4 * Copyright (C) 2011-2014 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__
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.
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.
50 * Preprocessor Macros and Typedefs
51 * --------------------------------
53 * Some default values.
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
80 * Callback: `TA_Progress_Func`
81 * ----------------------------
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).
88 * *curr_sfnt* gives the current subfont within a TrueType Collection (TTC),
89 * and *num_sfnts* the total number of subfonts.
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
95 * *progress_data* is a void pointer to user-supplied data.
101 (*TA_Progress_Func
)(long curr_idx
,
105 void* progress_data
);
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`
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.
139 (*TA_Error_Func
)(TA_Error error
,
140 const char* error_string
,
141 unsigned int linenum
,
153 * Callback: `TA_Info_Func`
154 * ------------------------
156 * A callback function to manipulate strings in the `name` table.
157 * *platform_id*, *encoding_id*, *language_id*, and *name_id* are the
158 * identifiers of a `name` table entry pointed to by *str* with a length
159 * pointed to by *str_len* (in bytes; the string has no trailing NULL byte).
160 * Please refer to the [OpenType specification of the `name` table] for a
161 * detailed description of the various parameters, in particular which
162 * encoding is used for a given platform and encoding ID.
164 * [OpenType specification of the `name` table]: http://www.microsoft.com/typography/otspec/name.htm
166 * The string *str* is allocated with `malloc`; the application should
167 * reallocate the data if necessary, ensuring that the string length doesn't
170 * *info_data* is a void pointer to user-supplied data.
172 * If an error occurs, return a non-zero value and don't modify *str* and
173 * *str_len* (such errors are handled as non-fatal).
179 (*TA_Info_Func
)(unsigned short platform_id
,
180 unsigned short encoding_id
,
181 unsigned short language_id
,
182 unsigned short name_id
,
183 unsigned short* str_len
,
196 * Error values in addition to the FT_Err_XXX constants from FreeType.
198 * All error values specific to ttfautohint start with `TA_Err_'.
200 #include <ttfautohint-errors.h>
206 * Function: `TTF_autohint`
207 * ------------------------
210 * Read a TrueType font, remove existing bytecode (in the SFNT tables
211 * `prep`, `fpgm`, `cvt `, and `glyf`), and write a new TrueType font with
212 * new bytecode based on the autohinting of the FreeType library.
214 * It expects a format string *options* and a variable number of arguments,
215 * depending on the fields in *options*. The fields are comma separated;
216 * whitespace within the format string is not significant, a trailing comma
217 * is ignored. Fields are parsed from left to right; if a field occurs
218 * multiple times, the last field's argument wins. The same is true for
219 * fields that are mutually exclusive. Depending on the field, zero or one
220 * argument is expected.
222 * Note that fields marked as 'not implemented yet' are subject to change.
228 * : A pointer of type `FILE*` to the data stream of the input font,
229 * opened for binary reading. Mutually exclusive with `in-buffer`.
232 * : A pointer of type `const char*` to a buffer that contains the input
233 * font. Needs `in-buffer-len`. Mutually exclusive with `in-file`.
236 * : A value of type `size_t`, giving the length of the input buffer.
240 * : A pointer of type `FILE*` to the data stream of the output font,
241 * opened for binary writing. Mutually exclusive with `out-buffer`.
244 * : A pointer of type `char**` to a buffer that contains the output
245 * font. Needs `out-buffer-len`. Mutually exclusive with `out-file`.
246 * Deallocate the memory with `free`.
249 * : A pointer of type `size_t*` to a value giving the length of the
250 * output buffer. Needs `out-buffer`.
253 * : A pointer of type `FILE*` to the data stream of control instructions.
254 * Mutually exclusive with `control-buffer`.
256 * An entry in a control instructions file or buffer has one of the
257 * following syntax forms:
259 * > *\[* font-idx *\]*\ \ glyph-id\ \ *`l`|`r`* points\ \ *\[* *`(`* left-offset *`,`* right-offset *`)`* *\]*\
260 * > *\[* font-idx *\]*\ \ glyph-id\ \ *`n`* points\
261 * > *\[* font-idx *\]*\ \ glyph-id\ \ *`p`* points\ \ *\[* *`x`* x-shift *\]*\ \ *\[* *`y`* y-shift *\]*\ \ *`@`* ppems
263 * *font-idx* gives the index of the font in a TrueType Collection. If
264 * missing, it is set to zero. For normal TrueType fonts, only value
265 * zero is valid. If starting with `0x` the number is interpreted as
266 * hexadecimal. If starting with `0` it gets interpreted as an octal
267 * value, and as a decimal value otherwise.
269 * *glyph-id* is a glyph's name as listed in the `post` SFNT table or a
270 * glyph index. A glyph name consists of characters from the set
271 * '`A-Za-z0-9._`' only and does not start with a digit or period, with
272 * the exceptions of the names '`.notdef`' and '`.null`'. A glyph index
273 * can be specified in decimal, octal, or hexadecimal format, the latter
274 * two indicated by the prefixes `0` and `0x`, respectively.
276 * The mutually exclusive parameters '`l`' and '`r`' indicate that the
277 * following points have left or right 'out' direction, respectively,
278 * overriding ttfautohint's algorithm for setting point directions. The
279 * 'out direction' of a point is the direction of the outline *leaving*
280 * the point (or passing the control point). If the specified direction
281 * is identical to what ttfautohint computes, nothing special happens.
282 * Otherwise, a one-point segment with the specified direction gets
283 * created. By default, its length is zero. Setting *left-offset* and
284 * *right-offset*, you can change the segment's horizontal start and end
285 * position relative to the point position. *left-offset* and
286 * *right-offset* are integers measured in font units.
288 * Parameter '`n`' sets the 'out' direction of the following points to
289 * 'no direction'. If the specified direction is identical to what
290 * ttfautohint computes, nothing special happens. Otherwise,
291 * ttfautohint no longer considers those points as part of horizontal
292 * segments, thus treating them as 'weak' points.
294 * Modifying or adding segments don't directly modify the outlines; it
295 * only influences the hinting process.
297 * Parameter '`p`' makes ttfautohint apply delta exceptions for the
298 * given points, shifting the points by the given values. Note that
299 * those delta exceptions are applied *after* the final `IUP`
300 * instructions in the bytecode; as a consequence, they are (partially)
301 * ignored by rasterizers if in ClearType mode.
303 * Both *points* and *ppems* are number ranges, similar to the
304 * `x-height-snapping-exceptions` syntax.
306 * *x-shift* and *y-shift* represent real numbers that get rounded to
307 * multiples of 1/8 pixels. The entries for '`x`' and '`y`' are
308 * optional; if missing, the corresponding value is set to zero.
310 * Values for *x-shift* and *y-shift* must be in the range [-1.0;1.0].
311 * Values for *ppems* must be in the range [6;53]. Values for *points*
312 * are limited by the number of points in the glyph.
314 * Control instruction entries can be either separated with newlines or
315 * with character '`;`'. Additionally, a line can be continued on the
316 * next line by ending it with backslash character ('`\`'). A backslash
317 * followed by a newline gets treated similar to a whitespace character.
319 * A comment starts with character '`#`'; the rest of the line is
320 * ignored. An empty line is ignored also.
322 * Note that only character '`.`' is recognized as a decimal point, and
323 * a thousands separator is not accepted.
326 * : A pointer of type `const char*` to a buffer that contains control
327 * instructions. Needs `control-buffer-len`. Mutually exclusive with
330 * `control-buffer-len`
331 * : A value of type `size_t`, giving the length of the control
332 * instructions buffer. Needs `control-buffer`.
335 * ### Messages and Callbacks
337 * `progress-callback`
338 * : A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
339 * specifying a callback function for progress reports. This function
340 * gets called after a single glyph has been processed. If this field
341 * is not set or set to NULL, no progress callback function is used.
343 * `progress-callback-data`
344 * : A pointer of type `void*` to user data that is passed to the
345 * progress callback function.
348 * : A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
349 * that verbally describes the error code. You must not change the
353 * : A pointer of type [`TA_Error_Func`](#callback-ta_error_func),
354 * specifying a callback function for error messages. This function
355 * gets called right before `TTF_autohint` exits. If this field is not
356 * set or set to NULL, no error callback function is used.
358 * Use it as a more sophisticated alternative to `error-string`.
360 * `error-callback-data`
361 * : A point of type `void*` to user data that is passed to the error
365 * : A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
366 * specifying a callback function for manipulating the `name` table.
367 * This function gets called for each `name` table entry. If not set or
368 * set to NULL, the table data stays unmodified.
370 * `info-callback-data`
371 * : A pointer of type `void*` to user data that is passed to the info
375 * : If this integer is set to\ 1, lots of debugging information is print
376 * to stderr. The default value is\ 0.
379 * ### General Hinting Options
381 * `hinting-range-min`
382 * : An integer (which must be larger than or equal to\ 2) giving the
383 * lowest PPEM value used for autohinting. If this field is not set, it
384 * defaults to `TA_HINTING_RANGE_MIN`.
386 * `hinting-range-max`
387 * : An integer (which must be larger than or equal to the value of
388 * `hinting-range-min`) giving the highest PPEM value used for
389 * autohinting. If this field is not set, it defaults to
390 * `TA_HINTING_RANGE_MAX`.
393 * : An integer (which must be larger than or equal to the value of
394 * `hinting-range-max`) that gives the largest PPEM value at which
395 * hinting is applied. For larger values, hinting is switched off. If
396 * this field is not set, it defaults to `TA_HINTING_LIMIT`. If it is
397 * set to\ 0, no hinting limit is added to the bytecode.
400 * : If this integer is set to\ 1, composite glyphs get separate hints.
401 * This implies adding a special glyph to the font called
402 * ['.ttfautohint'](#the-.ttfautohint-glyph). Setting it to\ 0 (which
403 * is the default), the hints of the composite glyphs' components are
404 * used. Adding hints for composite glyphs increases the size of the
405 * resulting bytecode a lot, but it might deliver better hinting
406 * results. However, this depends on the processed font and must be
407 * checked by inspection.
410 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) to
411 * specify whether native TrueType hinting of the *input font* shall be
412 * applied to all glyphs before passing them to the (internal)
413 * autohinter. The used resolution is the em-size in font units; for
414 * most fonts this is 2048ppem. Use this only if the old hints move or
415 * scale subglyphs independently of the output resolution, for example
416 * some exotic CJK fonts.
418 * `pre-hinting` is a deprecated alias name for this option.
421 * ### Hinting Algorithms
423 * `gray-strong-stem-width`
424 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
425 * specifies whether horizontal stems should be snapped and positioned
426 * to integer pixel values for normal grayscale rendering.
428 * `gdi-cleartype-strong-stem-width`
429 * : An integer (1\ for 'on', which is the default, and 0\ for 'off') that
430 * specifies whether horizontal stems should be snapped and positioned
431 * to integer pixel values for GDI ClearType rendering, this is, the
432 * rasterizer version (as returned by the GETINFO bytecode instruction)
433 * is in the range 36\ <= version <\ 38 and ClearType is enabled.
435 * `dw-cleartype-strong-stem-width`
436 * : An integer (1\ for 'on' and 0\ for 'off', which is the default) that
437 * specifies whether horizontal stems should be snapped and positioned
438 * to integer pixel values for DW ClearType rendering, this is, the
439 * rasterizer version (as returned by the GETINFO bytecode instruction)
440 * is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
443 * `increase-x-height`
444 * : An integer. For PPEM values in the range 6\ <= PPEM
445 * <= `increase-x-height`, round up the font's x\ height much more often
446 * than normally (to use the terminology of TrueType's 'Super Round'
447 * bytecode instruction, the threshold gets increased from 5/8px to
448 * 13/16px). If it is set to\ 0, this feature is switched off. If this
449 * field is not set, it defaults to `TA_INCREASE_X_HEIGHT`. Use this
450 * flag to improve the legibility of small font sizes if necessary.
452 * `x-height-snapping-exceptions`
453 * : A pointer of type `const char*` to a null-terminated string that
454 * gives a list of comma separated PPEM values or value ranges at which
455 * no x\ height snapping shall be applied. A value range has the form
456 * *value*~1~`-`*value*~2~, meaning *value*~1~ <= PPEM <= *value*~2~.
457 * *value*~1~ or *value*~2~ (or both) can be missing; a missing value is
458 * replaced by the beginning or end of the whole interval of valid PPEM
459 * values, respectively. Whitespace is not significant; superfluous
460 * commas are ignored, and ranges must be specified in increasing order.
461 * For example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7,
462 * 9, 10, 11, 12, etc. Consequently, if the supplied argument is `"-"`,
463 * no x\ height snapping takes place at all. The default is the empty
464 * string (`""`), meaning no snapping exceptions.
466 * `windows-compatibility`
467 * : If this integer is set to\ 1, two artificial blue zones are used,
468 * positioned at the `usWinAscent` and `usWinDescent` values (from the
469 * font's `OS/2` table). The idea is to help ttfautohint so that the
470 * hinted glyphs stay within this horizontal stripe since Windows clips
471 * everything falling outside. The default is\ 0.
477 * : A string consisting of four lowercase characters that specifies the
478 * default script for OpenType features. After applying all features
479 * that are handled specially, use this value for the remaining
480 * features. The default value is `"latn"`; if set to `"none"`, no
481 * script is used. Valid values can be found in the header file
482 * `ttfautohint-scripts.h`.
485 * : A string consisting of four lowercase characters that specifies the
486 * default script for glyphs that can't be mapped to a script
487 * automatically. If set to `"none"` (which is the default), no script
488 * is used. Valid values can be found in the header file
489 * `ttfautohint-scripts.h`.
492 * : Set this integer to\ 1 if you want to process a font that ttfautohint
493 * would refuse otherwise because it can't find a single standard
494 * character for any of the supported scripts. ttfautohint then uses a
495 * default (hinting) value for the standard stem width instead of
496 * deriving it from a script's set of standard characters (for the latin
497 * script, one of them is character 'o'). The default value of this
500 * `fallback-stem-width`
501 * : Set the horizontal stem width (hinting) value for all scripts that
502 * lack proper standard characters. The value is given in font units
503 * and must be a positive integer. If not set, or the value is zero,
504 * ttfautohint uses a hard-coded default (50\ units at 2048 units per
505 * EM, and linearly scaled for other UPEM values, for example 24\ units
508 * For symbol fonts (i.e., option `symbol` is given),
509 * `fallback-stem-width` has an effect only if `fallback-script` is set
515 * `ignore-restrictions`
516 * : If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
517 * the ttfautohint library refuses to process the font since a
518 * permission to do that is required from the font's legal owner. In
519 * case you have such a permission you might set the integer argument to
520 * value\ 1 to make ttfautohint handle the font. The default value
524 * : If set to\ 1, ttfautohint creates an SFNT table called `TTFA` and
525 * fills it with information on the parameters used while calling
526 * `TTF_autohint`. The format of the output data resembles the
527 * information at the very beginning of the dump emitted by option
528 * `debug`. The default value is\ 0.
530 * Main use of this option is for font editing purposes. For example,
531 * after a font editor has added some glyphs, a front-end to
532 * `TTF_autohint` can parse `TTFA` and feed the parameters into another
533 * call of `TTF_autohint`. The new glyphs are then hinted while hints
534 * of the old glyphs stay unchanged.
536 * If this option is not set, and the font to be processed contains a
537 * `TTFA` table, it gets removed.
539 * Note that such a `TTFA` table gets ignored by all font rendering
540 * engines. In TrueType Collections, the `TTFA` table is added to the
544 * : If set to\ 1, remove all hints from the font. All other hinting
545 * options are ignored.
550 * * Obviously, it is necessary to have an input and an output data
551 * stream. All other options are optional.
553 * * `hinting-range-min` and `hinting-range-max` specify the range for
554 * which the autohinter generates optimized hinting code. If a PPEM
555 * value is smaller than the value of `hinting-range-min`, hinting still
556 * takes place but the configuration created for `hinting-range-min` is
557 * used. The analogous action is taken for `hinting-range-max`, only
558 * limited by the value given with `hinting-limit`. The font's `gasp`
559 * table is set up to always use grayscale rendering with grid-fitting
560 * for standard hinting, and symmetric grid-fitting and symmetric
561 * smoothing for horizontal subpixel hinting (ClearType).
563 * * ttfautohint can process its own output a second time only if option
564 * `hint-composites` is not set (or if the font doesn't contain
565 * composite glyphs at all). This limitation might change in the
572 TTF_autohint(const char* options
,
586 #endif /* __TTFAUTOHINT_H__ */
588 /* end of ttfautohint.h */