lib/ttfautohint.h

   1 /* ttfautohint.h */
   2
   3 /*
   4  * Copyright (C) 2011-2016 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  */
  14
  15
  16 #ifndef TTFAUTOHINT_H_
  17 #define TTFAUTOHINT_H_
  18
  19 #include <stdarg.h>
  20 #include <stdint.h>
  21
  22 #ifdef __cplusplus
  23 extern "C" {
  24 #endif
  25
  26
  27 /*
  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.
  33  */
  34
  35
  36 /* pandoc-start */
  37
  38 /*
  39  * The ttfautohint API
  40  * ===================
  41  *
  42  * This section documents the single function of the ttfautohint library,
  43  * `TTF_autohint`, together with its callback functions, `TA_Progress_Func`
  44  * and `TA_Info_Func`.  All information has been directly extracted from the
  45  * `ttfautohint.h` header file.
  46  *
  47  */
  48
  49
  50 /*
  51  * Preprocessor Macros and Typedefs
  52  * --------------------------------
  53  *
  54  * Some default values.
  55  *
  56  * ```C
  57  */
  58
  59 #define TA_HINTING_RANGE_MIN 8
  60 #define TA_HINTING_RANGE_MAX 50
  61 #define TA_HINTING_LIMIT 200
  62 #define TA_INCREASE_X_HEIGHT 14
  63
  64 /*
  65  *```
  66  *
  67  * An error type.
  68  *
  69  * ```C
  70  */
  71
  72 typedef int TA_Error;
  73
  74 /*
  75  * ```
  76  *
  77  */
  78
  79
  80 /*
  81  * Callback: `TA_Progress_Func`
  82  * ----------------------------
  83  *
  84  * A callback function to get progress information.  *curr_idx* gives the
  85  * currently processed glyph index; if it is negative, an error has
  86  * occurred.  *num_glyphs* holds the total number of glyphs in the font
  87  * (this value can't be larger than 65535).
  88  *
  89  * *curr_sfnt* gives the current subfont within a TrueType Collection (TTC),
  90  * and *num_sfnts* the total number of subfonts.
  91  *
  92  * If the return value is non-zero, `TTF_autohint` aborts with
  93  * `TA_Err_Canceled`.  Use this for a 'Cancel' button or similar features in
  94  * interactive use.
  95  *
  96  * *progress_data* is a void pointer to user-supplied data.
  97  *
  98  * ```C
  99  */
 100
 101 typedef int
 102 (*TA_Progress_Func)(long curr_idx,
 103                     long num_glyphs,
 104                     long curr_sfnt,
 105                     long num_sfnts,
 106                     void* progress_data);
 107
 108 /*
 109  * ```
 110  *
 111  */
 112
 113
 114 /*
 115  * Callback: `TA_Error_Func`
 116  * -------------------------
 117  *
 118  * A callback function to get error information.
 119  *
 120  * *error* is the value `TTF_autohint` returns.  See file
 121  * `ttfautohint-errors.h` for a list.  Error codes not in this list are
 122  * directly taken from FreeType; see the FreeType header file `fterrdef.h`
 123  * for more.
 124  *
 125  * *error_string*, if non-NULL, is a pointer to an error message that
 126  * represents *error*.
 127  *
 128  * The next three parameters help identify the origin of text string parsing
 129  * errors.  *linenum*, if non-zero, contains the line number.  *line*, if
 130  * non-NULL, is a pointer to the input line that can't be processed.
 131  * *errpos*, if non-NULL, holds a pointer to the position in *line* where
 132  * the problem occurs.
 133  *
 134  * *error_data* is a void pointer to user-supplied data.
 135  *
 136  * ```C
 137  */
 138
 139 typedef void
 140 (*TA_Error_Func)(TA_Error error,
 141                  const char* error_string,
 142                  unsigned int linenum,
 143                  const char* line,
 144                  const char* errpos,
 145                  void* error_data);
 146
 147 /*
 148  * ```
 149  *
 150  */
 151
 152
 153 /*
 154  * Callback: `TA_Info_Func`
 155  * ------------------------
 156  *
 157  * A callback function to access or modify strings in the `name` table; it
 158  * is called in a loop that iterates over all `name` table entries.  If
 159  * defined, [`TA_Info_Post_Func`](#callback-ta_info_post_func) gets executed
 160  * after this loop so that the collected data can be written back to the
 161  * `name` table.
 162  *
 163  * *platform_id*, *encoding_id*, *language_id*, and *name_id* are the
 164  * identifiers of a `name` table entry pointed to by *str* with a length
 165  * pointed to by *str_len* (in bytes; the string has no trailing NULL byte).
 166  * Please refer to the [OpenType specification of the `name` table] for a
 167  * detailed description of the various parameters, in particular which
 168  * encoding is used for a given platform and encoding ID.
 169  *
 170  * [OpenType specification of the `name` table]: http://www.microsoft.com/typography/otspec/name.htm
 171  *
 172  * The string *str* is allocated with `malloc`; the application should
 173  * reallocate the data if necessary, ensuring that the string length doesn't
 174  * exceed 0xFFFF.
 175  *
 176  * *info_data* is a void pointer to user-supplied data.
 177  *
 178  * If an error occurs, return a non-zero value and don't modify *str* and
 179  * *str_len* (such errors are handled as non-fatal).
 180  *
 181  * ```C
 182  */
 183
 184 typedef int
 185 (*TA_Info_Func)(unsigned short platform_id,
 186                 unsigned short encoding_id,
 187                 unsigned short language_id,
 188                 unsigned short name_id,
 189                 unsigned short* str_len,
 190                 unsigned char** str,
 191                 void* info_data);
 192
 193 /*
 194  * ```
 195  *
 196  */
 197
 198
 199 /*
 200  * Callback: `TA_Info_Post_Func`
 201  * -----------------------------
 202  *
 203  * A callback function, giving the application the possibility to access or
 204  * modify strings in the `name` table after
 205  * [`TA_Info_Func`](#callback-ta_info_func) has iterated over all `name`
 206  * table entries.
 207  *
 208  * It is expected that `TA_Info_Func` stores pointers to the `name` table
 209  * entries it wants to access or modify; the only parameter is thus
 210  * *info_data*, which is a void pointer to the user-supplied data already
 211  * provided to `TA_Info_Func`.  Obviously, calling `TA_Info_Post_Func` with
 212  * `TA_Info_Func` undefined has no effect.
 213  *
 214  * The `name` table strings are allocated with `malloc`; the application
 215  * should reallocate the data if necessary, ensuring that no string length
 216  * exceeds 0xFFFF.
 217  *
 218  * If an error occurs, return a non-zero value and don't modify the affected
 219  * string and string length (such errors are handled as non-fatal).
 220  *
 221  * ```C
 222  */
 223
 224 typedef int
 225 (*TA_Info_Post_Func)(void* info_data);
 226
 227 /*
 228  * ```
 229  *
 230  */
 231
 232 /* pandoc-end */
 233
 234
 235 /*
 236  * Error values in addition to the FT_Err_XXX constants from FreeType.
 237  *
 238  * All error values specific to ttfautohint start with `TA_Err_'.
 239  */
 240 #include <ttfautohint-errors.h>
 241
 242
 243 /* pandoc-start */
 244
 245 /*
 246  * Function: `TTF_autohint`
 247  * ------------------------
 248  *
 249  *
 250  * Read a TrueType font, remove existing bytecode (in the SFNT tables
 251  * `prep`, `fpgm`, `cvt `, and `glyf`), and write a new TrueType font with
 252  * new bytecode based on the autohinting of the FreeType library.
 253  *
 254  * It expects a format string *options* and a variable number of arguments,
 255  * depending on the fields in *options*.  The fields are comma separated;
 256  * whitespace within the format string is not significant, a trailing comma
 257  * is ignored.  Fields are parsed from left to right; if a field occurs
 258  * multiple times, the last field's argument wins.  The same is true for
 259  * fields that are mutually exclusive.  Depending on the field, zero or one
 260  * argument is expected.
 261  *
 262  * Note that fields marked as 'not implemented yet' are subject to change.
 263  *
 264  *
 265  * ### I/O
 266  *
 267  * `in-file`
 268  * :   A pointer of type `FILE*` to the data stream of the input font,
 269  *     opened for binary reading.  Mutually exclusive with `in-buffer`.
 270  *
 271  * `in-buffer`
 272  * :   A pointer of type `const char*` to a buffer that contains the input
 273  *     font.  Needs `in-buffer-len`.  Mutually exclusive with `in-file`.
 274  *
 275  * `in-buffer-len`
 276  * :   A value of type `size_t`, giving the length of the input buffer.
 277  *     Needs `in-buffer`.
 278  *
 279  * `out-file`
 280  * :   A pointer of type `FILE*` to the data stream of the output font,
 281  *     opened for binary writing.  Mutually exclusive with `out-buffer`.
 282  *
 283  * `out-buffer`
 284  * :   A pointer of type `char**` to a buffer that contains the output
 285  *     font.  Needs `out-buffer-len`.  Mutually exclusive with `out-file`.
 286  *     Deallocate the memory with `free`.
 287  *
 288  * `out-buffer-len`
 289  * :   A pointer of type `size_t*` to a value giving the length of the
 290  *     output buffer.  Needs `out-buffer`.
 291  *
 292  * `control-file`
 293  * :   A pointer of type `FILE*` to the data stream of control instructions.
 294  *     Mutually exclusive with `control-buffer`.
 295  *
 296  *     See '[Control Instructions](#control-instructions)' for the syntax
 297  *     used in such a file or buffer.
 298  *
 299  * `control-buffer`
 300  * :   A pointer of type `const char*` to a buffer that contains control
 301  *     instructions.  Needs `control-buffer-len`.  Mutually exclusive with
 302  *     `control-file`.
 303  *
 304  * `control-buffer-len`
 305  * :   A value of type `size_t`, giving the length of the control
 306  *     instructions buffer.  Needs `control-buffer`.
 307  *
 308  *
 309  * ### Messages and Callbacks
 310  *
 311  * `progress-callback`
 312  * :   A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
 313  *     specifying a callback function for progress reports.  This function
 314  *     gets called after a single glyph has been processed.  If this field
 315  *     is not set or set to NULL, no progress callback function is used.
 316  *
 317  * `progress-callback-data`
 318  * :   A pointer of type `void*` to user data that is passed to the
 319  *     progress callback function.
 320  *
 321  * `error-string`
 322  * :   A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
 323  *     that verbally describes the error code.  You must not change the
 324  *     returned value.
 325  *
 326  * `error-callback`
 327  * :   A pointer of type [`TA_Error_Func`](#callback-ta_error_func),
 328  *     specifying a callback function for error messages.  This function
 329  *     gets called right before `TTF_autohint` exits.  If this field is not
 330  *     set or set to NULL, no error callback function is used.
 331  *
 332  *     Use it as a more sophisticated alternative to `error-string`.
 333  *
 334  * `error-callback-data`
 335  * :   A point of type `void*` to user data that is passed to the error
 336  *     callback function.
 337  *
 338  * `info-callback`
 339  * :   A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
 340  *     specifying a callback function for manipulating the `name` table.
 341  *     This function gets called for each `name` table entry.  If not set or
 342  *     set to NULL, `TA_Info_Func` is not called.
 343  *
 344  * `info-post-callback`
 345  * :   A pointer of type [`TA_Info_Post_Func`](#callback-ta_info_post_func),
 346  *     specifying a callback function for manipulating the `name` table.  It
 347  *     is called after the function specified with `info-callback` has
 348  *     iterated over all `name` table entries.  If not set or set to NULL,
 349  *     `TA_Info_Post_Func` is not called.
 350  *
 351  * `info-callback-data`
 352  * :   A pointer of type `void*` to user data that is passed to the info
 353  *     callback functions.
 354  *
 355  * `debug`
 356  * :   If this integer is set to\ 1, lots of debugging information is print
 357  *     to stderr.  The default value is\ 0.
 358  *
 359  *
 360  * ### General Hinting Options
 361  *
 362  * `hinting-range-min`
 363  * :   An integer (which must be larger than or equal to\ 2) giving the
 364  *     lowest PPEM value used for autohinting.  If this field is not set, it
 365  *     defaults to `TA_HINTING_RANGE_MIN`.
 366  *
 367  * `hinting-range-max`
 368  * :   An integer (which must be larger than or equal to the value of
 369  *     `hinting-range-min`) giving the highest PPEM value used for
 370  *     autohinting.  If this field is not set, it defaults to
 371  *     `TA_HINTING_RANGE_MAX`.
 372  *
 373  * `hinting-limit`
 374  * :   An integer (which must be larger than or equal to the value of
 375  *     `hinting-range-max`) that gives the largest PPEM value at which
 376  *     hinting is applied.  For larger values, hinting is switched off.  If
 377  *     this field is not set, it defaults to `TA_HINTING_LIMIT`.  If it is
 378  *     set to\ 0, no hinting limit is added to the bytecode.
 379  *
 380  * `hint-composites`
 381  * :   If this integer is set to\ 1, composite glyphs get separate hints.
 382  *     This implies adding a special glyph to the font called
 383  *     ['.ttfautohint'](#the-.ttfautohint-glyph).  Setting it to\ 0 (which
 384  *     is the default), the hints of the composite glyphs' components are
 385  *     used.  Adding hints for composite glyphs increases the size of the
 386  *     resulting bytecode a lot, but it might deliver better hinting
 387  *     results.  However, this depends on the processed font and must be
 388  *     checked by inspection.
 389  *
 390  * `adjust-subglyphs`
 391  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) to
 392  *     specify whether native TrueType hinting of the *input font* shall be
 393  *     applied to all glyphs before passing them to the (internal)
 394  *     autohinter.  The used resolution is the em-size in font units; for
 395  *     most fonts this is 2048ppem.  Use this only if the old hints move or
 396  *     scale subglyphs independently of the output resolution, for example
 397  *     some exotic CJK fonts.
 398  *
 399  *     `pre-hinting` is a deprecated alias name for this option.
 400  *
 401  *
 402  * ### Hinting Algorithms
 403  *
 404  * `gray-strong-stem-width`
 405  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 406  *     specifies whether horizontal stems should be snapped and positioned
 407  *     to integer pixel values for normal grayscale rendering.
 408  *
 409  * `gdi-cleartype-strong-stem-width`
 410  * :   An integer (1\ for 'on', which is the default, and 0\ for 'off') that
 411  *     specifies whether horizontal stems should be snapped and positioned
 412  *     to integer pixel values for GDI ClearType rendering, this is, the
 413  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 414  *     is in the range 36\ <= version <\ 38 and ClearType is enabled.
 415  *
 416  * `dw-cleartype-strong-stem-width`
 417  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 418  *     specifies whether horizontal stems should be snapped and positioned
 419  *     to integer pixel values for DW ClearType rendering, this is, the
 420  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 421  *     is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
 422  *     also.
 423  *
 424  * `increase-x-height`
 425  * :   An integer.  For PPEM values in the range 6\ <= PPEM
 426  *     <= `increase-x-height`, round up the font's x\ height much more often
 427  *     than normally (to use the terminology of TrueType's 'Super Round'
 428  *     bytecode instruction, the threshold gets increased from 5/8px to
 429  *     13/16px).  If it is set to\ 0, this feature is switched off.  If this
 430  *     field is not set, it defaults to `TA_INCREASE_X_HEIGHT`.  Use this
 431  *     flag to improve the legibility of small font sizes if necessary.
 432  *
 433  * `x-height-snapping-exceptions`
 434  * :   A pointer of type `const char*` to a null-terminated string that
 435  *     gives a list of comma separated PPEM values or value ranges at which
 436  *     no x\ height snapping shall be applied.  A value range has the form
 437  *     *value*~1~`-`*value*~2~, meaning *value*~1~ <= PPEM <= *value*~2~.
 438  *     *value*~1~ or *value*~2~ (or both) can be missing; a missing value is
 439  *     replaced by the beginning or end of the whole interval of valid PPEM
 440  *     values, respectively.  Whitespace is not significant; superfluous
 441  *     commas are ignored, and ranges must be specified in increasing order.
 442  *     For example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7,
 443  *     9, 10, 11, 12, etc.  Consequently, if the supplied argument is `"-"`,
 444  *     no x\ height snapping takes place at all.  The default is the empty
 445  *     string (`""`), meaning no snapping exceptions.
 446  *
 447  * `windows-compatibility`
 448  * :   If this integer is set to\ 1, two artificial blue zones are used,
 449  *     positioned at the `usWinAscent` and `usWinDescent` values (from the
 450  *     font's `OS/2` table).  The idea is to help ttfautohint so that the
 451  *     hinted glyphs stay within this horizontal stripe since Windows clips
 452  *     everything falling outside.  The default is\ 0.
 453  *
 454  *
 455  * ### Scripts
 456  *
 457  * `default-script`
 458  * :   A string consisting of four lowercase characters that specifies the
 459  *     default script for OpenType features.  After applying all features
 460  *     that are handled specially, use this value for the remaining
 461  *     features.  The default value is `"latn"`; if set to `"none"`, no
 462  *     script is used.  Valid values can be found in the header file
 463  *     `ttfautohint-scripts.h`.
 464  *
 465  * `fallback-script`
 466  * :   A string consisting of four lowercase characters, specifying the
 467  *     default script for glyphs that can't be mapped to a script
 468  *     automatically.  By default, such glyphs are hinted; if option
 469  *     `fallback-scaling` is set, they are scaled only instead.  Valid
 470  *     values can be found in the header file `ttfautohint-scripts.h`.
 471  *
 472  *     Default value is `"none"`, which means hinting without using a
 473  *     script's blue zones if `fallback-scaling` isn't set.  If
 474  *     `fallback_scaling` is set, value `"none"` implies no hinting for
 475  *     unmapped glyphs.
 476  *
 477  * `fallback-scaling`
 478  * :   Set this integer to\ 1 if glyphs handled by the fallback script
 479  *     should be scaled only with the fallback script's scaling value,
 480  *     instead of being hinted with the fallback script's hinting
 481  *     parameters.
 482  *
 483  * `symbol`
 484  * :   Set this integer to\ 1 if you want to process a font that ttfautohint
 485  *     would refuse otherwise because it can't find a single standard
 486  *     character for any of the supported scripts.  ttfautohint then uses a
 487  *     default (hinting) value for the standard stem width instead of
 488  *     deriving it from a script's set of standard characters (for the latin
 489  *     script, one of them is character 'o').  The default value of this
 490  *     option is\ 0.
 491  *
 492  * `fallback-stem-width`
 493  * :   Set the horizontal stem width (hinting) value for all scripts that
 494  *     lack proper standard characters.  The value is given in font units
 495  *     and must be a positive integer.  If not set, or the value is zero,
 496  *     ttfautohint uses a hard-coded default (50\ units at 2048 units per
 497  *     EM, and linearly scaled for other UPEM values, for example 24\ units
 498  *     at 1000 UPEM).
 499  *
 500  *     For symbol fonts (i.e., option `symbol` is given),
 501  *     `fallback-stem-width` has an effect only if `fallback-script` is set
 502  *     also.
 503  *
 504  *
 505  * ### Miscellaneous
 506  *
 507  * `ignore-restrictions`
 508  * :   If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
 509  *     the ttfautohint library refuses to process the font since a
 510  *     permission to do that is required from the font's legal owner.  In
 511  *     case you have such a permission you might set the integer argument to
 512  *     value\ 1 to make ttfautohint handle the font.  The default value
 513  *     is\ 0.
 514  *
 515  * `TTFA-info`
 516  * :   If set to\ 1, ttfautohint creates an SFNT table called `TTFA` and
 517  *     fills it with information on the parameters used while calling
 518  *     `TTF_autohint`.  The format of the output data resembles the
 519  *     information at the very beginning of the dump emitted by option
 520  *     `debug`.  The default value is\ 0.
 521  *
 522  *     Main use of this option is for font editing purposes.  For example,
 523  *     after a font editor has added some glyphs, a front-end to
 524  *     `TTF_autohint` can parse `TTFA` and feed the parameters into another
 525  *     call of `TTF_autohint`.  The new glyphs are then hinted while hints
 526  *     of the old glyphs stay unchanged.
 527  *
 528  *     If this option is not set, and the font to be processed contains a
 529  *     `TTFA` table, it gets removed.
 530  *
 531  *     Note that such a `TTFA` table gets ignored by all font rendering
 532  *     engines.  In TrueType Collections, the `TTFA` table is added to the
 533  *     first subfont.
 534  *
 535  * `dehint`
 536  * :   If set to\ 1, remove all hints from the font.  All other hinting
 537  *     options are ignored.
 538  *
 539  * `epoch`
 540  * :   An integer of type `unsigned long long`, defined as the number of
 541  *     seconds (excluding leap seconds) since 01 Jan 1970 00:00:00 UTC.  If
 542  *     set, or if the value is not equal to `ULLONG_MAX`, this epoch gets
 543  *     used instead of the current date and time for the 'modification time'
 544  *     field in the TTF header.  Use this to get [reproducible
 545  *     builds](https://reproducible-builds.org/).
 546  *
 547  *
 548  * ### Remarks
 549  *
 550  *   * Obviously, it is necessary to have an input and an output data
 551  *     stream.  All other options are optional.
 552  *
 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).
 562  *
 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
 566  *     future.
 567  *
 568  * ```C
 569  */
 570
 571 TA_Error
 572 TTF_autohint(const char* options,
 573              ...);
 574
 575 /*
 576  * ```
 577  *
 578  */
 579
 580 /* pandoc-end */
 581
 582 #ifdef __cplusplus
 583 } /* extern "C" */
 584 #endif
 585
 586 #endif /* TTFAUTOHINT_H_ */
 587
 588 /* end of ttfautohint.h */