1 /****************************************************************************
2 *
3 * ftdriver.h
4 *
5 * FreeType API for controlling driver modules (specification only).
6 *
7 * Copyright (C) 2017-2019 by
8 * David Turner, Robert Wilhelm, and Werner Lemberg.
9 *
10 * This file is part of the FreeType project, and may only be used,
11 * modified, and distributed under the terms of the FreeType project
12 * license, LICENSE.TXT. By continuing to use, modify, or distribute
13 * this file you indicate that you have read the license and
14 * understand and accept it fully.
15 *
16 */
17
18
19 #ifndef FTDRIVER_H_
20 #define FTDRIVER_H_
21
22 #include <ft2build.h>
23 #include FT_FREETYPE_H
24 #include FT_PARAMETER_TAGS_H
25
26 #ifdef FREETYPE_H
27 #error "freetype.h of FreeType 1 has been loaded!"
28 #error "Please fix the directory search order for header files"
29 #error "so that freetype.h of FreeType 2 is found first."
30 #endif
31
32
33 FT_BEGIN_HEADER
34
35
36 /**************************************************************************
37 *
38 * @section:
39 * auto_hinter
40 *
41 * @title:
42 * The auto-hinter
43 *
44 * @abstract:
45 * Controlling the auto-hinting module.
46 *
47 * @description:
48 * While FreeType's auto-hinter doesn't expose API functions by itself,
49 * it is possible to control its behaviour with @FT_Property_Set and
50 * @FT_Property_Get. The following lists the available properties
51 * together with the necessary macros and structures.
52 *
53 * Note that the auto-hinter's module name is 'autofitter' for historical
54 * reasons.
55 *
56 * Available properties are @increase-x-height, @no-stem-darkening
57 * (experimental), @darkening-parameters (experimental), @warping
58 * (experimental), @glyph-to-script-map (experimental), @fallback-script
59 * (experimental), and @default-script (experimental), as documented in
60 * the @properties section.
61 *
62 */
63
64
65 /**************************************************************************
66 *
67 * @section:
68 * cff_driver
69 *
70 * @title:
71 * The CFF driver
72 *
73 * @abstract:
74 * Controlling the CFF driver module.
75 *
76 * @description:
77 * While FreeType's CFF driver doesn't expose API functions by itself, it
78 * is possible to control its behaviour with @FT_Property_Set and
79 * @FT_Property_Get.
80 *
81 * The CFF driver's module name is 'cff'.
82 *
83 * Available properties are @hinting-engine, @no-stem-darkening,
84 * @darkening-parameters, and @random-seed, as documented in the
85 * @properties section.
86 *
87 *
88 * **Hinting and antialiasing principles of the new engine**
89 *
90 * The rasterizer is positioning horizontal features (e.g., ascender
91 * height & x-height, or crossbars) on the pixel grid and minimizing the
92 * amount of antialiasing applied to them, while placing vertical
93 * features (vertical stems) on the pixel grid without hinting, thus
94 * representing the stem position and weight accurately. Sometimes the
95 * vertical stems may be only partially black. In this context,
96 * 'antialiasing' means that stems are not positioned exactly on pixel
97 * borders, causing a fuzzy appearance.
98 *
99 * There are two principles behind this approach.
100 *
101 * 1) No hinting in the horizontal direction: Unlike 'superhinted'
102 * TrueType, which changes glyph widths to accommodate regular
103 * inter-glyph spacing, Adobe's approach is 'faithful to the design' in
104 * representing both the glyph width and the inter-glyph spacing designed
105 * for the font. This makes the screen display as close as it can be to
106 * the result one would get with infinite resolution, while preserving
107 * what is considered the key characteristics of each glyph. Note that
108 * the distances between unhinted and grid-fitted positions at small
109 * sizes are comparable to kerning values and thus would be noticeable
110 * (and distracting) while reading if hinting were applied.
111 *
112 * One of the reasons to not hint horizontally is antialiasing for LCD
113 * screens: The pixel geometry of modern displays supplies three vertical
114 * subpixels as the eye moves horizontally across each visible pixel. On
115 * devices where we can be certain this characteristic is present a
116 * rasterizer can take advantage of the subpixels to add increments of
117 * weight. In Western writing systems this turns out to be the more
118 * critical direction anyway; the weights and spacing of vertical stems
119 * (see above) are central to Armenian, Cyrillic, Greek, and Latin type
120 * designs. Even when the rasterizer uses greyscale antialiasing instead
121 * of color (a necessary compromise when one doesn't know the screen
122 * characteristics), the unhinted vertical features preserve the design's
123 * weight and spacing much better than aliased type would.
124 *
125 * 2) Alignment in the vertical direction: Weights and spacing along the
126 * y~axis are less critical; what is much more important is the visual
127 * alignment of related features (like cap-height and x-height). The
128 * sense of alignment for these is enhanced by the sharpness of grid-fit
129 * edges, while the cruder vertical resolution (full pixels instead of
130 * 1/3 pixels) is less of a problem.
131 *
132 * On the technical side, horizontal alignment zones for ascender,
133 * x-height, and other important height values (traditionally called
134 * 'blue zones') as defined in the font are positioned independently,
135 * each being rounded to the nearest pixel edge, taking care of overshoot
136 * suppression at small sizes, stem darkening, and scaling.
137 *
138 * Hstems (this is, hint values defined in the font to help align
139 * horizontal features) that fall within a blue zone are said to be
140 * 'captured' and are aligned to that zone. Uncaptured stems are moved
141 * in one of four ways, top edge up or down, bottom edge up or down.
142 * Unless there are conflicting hstems, the smallest movement is taken to
143 * minimize distortion.
144 *
145 */
146
147
148 /**************************************************************************
149 *
150 * @section:
151 * pcf_driver
152 *
153 * @title:
154 * The PCF driver
155 *
156 * @abstract:
157 * Controlling the PCF driver module.
158 *
159 * @description:
160 * While FreeType's PCF driver doesn't expose API functions by itself, it
161 * is possible to control its behaviour with @FT_Property_Set and
162 * @FT_Property_Get. Right now, there is a single property
163 * @no-long-family-names available if FreeType is compiled with
164 * PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
165 *
166 * The PCF driver's module name is 'pcf'.
167 *
168 */
169
170
171 /**************************************************************************
172 *
173 * @section:
174 * t1_cid_driver
175 *
176 * @title:
177 * The Type 1 and CID drivers
178 *
179 * @abstract:
180 * Controlling the Type~1 and CID driver modules.
181 *
182 * @description:
183 * It is possible to control the behaviour of FreeType's Type~1 and
184 * Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
185 *
186 * Behind the scenes, both drivers use the Adobe CFF engine for hinting;
187 * however, the used properties must be specified separately.
188 *
189 * The Type~1 driver's module name is 'type1'; the CID driver's module
190 * name is 't1cid'.
191 *
192 * Available properties are @hinting-engine, @no-stem-darkening,
193 * @darkening-parameters, and @random-seed, as documented in the
194 * @properties section.
195 *
196 * Please see the @cff_driver section for more details on the new hinting
197 * engine.
198 *
199 */
200
201
202 /**************************************************************************
203 *
204 * @section:
205 * tt_driver
206 *
207 * @title:
208 * The TrueType driver
209 *
210 * @abstract:
211 * Controlling the TrueType driver module.
212 *
213 * @description:
214 * While FreeType's TrueType driver doesn't expose API functions by
215 * itself, it is possible to control its behaviour with @FT_Property_Set
216 * and @FT_Property_Get. The following lists the available properties
217 * together with the necessary macros and structures.
218 *
219 * The TrueType driver's module name is 'truetype'.
220 *
221 * A single property @interpreter-version is available, as documented in
222 * the @properties section.
223 *
224 * We start with a list of definitions, kindly provided by Greg
225 * Hitchcock.
226 *
227 * _Bi-Level Rendering_
228 *
229 * Monochromatic rendering, exclusively used in the early days of
230 * TrueType by both Apple and Microsoft. Microsoft's GDI interface
231 * supported hinting of the right-side bearing point, such that the
232 * advance width could be non-linear. Most often this was done to
233 * achieve some level of glyph symmetry. To enable reasonable
234 * performance (e.g., not having to run hinting on all glyphs just to get
235 * the widths) there was a bit in the head table indicating if the side
236 * bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache
237 * hinting widths across multiple sizes and device aspect ratios.
238 *
239 * _Font Smoothing_
240 *
241 * Microsoft's GDI implementation of anti-aliasing. Not traditional
242 * anti-aliasing as the outlines were hinted before the sampling. The
243 * widths matched the bi-level rendering.
244 *
245 * _ClearType Rendering_
246 *
247 * Technique that uses physical subpixels to improve rendering on LCD
248 * (and other) displays. Because of the higher resolution, many methods
249 * of improving symmetry in glyphs through hinting the right-side bearing
250 * were no longer necessary. This lead to what GDI calls 'natural
251 * widths' ClearType, see
252 * http://rastertragedy.com/RTRCh4.htm#Sec21. Since hinting
253 * has extra resolution, most non-linearity went away, but it is still
254 * possible for hints to change the advance widths in this mode.
255 *
256 * _ClearType Compatible Widths_
257 *
258 * One of the earliest challenges with ClearType was allowing the
259 * implementation in GDI to be selected without requiring all UI and
260 * documents to reflow. To address this, a compatible method of
261 * rendering ClearType was added where the font hints are executed once
262 * to determine the width in bi-level rendering, and then re-run in
263 * ClearType, with the difference in widths being absorbed in the font
264 * hints for ClearType (mostly in the white space of hints); see
265 * http://rastertragedy.com/RTRCh4.htm#Sec20. Somewhat by
266 * definition, compatible width ClearType allows for non-linear widths,
267 * but only when the bi-level version has non-linear widths.
268 *
269 * _ClearType Subpixel Positioning_
270 *
271 * One of the nice benefits of ClearType is the ability to more crisply
272 * display fractional widths; unfortunately, the GDI model of integer
273 * bitmaps did not support this. However, the WPF and Direct Write
274 * frameworks do support fractional widths. DWrite calls this 'natural
275 * mode', not to be confused with GDI's 'natural widths'. Subpixel
276 * positioning, in the current implementation of Direct Write,
277 * unfortunately does not support hinted advance widths, see
278 * http://rastertragedy.com/RTRCh4.htm#Sec22. Note that the
279 * TrueType interpreter fully allows the advance width to be adjusted in
280 * this mode, just the DWrite client will ignore those changes.
281 *
282 * _ClearType Backward Compatibility_
283 *
284 * This is a set of exceptions made in the TrueType interpreter to
285 * minimize hinting techniques that were problematic with the extra
286 * resolution of ClearType; see
287 * http://rastertragedy.com/RTRCh4.htm#Sec1 and
288 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
289 * This technique is not to be confused with ClearType compatible widths.
290 * ClearType backward compatibility has no direct impact on changing
291 * advance widths, but there might be an indirect impact on disabling
292 * some deltas. This could be worked around in backward compatibility
293 * mode.
294 *
295 * _Native ClearType Mode_
296 *
297 * (Not to be confused with 'natural widths'.) This mode removes all the
298 * exceptions in the TrueType interpreter when running with ClearType.
299 * Any issues on widths would still apply, though.
300 *
301 */
302
303
304 /**************************************************************************
305 *
306 * @section:
307 * properties
308 *
309 * @title:
310 * Driver properties
311 *
312 * @abstract:
313 * Controlling driver modules.
314 *
315 * @description:
316 * Driver modules can be controlled by setting and unsetting properties,
317 * using the functions @FT_Property_Set and @FT_Property_Get. This
318 * section documents the available properties, together with auxiliary
319 * macros and structures.
320 *
321 */
322
323
324 /**************************************************************************
325 *
326 * @enum:
327 * FT_HINTING_XXX
328 *
329 * @description:
330 * A list of constants used for the @hinting-engine property to select
331 * the hinting engine for CFF, Type~1, and CID fonts.
332 *
333 * @values:
334 * FT_HINTING_FREETYPE ::
335 * Use the old FreeType hinting engine.
336 *
337 * FT_HINTING_ADOBE ::
338 * Use the hinting engine contributed by Adobe.
339 *
340 * @since:
341 * 2.9
342 *
343 */
344 #define FT_HINTING_FREETYPE 0
345 #define FT_HINTING_ADOBE 1
346
347 /* these constants (introduced in 2.4.12) are deprecated */
348 #define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE
349 #define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE
350
351
352 /**************************************************************************
353 *
354 * @property:
355 * hinting-engine
356 *
357 * @description:
358 * Thanks to Adobe, which contributed a new hinting (and parsing) engine,
359 * an application can select between 'freetype' and 'adobe' if compiled
360 * with `CFF_CONFIG_OPTION_OLD_ENGINE`. If this configuration macro
361 * isn't defined, 'hinting-engine' does nothing.
362 *
363 * The same holds for the Type~1 and CID modules if compiled with
364 * `T1_CONFIG_OPTION_OLD_ENGINE`.
365 *
366 * For the 'cff' module, the default engine is 'freetype' if
367 * `CFF_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe' otherwise.
368 *
369 * For both the 'type1' and 't1cid' modules, the default engine is
370 * 'freetype' if `T1_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe'
371 * otherwise.
372 *
373 * @note:
374 * This property can be used with @FT_Property_Get also.
375 *
376 * This property can be set via the `FREETYPE_PROPERTIES` environment
377 * variable (using values 'adobe' or 'freetype').
378 *
379 * @example:
380 * The following example code demonstrates how to select Adobe's hinting
381 * engine for the 'cff' module (omitting the error handling).
382 *
383 * ```
384 * FT_Library library;
385 * FT_UInt hinting_engine = FT_HINTING_ADOBE;
386 *
387 *
388 * FT_Init_FreeType( &library );
389 *
390 * FT_Property_Set( library, "cff",
391 * "hinting-engine", &hinting_engine );
392 * ```
393 *
394 * @since:
395 * 2.4.12 (for 'cff' module)
396 *
397 * 2.9 (for 'type1' and 't1cid' modules)
398 *
399 */
400
401
402 /**************************************************************************
403 *
404 * @property:
405 * no-stem-darkening
406 *
407 * @description:
408 * All glyphs that pass through the auto-hinter will be emboldened unless
409 * this property is set to TRUE. The same is true for the CFF, Type~1,
410 * and CID font modules if the 'Adobe' engine is selected (which is the
411 * default).
412 *
413 * Stem darkening emboldens glyphs at smaller sizes to make them more
414 * readable on common low-DPI screens when using linear alpha blending
415 * and gamma correction, see @FT_Render_Glyph. When not using linear
416 * alpha blending and gamma correction, glyphs will appear heavy and
417 * fuzzy!
418 *
419 * Gamma correction essentially lightens fonts since shades of grey are
420 * shifted to higher pixel values (=~higher brightness) to match the
421 * original intention to the reality of our screens. The side-effect is
422 * that glyphs 'thin out'. Mac OS~X and Adobe's proprietary font
423 * rendering library implement a counter-measure: stem darkening at
424 * smaller sizes where shades of gray dominate. By emboldening a glyph
425 * slightly in relation to its pixel size, individual pixels get higher
426 * coverage of filled-in outlines and are therefore 'blacker'. This
427 * counteracts the 'thinning out' of glyphs, making text remain readable
428 * at smaller sizes.
429 *
430 * By default, the Adobe engines for CFF, Type~1, and CID fonts darken
431 * stems at smaller sizes, regardless of hinting, to enhance contrast.
432 * Setting this property, stem darkening gets switched off.
433 *
434 * For the auto-hinter, stem-darkening is experimental currently and thus
435 * switched off by default (this is, `no-stem-darkening` is set to TRUE
436 * by default). Total consistency with the CFF driver is not achieved
437 * right now because the emboldening method differs and glyphs must be
438 * scaled down on the Y-axis to keep outline points inside their
439 * precomputed blue zones. The smaller the size (especially 9ppem and
440 * down), the higher the loss of emboldening versus the CFF driver.
441 *
442 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
443 *
444 * @note:
445 * This property can be used with @FT_Property_Get also.
446 *
447 * This property can be set via the `FREETYPE_PROPERTIES` environment
448 * variable (using values 1 and 0 for 'on' and 'off', respectively). It
449 * can also be set per face using @FT_Face_Properties with
450 * @FT_PARAM_TAG_STEM_DARKENING.
451 *
452 * @example:
453 * ```
454 * FT_Library library;
455 * FT_Bool no_stem_darkening = TRUE;
456 *
457 *
458 * FT_Init_FreeType( &library );
459 *
460 * FT_Property_Set( library, "cff",
461 * "no-stem-darkening", &no_stem_darkening );
462 * ```
463 *
464 * @since:
465 * 2.4.12 (for 'cff' module)
466 *
467 * 2.6.2 (for 'autofitter' module)
468 *
469 * 2.9 (for 'type1' and 't1cid' modules)
470 *
471 */
472
473
474 /**************************************************************************
475 *
476 * @property:
477 * darkening-parameters
478 *
479 * @description:
480 * By default, the Adobe hinting engine, as used by the CFF, Type~1, and
481 * CID font drivers, darkens stems as follows (if the `no-stem-darkening`
482 * property isn't set):
483 *
484 * ```
485 * stem width <= 0.5px: darkening amount = 0.4px
486 * stem width = 1px: darkening amount = 0.275px
487 * stem width = 1.667px: darkening amount = 0.275px
488 * stem width >= 2.333px: darkening amount = 0px
489 * ```
490 *
491 * and piecewise linear in-between. At configuration time, these four
492 * control points can be set with the macro
493 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID
494 * drivers share these values. At runtime, the control points can be
495 * changed using the `darkening-parameters` property (see the example
496 * below that demonstrates this for the Type~1 driver).
497 *
498 * The x~values give the stem width, and the y~values the darkening
499 * amount. The unit is 1000th of pixels. All coordinate values must be
500 * positive; the x~values must be monotonically increasing; the y~values
501 * must be monotonically decreasing and smaller than or equal to 500
502 * (corresponding to half a pixel); the slope of each linear piece must
503 * be shallower than -1 (e.g., -.4).
504 *
505 * The auto-hinter provides this property, too, as an experimental
506 * feature. See @no-stem-darkening for more.
507 *
508 * @note:
509 * This property can be used with @FT_Property_Get also.
510 *
511 * This property can be set via the `FREETYPE_PROPERTIES` environment
512 * variable, using eight comma-separated integers without spaces. Here
513 * the above example, using `\` to break the line for readability.
514 *
515 * ```
516 * FREETYPE_PROPERTIES=\
517 * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0
518 * ```
519 *
520 * @example:
521 * ```
522 * FT_Library library;
523 * FT_Int darken_params[8] = { 500, 300, // x1, y1
524 * 1000, 200, // x2, y2
525 * 1500, 100, // x3, y3
526 * 2000, 0 }; // x4, y4
527 *
528 *
529 * FT_Init_FreeType( &library );
530 *
531 * FT_Property_Set( library, "type1",
532 * "darkening-parameters", darken_params );
533 * ```
534 *
535 * @since:
536 * 2.5.1 (for 'cff' module)
537 *
538 * 2.6.2 (for 'autofitter' module)
539 *
540 * 2.9 (for 'type1' and 't1cid' modules)
541 *
542 */
543
544
545 /**************************************************************************
546 *
547 * @property:
548 * random-seed
549 *
550 * @description:
551 * By default, the seed value for the CFF 'random' operator and the
552 * similar '0 28 callothersubr pop' command for the Type~1 and CID
553 * drivers is set to a random value. However, mainly for debugging
554 * purposes, it is often necessary to use a known value as a seed so that
555 * the pseudo-random number sequences generated by 'random' are
556 * repeatable.
557 *
558 * The `random-seed` property does that. Its argument is a signed 32bit
559 * integer; if the value is zero or negative, the seed given by the
560 * `intitialRandomSeed` private DICT operator in a CFF file gets used (or
561 * a default value if there is no such operator). If the value is
562 * positive, use it instead of `initialRandomSeed`, which is consequently
563 * ignored.
564 *
565 * @note:
566 * This property can be set via the `FREETYPE_PROPERTIES` environment
567 * variable. It can also be set per face using @FT_Face_Properties with
568 * @FT_PARAM_TAG_RANDOM_SEED.
569 *
570 * @since:
571 * 2.8 (for 'cff' module)
572 *
573 * 2.9 (for 'type1' and 't1cid' modules)
574 *
575 */
576
577
578 /**************************************************************************
579 *
580 * @property:
581 * no-long-family-names
582 *
583 * @description:
584 * If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling
585 * FreeType, the PCF driver constructs long family names.
586 *
587 * There are many PCF fonts just called 'Fixed' which look completely
588 * different, and which have nothing to do with each other. When
589 * selecting 'Fixed' in KDE or Gnome one gets results that appear rather
590 * random, the style changes often if one changes the size and one cannot
591 * select some fonts at all. The improve this situation, the PCF module
592 * prepends the foundry name (plus a space) to the family name. It also
593 * checks whether there are 'wide' characters; all put together, family
594 * names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed.
595 *
596 * If `no-long-family-names` is set, this feature gets switched off.
597 *
598 * @note:
599 * This property can be used with @FT_Property_Get also.
600 *
601 * This property can be set via the `FREETYPE_PROPERTIES` environment
602 * variable (using values 1 and 0 for 'on' and 'off', respectively).
603 *
604 * @example:
605 * ```
606 * FT_Library library;
607 * FT_Bool no_long_family_names = TRUE;
608 *
609 *
610 * FT_Init_FreeType( &library );
611 *
612 * FT_Property_Set( library, "pcf",
613 * "no-long-family-names",
614 * &no_long_family_names );
615 * ```
616 *
617 * @since:
618 * 2.8
619 */
620
621
622 /**************************************************************************
623 *
624 * @enum:
625 * TT_INTERPRETER_VERSION_XXX
626 *
627 * @description:
628 * A list of constants used for the @interpreter-version property to
629 * select the hinting engine for Truetype fonts.
630 *
631 * The numeric value in the constant names represents the version number
632 * as returned by the 'GETINFO' bytecode instruction.
633 *
634 * @values:
635 * TT_INTERPRETER_VERSION_35 ::
636 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
637 * Windows~98; only grayscale and B/W rasterizing is supported.
638 *
639 * TT_INTERPRETER_VERSION_38 ::
640 * Version~38 corresponds to MS rasterizer v.1.9; it is roughly
641 * equivalent to the hinting provided by DirectWrite ClearType (as can
642 * be found, for example, in the Internet Explorer~9 running on
643 * Windows~7). It is used in FreeType to select the 'Infinality'
644 * subpixel hinting code. The code may be removed in a future version.
645 *
646 * TT_INTERPRETER_VERSION_40 ::
647 * Version~40 corresponds to MS rasterizer v.2.1; it is roughly
648 * equivalent to the hinting provided by DirectWrite ClearType (as can
649 * be found, for example, in Microsoft's Edge Browser on Windows~10).
650 * It is used in FreeType to select the 'minimal' subpixel hinting
651 * code, a stripped-down and higher performance version of the
652 * 'Infinality' code.
653 *
654 * @note:
655 * This property controls the behaviour of the bytecode interpreter and
656 * thus how outlines get hinted. It does **not** control how glyph get
657 * rasterized! In particular, it does not control subpixel color
658 * filtering.
659 *
660 * If FreeType has not been compiled with the configuration option
661 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 causes
662 * an `FT_Err_Unimplemented_Feature` error.
663 *
664 * Depending on the graphics framework, Microsoft uses different bytecode
665 * and rendering engines. As a consequence, the version numbers returned
666 * by a call to the 'GETINFO' bytecode instruction are more convoluted
667 * than desired.
668 *
669 * Here are two tables that try to shed some light on the possible values
670 * for the MS rasterizer engine, together with the additional features
671 * introduced by it.
672 *
673 * ```
674 * GETINFO framework version feature
675 * -------------------------------------------------------------------
676 * 3 GDI (Win 3.1), v1.0 16-bit, first version
677 * TrueImage
678 * 33 GDI (Win NT 3.1), v1.5 32-bit
679 * HP Laserjet
680 * 34 GDI (Win 95) v1.6 font smoothing,
681 * new SCANTYPE opcode
682 * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET
683 * bits in composite glyphs
684 * 36 MGDI (Win CE 2) v1.6+ classic ClearType
685 * 37 GDI (XP and later), v1.8 ClearType
686 * GDI+ old (before Vista)
687 * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType,
688 * WPF Y-direction ClearType,
689 * additional error checking
690 * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags
691 * in GETINFO opcode,
692 * bug fixes
693 * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag
694 * DWrite (Win 8) in GETINFO opcode,
695 * Gray ClearType
696 * ```
697 *
698 * The 'version' field gives a rough orientation only, since some
699 * applications provided certain features much earlier (as an example,
700 * Microsoft Reader used subpixel and Y-direction ClearType already in
701 * Windows 2000). Similarly, updates to a given framework might include
702 * improved hinting support.
703 *
704 * ```
705 * version sampling rendering comment
706 * x y x y
707 * --------------------------------------------------------------
708 * v1.0 normal normal B/W B/W bi-level
709 * v1.6 high high gray gray grayscale
710 * v1.8 high normal color-filter B/W (GDI) ClearType
711 * v1.9 high high color-filter gray Color ClearType
712 * v2.1 high normal gray B/W Gray ClearType
713 * v2.1 high high gray gray Gray ClearType
714 * ```
715 *
716 * Color and Gray ClearType are the two available variants of
717 * 'Y-direction ClearType', meaning grayscale rasterization along the
718 * Y-direction; the name used in the TrueType specification for this
719 * feature is 'symmetric smoothing'. 'Classic ClearType' is the original
720 * algorithm used before introducing a modified version in Win~XP.
721 * Another name for v1.6's grayscale rendering is 'font smoothing', and
722 * 'Color ClearType' is sometimes also called 'DWrite ClearType'. To
723 * differentiate between today's Color ClearType and the earlier
724 * ClearType variant with B/W rendering along the vertical axis, the
725 * latter is sometimes called 'GDI ClearType'.
726 *
727 * 'Normal' and 'high' sampling describe the (virtual) resolution to
728 * access the rasterized outline after the hinting process. 'Normal'
729 * means 1 sample per grid line (i.e., B/W). In the current Microsoft
730 * implementation, 'high' means an extra virtual resolution of 16x16 (or
731 * 16x1) grid lines per pixel for bytecode instructions like 'MIRP'.
732 * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
733 * lines for color filtering if Color ClearType is activated.
734 *
735 * Note that 'Gray ClearType' is essentially the same as v1.6's grayscale
736 * rendering. However, the GETINFO instruction handles it differently:
737 * v1.6 returns bit~12 (hinting for grayscale), while v2.1 returns
738 * bits~13 (hinting for ClearType), 18 (symmetrical smoothing), and~19
739 * (Gray ClearType). Also, this mode respects bits 2 and~3 for the
740 * version~1 gasp table exclusively (like Color ClearType), while v1.6
741 * only respects the values of version~0 (bits 0 and~1).
742 *
743 * Keep in mind that the features of the above interpreter versions might
744 * not map exactly to FreeType features or behavior because it is a
745 * fundamentally different library with different internals.
746 *
747 */
748 #define TT_INTERPRETER_VERSION_35 35
749 #define TT_INTERPRETER_VERSION_38 38
750 #define TT_INTERPRETER_VERSION_40 40
751
752
753 /**************************************************************************
754 *
755 * @property:
756 * interpreter-version
757 *
758 * @description:
759 * Currently, three versions are available, two representing the bytecode
760 * interpreter with subpixel hinting support (old 'Infinality' code and
761 * new stripped-down and higher performance 'minimal' code) and one
762 * without, respectively. The default is subpixel support if
763 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING` is defined, and no subpixel
764 * support otherwise (since it isn't available then).
765 *
766 * If subpixel hinting is on, many TrueType bytecode instructions behave
767 * differently compared to B/W or grayscale rendering (except if 'native
768 * ClearType' is selected by the font). Microsoft's main idea is to
769 * render at a much increased horizontal resolution, then sampling down
770 * the created output to subpixel precision. However, many older fonts
771 * are not suited to this and must be specially taken care of by applying
772 * (hardcoded) tweaks in Microsoft's interpreter.
773 *
774 * Details on subpixel hinting and some of the necessary tweaks can be
775 * found in Greg Hitchcock's whitepaper at
776 * 'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
777 * Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2,
778 * or 6x5 supersampling) like discussed in the paper. Depending on the
779 * chosen interpreter, it simply ignores instructions on vertical stems
780 * to arrive at very similar results.
781 *
782 * @note:
783 * This property can be used with @FT_Property_Get also.
784 *
785 * This property can be set via the `FREETYPE_PROPERTIES` environment
786 * variable (using values '35', '38', or '40').
787 *
788 * @example:
789 * The following example code demonstrates how to deactivate subpixel
790 * hinting (omitting the error handling).
791 *
792 * ```
793 * FT_Library library;
794 * FT_Face face;
795 * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35;
796 *
797 *
798 * FT_Init_FreeType( &library );
799 *
800 * FT_Property_Set( library, "truetype",
801 * "interpreter-version",
802 * &interpreter_version );
803 * ```
804 *
805 * @since:
806 * 2.5
807 */
808
809
810 /**************************************************************************
811 *
812 * @property:
813 * glyph-to-script-map
814 *
815 * @description:
816 * **Experimental only**
817 *
818 * The auto-hinter provides various script modules to hint glyphs.
819 * Examples of supported scripts are Latin or CJK. Before a glyph is
820 * auto-hinted, the Unicode character map of the font gets examined, and
821 * the script is then determined based on Unicode character ranges, see
822 * below.
823 *
824 * OpenType fonts, however, often provide much more glyphs than character
825 * codes (small caps, superscripts, ligatures, swashes, etc.), to be
826 * controlled by so-called 'features'. Handling OpenType features can be
827 * quite complicated and thus needs a separate library on top of
828 * FreeType.
829 *
830 * The mapping between glyph indices and scripts (in the auto-hinter
831 * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array
832 * with `num_glyphs` elements, as found in the font's @FT_Face structure.
833 * The `glyph-to-script-map` property returns a pointer to this array,
834 * which can be modified as needed. Note that the modification should
835 * happen before the first glyph gets processed by the auto-hinter so
836 * that the global analysis of the font shapes actually uses the modified
837 * mapping.
838 *
839 * @example:
840 * The following example code demonstrates how to access it (omitting the
841 * error handling).
842 *
843 * ```
844 * FT_Library library;
845 * FT_Face face;
846 * FT_Prop_GlyphToScriptMap prop;
847 *
848 *
849 * FT_Init_FreeType( &library );
850 * FT_New_Face( library, "foo.ttf", 0, &face );
851 *
852 * prop.face = face;
853 *
854 * FT_Property_Get( library, "autofitter",
855 * "glyph-to-script-map", &prop );
856 *
857 * // adjust `prop.map' as needed right here
858 *
859 * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
860 * ```
861 *
862 * @since:
863 * 2.4.11
864 *
865 */
866
867
868 /**************************************************************************
869 *
870 * @enum:
871 * FT_AUTOHINTER_SCRIPT_XXX
872 *
873 * @description:
874 * **Experimental only**
875 *
876 * A list of constants used for the @glyph-to-script-map property to
877 * specify the script submodule the auto-hinter should use for hinting a
878 * particular glyph.
879 *
880 * @values:
881 * FT_AUTOHINTER_SCRIPT_NONE ::
882 * Don't auto-hint this glyph.
883 *
884 * FT_AUTOHINTER_SCRIPT_LATIN ::
885 * Apply the latin auto-hinter. For the auto-hinter, 'latin' is a very
886 * broad term, including Cyrillic and Greek also since characters from
887 * those scripts share the same design constraints.
888 *
889 * By default, characters from the following Unicode ranges are
890 * assigned to this submodule.
891 *
892 * ```
893 * U+0020 - U+007F // Basic Latin (no control characters)
894 * U+00A0 - U+00FF // Latin-1 Supplement (no control characters)
895 * U+0100 - U+017F // Latin Extended-A
896 * U+0180 - U+024F // Latin Extended-B
897 * U+0250 - U+02AF // IPA Extensions
898 * U+02B0 - U+02FF // Spacing Modifier Letters
899 * U+0300 - U+036F // Combining Diacritical Marks
900 * U+0370 - U+03FF // Greek and Coptic
901 * U+0400 - U+04FF // Cyrillic
902 * U+0500 - U+052F // Cyrillic Supplement
903 * U+1D00 - U+1D7F // Phonetic Extensions
904 * U+1D80 - U+1DBF // Phonetic Extensions Supplement
905 * U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement
906 * U+1E00 - U+1EFF // Latin Extended Additional
907 * U+1F00 - U+1FFF // Greek Extended
908 * U+2000 - U+206F // General Punctuation
909 * U+2070 - U+209F // Superscripts and Subscripts
910 * U+20A0 - U+20CF // Currency Symbols
911 * U+2150 - U+218F // Number Forms
912 * U+2460 - U+24FF // Enclosed Alphanumerics
913 * U+2C60 - U+2C7F // Latin Extended-C
914 * U+2DE0 - U+2DFF // Cyrillic Extended-A
915 * U+2E00 - U+2E7F // Supplemental Punctuation
916 * U+A640 - U+A69F // Cyrillic Extended-B
917 * U+A720 - U+A7FF // Latin Extended-D
918 * U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures)
919 * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
920 * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
921 * ```
922 *
923 * FT_AUTOHINTER_SCRIPT_CJK ::
924 * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
925 * Vietnamese, and some other scripts.
926 *
927 * By default, characters from the following Unicode ranges are
928 * assigned to this submodule.
929 *
930 * ```
931 * U+1100 - U+11FF // Hangul Jamo
932 * U+2E80 - U+2EFF // CJK Radicals Supplement
933 * U+2F00 - U+2FDF // Kangxi Radicals
934 * U+2FF0 - U+2FFF // Ideographic Description Characters
935 * U+3000 - U+303F // CJK Symbols and Punctuation
936 * U+3040 - U+309F // Hiragana
937 * U+30A0 - U+30FF // Katakana
938 * U+3100 - U+312F // Bopomofo
939 * U+3130 - U+318F // Hangul Compatibility Jamo
940 * U+3190 - U+319F // Kanbun
941 * U+31A0 - U+31BF // Bopomofo Extended
942 * U+31C0 - U+31EF // CJK Strokes
943 * U+31F0 - U+31FF // Katakana Phonetic Extensions
944 * U+3200 - U+32FF // Enclosed CJK Letters and Months
945 * U+3300 - U+33FF // CJK Compatibility
946 * U+3400 - U+4DBF // CJK Unified Ideographs Extension A
947 * U+4DC0 - U+4DFF // Yijing Hexagram Symbols
948 * U+4E00 - U+9FFF // CJK Unified Ideographs
949 * U+A960 - U+A97F // Hangul Jamo Extended-A
950 * U+AC00 - U+D7AF // Hangul Syllables
951 * U+D7B0 - U+D7FF // Hangul Jamo Extended-B
952 * U+F900 - U+FAFF // CJK Compatibility Ideographs
953 * U+FE10 - U+FE1F // Vertical forms
954 * U+FE30 - U+FE4F // CJK Compatibility Forms
955 * U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms
956 * U+1B000 - U+1B0FF // Kana Supplement
957 * U+1D300 - U+1D35F // Tai Xuan Hing Symbols
958 * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
959 * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
960 * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
961 * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
962 * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
963 * ```
964 *
965 * FT_AUTOHINTER_SCRIPT_INDIC ::
966 * Apply the indic auto-hinter, covering all major scripts from the
967 * Indian sub-continent and some other related scripts like Thai, Lao,
968 * or Tibetan.
969 *
970 * By default, characters from the following Unicode ranges are
971 * assigned to this submodule.
972 *
973 * ```
974 * U+0900 - U+0DFF // Indic Range
975 * U+0F00 - U+0FFF // Tibetan
976 * U+1900 - U+194F // Limbu
977 * U+1B80 - U+1BBF // Sundanese
978 * U+A800 - U+A82F // Syloti Nagri
979 * U+ABC0 - U+ABFF // Meetei Mayek
980 * U+11800 - U+118DF // Sharada
981 * ```
982 *
983 * Note that currently Indic support is rudimentary only, missing blue
984 * zone support.
985 *
986 * @since:
987 * 2.4.11
988 *
989 */
990 #define FT_AUTOHINTER_SCRIPT_NONE 0
991 #define FT_AUTOHINTER_SCRIPT_LATIN 1
992 #define FT_AUTOHINTER_SCRIPT_CJK 2
993 #define FT_AUTOHINTER_SCRIPT_INDIC 3
994
995
996 /**************************************************************************
997 *
998 * @struct:
999 * FT_Prop_GlyphToScriptMap
1000 *
1001 * @description:
1002 * **Experimental only**
1003 *
1004 * The data exchange structure for the @glyph-to-script-map property.
1005 *
1006 * @since:
1007 * 2.4.11
1008 *
1009 */
1010 typedef struct FT_Prop_GlyphToScriptMap_
1011 {
1012 FT_Face face;
1013 FT_UShort* map;
1014
1015 } FT_Prop_GlyphToScriptMap;
1016
1017
1018 /**************************************************************************
1019 *
1020 * @property:
1021 * fallback-script
1022 *
1023 * @description:
1024 * **Experimental only**
1025 *
1026 * If no auto-hinter script module can be assigned to a glyph, a fallback
1027 * script gets assigned to it (see also the @glyph-to-script-map
1028 * property). By default, this is @FT_AUTOHINTER_SCRIPT_CJK. Using the
1029 * `fallback-script` property, this fallback value can be changed.
1030 *
1031 * @note:
1032 * This property can be used with @FT_Property_Get also.
1033 *
1034 * It's important to use the right timing for changing this value: The
1035 * creation of the glyph-to-script map that eventually uses the fallback
1036 * script value gets triggered either by setting or reading a
1037 * face-specific property like @glyph-to-script-map, or by auto-hinting
1038 * any glyph from that face. In particular, if you have already created
1039 * an @FT_Face structure but not loaded any glyph (using the
1040 * auto-hinter), a change of the fallback script will affect this face.
1041 *
1042 * @example:
1043 * ```
1044 * FT_Library library;
1045 * FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
1046 *
1047 *
1048 * FT_Init_FreeType( &library );
1049 *
1050 * FT_Property_Set( library, "autofitter",
1051 * "fallback-script", &fallback_script );
1052 * ```
1053 *
1054 * @since:
1055 * 2.4.11
1056 *
1057 */
1058
1059
1060 /**************************************************************************
1061 *
1062 * @property:
1063 * default-script
1064 *
1065 * @description:
1066 * **Experimental only**
1067 *
1068 * If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make
1069 * the HarfBuzz library access OpenType features for getting better glyph
1070 * coverages, this property sets the (auto-fitter) script to be used for
1071 * the default (OpenType) script data of a font's GSUB table. Features
1072 * for the default script are intended for all scripts not explicitly
1073 * handled in GSUB; an example is a 'dlig' feature, containing the
1074 * combination of the characters 'T', 'E', and 'L' to form a 'TEL'
1075 * ligature.
1076 *
1077 * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the
1078 * `default-script` property, this default value can be changed.
1079 *
1080 * @note:
1081 * This property can be used with @FT_Property_Get also.
1082 *
1083 * It's important to use the right timing for changing this value: The
1084 * creation of the glyph-to-script map that eventually uses the default
1085 * script value gets triggered either by setting or reading a
1086 * face-specific property like @glyph-to-script-map, or by auto-hinting
1087 * any glyph from that face. In particular, if you have already created
1088 * an @FT_Face structure but not loaded any glyph (using the
1089 * auto-hinter), a change of the default script will affect this face.
1090 *
1091 * @example:
1092 * ```
1093 * FT_Library library;
1094 * FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
1095 *
1096 *
1097 * FT_Init_FreeType( &library );
1098 *
1099 * FT_Property_Set( library, "autofitter",
1100 * "default-script", &default_script );
1101 * ```
1102 *
1103 * @since:
1104 * 2.5.3
1105 *
1106 */
1107
1108
1109 /**************************************************************************
1110 *
1111 * @property:
1112 * increase-x-height
1113 *
1114 * @description:
1115 * For ppem values in the range 6~<= ppem <= `increase-x-height`, round
1116 * up the font's x~height much more often than normally. If the value is
1117 * set to~0, which is the default, this feature is switched off. Use
1118 * this property to improve the legibility of small font sizes if
1119 * necessary.
1120 *
1121 * @note:
1122 * This property can be used with @FT_Property_Get also.
1123 *
1124 * Set this value right after calling @FT_Set_Char_Size, but before
1125 * loading any glyph (using the auto-hinter).
1126 *
1127 * @example:
1128 * ```
1129 * FT_Library library;
1130 * FT_Face face;
1131 * FT_Prop_IncreaseXHeight prop;
1132 *
1133 *
1134 * FT_Init_FreeType( &library );
1135 * FT_New_Face( library, "foo.ttf", 0, &face );
1136 * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
1137 *
1138 * prop.face = face;
1139 * prop.limit = 14;
1140 *
1141 * FT_Property_Set( library, "autofitter",
1142 * "increase-x-height", &prop );
1143 * ```
1144 *
1145 * @since:
1146 * 2.4.11
1147 *
1148 */
1149
1150
1151 /**************************************************************************
1152 *
1153 * @struct:
1154 * FT_Prop_IncreaseXHeight
1155 *
1156 * @description:
1157 * The data exchange structure for the @increase-x-height property.
1158 *
1159 */
1160 typedef struct FT_Prop_IncreaseXHeight_
1161 {
1162 FT_Face face;
1163 FT_UInt limit;
1164
1165 } FT_Prop_IncreaseXHeight;
1166
1167
1168 /**************************************************************************
1169 *
1170 * @property:
1171 * warping
1172 *
1173 * @description:
1174 * **Experimental only**
1175 *
1176 * If FreeType gets compiled with option `AF_CONFIG_OPTION_USE_WARPER` to
1177 * activate the warp hinting code in the auto-hinter, this property
1178 * switches warping on and off.
1179 *
1180 * Warping only works in 'normal' auto-hinting mode replacing it. The
1181 * idea of the code is to slightly scale and shift a glyph along the
1182 * non-hinted dimension (which is usually the horizontal axis) so that as
1183 * much of its segments are aligned (more or less) to the grid. To find
1184 * out a glyph's optimal scaling and shifting value, various parameter
1185 * combinations are tried and scored.
1186 *
1187 * By default, warping is off.
1188 *
1189 * @note:
1190 * This property can be used with @FT_Property_Get also.
1191 *
1192 * This property can be set via the `FREETYPE_PROPERTIES` environment
1193 * variable (using values 1 and 0 for 'on' and 'off', respectively).
1194 *
1195 * The warping code can also change advance widths. Have a look at the
1196 * `lsb_delta` and `rsb_delta` fields in the @FT_GlyphSlotRec structure
1197 * for details on improving inter-glyph distances while rendering.
1198 *
1199 * Since warping is a global property of the auto-hinter it is best to
1200 * change its value before rendering any face. Otherwise, you should
1201 * reload all faces that get auto-hinted in 'normal' hinting mode.
1202 *
1203 * @example:
1204 * This example shows how to switch on warping (omitting the error
1205 * handling).
1206 *
1207 * ```
1208 * FT_Library library;
1209 * FT_Bool warping = 1;
1210 *
1211 *
1212 * FT_Init_FreeType( &library );
1213 *
1214 * FT_Property_Set( library, "autofitter", "warping", &warping );
1215 * ```
1216 *
1217 * @since:
1218 * 2.6
1219 *
1220 */
1221
1222
1223 /* */
1224
1225
1226 FT_END_HEADER
1227
1228
1229 #endif /* FTDRIVER_H_ */
1230
1231
1232 /* END */