Minor bug fix.
[ttfautohint.git] / lib / ttfautohint.h
blobef3fa341b92dc97b032779dac2f44791ccd4ae48
1 /* ttfautohint.h */
3 /*
4 * Copyright (C) 2011-2015 by Werner Lemberg.
5 *
6 * This file is part of the ttfautohint library, and may only be used,
7 * modified, and distributed under the terms given in `COPYING'. By
8 * continuing to use, modify, or distribute this file you indicate that you
9 * have read `COPYING' and understand and accept it fully.
10 *
11 * The file `COPYING' mentioned in the previous paragraph is distributed
12 * with the ttfautohint library.
13 */
16 #ifndef __TTFAUTOHINT_H__
17 #define __TTFAUTOHINT_H__
19 #include <stdarg.h>
21 #ifdef __cplusplus
22 extern "C" {
23 #endif
26 /*
27 * This file gets processed with a simple sed script to extract the
28 * documentation (written in pandoc's markdown format); code between the
29 * `pandoc' markers are retained, everything else is discarded. C comments
30 * are uncommented so that column 4 becomes column 1; empty lines outside of
31 * comments are removed.
32 */
35 /* pandoc-start */
37 /*
38 * The ttfautohint API
39 * ===================
40 *
41 * This section documents the single function of the ttfautohint library,
42 * `TTF_autohint`, together with its callback functions, `TA_Progress_Func`
43 * and `TA_Info_Func`. All information has been directly extracted from the
44 * `ttfautohint.h` header file.
45 *
46 */
49 /*
50 * Preprocessor Macros and Typedefs
51 * --------------------------------
52 *
53 * Some default values.
54 *
55 * ```C
56 */
58 #define TA_HINTING_RANGE_MIN 8
59 #define TA_HINTING_RANGE_MAX 50
60 #define TA_HINTING_LIMIT 200
61 #define TA_INCREASE_X_HEIGHT 14
63 /*
64 *```
65 *
66 * An error type.
67 *
68 * ```C
69 */
71 typedef int TA_Error;
73 /*
74 * ```
75 *
76 */
79 /*
80 * Callback: `TA_Progress_Func`
81 * ----------------------------
82 *
83 * A callback function to get progress information. *curr_idx* gives the
84 * currently processed glyph index; if it is negative, an error has
85 * occurred. *num_glyphs* holds the total number of glyphs in the font
86 * (this value can't be larger than 65535).
87 *
88 * *curr_sfnt* gives the current subfont within a TrueType Collection (TTC),
89 * and *num_sfnts* the total number of subfonts.
90 *
91 * If the return value is non-zero, `TTF_autohint` aborts with
92 * `TA_Err_Canceled`. Use this for a 'Cancel' button or similar features in
93 * interactive use.
94 *
95 * *progress_data* is a void pointer to user-supplied data.
96 *
97 * ```C
98 */
100 typedef int
101 (*TA_Progress_Func)(long curr_idx,
102 long num_glyphs,
103 long curr_sfnt,
104 long num_sfnts,
105 void* progress_data);
107 /*
108 * ```
110 */
113 /*
114 * Callback: `TA_Error_Func`
115 * -------------------------
117 * A callback function to get error information.
119 * *error* is the value `TTF_autohint` returns. See file
120 * `ttfautohint-errors.h` for a list. Error codes not in this list are
121 * directly taken from FreeType; see the FreeType header file `fterrdef.h`
122 * for more.
124 * *error_string*, if non-NULL, is a pointer to an error message that
125 * represents *error*.
127 * The next three parameters help identify the origin of text string parsing
128 * errors. *linenum*, if non-zero, contains the line number. *line*, if
129 * non-NULL, is a pointer to the input line that can't be processed.
130 * *errpos*, if non-NULL, holds a pointer to the position in *line* where
131 * the problem occurs.
133 * *error_data* is a void pointer to user-supplied data.
135 * ```C
136 */
138 typedef void
139 (*TA_Error_Func)(TA_Error error,
140 const char* error_string,
141 unsigned int linenum,
142 const char* line,
143 const char* errpos,
144 void* error_data);
146 /*
147 * ```
149 */
152 /*
153 * Callback: `TA_Info_Func`
154 * ------------------------
156 * A callback function to access or modify strings in the `name` table; it
157 * is called in a loop that iterates over all `name` table entries. If
158 * defined, [`TA_Info_Post_Func`](#callback-ta_info_post_func) gets executed
159 * after this loop so that the collected data can be written back to the
160 * `name` table.
162 * *platform_id*, *encoding_id*, *language_id*, and *name_id* are the
163 * identifiers of a `name` table entry pointed to by *str* with a length
164 * pointed to by *str_len* (in bytes; the string has no trailing NULL byte).
165 * Please refer to the [OpenType specification of the `name` table] for a
166 * detailed description of the various parameters, in particular which
167 * encoding is used for a given platform and encoding ID.
169 * [OpenType specification of the `name` table]: http://www.microsoft.com/typography/otspec/name.htm
171 * The string *str* is allocated with `malloc`; the application should
172 * reallocate the data if necessary, ensuring that the string length doesn't
173 * exceed 0xFFFF.
175 * *info_data* is a void pointer to user-supplied data.
177 * If an error occurs, return a non-zero value and don't modify *str* and
178 * *str_len* (such errors are handled as non-fatal).
180 * ```C
181 */
183 typedef int
184 (*TA_Info_Func)(unsigned short platform_id,
185 unsigned short encoding_id,
186 unsigned short language_id,
187 unsigned short name_id,
188 unsigned short* str_len,
189 unsigned char** str,
190 void* info_data);
192 /*
193 * ```
195 */
198 /*
199 * Callback: `TA_Info_Post_Func`
200 * -----------------------------
202 * A callback function, giving the application the possibility to access or
203 * modify strings in the `name` table after
204 * [`TA_Info_Func`](#callback-ta_info_func) has iterated over all `name`
205 * table entries.
207 * It is expected that `TA_Info_Func` stores pointers to the `name` table
208 * entries it wants to access or modify; the only parameter is thus
209 * *info_data*, which is a void pointer to the user-supplied data already
210 * provided to `TA_Info_Func`. Obviously, calling `TA_Info_Post_Func` with
211 * `TA_Info_Func` undefined has no effect.
213 * The `name` table strings are allocated with `malloc`; the application
214 * should reallocate the data if necessary, ensuring that no string length
215 * exceeds 0xFFFF.
217 * If an error occurs, return a non-zero value and don't modify the affected
218 * string and string length (such errors are handled as non-fatal).
220 * ```C
221 */
223 typedef int
224 (*TA_Info_Post_Func)(void* info_data);
226 /*
227 * ```
229 */
231 /* pandoc-end */
234 /*
235 * Error values in addition to the FT_Err_XXX constants from FreeType.
237 * All error values specific to ttfautohint start with `TA_Err_'.
238 */
239 #include <ttfautohint-errors.h>
242 /* pandoc-start */
244 /*
245 * Function: `TTF_autohint`
246 * ------------------------
249 * Read a TrueType font, remove existing bytecode (in the SFNT tables
250 * `prep`, `fpgm`, `cvt `, and `glyf`), and write a new TrueType font with
251 * new bytecode based on the autohinting of the FreeType library.
253 * It expects a format string *options* and a variable number of arguments,
254 * depending on the fields in *options*. The fields are comma separated;
255 * whitespace within the format string is not significant, a trailing comma
256 * is ignored. Fields are parsed from left to right; if a field occurs
257 * multiple times, the last field's argument wins. The same is true for
258 * fields that are mutually exclusive. Depending on the field, zero or one
259 * argument is expected.
261 * Note that fields marked as 'not implemented yet' are subject to change.
264 * ### I/O
266 * `in-file`
267 * : A pointer of type `FILE*` to the data stream of the input font,
268 * opened for binary reading. Mutually exclusive with `in-buffer`.
270 * `in-buffer`
271 * : A pointer of type `const char*` to a buffer that contains the input
272 * font. Needs `in-buffer-len`. Mutually exclusive with `in-file`.
274 * `in-buffer-len`
275 * : A value of type `size_t`, giving the length of the input buffer.
276 * Needs `in-buffer`.
278 * `out-file`
279 * : A pointer of type `FILE*` to the data stream of the output font,
280 * opened for binary writing. Mutually exclusive with `out-buffer`.
282 * `out-buffer`
283 * : A pointer of type `char**` to a buffer that contains the output
284 * font. Needs `out-buffer-len`. Mutually exclusive with `out-file`.
285 * Deallocate the memory with `free`.
287 * `out-buffer-len`
288 * : A pointer of type `size_t*` to a value giving the length of the
289 * output buffer. Needs `out-buffer`.
291 * `control-file`
292 * : A pointer of type `FILE*` to the data stream of control instructions.
293 * Mutually exclusive with `control-buffer`.
295 * See '[Control Instructions](#control-instructions)' for the syntax
296 * used in such a file or buffer.
298 * `control-buffer`
299 * : A pointer of type `const char*` to a buffer that contains control
300 * instructions. Needs `control-buffer-len`. Mutually exclusive with
301 * `control-file`.
303 * `control-buffer-len`
304 * : A value of type `size_t`, giving the length of the control
305 * instructions buffer. Needs `control-buffer`.
308 * ### Messages and Callbacks
310 * `progress-callback`
311 * : A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
312 * specifying a callback function for progress reports. This function
313 * gets called after a single glyph has been processed. If this field
314 * is not set or set to NULL, no progress callback function is used.
316 * `progress-callback-data`
317 * : A pointer of type `void*` to user data that is passed to the
318 * progress callback function.
320 * `error-string`
321 * : A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
322 * that verbally describes the error code. You must not change the
323 * returned value.
325 * `error-callback`
326 * : A pointer of type [`TA_Error_Func`](#callback-ta_error_func),
327 * specifying a callback function for error messages. This function
328 * gets called right before `TTF_autohint` exits. If this field is not
329 * set or set to NULL, no error callback function is used.
331 * Use it as a more sophisticated alternative to `error-string`.
333 * `error-callback-data`
334 * : A point of type `void*` to user data that is passed to the error
335 * callback function.
337 * `info-callback`
338 * : A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
339 * specifying a callback function for manipulating the `name` table.
340 * This function gets called for each `name` table entry. If not set or
341 * set to NULL, `TA_Info_Func` is not called.
343 * `info-post-callback`
344 * : A pointer of type [`TA_Info_Post_Func`](#callback-ta_info_post_func),
345 * specifying a callback function for manipulating the `name` table. It
346 * is called after the function specified with `info-callback` has
347 * iterated over all `name` table entries. If not set or set to NULL,
348 * `TA_Info_Post_Func` is not called.
350 * `info-callback-data`
351 * : A pointer of type `void*` to user data that is passed to the info
352 * callback functions.
354 * `debug`
355 * : If this integer is set to\ 1, lots of debugging information is print
356 * to stderr. The default value is\ 0.
359 * ### General Hinting Options
361 * `hinting-range-min`
362 * : An integer (which must be larger than or equal to\ 2) giving the
363 * lowest PPEM value used for autohinting. If this field is not set, it
364 * defaults to `TA_HINTING_RANGE_MIN`.
366 * `hinting-range-max`
367 * : An integer (which must be larger than or equal to the value of
368 * `hinting-range-min`) giving the highest PPEM value used for
369 * autohinting. If this field is not set, it defaults to
370 * `TA_HINTING_RANGE_MAX`.
372 * `hinting-limit`
373 * : An integer (which must be larger than or equal to the value of
374 * `hinting-range-max`) that gives the largest PPEM value at which
375 * hinting is applied. For larger values, hinting is switched off. If
376 * this field is not set, it defaults to `TA_HINTING_LIMIT`. If it is
377 * set to\ 0, no hinting limit is added to the bytecode.
379 * `hint-composites`
380 * : If this integer is set to\ 1, composite glyphs get separate hints.
381 * This implies adding a special glyph to the font called
382 * ['.ttfautohint'](#the-.ttfautohint-glyph). Setting it to\ 0 (which
383 * is the default), the hints of the composite glyphs' components are
384 * used. Adding hints for composite glyphs increases the size of the
385 * resulting bytecode a lot, but it might deliver better hinting
386 * results. However, this depends on the processed font and must be
387 * checked by inspection.
389 * `adjust-subglyphs`
390 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) to
391 * specify whether native TrueType hinting of the *input font* shall be
392 * applied to all glyphs before passing them to the (internal)
393 * autohinter. The used resolution is the em-size in font units; for
394 * most fonts this is 2048ppem. Use this only if the old hints move or
395 * scale subglyphs independently of the output resolution, for example
396 * some exotic CJK fonts.
398 * `pre-hinting` is a deprecated alias name for this option.
401 * ### Hinting Algorithms
403 * `gray-strong-stem-width`
404 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
405 * specifies whether horizontal stems should be snapped and positioned
406 * to integer pixel values for normal grayscale rendering.
408 * `gdi-cleartype-strong-stem-width`
409 * : An integer (1\ for 'on', which is the default, and 0\ for 'off') that
410 * specifies whether horizontal stems should be snapped and positioned
411 * to integer pixel values for GDI ClearType rendering, this is, the
412 * rasterizer version (as returned by the GETINFO bytecode instruction)
413 * is in the range 36\ <= version <\ 38 and ClearType is enabled.
415 * `dw-cleartype-strong-stem-width`
416 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
417 * specifies whether horizontal stems should be snapped and positioned
418 * to integer pixel values for DW ClearType rendering, this is, the
419 * rasterizer version (as returned by the GETINFO bytecode instruction)
420 * is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
421 * also.
423 * `increase-x-height`
424 * : An integer. For PPEM values in the range 6\ <= PPEM
425 * <= `increase-x-height`, round up the font's x\ height much more often
426 * than normally (to use the terminology of TrueType's 'Super Round'
427 * bytecode instruction, the threshold gets increased from 5/8px to
428 * 13/16px). If it is set to\ 0, this feature is switched off. If this
429 * field is not set, it defaults to `TA_INCREASE_X_HEIGHT`. Use this
430 * flag to improve the legibility of small font sizes if necessary.
432 * `x-height-snapping-exceptions`
433 * : A pointer of type `const char*` to a null-terminated string that
434 * gives a list of comma separated PPEM values or value ranges at which
435 * no x\ height snapping shall be applied. A value range has the form
436 * *value*~1~`-`*value*~2~, meaning *value*~1~ <= PPEM <= *value*~2~.
437 * *value*~1~ or *value*~2~ (or both) can be missing; a missing value is
438 * replaced by the beginning or end of the whole interval of valid PPEM
439 * values, respectively. Whitespace is not significant; superfluous
440 * commas are ignored, and ranges must be specified in increasing order.
441 * For example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7,
442 * 9, 10, 11, 12, etc. Consequently, if the supplied argument is `"-"`,
443 * no x\ height snapping takes place at all. The default is the empty
444 * string (`""`), meaning no snapping exceptions.
446 * `windows-compatibility`
447 * : If this integer is set to\ 1, two artificial blue zones are used,
448 * positioned at the `usWinAscent` and `usWinDescent` values (from the
449 * font's `OS/2` table). The idea is to help ttfautohint so that the
450 * hinted glyphs stay within this horizontal stripe since Windows clips
451 * everything falling outside. The default is\ 0.
454 * ### Scripts
456 * `default-script`
457 * : A string consisting of four lowercase characters that specifies the
458 * default script for OpenType features. After applying all features
459 * that are handled specially, use this value for the remaining
460 * features. The default value is `"latn"`; if set to `"none"`, no
461 * script is used. Valid values can be found in the header file
462 * `ttfautohint-scripts.h`.
464 * `fallback-script`
465 * : A string consisting of four lowercase characters that specifies the
466 * default script for glyphs that can't be mapped to a script
467 * automatically. If set to `"none"` (which is the default), no script
468 * is used. Valid values can be found in the header file
469 * `ttfautohint-scripts.h`.
471 * `symbol`
472 * : Set this integer to\ 1 if you want to process a font that ttfautohint
473 * would refuse otherwise because it can't find a single standard
474 * character for any of the supported scripts. ttfautohint then uses a
475 * default (hinting) value for the standard stem width instead of
476 * deriving it from a script's set of standard characters (for the latin
477 * script, one of them is character 'o'). The default value of this
478 * option is\ 0.
480 * `fallback-stem-width`
481 * : Set the horizontal stem width (hinting) value for all scripts that
482 * lack proper standard characters. The value is given in font units
483 * and must be a positive integer. If not set, or the value is zero,
484 * ttfautohint uses a hard-coded default (50\ units at 2048 units per
485 * EM, and linearly scaled for other UPEM values, for example 24\ units
486 * at 1000 UPEM).
488 * For symbol fonts (i.e., option `symbol` is given),
489 * `fallback-stem-width` has an effect only if `fallback-script` is set
490 * also.
493 * ### Miscellaneous
495 * `ignore-restrictions`
496 * : If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
497 * the ttfautohint library refuses to process the font since a
498 * permission to do that is required from the font's legal owner. In
499 * case you have such a permission you might set the integer argument to
500 * value\ 1 to make ttfautohint handle the font. The default value
501 * is\ 0.
503 * `TTFA-info`
504 * : If set to\ 1, ttfautohint creates an SFNT table called `TTFA` and
505 * fills it with information on the parameters used while calling
506 * `TTF_autohint`. The format of the output data resembles the
507 * information at the very beginning of the dump emitted by option
508 * `debug`. The default value is\ 0.
510 * Main use of this option is for font editing purposes. For example,
511 * after a font editor has added some glyphs, a front-end to
512 * `TTF_autohint` can parse `TTFA` and feed the parameters into another
513 * call of `TTF_autohint`. The new glyphs are then hinted while hints
514 * of the old glyphs stay unchanged.
516 * If this option is not set, and the font to be processed contains a
517 * `TTFA` table, it gets removed.
519 * Note that such a `TTFA` table gets ignored by all font rendering
520 * engines. In TrueType Collections, the `TTFA` table is added to the
521 * first subfont.
523 * `dehint`
524 * : If set to\ 1, remove all hints from the font. All other hinting
525 * options are ignored.
528 * ### Remarks
530 * * Obviously, it is necessary to have an input and an output data
531 * stream. All other options are optional.
533 * * `hinting-range-min` and `hinting-range-max` specify the range for
534 * which the autohinter generates optimized hinting code. If a PPEM
535 * value is smaller than the value of `hinting-range-min`, hinting still
536 * takes place but the configuration created for `hinting-range-min` is
537 * used. The analogous action is taken for `hinting-range-max`, only
538 * limited by the value given with `hinting-limit`. The font's `gasp`
539 * table is set up to always use grayscale rendering with grid-fitting
540 * for standard hinting, and symmetric grid-fitting and symmetric
541 * smoothing for horizontal subpixel hinting (ClearType).
543 * * ttfautohint can process its own output a second time only if option
544 * `hint-composites` is not set (or if the font doesn't contain
545 * composite glyphs at all). This limitation might change in the
546 * future.
548 * ```C
549 */
551 TA_Error
552 TTF_autohint(const char* options,
553 ...);
555 /*
556 * ```
558 */
560 /* pandoc-end */
562 #ifdef __cplusplus
563 } /* extern "C" */
564 #endif
566 #endif /* __TTFAUTOHINT_H__ */
568 /* end of ttfautohint.h */