1 /***************************************************************************/
2 /* */
3 /* autohint.h */
4 /* */
5 /* High-level `autohint' module-specific interface (specification). */
6 /* */
7 /* Copyright 1996-2018 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 */
34 /* clarify 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 */
42 /* hints 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 */
49 /* performing fast computations for both global and glyph hints. */
50 /* However, we might be interested in introducing more complex and */
51 /* powerful algorithms in the future, like the one described in the John */
52 /* D. Hobby paper, which 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 */
56 /* memory usage, it is a good idea to be able to avoid recomputing */
57 /* global hints 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 */
66 /* to cache these too, you are simply in need of a new font format, */
67 /* where all this information could be stored within the font file and */
68 /* decoded on the 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 */
91 /* call to FT_Done_Face(). It must be discarded through the API */
92 /* FT_AutoHinter_GlobalDoneFunc(). */
93 /* */
94 /* <Input> */
95 /* hinter :: A handle to the source auto-hinter. */
96 /* */
97 /* face :: A handle to the source face object. */
98 /* */
99 /* <Output> */
100 /* global_hints :: A typeless pointer to the global hints. */
101 /* */
102 /* global_len :: The size in bytes of the global hints. */
103 /* */
104 typedef void
105 (*FT_AutoHinter_GlobalGetFunc)( FT_AutoHinter hinter,
106 FT_Face face,
107 void** global_hints,
108 long* global_len );
109
110
111 /*************************************************************************/
112 /* */
113 /* <FuncType> */
114 /* FT_AutoHinter_GlobalDoneFunc */
115 /* */
116 /* <Description> */
117 /* Discard the global hints retrieved through */
118 /* FT_AutoHinter_GlobalGetFunc(). This is the only way these hints */
119 /* are freed from memory. */
120 /* */
121 /* <Input> */
122 /* hinter :: A handle to the auto-hinter module. */
123 /* */
124 /* global :: A pointer to retrieved global hints to discard. */
125 /* */
126 typedef void
127 (*FT_AutoHinter_GlobalDoneFunc)( FT_AutoHinter hinter,
128 void* global );
129
130
131 /*************************************************************************/
132 /* */
133 /* <FuncType> */
134 /* FT_AutoHinter_GlobalResetFunc */
135 /* */
136 /* <Description> */
137 /* This function is used to recompute the global metrics in a given */
138 /* font. This is useful when global font data changes (e.g. Multiple */
139 /* Masters fonts where blend coordinates change). */
140 /* */
141 /* <Input> */
142 /* hinter :: A handle to the source auto-hinter. */
143 /* */
144 /* face :: A handle to the face. */
145 /* */
146 typedef void
147 (*FT_AutoHinter_GlobalResetFunc)( FT_AutoHinter hinter,
148 FT_Face face );
149
150
151 /*************************************************************************/
152 /* */
153 /* <FuncType> */
154 /* FT_AutoHinter_GlyphLoadFunc */
155 /* */
156 /* <Description> */
157 /* This function is used to load, scale, and automatically hint a */
158 /* glyph from a given face. */
159 /* */
160 /* <Input> */
161 /* face :: A handle to the face. */
162 /* */
163 /* glyph_index :: The glyph index. */
164 /* */
165 /* load_flags :: The load flags. */
166 /* */
167 /* <Note> */
168 /* This function is capable of loading composite glyphs by hinting */
169 /* each sub-glyph independently (which improves quality). */
170 /* */
171 /* It will call the font driver with @FT_Load_Glyph, with */
172 /* @FT_LOAD_NO_SCALE set. */
173 /* */
174 typedef FT_Error
175 (*FT_AutoHinter_GlyphLoadFunc)( FT_AutoHinter hinter,
176 FT_GlyphSlot slot,
177 FT_Size size,
178 FT_UInt glyph_index,
179 FT_Int32 load_flags );
180
181
182 /*************************************************************************/
183 /* */
184 /* <Struct> */
185 /* FT_AutoHinter_InterfaceRec */
186 /* */
187 /* <Description> */
188 /* The auto-hinter module's interface. */
189 /* */
190 typedef struct FT_AutoHinter_InterfaceRec_
191 {
192 FT_AutoHinter_GlobalResetFunc reset_face;
193 FT_AutoHinter_GlobalGetFunc get_global_hints;
194 FT_AutoHinter_GlobalDoneFunc done_global_hints;
195 FT_AutoHinter_GlyphLoadFunc load_glyph;
196
197 } FT_AutoHinter_InterfaceRec, *FT_AutoHinter_Interface;
198
199
200 #ifndef FT_CONFIG_OPTION_PIC
201
202 #define FT_DEFINE_AUTOHINTER_INTERFACE( \
203 class_, \
204 reset_face_, \
205 get_global_hints_, \
206 done_global_hints_, \
207 load_glyph_ ) \
208 FT_CALLBACK_TABLE_DEF \
209 const FT_AutoHinter_InterfaceRec class_ = \
210 { \
211 reset_face_, \
212 get_global_hints_, \
213 done_global_hints_, \
214 load_glyph_ \
215 };
216
217 #else /* FT_CONFIG_OPTION_PIC */
218
219 #define FT_DEFINE_AUTOHINTER_INTERFACE( \
220 class_, \
221 reset_face_, \
222 get_global_hints_, \
223 done_global_hints_, \
224 load_glyph_ ) \
225 void \
226 FT_Init_Class_ ## class_( FT_Library library, \
227 FT_AutoHinter_InterfaceRec* clazz ) \
228 { \
229 FT_UNUSED( library ); \
230 \
231 clazz->reset_face = reset_face_; \
232 clazz->get_global_hints = get_global_hints_; \
233 clazz->done_global_hints = done_global_hints_; \
234 clazz->load_glyph = load_glyph_; \
235 }
236
237 #endif /* FT_CONFIG_OPTION_PIC */
238
239 FT_END_HEADER
240
241 #endif /* AUTOHINT_H_ */
242
243
244 /* END */