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[ttfautohint.git] / lib / ttfautohint.h
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1 /* ttfautohint.h */
3 /*
4 * Copyright (C) 2011-2017 by Werner Lemberg.
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.
11 * The file `COPYING' mentioned in the previous paragraph is distributed
12 * with the ttfautohint library.
16 #ifndef TTFAUTOHINT_H_
17 #define TTFAUTOHINT_H_
19 #include <stdarg.h>
20 #include <stdint.h>
22 #ifdef __cplusplus
23 extern "C" {
24 #endif
28 * This file gets processed with a simple sed script to extract the
29 * documentation (written in pandoc's markdown format); code between the
30 * `pandoc' markers are retained, everything else is discarded. C comments
31 * are uncommented so that column 4 becomes column 1; empty lines outside of
32 * comments are removed.
36 /* pandoc-start */
39 * The ttfautohint API
40 * ===================
42 * This section documents the single function of the ttfautohint library,
43 * `TTF_autohint`, together with its callback functions (`TA_Progress_Func`
44 * `TA_Error_Func`, `TA_Info_Func`, and `TA_Info_Post_Func`). All
45 * information has been directly extracted from the `ttfautohint.h` header
46 * file.
52 * Preprocessor Macros and Typedefs
53 * --------------------------------
55 * Some default values.
57 * ```C
60 #define TA_HINTING_RANGE_MIN 8
61 #define TA_HINTING_RANGE_MAX 50
62 #define TA_HINTING_LIMIT 200
63 #define TA_INCREASE_X_HEIGHT 14
66 *```
68 * An error type.
70 * ```C
73 typedef int TA_Error;
76 * ```
82 * Callback: `TA_Progress_Func`
83 * ----------------------------
85 * A callback function to get progress information. *curr_idx* gives the
86 * currently processed glyph index; if it is negative, an error has
87 * occurred. *num_glyphs* holds the total number of glyphs in the font
88 * (this value can't be larger than 65535).
90 * *curr_sfnt* gives the current subfont within a TrueType Collection (TTC),
91 * and *num_sfnts* the total number of subfonts.
93 * If the return value is non-zero, `TTF_autohint` aborts with
94 * `TA_Err_Canceled`. Use this for a 'Cancel' button or similar features in
95 * interactive use.
97 * *progress_data* is a void pointer to user-supplied data.
99 * ```C
102 typedef int
103 (*TA_Progress_Func)(long curr_idx,
104 long num_glyphs,
105 long curr_sfnt,
106 long num_sfnts,
107 void* progress_data);
110 * ```
116 * Callback: `TA_Error_Func`
117 * -------------------------
119 * A callback function to get error information.
121 * *error* is the value `TTF_autohint` returns. See file
122 * `ttfautohint-errors.h` for a list. Error codes not in this list are
123 * directly taken from FreeType; see the FreeType header file `fterrdef.h`
124 * for more.
126 * *error_string*, if non-NULL, is a pointer to an error message that
127 * represents *error*.
129 * The next three parameters help identify the origin of text string parsing
130 * errors. *linenum*, if non-zero, contains the line number. *line*, if
131 * non-NULL, is a pointer to the input line that can't be processed.
132 * *errpos*, if non-NULL, holds a pointer to the position in *line* where
133 * the problem occurs.
135 * *error_data* is a void pointer to user-supplied data.
137 * ```C
140 typedef void
141 (*TA_Error_Func)(TA_Error error,
142 const char* error_string,
143 unsigned int linenum,
144 const char* line,
145 const char* errpos,
146 void* error_data);
149 * ```
155 * Callback: `TA_Info_Func`
156 * ------------------------
158 * A callback function to access or modify strings in the `name` table; it
159 * is called in a loop that iterates over all `name` table entries. If
160 * defined, [`TA_Info_Post_Func`](#callback-ta_info_post_func) gets executed
161 * after this loop so that the collected data can be written back to the
162 * `name` table.
164 * *platform_id*, *encoding_id*, *language_id*, and *name_id* are the
165 * identifiers of a `name` table entry pointed to by *str* with a length
166 * pointed to by *str_len* (in bytes; the string has no trailing NULL byte).
167 * Please refer to the [OpenType specification of the `name` table] for a
168 * detailed description of the various parameters, in particular which
169 * encoding is used for a given platform and encoding ID.
171 * [OpenType specification of the `name` table]: http://www.microsoft.com/typography/otspec/name.htm
173 * The string *str* is allocated with `malloc`; the application should
174 * reallocate the data if necessary, ensuring that the string length doesn't
175 * exceed 0xFFFF.
177 * *info_data* is a void pointer to user-supplied data.
179 * If an error occurs, return a non-zero value and don't modify *str* and
180 * *str_len* (such errors are handled as non-fatal).
182 * ```C
185 typedef int
186 (*TA_Info_Func)(unsigned short platform_id,
187 unsigned short encoding_id,
188 unsigned short language_id,
189 unsigned short name_id,
190 unsigned short* str_len,
191 unsigned char** str,
192 void* info_data);
195 * ```
201 * Callback: `TA_Info_Post_Func`
202 * -----------------------------
204 * A callback function, giving the application the possibility to access or
205 * modify strings in the `name` table after
206 * [`TA_Info_Func`](#callback-ta_info_func) has iterated over all `name`
207 * table entries.
209 * It is expected that `TA_Info_Func` stores pointers to the `name` table
210 * entries it wants to access or modify; the only parameter is thus
211 * *info_data*, which is a void pointer to the user-supplied data already
212 * provided to `TA_Info_Func`. Obviously, calling `TA_Info_Post_Func` with
213 * `TA_Info_Func` undefined has no effect.
215 * The `name` table strings are allocated with `malloc`; the application
216 * should reallocate the data if necessary, ensuring that no string length
217 * exceeds 0xFFFF.
219 * If an error occurs, return a non-zero value and don't modify the affected
220 * string and string length (such errors are handled as non-fatal).
222 * ```C
225 typedef int
226 (*TA_Info_Post_Func)(void* info_data);
229 * ```
233 /* pandoc-end */
237 * Error values in addition to the FT_Err_XXX constants from FreeType.
239 * All error values specific to ttfautohint start with `TA_Err_'.
241 #include <ttfautohint-errors.h>
244 /* pandoc-start */
247 * Function: `TTF_autohint`
248 * ------------------------
251 * Read a TrueType font, remove existing bytecode (in the SFNT tables
252 * `prep`, `fpgm`, `cvt `, and `glyf`), and write a new TrueType font with
253 * new bytecode based on the autohinting of the FreeType library, optionally
254 * using a reference font to derive blue zones.
256 * It expects a format string *options* and a variable number of arguments,
257 * depending on the fields in *options*. The fields are comma separated;
258 * whitespace within the format string is not significant, a trailing comma
259 * is ignored. Fields are parsed from left to right; if a field occurs
260 * multiple times, the last field's argument wins. The same is true for
261 * fields that are mutually exclusive. Depending on the field, zero or one
262 * argument is expected.
264 * Note that fields marked as 'not implemented yet' are subject to change.
267 * ### I/O
269 * `in-file`
270 * : A pointer of type `FILE*` to the data stream of the input font,
271 * opened for binary reading. Mutually exclusive with `in-buffer`.
273 * `in-buffer`
274 * : A pointer of type `const char*` to a buffer that contains the input
275 * font. Needs `in-buffer-len`. Mutually exclusive with `in-file`.
277 * `in-buffer-len`
278 * : A value of type `size_t`, giving the length of the input buffer.
279 * Needs `in-buffer`.
281 * `out-file`
282 * : A pointer of type `FILE*` to the data stream of the output font,
283 * opened for binary writing. Mutually exclusive with `out-buffer`.
285 * `out-buffer`
286 * : A pointer of type `char**` to a buffer that contains the output
287 * font. Needs `out-buffer-len`. Mutually exclusive with `out-file`.
288 * Deallocate the memory with `free`.
290 * `out-buffer-len`
291 * : A pointer of type `size_t*` to a value giving the length of the
292 * output buffer. Needs `out-buffer`.
294 * `control-file`
295 * : A pointer of type `FILE*` to the data stream of control instructions.
296 * Mutually exclusive with `control-buffer`.
298 * See '[Control Instructions](#control-instructions)' for the syntax
299 * used in such a file or buffer.
301 * `control-buffer`
302 * : A pointer of type `const char*` to a buffer that contains control
303 * instructions. Needs `control-buffer-len`. Mutually exclusive with
304 * `control-file`.
306 * `control-buffer-len`
307 * : A value of type `size_t`, giving the length of the control
308 * instructions buffer. Needs `control-buffer`.
310 * `reference-file`
311 * : A pointer of type `FILE*` to the data stream of the reference font,
312 * opened for binary reading. Mutually exclusive with
313 * `reference-buffer`.
315 * `reference-buffer`
316 * : A pointer of type `const char*` to a buffer that contains the
317 * reference font. Needs `reference-buffer-len`. Mutually exclusive
318 * with `reference-file`.
320 * `reference-buffer-len`
321 * : A value of type `size_t`, giving the length of the reference buffer.
322 * Needs `reference-buffer`.
324 * `reference-index`
325 * : The face index to be used in the reference font. The default value
326 * is\ 0.
328 * `reference-name`
329 * : A string that specifies the name of the reference font. It is only
330 * used to emit a sensible value for the `TTFA` table if `TTFA-info` is
331 * set.
334 * ### Messages and Callbacks
336 * `progress-callback`
337 * : A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
338 * specifying a callback function for progress reports. This function
339 * gets called after a single glyph has been processed. If this field
340 * is not set or set to NULL, no progress callback function is used.
342 * `progress-callback-data`
343 * : A pointer of type `void*` to user data that is passed to the
344 * progress callback function.
346 * `error-string`
347 * : A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
348 * that verbally describes the error code. You must not change the
349 * returned value.
351 * `error-callback`
352 * : A pointer of type [`TA_Error_Func`](#callback-ta_error_func),
353 * specifying a callback function for error messages. This function
354 * gets called right before `TTF_autohint` exits. If this field is not
355 * set or set to NULL, no error callback function is used.
357 * Use it as a more sophisticated alternative to `error-string`.
359 * `error-callback-data`
360 * : A point of type `void*` to user data that is passed to the error
361 * callback function.
363 * `info-callback`
364 * : A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
365 * specifying a callback function for manipulating the `name` table.
366 * This function gets called for each `name` table entry. If not set or
367 * set to NULL, `TA_Info_Func` is not called.
369 * `info-post-callback`
370 * : A pointer of type [`TA_Info_Post_Func`](#callback-ta_info_post_func),
371 * specifying a callback function for manipulating the `name` table. It
372 * is called after the function specified with `info-callback` has
373 * iterated over all `name` table entries. If not set or set to NULL,
374 * `TA_Info_Post_Func` is not called.
376 * `info-callback-data`
377 * : A pointer of type `void*` to user data that is passed to the info
378 * callback functions.
380 * `debug`
381 * : If this integer is set to\ 1, lots of debugging information is print
382 * to stderr. The default value is\ 0.
385 * ### General Hinting Options
387 * `hinting-range-min`
388 * : An integer (which must be larger than or equal to\ 2) giving the
389 * lowest PPEM value used for autohinting. If this field is not set, it
390 * defaults to `TA_HINTING_RANGE_MIN`.
392 * `hinting-range-max`
393 * : An integer (which must be larger than or equal to the value of
394 * `hinting-range-min`) giving the highest PPEM value used for
395 * autohinting. If this field is not set, it defaults to
396 * `TA_HINTING_RANGE_MAX`.
398 * `hinting-limit`
399 * : An integer (which must be larger than or equal to the value of
400 * `hinting-range-max`) that gives the largest PPEM value at which
401 * hinting is applied. For larger values, hinting is switched off. If
402 * this field is not set, it defaults to `TA_HINTING_LIMIT`. If it is
403 * set to\ 0, no hinting limit is added to the bytecode.
405 * `hint-composites`
406 * : If this integer is set to\ 1, composite glyphs get separate hints.
407 * This implies adding a special glyph to the font called
408 * ['.ttfautohint'](#the-.ttfautohint-glyph). Setting it to\ 0 (which
409 * is the default), the hints of the composite glyphs' components are
410 * used. Adding hints for composite glyphs increases the size of the
411 * resulting bytecode a lot, but it might deliver better hinting
412 * results. However, this depends on the processed font and must be
413 * checked by inspection.
415 * `adjust-subglyphs`
416 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) to
417 * specify whether native TrueType hinting of the *input font* shall be
418 * applied to all glyphs before passing them to the (internal)
419 * autohinter. The used resolution is the em-size in font units; for
420 * most fonts this is 2048ppem. Use this only if the old hints move or
421 * scale subglyphs independently of the output resolution, for example
422 * some exotic CJK fonts.
424 * `pre-hinting` is a deprecated alias name for this option.
427 * ### Hinting Algorithms
429 * `gray-strong-stem-width`
430 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
431 * specifies whether horizontal stems should be snapped and positioned
432 * to integer pixel values for normal grayscale rendering.
434 * `gdi-cleartype-strong-stem-width`
435 * : An integer (1\ for 'on', which is the default, and 0\ for 'off') that
436 * specifies whether horizontal stems should be snapped and positioned
437 * to integer pixel values for GDI ClearType rendering, this is, the
438 * rasterizer version (as returned by the GETINFO bytecode instruction)
439 * is in the range 36\ <= version <\ 38 and ClearType is enabled.
441 * `dw-cleartype-strong-stem-width`
442 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
443 * specifies whether horizontal stems should be snapped and positioned
444 * to integer pixel values for DW ClearType rendering, this is, the
445 * rasterizer version (as returned by the GETINFO bytecode instruction)
446 * is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
447 * also.
449 * `increase-x-height`
450 * : An integer. For PPEM values in the range 6\ <= PPEM
451 * <= `increase-x-height`, round up the font's x\ height much more often
452 * than normally (to use the terminology of TrueType's 'Super Round'
453 * bytecode instruction, the threshold gets increased from 5/8px to
454 * 13/16px). If it is set to\ 0, this feature is switched off. If this
455 * field is not set, it defaults to `TA_INCREASE_X_HEIGHT`. Use this
456 * flag to improve the legibility of small font sizes if necessary.
458 * `x-height-snapping-exceptions`
459 * : A pointer of type `const char*` to a null-terminated string that
460 * gives a list of comma separated PPEM values or value ranges at which
461 * no x\ height snapping shall be applied. A value range has the form
462 * *value*~1~`-`*value*~2~, meaning *value*~1~ <= PPEM <= *value*~2~.
463 * *value*~1~ or *value*~2~ (or both) can be missing; a missing value is
464 * replaced by the beginning or end of the whole interval of valid PPEM
465 * values, respectively. Whitespace is not significant; superfluous
466 * commas are ignored, and ranges must be specified in increasing order.
467 * For example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7,
468 * 9, 10, 11, 12, etc. Consequently, if the supplied argument is `"-"`,
469 * no x\ height snapping takes place at all. The default is the empty
470 * string (`""`), meaning no snapping exceptions.
472 * `windows-compatibility`
473 * : If this integer is set to\ 1, two artificial blue zones are used,
474 * positioned at the `usWinAscent` and `usWinDescent` values (from the
475 * font's `OS/2` table). The idea is to help ttfautohint so that the
476 * hinted glyphs stay within this horizontal stripe since Windows clips
477 * everything falling outside. The default is\ 0.
480 * ### Scripts
482 * `default-script`
483 * : A string consisting of four lowercase characters that specifies the
484 * default script for OpenType features. After applying all features
485 * that are handled specially, use this value for the remaining
486 * features. The default value is `"latn"`; if set to `"none"`, no
487 * script is used. Valid values can be found in the header file
488 * `ttfautohint-scripts.h`.
490 * `fallback-script`
491 * : A string consisting of four lowercase characters, specifying the
492 * default script for glyphs that can't be mapped to a script
493 * automatically. By default, such glyphs are hinted; if option
494 * `fallback-scaling` is set, they are scaled only instead. Valid
495 * values can be found in the header file `ttfautohint-scripts.h`.
497 * Default value is `"none"`, which means hinting without using a
498 * script's blue zones if `fallback-scaling` isn't set. If
499 * `fallback_scaling` is set, value `"none"` implies no hinting for
500 * unmapped glyphs.
502 * `fallback-scaling`
503 * : Set this integer to\ 1 if glyphs handled by the fallback script
504 * should be scaled only with the fallback script's scaling value,
505 * instead of being hinted with the fallback script's hinting
506 * parameters.
508 * `symbol`
509 * : Set this integer to\ 1 if you want to process a font that ttfautohint
510 * would refuse otherwise because it can't find a single standard
511 * character for any of the supported scripts. ttfautohint then uses a
512 * default (hinting) value for the standard stem width instead of
513 * deriving it from a script's set of standard characters (for the latin
514 * script, one of them is character 'o'). The default value of this
515 * option is\ 0.
517 * `fallback-stem-width`
518 * : Set the horizontal stem width (hinting) value for all scripts that
519 * lack proper standard characters. The value is given in font units
520 * and must be a positive integer. If not set, or the value is zero,
521 * ttfautohint uses a hard-coded default (50\ units at 2048 units per
522 * EM, and linearly scaled for other UPEM values, for example 24\ units
523 * at 1000 UPEM).
525 * For symbol fonts (i.e., option `symbol` is given),
526 * `fallback-stem-width` has an effect only if `fallback-script` is set
527 * also.
530 * ### Miscellaneous
532 * `ignore-restrictions`
533 * : If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
534 * the ttfautohint library refuses to process the font since a
535 * permission to do that is required from the font's legal owner. In
536 * case you have such a permission you might set the integer argument to
537 * value\ 1 to make ttfautohint handle the font. The default value
538 * is\ 0.
540 * `TTFA-info`
541 * : If set to\ 1, ttfautohint creates an SFNT table called `TTFA` and
542 * fills it with information on the parameters used while calling
543 * `TTF_autohint`. The format of the output data resembles the
544 * information at the very beginning of the dump emitted by option
545 * `debug`. The default value is\ 0.
547 * Main use of this option is for font editing purposes. For example,
548 * after a font editor has added some glyphs, a front-end to
549 * `TTF_autohint` can parse `TTFA` and feed the parameters into another
550 * call of `TTF_autohint`. The new glyphs are then hinted while hints
551 * of the old glyphs stay unchanged.
553 * If this option is not set, and the font to be processed contains a
554 * `TTFA` table, it gets removed.
556 * Note that such a `TTFA` table gets ignored by all font rendering
557 * engines. In TrueType Collections, the `TTFA` table is added to the
558 * first subfont.
560 * `dehint`
561 * : If set to\ 1, remove all hints from the font. All other hinting
562 * options are ignored.
564 * `epoch`
565 * : An integer of type `unsigned long long`, defined as the number of
566 * seconds (excluding leap seconds) since 01 Jan 1970 00:00:00 UTC. If
567 * set, or if the value is not equal to `ULLONG_MAX`, this epoch gets
568 * used instead of the current date and time for the 'modification time'
569 * field in the TTF header. Use this to get [reproducible
570 * builds](https://reproducible-builds.org/).
573 * ### Remarks
575 * * Obviously, it is necessary to have an input and an output data
576 * stream. All other options are optional.
578 * * `hinting-range-min` and `hinting-range-max` specify the range for
579 * which the autohinter generates optimized hinting code. If a PPEM
580 * value is smaller than the value of `hinting-range-min`, hinting still
581 * takes place but the configuration created for `hinting-range-min` is
582 * used. The analogous action is taken for `hinting-range-max`, only
583 * limited by the value given with `hinting-limit`. The font's `gasp`
584 * table is set up to always use grayscale rendering with grid-fitting
585 * for standard hinting, and symmetric grid-fitting and symmetric
586 * smoothing for horizontal subpixel hinting (ClearType).
588 * * ttfautohint can process its own output a second time only if option
589 * `hint-composites` is not set (or if the font doesn't contain
590 * composite glyphs at all). This limitation might change in the
591 * future.
593 * ```C
596 TA_Error
597 TTF_autohint(const char* options,
598 ...);
601 * ```
605 /* pandoc-end */
607 #ifdef __cplusplus
608 } /* extern "C" */
609 #endif
611 #endif /* TTFAUTOHINT_H_ */
613 /* end of ttfautohint.h */