lib/ttfautohint.h

   1 /* ttfautohint.h */
   2
   3 /*
   4  * Copyright (C) 2011-2014 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
  21 #ifdef __cplusplus
  22 extern "C" {
  23 #endif
  24
  25
  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  */
  33
  34
  35 /* pandoc-start */
  36
  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  */
  47
  48
  49 /*
  50  * Preprocessor Macros and Typedefs
  51  * --------------------------------
  52  *
  53  * Some default values.
  54  *
  55  * ```C
  56  */
  57
  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
  62
  63 /*
  64  *```
  65  *
  66  * An error type.
  67  *
  68  * ```C
  69  */
  70
  71 typedef int TA_Error;
  72
  73 /*
  74  * ```
  75  *
  76  */
  77
  78
  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  */
  99
 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);
 106
 107 /*
 108  * ```
 109  *
 110  */
 111
 112
 113 /*
 114  * Callback: `TA_Error_Func`
 115  * -------------------------
 116  *
 117  * A callback function to get error information.
 118  *
 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.
 123  *
 124  * *error_string*, if non-NULL, is a pointer to an error message that
 125  * represents *error*.
 126  *
 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.
 132  *
 133  * *error_data* is a void pointer to user-supplied data.
 134  *
 135  * ```C
 136  */
 137
 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);
 145
 146 /*
 147  * ```
 148  *
 149  */
 150
 151
 152 /*
 153  * Callback: `TA_Info_Func`
 154  * ------------------------
 155  *
 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.
 163  *
 164  * [OpenType specification of the `name` table]: http://www.microsoft.com/typography/otspec/name.htm
 165  *
 166  * The string *str* is allocated with `malloc`; the application should
 167  * reallocate the data if necessary, ensuring that the string length doesn't
 168  * exceed 0xFFFF.
 169  *
 170  * *info_data* is a void pointer to user-supplied data.
 171  *
 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).
 174  *
 175  * ```C
 176  */
 177
 178 typedef int
 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,
 184                 unsigned char** str,
 185                 void* info_data);
 186
 187 /*
 188  * ```
 189  *
 190  */
 191
 192 /* pandoc-end */
 193
 194
 195 /*
 196  * Error values in addition to the FT_Err_XXX constants from FreeType.
 197  *
 198  * All error values specific to ttfautohint start with `TA_Err_'.
 199  */
 200 #include <ttfautohint-errors.h>
 201
 202
 203 /* pandoc-start */
 204
 205 /*
 206  * Function: `TTF_autohint`
 207  * ------------------------
 208  *
 209  *
 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.
 213  *
 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.
 221  *
 222  * Note that fields marked as 'not implemented yet' are subject to change.
 223  *
 224  *
 225  * ### I/O
 226  *
 227  * `in-file`
 228  * :   A pointer of type `FILE*` to the data stream of the input font,
 229  *     opened for binary reading.  Mutually exclusive with `in-buffer`.
 230  *
 231  * `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`.
 234  *
 235  * `in-buffer-len`
 236  * :   A value of type `size_t`, giving the length of the input buffer.
 237  *     Needs `in-buffer`.
 238  *
 239  * `out-file`
 240  * :   A pointer of type `FILE*` to the data stream of the output font,
 241  *     opened for binary writing.  Mutually exclusive with `out-buffer`.
 242  *
 243  * `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`.
 247  *
 248  * `out-buffer-len`
 249  * :   A pointer of type `size_t*` to a value giving the length of the
 250  *     output buffer.  Needs `out-buffer`.
 251  *
 252  *
 253  * ### Messages and Callbacks
 254  *
 255  * `progress-callback`
 256  * :   A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
 257  *     specifying a callback function for progress reports.  This function
 258  *     gets called after a single glyph has been processed.  If this field
 259  *     is not set or set to NULL, no progress callback function is used.
 260  *
 261  * `progress-callback-data`
 262  * :   A pointer of type `void*` to user data that is passed to the
 263  *     progress callback function.
 264  *
 265  * `error-string`
 266  * :   A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
 267  *     that verbally describes the error code.  You must not change the
 268  *     returned value.
 269  *
 270  * `error-callback`
 271  * :   A pointer of type [`TA_Error_Func`](#callback-ta_error_func),
 272  *     specifying a callback function for error messages.  This function
 273  *     gets called right before `TTF_autohint` exits.  If this field is not
 274  *     set or set to NULL, no error callback function is used.
 275  *
 276  *     Use it as a more sophisticated alternative to `error-string`.
 277  *
 278  * `error-callback-data`
 279  * :   A point of type `void*` to user data that is passed to the error
 280  *     callback function.
 281  *
 282  * `info-callback`
 283  * :   A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
 284  *     specifying a callback function for manipulating the `name` table.
 285  *     This function gets called for each `name` table entry.  If not set or
 286  *     set to NULL, the table data stays unmodified.
 287  *
 288  * `info-callback-data`
 289  * :   A pointer of type `void*` to user data that is passed to the info
 290  *     callback function.
 291  *
 292  * `debug`
 293  * :   If this integer is set to\ 1, lots of debugging information is print
 294  *     to stderr.  The default value is\ 0.
 295  *
 296  *
 297  * ### General Hinting Options
 298  *
 299  * `hinting-range-min`
 300  * :   An integer (which must be larger than or equal to\ 2) giving the
 301  *     lowest PPEM value used for autohinting.  If this field is not set, it
 302  *     defaults to `TA_HINTING_RANGE_MIN`.
 303  *
 304  * `hinting-range-max`
 305  * :   An integer (which must be larger than or equal to the value of
 306  *     `hinting-range-min`) giving the highest PPEM value used for
 307  *     autohinting.  If this field is not set, it defaults to
 308  *     `TA_HINTING_RANGE_MAX`.
 309  *
 310  * `hinting-limit`
 311  * :   An integer (which must be larger than or equal to the value of
 312  *     `hinting-range-max`) that gives the largest PPEM value at which
 313  *     hinting is applied.  For larger values, hinting is switched off.  If
 314  *     this field is not set, it defaults to `TA_HINTING_LIMIT`.  If it is
 315  *     set to\ 0, no hinting limit is added to the bytecode.
 316  *
 317  * `hint-composites`
 318  * :   If this integer is set to\ 1, composite glyphs get separate hints.
 319  *     This implies adding a special glyph to the font called
 320  *     ['.ttfautohint'](#the-.ttfautohint-glyph).  Setting it to\ 0 (which
 321  *     is the default), the hints of the composite glyphs' components are
 322  *     used.  Adding hints for composite glyphs increases the size of the
 323  *     resulting bytecode a lot, but it might deliver better hinting
 324  *     results.  However, this depends on the processed font and must be
 325  *     checked by inspection.
 326  *
 327  * `adjust-subglyphs`
 328  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) to
 329  *     specify whether native TrueType hinting of the *input font* shall be
 330  *     applied to all glyphs before passing them to the (internal)
 331  *     autohinter.  The used resolution is the em-size in font units; for
 332  *     most fonts this is 2048ppem.  Use this only if the old hints move or
 333  *     scale subglyphs independently of the output resolution, for example
 334  *     some exotic CJK fonts.
 335  *
 336  *     `pre-hinting` is a deprecated alias name for this option.
 337  *
 338  *
 339  * ### Hinting Algorithms
 340  *
 341  * `gray-strong-stem-width`
 342  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 343  *     specifies whether horizontal stems should be snapped and positioned
 344  *     to integer pixel values for normal grayscale rendering.
 345  *
 346  * `gdi-cleartype-strong-stem-width`
 347  * :   An integer (1\ for 'on', which is the default, and 0\ for 'off') that
 348  *     specifies whether horizontal stems should be snapped and positioned
 349  *     to integer pixel values for GDI ClearType rendering, this is, the
 350  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 351  *     is in the range 36\ <= version <\ 38 and ClearType is enabled.
 352  *
 353  * `dw-cleartype-strong-stem-width`
 354  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 355  *     specifies whether horizontal stems should be snapped and positioned
 356  *     to integer pixel values for DW ClearType rendering, this is, the
 357  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 358  *     is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
 359  *     also.
 360  *
 361  * `increase-x-height`
 362  * :   An integer.  For PPEM values in the range 6\ <= PPEM <=\
 363  *     `increase-x-height`, round up the font's x\ height much more often
 364  *     than normally (to use the terminology of TrueType's 'Super Round'
 365  *     bytecode instruction, the threshold gets increased from 5/8px to
 366  *     13/16px).  If it is set to\ 0, this feature is switched off.  If this
 367  *     field is not set, it defaults to `TA_INCREASE_X_HEIGHT`.  Use this
 368  *     flag to improve the legibility of small font sizes if necessary.
 369  *
 370  * `x-height-snapping-exceptions`
 371  * :   A pointer of type `const char*` to a null-terminated string that
 372  *     gives a list of comma separated PPEM values or value ranges at which
 373  *     no x\ height snapping shall be applied.  A value range has the form
 374  *     *value1*`-`*value2*, meaning *value1* <= PPEM <= *value2*.  *value1*
 375  *     or *value2* (or both) can be missing; a missing value is replaced by
 376  *     the beginning or end of the whole interval of valid PPEM values,
 377  *     respectively.  Whitespace is not significant; superfluous commas are
 378  *     ignored, and ranges must be specified in increasing order.  For
 379  *     example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7, 9,
 380  *     10, 11, 12, etc.  Consequently, if the supplied argument is `"-"`, no
 381  *     x\ height snapping takes place at all.  The default is the empty
 382  *     string (`""`), meaning no snapping exceptions.
 383  *
 384  * `windows-compatibility`
 385  * :   If this integer is set to\ 1, two artificial blue zones are used,
 386  *     positioned at the `usWinAscent` and `usWinDescent` values (from the
 387  *     font's `OS/2` table).  The idea is to help ttfautohint so that the
 388  *     hinted glyphs stay within this horizontal stripe since Windows clips
 389  *     everything falling outside.  The default is\ 0.
 390  *
 391  *
 392  * ### Scripts
 393  *
 394  * `default-script`
 395  * :   A string consisting of four lowercase characters that specifies the
 396  *     default script for OpenType features.  After applying all features
 397  *     that are handled specially, use this value for the remaining
 398  *     features.  The default value is `"latn"`; if set to `"none"`, no
 399  *     script is used.  Valid values can be found in the header file
 400  *     `ttfautohint-scripts.h`.
 401  *
 402  * `fallback-script`
 403  * :   A string consisting of four lowercase characters that specifies the
 404  *     default script for glyphs that can't be mapped to a script
 405  *     automatically.  If set to `"none"` (which is the default), no script
 406  *     is used.  Valid values can be found in the header file
 407  *     `ttfautohint-scripts.h`.
 408  *
 409  * `symbol`
 410  * :   Set this integer to\ 1 if you want to process a font that ttfautohint
 411  *     would refuse otherwise because it can't find a single standard
 412  *     character for any of the supported scripts.  ttfautohint then uses a
 413  *     default (hinting) value for the standard stem width instead of
 414  *     deriving it from a script's set of standard characters (for the latin
 415  *     script, one of them is character 'o').  The default value of this
 416  *     option is\ 0.
 417  *
 418  * `fallback-stem-width`
 419  * :   Set the horizontal stem width (hinting) value for all scripts that
 420  *     lack proper standard characters.  The value is given in font units
 421  *     and must be a positive integer.  If not set, or the value is zero,
 422  *     ttfautohint uses a hard-coded default (50\ units at 2048 units per
 423  *     EM, and linearly scaled for other UPEM values, for example 24\ units
 424  *     at 1000 UPEM).
 425  *
 426  *     For symbol fonts (i.e., option `symbol` is given),
 427  *     `fallback-stem-width` has an effect only if `fallback-script` is set
 428  *     also.
 429  *
 430  *
 431  * ### Miscellaneous
 432  *
 433  * `ignore-restrictions`
 434  * :   If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
 435  *     the ttfautohint library refuses to process the font since a
 436  *     permission to do that is required from the font's legal owner.  In
 437  *     case you have such a permission you might set the integer argument to
 438  *     value\ 1 to make ttfautohint handle the font.  The default value
 439  *     is\ 0.
 440  *
 441  * `dehint`
 442  * :   If set to\ 1, remove all hints from the font.  All other hinting
 443  *     options are ignored.
 444  *
 445  *
 446  * ### Remarks
 447  *
 448  *   * Obviously, it is necessary to have an input and an output data
 449  *     stream.  All other options are optional.
 450  *
 451  *   * `hinting-range-min` and `hinting-range-max` specify the range for
 452  *     which the autohinter generates optimized hinting code.  If a PPEM
 453  *     value is smaller than the value of `hinting-range-min`, hinting still
 454  *     takes place but the configuration created for `hinting-range-min` is
 455  *     used.  The analogous action is taken for `hinting-range-max`, only
 456  *     limited by the value given with `hinting-limit`.  The font's `gasp`
 457  *     table is set up to always use grayscale rendering with grid-fitting
 458  *     for standard hinting, and symmetric grid-fitting and symmetric
 459  *     smoothing for horizontal subpixel hinting (ClearType).
 460  *
 461  *   * ttfautohint can process its own output a second time only if option
 462  *     `hint-composites` is not set (or if the font doesn't contain
 463  *     composite glyphs at all).  This limitation might change in the
 464  *     future.
 465  *
 466  * ```C
 467  */
 468
 469 TA_Error
 470 TTF_autohint(const char* options,
 471              ...);
 472
 473 /*
 474  * ```
 475  *
 476  */
 477
 478 /* pandoc-end */
 479
 480 #ifdef __cplusplus
 481 } /* extern "C" */
 482 #endif
 483
 484 #endif /* __TTFAUTOHINT_H__ */
 485
 486 /* end of ttfautohint.h */