from memory.
124 *
125 * @input:
126 * hinter ::
127 * A handle to the auto-hinter module.
128 *
129 * global ::
130 * A pointer to retrieved global hints to discard.
131 */
132 typedef void
133 (*FT_AutoHinter_GlobalDoneFunc)( FT_AutoHinter hinter,
134 void* global );
135
136
137 /**************************************************************************
138 *
139 * @functype:
140 * FT_AutoHinter_GlobalResetFunc
141 *
142 * @description:
143 * This function is used to recompute the global metrics in a given font.
144 * This is useful when global font data changes (e.g. Multiple Masters
145 * fonts where blend coordinates change).
146 *
147 * @input:
148 * hinter ::
149 * A handle to the source auto-hinter.
150 *
151 * face ::
152 * A handle to the face.
153 */
154 typedef void
155 (*FT_AutoHinter_GlobalResetFunc)( FT_AutoHinter hinter,
156 FT_Face face );
157
158
159 /**************************************************************************
160 *
161 * @functype:
162 * FT_AutoHinter_GlyphLoadFunc
163 *
164 * @description:
165 * This function is used to load, scale, and automatically hint a glyph
166 * from a given face.
167 *
168 * @input:
169 * face ::
170 * A handle to the face.
171 *
172 * glyph_index ::
173 * The glyph index.
174 *
175 * load_flags ::
176 * The load flags.
177 *
178 * @note:
179 * This function is capable of loading composite glyphs by hinting each
180 * sub-glyph independently (which improves quality).
181 *
182 * It will call the font driver with @FT_Load_Glyph, with
183 * @FT_LOAD_NO_SCALE set.
184 */
185 typedef FT_Error
186 (*FT_AutoHinter_GlyphLoadFunc)( FT_AutoHinter hinter,
187 FT_GlyphSlot slot,
188 FT_Size size,
189 FT_UInt glyph_index,
190 FT_Int32 load_flags );
191
192
193 /**************************************************************************
194 *
195 * @struct:
196 * FT_AutoHinter_InterfaceRec
197 *
198 * @description:
199 * The auto-hinter module's interface.
200 */
201 typedef struct FT_AutoHinter_InterfaceRec_
202 {
203 FT_AutoHinter_GlobalResetFunc reset_face;
204 FT_AutoHinter_GlobalGetFunc get_global_hints;
205 FT_AutoHinter_GlobalDoneFunc done_global_hints;
206 FT_AutoHinter_GlyphLoadFunc load_glyph;
207
208 } FT_AutoHinter_InterfaceRec, *FT_AutoHinter_Interface;
209
210
211 #define FT_DEFINE_AUTOHINTER_INTERFACE( \
212 class_, \
213 reset_face_, \
214 get_global_hints_, \
215 done_global_hints_, \
216 load_glyph_ ) \
217 FT_CALLBACK_TABLE_DEF \
218 const FT_AutoHinter_InterfaceRec class_ = \
219 { \
220 reset_face_, \
221 get_global_hints_, \
222 done_global_hints_, \
223 load_glyph_ \
224 };
225
226
227 FT_END_HEADER
228
229 #endif /* AUTOHINT_H_ */
230
231
232 /* END */