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_Info_Func`
 115  * ------------------------
 116  *
 117  * A callback function to manipulate strings in the `name` table.
 118  * *platform_id*, *encoding_id*, *language_id*, and *name_id* are the
 119  * identifiers of a `name` table entry pointed to by *str* with a length
 120  * pointed to by *str_len* (in bytes; the string has no trailing NULL byte).
 121  * Please refer to the [OpenType specification] for a detailed description
 122  * of the various parameters, in particular which encoding is used for a
 123  * given platform and encoding ID.
 124  *
 125  * [OpenType specification]: http://www.microsoft.com/typography/otspec/name.htm
 126  *
 127  * The string *str* is allocated with `malloc`; the application should
 128  * reallocate the data if necessary, ensuring that the string length doesn't
 129  * exceed 0xFFFF.
 130  *
 131  * *info_data* is a void pointer to user-supplied data.
 132  *
 133  * If an error occurs, return a non-zero value and don't modify *str* and
 134  * *str_len* (such errors are handled as non-fatal).
 135  *
 136  * ```C
 137  */
 138
 139 typedef int
 140 (*TA_Info_Func)(unsigned short platform_id,
 141                 unsigned short encoding_id,
 142                 unsigned short language_id,
 143                 unsigned short name_id,
 144                 unsigned short* str_len,
 145                 unsigned char** str,
 146                 void* info_data);
 147
 148 /*
 149  * ```
 150  *
 151  */
 152
 153 /* pandoc-end */
 154
 155
 156 /*
 157  * Error values in addition to the FT_Err_XXX constants from FreeType.
 158  *
 159  * All error values specific to ttfautohint start with `TA_Err_'.
 160  */
 161 #include <ttfautohint-errors.h>
 162
 163
 164 /* pandoc-start */
 165
 166 /*
 167  * Function: `TTF_autohint`
 168  * ------------------------
 169  *
 170  *
 171  * Read a TrueType font, remove existing bytecode (in the SFNT tables
 172  * `prep`, `fpgm`, `cvt `, and `glyf`), and write a new TrueType font with
 173  * new bytecode based on the autohinting of the FreeType library.
 174  *
 175  * It expects a format string *options* and a variable number of arguments,
 176  * depending on the fields in *options*.  The fields are comma separated;
 177  * whitespace within the format string is not significant, a trailing comma
 178  * is ignored.  Fields are parsed from left to right; if a field occurs
 179  * multiple times, the last field's argument wins.  The same is true for
 180  * fields that are mutually exclusive.  Depending on the field, zero or one
 181  * argument is expected.
 182  *
 183  * Note that fields marked as 'not implemented yet' are subject to change.
 184  *
 185  *
 186  * ### I/O
 187  *
 188  * `in-file`
 189  * :   A pointer of type `FILE*` to the data stream of the input font,
 190  *     opened for binary reading.  Mutually exclusive with `in-buffer`.
 191  *
 192  * `in-buffer`
 193  * :   A pointer of type `const char*` to a buffer that contains the input
 194  *     font.  Needs `in-buffer-len`.  Mutually exclusive with `in-file`.
 195  *
 196  * `in-buffer-len`
 197  * :   A value of type `size_t`, giving the length of the input buffer.
 198  *     Needs `in-buffer`.
 199  *
 200  * `out-file`
 201  * :   A pointer of type `FILE*` to the data stream of the output font,
 202  *     opened for binary writing.  Mutually exclusive with `out-buffer`.
 203  *
 204  * `out-buffer`
 205  * :   A pointer of type `char**` to a buffer that contains the output
 206  *     font.  Needs `out-buffer-len`.  Mutually exclusive with `out-file`.
 207  *     Deallocate the memory with `free`.
 208  *
 209  * `out-buffer-len`
 210  * :   A pointer of type `size_t*` to a value giving the length of the
 211  *     output buffer.  Needs `out-buffer`.
 212  *
 213  *
 214  * ### Messages and Callbacks
 215  *
 216  * `progress-callback`
 217  * :   A pointer of type [`TA_Progress_Func`](#callback-ta_progress_func),
 218  *     specifying a callback function for progress reports.  This function
 219  *     gets called after a single glyph has been processed.  If this field
 220  *     is not set or set to NULL, no progress callback function is used.
 221  *
 222  * `progress-callback-data`
 223  * :   A pointer of type `void*` to user data that is passed to the
 224  *     progress callback function.
 225  *
 226  * `error-string`
 227  * :   A pointer of type `unsigned char**` to a string (in UTF-8 encoding)
 228  *     that verbally describes the error code.  You must not change the
 229  *     returned value.
 230  *
 231  * `info-callback`
 232  * :   A pointer of type [`TA_Info_Func`](#callback-ta_info_func),
 233  *     specifying a callback function for manipulating the `name` table.
 234  *     This function gets called for each `name` table entry.  If not set or
 235  *     set to NULL, the table data stays unmodified.
 236  *
 237  * `info-callback-data`
 238  * :   A pointer of type `void*` to user data that is passed to the info
 239  *     callback function.
 240  *
 241  * `debug`
 242  * :   If this integer is set to\ 1, lots of debugging information is print
 243  *     to stderr.  The default value is\ 0.
 244  *
 245  *
 246  * ### General Hinting Options
 247  *
 248  * `hinting-range-min`
 249  * :   An integer (which must be larger than or equal to\ 2) giving the
 250  *     lowest PPEM value used for autohinting.  If this field is not set, it
 251  *     defaults to `TA_HINTING_RANGE_MIN`.
 252  *
 253  * `hinting-range-max`
 254  * :   An integer (which must be larger than or equal to the value of
 255  *     `hinting-range-min`) giving the highest PPEM value used for
 256  *     autohinting.  If this field is not set, it defaults to
 257  *     `TA_HINTING_RANGE_MAX`.
 258  *
 259  * `hinting-limit`
 260  * :   An integer (which must be larger than or equal to the value of
 261  *     `hinting-range-max`) that gives the largest PPEM value at which
 262  *     hinting is applied.  For larger values, hinting is switched off.  If
 263  *     this field is not set, it defaults to `TA_HINTING_LIMIT`.  If it is
 264  *     set to\ 0, no hinting limit is added to the bytecode.
 265  *
 266  * `hint-composites`
 267  * :   If this integer is set to\ 1, composite glyphs get separate hints.
 268  *     This implies adding a special glyph to the font called
 269  *     ['.ttfautohint'](#the-.ttfautohint-glyph).  Setting it to\ 0 (which
 270  *     is the default), the hints of the composite glyphs' components are
 271  *     used.  Adding hints for composite glyphs increases the size of the
 272  *     resulting bytecode a lot, but it might deliver better hinting
 273  *     results.  However, this depends on the processed font and must be
 274  *     checked by inspection.
 275  *
 276  * `pre-hinting`
 277  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) to
 278  *     specify whether native TrueType hinting shall be applied to all
 279  *     glyphs before passing them to the (internal) autohinter.  The used
 280  *     resolution is the em-size in font units; for most fonts this is
 281  *     2048ppem.  Use this if the hints move or scale subglyphs
 282  *     independently of the output resolution.
 283  *
 284  *
 285  * ### Hinting Algorithms
 286  *
 287  * `gray-strong-stem-width`
 288  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 289  *     specifies whether horizontal stems should be snapped and positioned
 290  *     to integer pixel values for normal grayscale rendering.
 291  *
 292  * `gdi-cleartype-strong-stem-width`
 293  * :   An integer (1\ for 'on', which is the default, and 0\ for 'off') that
 294  *     specifies whether horizontal stems should be snapped and positioned
 295  *     to integer pixel values for GDI ClearType rendering, this is, the
 296  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 297  *     is in the range 36\ <= version <\ 38 and ClearType is enabled.
 298  *
 299  * `dw-cleartype-strong-stem-width`
 300  * :   An integer (1\ for 'on' and 0\ for 'off', which is the default) that
 301  *     specifies whether horizontal stems should be snapped and positioned
 302  *     to integer pixel values for DW ClearType rendering, this is, the
 303  *     rasterizer version (as returned by the GETINFO bytecode instruction)
 304  *     is >=\ 38, ClearType is enabled, and subpixel positioning is enabled
 305  *     also.
 306  *
 307  * `increase-x-height`
 308  * :   An integer.  For PPEM values in the range 6\ <= PPEM
 309  *     <=\ `increase-x-height`, round up the font's x\ height much more often
 310  *     than normally.  If it is set to\ 0, this feature is switched off.  If
 311  *     this field is not set, it defaults to `TA_INCREASE_X_HEIGHT`.  Use
 312  *     this flag to improve the legibility of small font sizes if necessary.
 313  *
 314  * `x-height-snapping-exceptions`
 315  * :   A pointer of type `const char*` to a null-terminated string that
 316  *     gives a list of comma separated PPEM values or value ranges at which
 317  *     no x-height snapping shall be applied.  A value range has the form
 318  *     *value1*`-`*value2*, meaning *value1* <= PPEM <= *value2*.  *value1*
 319  *     or *value2* (or both) can be missing; a missing value is replaced by
 320  *     the beginning or end of the whole interval of valid PPEM values,
 321  *     respectively.  Whitespace is not significant; superfluous commas are
 322  *     ignored, and ranges must be specified in increasing order.  For
 323  *     example, the string `"3, 5-7, 9-"` means the values 3, 5, 6, 7, 9,
 324  *     10, 11, 12, etc.  Consequently, if the supplied argument is `"-"`, no
 325  *     x-height snapping takes place at all.  The default is the empty
 326  *     string (`""`), meaning no snapping exceptions.
 327  *
 328  * `windows-compatibility`
 329  * :   If this integer is set to\ 1, two artificial blue zones are used,
 330  *     positioned at the `usWinAscent` and `usWinDescent` values (from the
 331  *     font's `OS/2` table).  The idea is to help ttfautohint so that the
 332  *     hinted glyphs stay within this horizontal stripe since Windows clips
 333  *     everything falling outside.  The default is\ 0.
 334  *
 335  *
 336  * ### Scripts
 337  *
 338  * `fallback-script`
 339  * :   A string consisting of four lowercase characters that specifies the
 340  *     default script for glyphs which can't be mapped to a script
 341  *     automatically.  If set to `"none"` (which is the default), no script
 342  *     is used.  Valid values can be found in the header file
 343  *     `ttfautohint-scripts.h`.
 344  *
 345  * `symbol`
 346  * :   Set this integer to\ 1 if you want to process a font that lacks the
 347  *     characters of a supported script, for example, a symbol font.
 348  *     ttfautohint then uses default values for the standard stem width and
 349  *     height instead of deriving these values from a script's key character
 350  *     (for the latin script, it is character 'o').  The default value
 351  *     is\ 0.
 352  *
 353  *
 354  * ### Miscellaneous
 355  *
 356  * `ignore-restrictions`
 357  * :   If the font has set bit\ 1 in the 'fsType' field of the `OS/2` table,
 358  *     the ttfautohint library refuses to process the font since a
 359  *     permission to do that is required from the font's legal owner.  In
 360  *     case you have such a permission you might set the integer argument to
 361  *     value\ 1 to make ttfautohint handle the font.  The default value
 362  *     is\ 0.
 363  *
 364  * `dehint`
 365  * :   If set to\ 1, remove all hints from the font.  All other hinting
 366  *     options are ignored.
 367  *
 368  *
 369  * ### Remarks
 370  *
 371  *   * Obviously, it is necessary to have an input and an output data
 372  *     stream.  All other options are optional.
 373  *
 374  *   * `hinting-range-min` and `hinting-range-max` specify the range for
 375  *     which the autohinter generates optimized hinting code.  If a PPEM
 376  *     value is smaller than the value of `hinting-range-min`, hinting still
 377  *     takes place but the configuration created for `hinting-range-min` is
 378  *     used.  The analogous action is taken for `hinting-range-max`, only
 379  *     limited by the value given with `hinting-limit`.  The font's `gasp`
 380  *     table is set up to always use grayscale rendering with grid-fitting
 381  *     for standard hinting, and symmetric grid-fitting and symmetric
 382  *     smoothing for horizontal subpixel hinting (ClearType).
 383  *
 384  *   * ttfautohint can process its own output a second time only if option
 385  *     `hint-composites` is not set (or if the font doesn't contain
 386  *     composite glyphs at all).  This limitation might change in the
 387  *     future.
 388  *
 389  * ```C
 390  */
 391
 392 TA_Error
 393 TTF_autohint(const char* options,
 394              ...);
 395
 396 /*
 397  * ```
 398  *
 399  */
 400
 401 /* pandoc-end */
 402
 403 #ifdef __cplusplus
 404 } /* extern "C" */
 405 #endif
 406
 407 #endif /* __TTFAUTOHINT_H__ */
 408
 409 /* end of ttfautohint.h */