1 /****************************************************************************
2 *
3 * ftincrem.h
4 *
5 * FreeType incremental loading (specification).
6 *
7 * Copyright (C) 2002-2020 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 #ifndef FTINCREM_H_
20 #define FTINCREM_H_
21
22 #include <ft2build.h>
23 #include FT_FREETYPE_H
24 #include FT_PARAMETER_TAGS_H
25
26 #ifdef FREETYPE_H
27 #error "freetype.h of FreeType 1 has been loaded!"
28 #error "Please fix the directory search order for header files"
29 #error "so that freetype.h of FreeType 2 is found first."
30 #endif
31
32
33 FT_BEGIN_HEADER
34
35 /**************************************************************************
36 *
37 * @section:
38 * incremental
39 *
40 * @title:
41 * Incremental Loading
42 *
43 * @abstract:
44 * Custom Glyph Loading.
45 *
46 * @description:
47 * This section contains various functions used to perform so-called
48 * 'incremental' glyph loading. This is a mode where all glyphs loaded
49 * from a given @FT_Face are provided by the client application.
50 *
51 * Apart from that, all other tables are loaded normally from the font
52 * file. This mode is useful when FreeType is used within another
53 * engine, e.g., a PostScript Imaging Processor.
54 *
55 * To enable this mode, you must use @FT_Open_Face, passing an
56 * @FT_Parameter with the @FT_PARAM_TAG_INCREMENTAL tag and an
57 * @FT_Incremental_Interface value. See the comments for
58 * @FT_Incremental_InterfaceRec for an example.
59 *
60 */
61
62
63 /**************************************************************************
64 *
65 * @type:
66 * FT_Incremental
67 *
68 * @description:
69 * An opaque type describing a user-provided object used to implement
70 * 'incremental' glyph loading within FreeType. This is used to support
71 * embedded fonts in certain environments (e.g., PostScript
72 * interpreters), where the glyph data isn't in the font file, or must be
73 * overridden by different values.
74 *
75 * @note:
76 * It is up to client applications to create and implement
77 * @FT_Incremental objects, as long as they provide implementations for
78 * the methods @FT_Incremental_GetGlyphDataFunc,
79 * @FT_Incremental_FreeGlyphDataFunc and
80 * @FT_Incremental_GetGlyphMetricsFunc.
81 *
82 * See the description of @FT_Incremental_InterfaceRec to understand how
83 * to use incremental objects with FreeType.
84 *
85 */
86 typedef struct FT_IncrementalRec_* FT_Incremental;
87
88
89 /**************************************************************************
90 *
91 * @struct:
92 * FT_Incremental_MetricsRec
93 *
94 * @description:
95 * A small structure used to contain the basic glyph metrics returned by
96 * the @FT_Incremental_GetGlyphMetricsFunc method.
97 *
98 * @fields:
99 * bearing_x ::
100 * Left bearing, in font units.
101 *
102 * bearing_y ::
103 * Top bearing, in font units.
104 *
105 * advance ::
106 * Horizontal component of glyph advance, in font units.
107 *
108 * advance_v ::
109 * Vertical component of glyph advance, in font units.
110 *
111 * @note:
112 * These correspond to horizontal or vertical metrics depending on the
113 * value of the `vertical` argument to the function
114 * @FT_Incremental_GetGlyphMetricsFunc.
115 *
116 */
117 typedef struct FT_Incremental_MetricsRec_
118 {
119 FT_Long bearing_x;
120 FT_Long bearing_y;
121 FT_Long advance;
122 FT_Long advance_v; /* since 2.3.12 */
123
124 } FT_Incremental_MetricsRec;
125
126
127 /**************************************************************************
128 *
129 * @struct:
130 * FT_Incremental_Metrics
131 *
132 * @description:
133 * A handle to an @FT_Incremental_MetricsRec structure.
134 *
135 */
136 typedef struct FT_Incremental_MetricsRec_* FT_Incremental_Metrics;
137
138
139 /**************************************************************************
140 *
141 * @type:
142 * FT_Incremental_GetGlyphDataFunc
143 *
144 * @description:
145 * A function called by FreeType to access a given glyph's data bytes
146 * during @FT_Load_Glyph or @FT_Load_Char if incremental loading is
147 * enabled.
148 *
149 * Note that the format of the glyph's data bytes depends on the font
150 * file format. For TrueType, it must correspond to the raw bytes within
151 * the 'glyf' table. For PostScript formats, it must correspond to the
152 * **unencrypted** charstring bytes, without any `lenIV` header. It is
153 * undefined for any other format.
154 *
155 * @input:
156 * incremental ::
157 * Handle to an opaque @FT_Incremental handle provided by the client
158 * application.
159 *
160 * glyph_index ::
161 * Index of relevant glyph.
162 *
163 * @output:
164 * adata ::
165 * A structure describing the returned glyph data bytes (which will be
166 * accessed as a read-only byte block).
167 *
168 * @return:
169 * FreeType error code. 0~means success.
170 *
171 * @note:
172 * If this function returns successfully the method
173 * @FT_Incremental_FreeGlyphDataFunc will be called later to release the
174 * data bytes.
175 *
176 * Nested calls to @FT_Incremental_GetGlyphDataFunc can happen for
177 * compound glyphs.
178 *
179 */
180 typedef FT_Error
181 (*FT_Incremental_GetGlyphDataFunc)( FT_Incremental incremental,
182 FT_UInt glyph_index,
183 FT_Data* adata );
184
185
186 /**************************************************************************
187 *
188 * @type:
189 * FT_Incremental_FreeGlyphDataFunc
190 *
191 * @description:
192 * A function used to release the glyph data bytes returned by a
193 * successful call to @FT_Incremental_GetGlyphDataFunc.
194 *
195 * @input:
196 * incremental ::
197 * A handle to an opaque @FT_Incremental handle provided by the client
198 * application.
199 *
200 * data ::
201 * A structure describing the glyph data bytes (which will be accessed
202 * as a read-only byte block).
203 *
204 */
205 typedef void
206 (*FT_Incremental_FreeGlyphDataFunc)( FT_Incremental incremental,
207 FT_Data* data );
208
209
210 /**************************************************************************
211 *
212 * @type:
213 * FT_Incremental_GetGlyphMetricsFunc
214 *
215 * @description:
216 * A function used to retrieve the basic metrics of a given glyph index
217 * before accessing its data. This is necessary because, in certain
218 * formats like TrueType, the metrics are stored in a different place
219 * from the glyph images proper.
220 *
221 * @input:
222 * incremental ::
223 * A handle to an opaque @FT_Incremental handle provided by the client
224 * application.
225 *
226 * glyph_index ::
227 * Index of relevant glyph.
228 *
229 * vertical ::
230 * If true, return vertical metrics.
231 *
232 * ametrics ::
233 * This parameter is used for both input and output. The original
234 * glyph metrics, if any, in font units. If metrics are not available
235 * all the values must be set to zero.
236 *
237 * @output:
238 * ametrics ::
239 * The replacement glyph metrics in font units.
240 *
241 */
242 typedef FT_Error
243 (*FT_Incremental_GetGlyphMetricsFunc)
244 ( FT_Incremental incremental,
245 FT_UInt glyph_index,
246 FT_Bool vertical,
247 FT_Incremental_MetricsRec *ametrics );
248
249
250 /**************************************************************************
251 *
252 * @struct:
253 * FT_Incremental_FuncsRec
254 *
255 * @description:
256 * A table of functions for accessing fonts that load data incrementally.
257 * Used in @FT_Incremental_InterfaceRec.
258 *
259 * @fields:
260 * get_glyph_data ::
261 * The function to get glyph data. Must not be null.
262 *
263 * free_glyph_data ::
264 * The function to release glyph data. Must not be null.
265 *
266 * get_glyph_metrics ::
267 * The function to get glyph metrics. May be null if the font does not
268 * provide overriding glyph metrics.
269 *
270 */
271 typedef struct FT_Incremental_FuncsRec_
272 {
273 FT_Incremental_GetGlyphDataFunc get_glyph_data;
274 FT_Incremental_FreeGlyphDataFunc free_glyph_data;
275 FT_Incremental_GetGlyphMetricsFunc get_glyph_metrics;
276
277 } FT_Incremental_FuncsRec;
278
279
280 /**************************************************************************
281 *
282 * @struct:
283 * FT_Incremental_InterfaceRec
284 *
285 * @description:
286 * A structure to be used with @FT_Open_Face to indicate that the user
287 * wants to support incremental glyph loading. You should use it with
288 * @FT_PARAM_TAG_INCREMENTAL as in the following example:
289 *
290 * ```
291 * FT_Incremental_InterfaceRec inc_int;
292 * FT_Parameter parameter;
293 * FT_Open_Args open_args;
294 *
295 *
296 * // set up incremental descriptor
297 * inc_int.funcs = my_funcs;
298 * inc_int.object = my_object;
299 *
300 * // set up optional parameter
301 * parameter.tag = FT_PARAM_TAG_INCREMENTAL;
302 * parameter.data = &inc_int;
303 *
304 * // set up FT_Open_Args structure
305 * open_args.flags = FT_OPEN_PATHNAME | FT_OPEN_PARAMS;
306 * open_args.pathname = my_font_pathname;
307 * open_args.num_params = 1;
308 * open_args.params = ¶meter; // we use one optional argument
309 *
310 * // open the font
311 * error = FT_Open_Face( library, &open_args, index, &face );
312 * ...
313 * ```
314 *
315 */
316 typedef struct FT_Incremental_InterfaceRec_
317 {
318 const FT_Incremental_FuncsRec* funcs;
319 FT_Incremental object;
320
321 } FT_Incremental_InterfaceRec;
322
323
324 /**************************************************************************
325 *
326 * @type:
327 * FT_Incremental_Interface
328 *
329 * @description:
330 * A pointer to an @FT_Incremental_InterfaceRec structure.
331 *
332 */
333 typedef FT_Incremental_InterfaceRec* FT_Incremental_Interface;
334
335
336 /* */
337
338
339 FT_END_HEADER
340
341 #endif /* FTINCREM_H_ */
342
343
344 /* END */