1 /****************************************************************************
2 *
3 * ftdriver.h
4 *
5 * FreeType API for controlling driver modules (specification only).
6 *
7 * Copyright (C) 2017-2023 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 <freetype/freetype.h>
23 #include <freetype/ftparams.h>
24
25 #ifdef FREETYPE_H
26 #error "freetype.h of FreeType 1 has been loaded!"
27 #error "Please fix the directory search order for header files"
28 #error "so that freetype.h of FreeType 2 is found first."
29 #endif
30
31
32 FT_BEGIN_HEADER
33
34
35 /**************************************************************************
36 *
37 * @section:
38 * auto_hinter
39 *
40 * @title:
41 * The auto-hinter
42 *
43 * @abstract:
44 * Controlling the auto-hinting module.
45 *
46 * @description:
47 * While FreeType's auto-hinter doesn't expose API functions by itself,
48 * it is possible to control its behaviour with @FT_Property_Set and
49 * @FT_Property_Get. The following lists the available properties
50 * together with the necessary macros and structures.
51 *
52 * Note that the auto-hinter's module name is 'autofitter' for historical
53 * reasons.
54 *
55 * Available properties are @increase-x-height, @no-stem-darkening
56 * (experimental), @darkening-parameters (experimental),
57 * @glyph-to-script-map (experimental), @fallback-script (experimental),
58 * and @default-script (experimental), as documented in the @properties
59 * section.
60 *
61 */
62
63
64 /**************************************************************************
65 *
66 * @section:
67 * cff_driver
68 *
69 * @title:
70 * The CFF driver
71 *
72 * @abstract:
73 * Controlling the CFF driver module.
74 *
75 * @description:
76 * While FreeType's CFF driver doesn't expose API functions by itself, it
77 * is possible to control its behaviour with @FT_Property_Set and
78 * @FT_Property_Get.
79 *
80 * The CFF driver's module name is 'cff'.
81 *
82 * Available properties are @hinting-engine, @no-stem-darkening,
83 * @darkening-parameters, and @random-seed, as documented in the
84 * @properties section.
85 *
86 *
87 * **Hinting and anti-aliasing principles of the new engine**
88 *
89 * The rasterizer is positioning horizontal features (e.g., ascender
90 * height & x-height, or crossbars) on the pixel grid and minimizing the
91 * amount of anti-aliasing applied to them, while placing vertical
92 * features (vertical stems) on the pixel grid without hinting, thus
93 * representing the stem position and weight accurately. Sometimes the
94 * vertical stems may be only partially black. In this context,
95 * 'anti-aliasing' means that stems are not positioned exactly on pixel
96 * borders, causing a fuzzy appearance.
97 *
98 * There are two principles behind this approach.
99 *
100 * 1) No hinting in the horizontal direction: Unlike 'superhinted'
101 * TrueType, which changes glyph widths to accommodate regular
102 * inter-glyph spacing, Adobe's approach is 'faithful to the design' in
103 * representing both the glyph width and the inter-glyph spacing designed
104 * for the font. This makes the screen display as close as it can be to
105 * the result one would get with infinite resolution, while preserving
106 * what is considered the key characteristics of each glyph. Note that
107 * the distances between unhinted and grid-fitted positions at small
108 * sizes are comparable to kerning values and thus would be noticeable
109 * (and distracting) while reading if hinting were applied.
110 *
111 * One of the reasons to not hint horizontally is anti-aliasing for LCD
112 * screens: The pixel geometry of modern displays supplies three vertical
113 * subpixels as the eye moves horizontally across each visible pixel. On
114 * devices where we can be certain this characteristic is present a
115 * rasterizer can take advantage of the subpixels to add increments of
116 * weight. In Western writing systems this turns out to be the more
117 * critical direction anyway; the weights and spacing of vertical stems
118 * (see above) are central to Armenian, Cyrillic, Greek, and Latin type
119 * designs. Even when the rasterizer uses greyscale anti-aliasing instead
120 * of color (a necessary compromise when one doesn't know the screen
121 * characteristics), the unhinted vertical features preserve the design's
122 * weight and spacing much better than aliased type would.
123 *
124 * 2) Alignment in the vertical direction: Weights and spacing along the
125 * y~axis are less critical; what is much more important is the visual
126 * alignment of related features (like cap-height and x-height). The
127 * sense of alignment for these is enhanced by the sharpness of grid-fit
128 * edges, while the cruder vertical resolution (full pixels instead of
129 * 1/3 pixels) is less of a problem.
130 *
131 * On the technical side, horizontal alignment zones for ascender,
132 * x-height, and other important height values (traditionally called
133 * 'blue zones') as defined in the font are positioned independently,
134 * each being rounded to the nearest pixel edge, taking care of overshoot
135 * suppression at small sizes, stem darkening, and scaling.
136 *
137 * Hstems (that is, hint values defined in the font to help align
138 * horizontal features) that fall within a blue zone are said to be
139 * 'captured' and are aligned to that zone. Uncaptured stems are moved
140 * in one of four ways, top edge up or down, bottom edge up or down.
141 * Unless there are conflicting hstems, the smallest movement is taken to
142 * minimize distortion.
143 *
144 */
145
146
147 /**************************************************************************
148 *
149 * @section:
150 * pcf_driver
151 *
152 * @title:
153 * The PCF driver
154 *
155 * @abstract:
156 * Controlling the PCF driver module.
157 *
158 * @description:
159 * While FreeType's PCF driver doesn't expose API functions by itself, it
160 * is possible to control its behaviour with @FT_Property_Set and
161 * @FT_Property_Get. Right now, there is a single property
162 * @no-long-family-names available if FreeType is compiled with
163 * PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
164 *
165 * The PCF driver's module name is 'pcf'.
166 *
167 */
168
169
170 /**************************************************************************
171 *
172 * @section:
173 * t1_cid_driver
174 *
175 * @title:
176 * The Type 1 and CID drivers
177 *
178 * @abstract:
179 * Controlling the Type~1 and CID driver modules.
180 *
181 * @description:
182 * It is possible to control the behaviour of FreeType's Type~1 and
183 * Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
184 *
185 * Behind the scenes, both drivers use the Adobe CFF engine for hinting;
186 * however, the used properties must be specified separately.
187 *
188 * The Type~1 driver's module name is 'type1'; the CID driver's module
189 * name is 't1cid'.
190 *
191 * Available properties are @hinting-engine, @no-stem-darkening,
192 * @darkening-parameters, and @random-seed, as documented in the
193 * @properties section.
194 *
195 * Please see the @cff_driver section for more details on the new hinting
196 * engine.
197 *
198 */
199
200
201 /**************************************************************************
202 *
203 * @section:
204 * tt_driver
205 *
206 * @title:
207 * The TrueType driver
208 *
209 * @abstract:
210 * Controlling the TrueType driver module.
211 *
212 * @description:
213 * While FreeType's TrueType driver doesn't expose API functions by
214 * itself, it is possible to control its behaviour with @FT_Property_Set
215 * and @FT_Property_Get.
216 *
217 * The TrueType driver's module name is 'truetype'; a single property
218 * @interpreter-version is available, as documented in the @properties
219 * section.
220 *
221 * To help understand the differences between interpreter versions, we
222 * introduce a list of definitions, kindly provided by Greg Hitchcock.
223 *
224 * _Bi-Level Rendering_
225 *
226 * Monochromatic rendering, exclusively used in the early days of
227 * TrueType by both Apple and Microsoft. Microsoft's GDI interface
228 * supported hinting of the right-side bearing point, such that the
229 * advance width could be non-linear. Most often this was done to
230 * achieve some level of glyph symmetry. To enable reasonable
231 * performance (e.g., not having to run hinting on all glyphs just to get
232 * the widths) there was a bit in the head table indicating if the side
233 * bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache
234 * hinting widths across multiple sizes and device aspect ratios.
235 *
236 * _Font Smoothing_
237 *
238 * Microsoft's GDI implementation of anti-aliasing. Not traditional
239 * anti-aliasing as the outlines were hinted before the sampling. The
240 * widths matched the bi-level rendering.
241 *
242 * _ClearType Rendering_
243 *
244 * Technique that uses physical subpixels to improve rendering on LCD
245 * (and other) displays. Because of the higher resolution, many methods
246 * of improving symmetry in glyphs through hinting the right-side bearing
247 * were no longer necessary. This lead to what GDI calls 'natural
248 * widths' ClearType, see
249 * http://rastertragedy.com/RTRCh4.htm#Sec21. Since hinting
250 * has extra resolution, most non-linearity went away, but it is still
251 * possible for hints to change the advance widths in this mode.
252 *
253 * _ClearType Compatible Widths_
254 *
255 * One of the earliest challenges with ClearType was allowing the
256 * implementation in GDI to be selected without requiring all UI and
257 * documents to reflow. To address this, a compatible method of
258 * rendering ClearType was added where the font hints are executed once
259 * to determine the width in bi-level rendering, and then re-run in
260 * ClearType, with the difference in widths being absorbed in the font
261 * hints for ClearType (mostly in the white space of hints); see
262 * http://rastertragedy.com/RTRCh4.htm#Sec20. Somewhat by
263 * definition, compatible width ClearType allows for non-linear widths,
264 * but only when the bi-level version has non-linear widths.
265 *
266 * _ClearType Subpixel Positioning_
267 *
268 * One of the nice benefits of ClearType is the ability to more crisply
269 * display fractional widths; unfortunately, the GDI model of integer
270 * bitmaps did not support this. However, the WPF and Direct Write
271 * frameworks do support fractional widths. DWrite calls this 'natural
272 * mode', not to be confused with GDI's 'natural widths'. Subpixel
273 * positioning, in the current implementation of Direct Write,
274 * unfortunately does not support hinted advance widths, see
275 * http://rastertragedy.com/RTRCh4.htm#Sec22. Note that the
276 * TrueType interpreter fully allows the advance width to be adjusted in
277 * this mode, just the DWrite client will ignore those changes.
278 *
279 * _ClearType Backward Compatibility_
280 *
281 * This is a set of exceptions made in the TrueType interpreter to
282 * minimize hinting techniques that were problematic with the extra
283 * resolution of ClearType; see
284 * http://rastertragedy.com/RTRCh4.htm#Sec1 and
285 * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
286 * This technique is not to be confused with ClearType compatible widths.
287 * ClearType backward compatibility has no direct impact on changing
288 * advance widths, but there might be an indirect impact on disabling
289 * some deltas. This could be worked around in backward compatibility
290 * mode.
291 *
292 * _Native ClearType Mode_
293 *
294 * (Not to be confused with 'natural widths'.) This mode removes all the
295 * exceptions in the TrueType interpreter when running with ClearType.
296 * Any issues on widths would still apply, though.
297 *
298 */
299
300
301 /**************************************************************************
302 *
303 * @section:
304 * ot_svg_driver
305 *
306 * @title:
307 * The SVG driver
308 *
309 * @abstract:
310 * Controlling the external rendering of OT-SVG glyphs.
311 *
312 * @description:
313 * By default, FreeType can only load the 'SVG~' table of OpenType fonts
314 * if configuration macro `FT_CONFIG_OPTION_SVG` is defined. To make it
315 * render SVG glyphs, an external SVG rendering library is needed. All
316 * details on the interface between FreeType and the external library
317 * via function hooks can be found in section @svg_fonts.
318 *
319 * The OT-SVG driver's module name is 'ot-svg'; it supports a single
320 * property called @svg-hooks, documented below in the @properties
321 * section.
322 *
323 */
324
325
326 /**************************************************************************
327 *
328 * @section:
329 * properties
330 *
331 * @title:
332 * Driver properties
333 *
334 * @abstract:
335 * Controlling driver modules.
336 *
337 * @description:
338 * Driver modules can be controlled by setting and unsetting properties,
339 * using the functions @FT_Property_Set and @FT_Property_Get. This
340 * section documents the available properties, together with auxiliary
341 * macros and structures.
342 *
343 */
344
345
346 /**************************************************************************
347 *
348 * @enum:
349 * FT_HINTING_XXX
350 *
351 * @description:
352 * A list of constants used for the @hinting-engine property to select
353 * the hinting engine for CFF, Type~1, and CID fonts.
354 *
355 * @values:
356 * FT_HINTING_FREETYPE ::
357 * Use the old FreeType hinting engine.
358 *
359 * FT_HINTING_ADOBE ::
360 * Use the hinting engine contributed by Adobe.
361 *
362 * @since:
363 * 2.9
364 *
365 */
366 #define FT_HINTING_FREETYPE 0
367 #define FT_HINTING_ADOBE 1
368
369 /* these constants (introduced in 2.4.12) are deprecated */
370 #define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE
371 #define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE
372
373
374 /**************************************************************************
375 *
376 * @property:
377 * hinting-engine
378 *
379 * @description:
380 * Thanks to Adobe, which contributed a new hinting (and parsing) engine,
381 * an application can select between 'freetype' and 'adobe' if compiled
382 * with `CFF_CONFIG_OPTION_OLD_ENGINE`. If this configuration macro
383 * isn't defined, 'hinting-engine' does nothing.
384 *
385 * The same holds for the Type~1 and CID modules if compiled with
386 * `T1_CONFIG_OPTION_OLD_ENGINE`.
387 *
388 * For the 'cff' module, the default engine is 'adobe'. For both the
389 * 'type1' and 't1cid' modules, the default engine is 'adobe', too.
390 *
391 * @note:
392 * This property can be used with @FT_Property_Get also.
393 *
394 * This property can be set via the `FREETYPE_PROPERTIES` environment
395 * variable (using values 'adobe' or 'freetype').
396 *
397 * @example:
398 * The following example code demonstrates how to select Adobe's hinting
399 * engine for the 'cff' module (omitting the error handling).
400 *
401 * ```
402 * FT_Library library;
403 * FT_UInt hinting_engine = FT_HINTING_ADOBE;
404 *
405 *
406 * FT_Init_FreeType( &library );
407 *
408 * FT_Property_Set( library, "cff",
409 * "hinting-engine", &hinting_engine );
410 * ```
411 *
412 * @since:
413 * 2.4.12 (for 'cff' module)
414 *
415 * 2.9 (for 'type1' and 't1cid' modules)
416 *
417 */
418
419
420 /**************************************************************************
421 *
422 * @property:
423 * no-stem-darkening
424 *
425 * @description:
426 * All glyphs that pass through the auto-hinter will be emboldened unless
427 * this property is set to TRUE. The same is true for the CFF, Type~1,
428 * and CID font modules if the 'Adobe' engine is selected (which is the
429 * default).
430 *
431 * Stem darkening emboldens glyphs at smaller sizes to make them more
432 * readable on common low-DPI screens when using linear alpha blending
433 * and gamma correction, see @FT_Render_Glyph. When not using linear
434 * alpha blending and gamma correction, glyphs will appear heavy and
435 * fuzzy!
436 *
437 * Gamma correction essentially lightens fonts since shades of grey are
438 * shifted to higher pixel values (=~higher brightness) to match the
439 * original intention to the reality of our screens. The side-effect is
440 * that glyphs 'thin out'. Mac OS~X and Adobe's proprietary font
441 * rendering library implement a counter-measure: stem darkening at
442 * smaller sizes where shades of gray dominate. By emboldening a glyph
443 * slightly in relation to its pixel size, individual pixels get higher
444 * coverage of filled-in outlines and are therefore 'blacker'. This
445 * counteracts the 'thinning out' of glyphs, making text remain readable
446 * at smaller sizes.
447 *
448 * For the auto-hinter, stem-darkening is experimental currently and thus
449 * switched off by default (that is, `no-stem-darkening` is set to TRUE
450 * by default). Total consistency with the CFF driver is not achieved
451 * right now because the emboldening method differs and glyphs must be
452 * scaled down on the Y-axis to keep outline points inside their
453 * precomputed blue zones. The smaller the size (especially 9ppem and
454 * down), the higher the loss of emboldening versus the CFF driver.
455 *
456 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
457 *
458 * @note:
459 * This property can be used with @FT_Property_Get also.
460 *
461 * This property can be set via the `FREETYPE_PROPERTIES` environment
462 * variable (using values 1 and 0 for 'on' and 'off', respectively). It
463 * can also be set per face using @FT_Face_Properties with
464 * @FT_PARAM_TAG_STEM_DARKENING.
465 *
466 * @example:
467 * ```
468 * FT_Library library;
469 * FT_Bool no_stem_darkening = TRUE;
470 *
471 *
472 * FT_Init_FreeType( &library );
473 *
474 * FT_Property_Set( library, "cff",
475 * "no-stem-darkening", &no_stem_darkening );
476 * ```
477 *
478 * @since:
479 * 2.4.12 (for 'cff' module)
480 *
481 * 2.6.2 (for 'autofitter' module)
482 *
483 * 2.9 (for 'type1' and 't1cid' modules)
484 *
485 */
486
487
488 /**************************************************************************
489 *
490 * @property:
491 * darkening-parameters
492 *
493 * @description:
494 * By default, the Adobe hinting engine, as used by the CFF, Type~1, and
495 * CID font drivers, darkens stems as follows (if the `no-stem-darkening`
496 * property isn't set):
497 *
498 * ```
499 * stem width <= 0.5px: darkening amount = 0.4px
500 * stem width = 1px: darkening amount = 0.275px
501 * stem width = 1.667px: darkening amount = 0.275px
502 * stem width >= 2.333px: darkening amount = 0px
503 * ```
504 *
505 * and piecewise linear in-between. At configuration time, these four
506 * control points can be set with the macro
507 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID
508 * drivers share these values. At runtime, the control points can be
509 * changed using the `darkening-parameters` property (see the example
510 * below that demonstrates this for the Type~1 driver).
511 *
512 * The x~values give the stem width, and the y~values the darkening
513 * amount. The unit is 1000th of pixels. All coordinate values must be
514 * positive; the x~values must be monotonically increasing; the y~values
515 * must be monotonically decreasing and smaller than or equal to 500
516 * (corresponding to half a pixel); the slope of each linear piece must
517 * be shallower than -1 (e.g., -.4).
518 *
519 * The auto-hinter provides this property, too, as an experimental
520 * feature. See @no-stem-darkening for more.
521 *
522 * @note:
523 * This property can be used with @FT_Property_Get also.
524 *
525 * This property can be set via the `FREETYPE_PROPERTIES` environment
526 * variable, using eight comma-separated integers without spaces. Here
527 * the above example, using `\` to break the line for readability.
528 *
529 * ```
530 * FREETYPE_PROPERTIES=\
531 * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0
532 * ```
533 *
534 * @example:
535 * ```
536 * FT_Library library;
537 * FT_Int darken_params[8] = { 500, 300, // x1, y1
538 * 1000, 200, // x2, y2
539 * 1500, 100, // x3, y3
540 * 2000, 0 }; // x4, y4
541 *
542 *
543 * FT_Init_FreeType( &library );
544 *
545 * FT_Property_Set( library, "type1",
546 * "darkening-parameters", darken_params );
547 * ```
548 *
549 * @since:
550 * 2.5.1 (for 'cff' module)
551 *
552 * 2.6.2 (for 'autofitter' module)
553 *
554 * 2.9 (for 'type1' and 't1cid' modules)
555 *
556 */
557
558
559 /**************************************************************************
560 *
561 * @property:
562 * random-seed
563 *
564 * @description:
565 * By default, the seed value for the CFF 'random' operator and the
566 * similar '0 28 callothersubr pop' command for the Type~1 and CID
567 * drivers is set to a random value. However, mainly for debugging
568 * purposes, it is often necessary to use a known value as a seed so that
569 * the pseudo-random number sequences generated by 'random' are
570 * repeatable.
571 *
572 * The `random-seed` property does that. Its argument is a signed 32bit
573 * integer; if the value is zero or negative, the seed given by the
574 * `intitialRandomSeed` private DICT operator in a CFF file gets used (or
575 * a default value if there is no such operator). If the value is
576 * positive, use it instead of `initialRandomSeed`, which is consequently
577 * ignored.
578 *
579 * @note:
580 * This property can be set via the `FREETYPE_PROPERTIES` environment
581 * variable. It can also be set per face using @FT_Face_Properties with
582 * @FT_PARAM_TAG_RANDOM_SEED.
583 *
584 * @since:
585 * 2.8 (for 'cff' module)
586 *
587 * 2.9 (for 'type1' and 't1cid' modules)
588 *
589 */
590
591
592 /**************************************************************************
593 *
594 * @property:
595 * no-long-family-names
596 *
597 * @description:
598 * If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling
599 * FreeType, the PCF driver constructs long family names.
600 *
601 * There are many PCF fonts just called 'Fixed' which look completely
602 * different, and which have nothing to do with each other. When
603 * selecting 'Fixed' in KDE or Gnome one gets results that appear rather
604 * random, the style changes often if one changes the size and one cannot
605 * select some fonts at all. The improve this situation, the PCF module
606 * prepends the foundry name (plus a space) to the family name. It also
607 * checks whether there are 'wide' characters; all put together, family
608 * names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed.
609 *
610 * If `no-long-family-names` is set, this feature gets switched off.
611 *
612 * @note:
613 * This property can be used with @FT_Property_Get also.
614 *
615 * This property can be set via the `FREETYPE_PROPERTIES` environment
616 * variable (using values 1 and 0 for 'on' and 'off', respectively).
617 *
618 * @example:
619 * ```
620 * FT_Library library;
621 * FT_Bool no_long_family_names = TRUE;
622 *
623 *
624 * FT_Init_FreeType( &library );
625 *
626 * FT_Property_Set( library, "pcf",
627 * "no-long-family-names",
628 * &no_long_family_names );
629 * ```
630 *
631 * @since:
632 * 2.8
633 */
634
635
636 /**************************************************************************
637 *
638 * @enum:
639 * TT_INTERPRETER_VERSION_XXX
640 *
641 * @description:
642 * A list of constants used for the @interpreter-version property to
643 * select the hinting engine for Truetype fonts.
644 *
645 * The numeric value in the constant names represents the version number
646 * as returned by the 'GETINFO' bytecode instruction.
647 *
648 * @values:
649 * TT_INTERPRETER_VERSION_35 ::
650 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
651 * Windows~98; only grayscale and B/W rasterizing is supported.
652 *
653 * TT_INTERPRETER_VERSION_38 ::
654 * Version~38 is the same Version~40. The original 'Infinality' code is
655 * no longer available.
656 *
657 * TT_INTERPRETER_VERSION_40 ::
658 * Version~40 corresponds to MS rasterizer v.2.1; it is roughly
659 * equivalent to the hinting provided by DirectWrite ClearType (as can
660 * be found, for example, in Microsoft's Edge Browser on Windows~10).
661 * It is used in FreeType to select the 'minimal' subpixel hinting
662 * code, a stripped-down and higher performance version of the
663 * 'Infinality' code.
664 *
665 * @note:
666 * This property controls the behaviour of the bytecode interpreter and
667 * thus how outlines get hinted. It does **not** control how glyph get
668 * rasterized! In particular, it does not control subpixel color
669 * filtering.
670 *
671 * If FreeType has not been compiled with the configuration option
672 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 causes
673 * an `FT_Err_Unimplemented_Feature` error.
674 *
675 * Depending on the graphics framework, Microsoft uses different bytecode
676 * and rendering engines. As a consequence, the version numbers returned
677 * by a call to the 'GETINFO' bytecode instruction are more convoluted
678 * than desired.
679 *
680 * Here are two tables that try to shed some light on the possible values
681 * for the MS rasterizer engine, together with the additional features
682 * introduced by it.
683 *
684 * ```
685 * GETINFO framework version feature
686 * -------------------------------------------------------------------
687 * 3 GDI (Win 3.1), v1.0 16-bit, first version
688 * TrueImage
689 * 33 GDI (Win NT 3.1), v1.5 32-bit
690 * HP Laserjet
691 * 34 GDI (Win 95) v1.6 font smoothing,
692 * new SCANTYPE opcode
693 * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET
694 * bits in composite glyphs
695 * 36 MGDI (Win CE 2) v1.6+ classic ClearType
696 * 37 GDI (XP and later), v1.8 ClearType
697 * GDI+ old (before Vista)
698 * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType,
699 * WPF Y-direction ClearType,
700 * additional error checking
701 * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags
702 * in GETINFO opcode,
703 * bug fixes
704 * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag
705 * DWrite (Win 8) in GETINFO opcode,
706 * Gray ClearType
707 * ```
708 *
709 * The 'version' field gives a rough orientation only, since some
710 * applications provided certain features much earlier (as an example,
711 * Microsoft Reader used subpixel and Y-direction ClearType already in
712 * Windows 2000). Similarly, updates to a given framework might include
713 * improved hinting support.
714 *
715 * ```
716 * version sampling rendering comment
717 * x y x y
718 * --------------------------------------------------------------
719 * v1.0 normal normal B/W B/W bi-level
720 * v1.6 high high gray gray grayscale
721 * v1.8 high normal color-filter B/W (GDI) ClearType
722 * v1.9 high high color-filter gray Color ClearType
723 * v2.1 high normal gray B/W Gray ClearType
724 * v2.1 high high gray gray Gray ClearType
725 * ```
726 *
727 * Color and Gray ClearType are the two available variants of
728 * 'Y-direction ClearType', meaning grayscale rasterization along the
729 * Y-direction; the name used in the TrueType specification for this
730 * feature is 'symmetric smoothing'. 'Classic ClearType' is the original
731 * algorithm used before introducing a modified version in Win~XP.
732 * Another name for v1.6's grayscale rendering is 'font smoothing', and
733 * 'Color ClearType' is sometimes also called 'DWrite ClearType'. To
734 * differentiate between today's Color ClearType and the earlier
735 * ClearType variant with B/W rendering along the vertical axis, the
736 * latter is sometimes called 'GDI ClearType'.
737 *
738 * 'Normal' and 'high' sampling describe the (virtual) resolution to
739 * access the rasterized outline after the hinting process. 'Normal'
740 * means 1 sample per grid line (i.e., B/W). In the current Microsoft
741 * implementation, 'high' means an extra virtual resolution of 16x16 (or
742 * 16x1) grid lines per pixel for bytecode instructions like 'MIRP'.
743 * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
744 * lines for color filtering if Color ClearType is activated.
745 *
746 * Note that 'Gray ClearType' is essentially the same as v1.6's grayscale
747 * rendering. However, the GETINFO instruction handles it differently:
748 * v1.6 returns bit~12 (hinting for grayscale), while v2.1 returns
749 * bits~13 (hinting for ClearType), 18 (symmetrical smoothing), and~19
750 * (Gray ClearType). Also, this mode respects bits 2 and~3 for the
751 * version~1 gasp table exclusively (like Color ClearType), while v1.6
752 * only respects the values of version~0 (bits 0 and~1).
753 *
754 * Keep in mind that the features of the above interpreter versions might
755 * not map exactly to FreeType features or behavior because it is a
756 * fundamentally different library with different internals.
757 *
758 */
759 #define TT_INTERPRETER_VERSION_35 35
760 #define TT_INTERPRETER_VERSION_38 38
761 #define TT_INTERPRETER_VERSION_40 40
762
763
764 /**************************************************************************
765 *
766 * @property:
767 * interpreter-version
768 *
769 * @description:
770 * Currently, three versions are available, two representing the bytecode
771 * interpreter with subpixel hinting support (old 'Infinality' code and
772 * new stripped-down and higher performance 'minimal' code) and one
773 * without, respectively. The default is subpixel support if
774 * `TT_CONFIG_OPTION_SUBPIXEL_HINTING` is defined, and no subpixel
775 * support otherwise (since it isn't available then).
776 *
777 * If subpixel hinting is on, many TrueType bytecode instructions behave
778 * differently compared to B/W or grayscale rendering (except if 'native
779 * ClearType' is selected by the font). Microsoft's main idea is to
780 * render at a much increased horizontal resolution, then sampling down
781 * the created output to subpixel precision. However, many older fonts
782 * are not suited to this and must be specially taken care of by applying
783 * (hardcoded) tweaks in Microsoft's interpreter.
784 *
785 * Details on subpixel hinting and some of the necessary tweaks can be
786 * found in Greg Hitchcock's whitepaper at
787 * 'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
788 * Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2,
789 * or 6x5 supersampling) like discussed in the paper. Depending on the
790 * chosen interpreter, it simply ignores instructions on vertical stems
791 * to arrive at very similar results.
792 *
793 * @note:
794 * This property can be used with @FT_Property_Get also.
795 *
796 * This property can be set via the `FREETYPE_PROPERTIES` environment
797 * variable (using values '35', '38', or '40').
798 *
799 * @example:
800 * The following example code demonstrates how to deactivate subpixel
801 * hinting (omitting the error handling).
802 *
803 * ```
804 * FT_Library library;
805 * FT_Face face;
806 * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35;
807 *
808 *
809 * FT_Init_FreeType( &library );
810 *
811 * FT_Property_Set( library, "truetype",
812 * "interpreter-version",
813 * &interpreter_version );
814 * ```
815 *
816 * @since:
817 * 2.5
818 */
819
820 /**************************************************************************
821 *
822 * @property:
823 * svg-hooks
824 *
825 * @description:
826 * Set up the interface between FreeType and an extern SVG rendering
827 * library like 'librsvg'. All details on the function hooks can be
828 * found in section @svg_fonts.
829 *
830 * @example:
831 * The following example code expects that the four hook functions
832 * `svg_*` are defined elsewhere. Error handling is omitted, too.
833 *
834 * ```
835 * FT_Library library;
836 * SVG_RendererHooks hooks = {
837 * (SVG_Lib_Init_Func)svg_init,
838 * (SVG_Lib_Free_Func)svg_free,
839 * (SVG_Lib_Render_Func)svg_render,
840 * (SVG_Lib_Preset_Slot_Func)svg_preset_slot };
841 *
842 *
843 * FT_Init_FreeType( &library );
844 *
845 * FT_Property_Set( library, "ot-svg",
846 * "svg-hooks", &hooks );
847 * ```
848 *
849 * @since:
850 * 2.12
851 */
852
853
854 /**************************************************************************
855 *
856 * @property:
857 * glyph-to-script-map
858 *
859 * @description:
860 * **Experimental only**
861 *
862 * The auto-hinter provides various script modules to hint glyphs.
863 * Examples of supported scripts are Latin or CJK. Before a glyph is
864 * auto-hinted, the Unicode character map of the font gets examined, and
865 * the script is then determined based on Unicode character ranges, see
866 * below.
867 *
868 * OpenType fonts, however, often provide much more glyphs than character
869 * codes (small caps, superscripts, ligatures, swashes, etc.), to be
870 * controlled by so-called 'features'. Handling OpenType features can be
871 * quite complicated and thus needs a separate library on top of
872 * FreeType.
873 *
874 * The mapping between glyph indices and scripts (in the auto-hinter
875 * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array
876 * with `num_glyphs` elements, as found in the font's @FT_Face structure.
877 * The `glyph-to-script-map` property returns a pointer to this array,
878 * which can be modified as needed. Note that the modification should
879 * happen before the first glyph gets processed by the auto-hinter so
880 * that the global analysis of the font shapes actually uses the modified
881 * mapping.
882 *
883 * @example:
884 * The following example code demonstrates how to access it (omitting the
885 * error handling).
886 *
887 * ```
888 * FT_Library library;
889 * FT_Face face;
890 * FT_Prop_GlyphToScriptMap prop;
891 *
892 *
893 * FT_Init_FreeType( &library );
894 * FT_New_Face( library, "foo.ttf", 0, &face );
895 *
896 * prop.face = face;
897 *
898 * FT_Property_Get( library, "autofitter",
899 * "glyph-to-script-map", &prop );
900 *
901 * // adjust `prop.map' as needed right here
902 *
903 * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
904 * ```
905 *
906 * @since:
907 * 2.4.11
908 *
909 */
910
911
912 /**************************************************************************
913 *
914 * @enum:
915 * FT_AUTOHINTER_SCRIPT_XXX
916 *
917 * @description:
918 * **Experimental only**
919 *
920 * A list of constants used for the @glyph-to-script-map property to
921 * specify the script submodule the auto-hinter should use for hinting a
922 * particular glyph.
923 *
924 * @values:
925 * FT_AUTOHINTER_SCRIPT_NONE ::
926 * Don't auto-hint this glyph.
927 *
928 * FT_AUTOHINTER_SCRIPT_LATIN ::
929 * Apply the latin auto-hinter. For the auto-hinter, 'latin' is a very
930 * broad term, including Cyrillic and Greek also since characters from
931 * those scripts share the same design constraints.
932 *
933 * By default, characters from the following Unicode ranges are
934 * assigned to this submodule.
935 *
936 * ```
937 * U+0020 - U+007F // Basic Latin (no control characters)
938 * U+00A0 - U+00FF // Latin-1 Supplement (no control characters)
939 * U+0100 - U+017F // Latin Extended-A
940 * U+0180 - U+024F // Latin Extended-B
941 * U+0250 - U+02AF // IPA Extensions
942 * U+02B0 - U+02FF // Spacing Modifier Letters
943 * U+0300 - U+036F // Combining Diacritical Marks
944 * U+0370 - U+03FF // Greek and Coptic
945 * U+0400 - U+04FF // Cyrillic
946 * U+0500 - U+052F // Cyrillic Supplement
947 * U+1D00 - U+1D7F // Phonetic Extensions
948 * U+1D80 - U+1DBF // Phonetic Extensions Supplement
949 * U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement
950 * U+1E00 - U+1EFF // Latin Extended Additional
951 * U+1F00 - U+1FFF // Greek Extended
952 * U+2000 - U+206F // General Punctuation
953 * U+2070 - U+209F // Superscripts and Subscripts
954 * U+20A0 - U+20CF // Currency Symbols
955 * U+2150 - U+218F // Number Forms
956 * U+2460 - U+24FF // Enclosed Alphanumerics
957 * U+2C60 - U+2C7F // Latin Extended-C
958 * U+2DE0 - U+2DFF // Cyrillic Extended-A
959 * U+2E00 - U+2E7F // Supplemental Punctuation
960 * U+A640 - U+A69F // Cyrillic Extended-B
961 * U+A720 - U+A7FF // Latin Extended-D
962 * U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures)
963 * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
964 * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
965 * ```
966 *
967 * FT_AUTOHINTER_SCRIPT_CJK ::
968 * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
969 * Vietnamese, and some other scripts.
970 *
971 * By default, characters from the following Unicode ranges are
972 * assigned to this submodule.
973 *
974 * ```
975 * U+1100 - U+11FF // Hangul Jamo
976 * U+2E80 - U+2EFF // CJK Radicals Supplement
977 * U+2F00 - U+2FDF // Kangxi Radicals
978 * U+2FF0 - U+2FFF // Ideographic Description Characters
979 * U+3000 - U+303F // CJK Symbols and Punctuation
980 * U+3040 - U+309F // Hiragana
981 * U+30A0 - U+30FF // Katakana
982 * U+3100 - U+312F // Bopomofo
983 * U+3130 - U+318F // Hangul Compatibility Jamo
984 * U+3190 - U+319F // Kanbun
985 * U+31A0 - U+31BF // Bopomofo Extended
986 * U+31C0 - U+31EF // CJK Strokes
987 * U+31F0 - U+31FF // Katakana Phonetic Extensions
988 * U+3200 - U+32FF // Enclosed CJK Letters and Months
989 * U+3300 - U+33FF // CJK Compatibility
990 * U+3400 - U+4DBF // CJK Unified Ideographs Extension A
991 * U+4DC0 - U+4DFF // Yijing Hexagram Symbols
992 * U+4E00 - U+9FFF // CJK Unified Ideographs
993 * U+A960 - U+A97F // Hangul Jamo Extended-A
994 * U+AC00 - U+D7AF // Hangul Syllables
995 * U+D7B0 - U+D7FF // Hangul Jamo Extended-B
996 * U+F900 - U+FAFF // CJK Compatibility Ideographs
997 * U+FE10 - U+FE1F // Vertical forms
998 * U+FE30 - U+FE4F // CJK Compatibility Forms
999 * U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms
1000 * U+1B000 - U+1B0FF // Kana Supplement
1001 * U+1D300 - U+1D35F // Tai Xuan Hing Symbols
1002 * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
1003 * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
1004 * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
1005 * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
1006 * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
1007 * ```
1008 *
1009 * FT_AUTOHINTER_SCRIPT_INDIC ::
1010 * Apply the indic auto-hinter, covering all major scripts from the
1011 * Indian sub-continent and some other related scripts like Thai, Lao,
1012 * or Tibetan.
1013 *
1014 * By default, characters from the following Unicode ranges are
1015 * assigned to this submodule.
1016 *
1017 * ```
1018 * U+0900 - U+0DFF // Indic Range
1019 * U+0F00 - U+0FFF // Tibetan
1020 * U+1900 - U+194F // Limbu
1021 * U+1B80 - U+1BBF // Sundanese
1022 * U+A800 - U+A82F // Syloti Nagri
1023 * U+ABC0 - U+ABFF // Meetei Mayek
1024 * U+11800 - U+118DF // Sharada
1025 * ```
1026 *
1027 * Note that currently Indic support is rudimentary only, missing blue
1028 * zone support.
1029 *
1030 * @since:
1031 * 2.4.11
1032 *
1033 */
1034 #define FT_AUTOHINTER_SCRIPT_NONE 0
1035 #define FT_AUTOHINTER_SCRIPT_LATIN 1
1036 #define FT_AUTOHINTER_SCRIPT_CJK 2
1037 #define FT_AUTOHINTER_SCRIPT_INDIC 3
1038
1039
1040 /**************************************************************************
1041 *
1042 * @struct:
1043 * FT_Prop_GlyphToScriptMap
1044 *
1045 * @description:
1046 * **Experimental only**
1047 *
1048 * The data exchange structure for the @glyph-to-script-map property.
1049 *
1050 * @since:
1051 * 2.4.11
1052 *
1053 */
1054 typedef struct FT_Prop_GlyphToScriptMap_
1055 {
1056 FT_Face face;
1057 FT_UShort* map;
1058
1059 } FT_Prop_GlyphToScriptMap;
1060
1061
1062 /**************************************************************************
1063 *
1064 * @property:
1065 * fallback-script
1066 *
1067 * @description:
1068 * **Experimental only**
1069 *
1070 * If no auto-hinter script module can be assigned to a glyph, a fallback
1071 * script gets assigned to it (see also the @glyph-to-script-map
1072 * property). By default, this is @FT_AUTOHINTER_SCRIPT_CJK. Using the
1073 * `fallback-script` property, this fallback value can be changed.
1074 *
1075 * @note:
1076 * This property can be used with @FT_Property_Get also.
1077 *
1078 * It's important to use the right timing for changing this value: The
1079 * creation of the glyph-to-script map that eventually uses the fallback
1080 * script value gets triggered either by setting or reading a
1081 * face-specific property like @glyph-to-script-map, or by auto-hinting
1082 * any glyph from that face. In particular, if you have already created
1083 * an @FT_Face structure but not loaded any glyph (using the
1084 * auto-hinter), a change of the fallback script will affect this face.
1085 *
1086 * @example:
1087 * ```
1088 * FT_Library library;
1089 * FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
1090 *
1091 *
1092 * FT_Init_FreeType( &library );
1093 *
1094 * FT_Property_Set( library, "autofitter",
1095 * "fallback-script", &fallback_script );
1096 * ```
1097 *
1098 * @since:
1099 * 2.4.11
1100 *
1101 */
1102
1103
1104 /**************************************************************************
1105 *
1106 * @property:
1107 * default-script
1108 *
1109 * @description:
1110 * **Experimental only**
1111 *
1112 * If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make
1113 * the HarfBuzz library access OpenType features for getting better glyph
1114 * coverages, this property sets the (auto-fitter) script to be used for
1115 * the default (OpenType) script data of a font's GSUB table. Features
1116 * for the default script are intended for all scripts not explicitly
1117 * handled in GSUB; an example is a 'dlig' feature, containing the
1118 * combination of the characters 'T', 'E', and 'L' to form a 'TEL'
1119 * ligature.
1120 *
1121 * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the
1122 * `default-script` property, this default value can be changed.
1123 *
1124 * @note:
1125 * This property can be used with @FT_Property_Get also.
1126 *
1127 * It's important to use the right timing for changing this value: The
1128 * creation of the glyph-to-script map that eventually uses the default
1129 * script value gets triggered either by setting or reading a
1130 * face-specific property like @glyph-to-script-map, or by auto-hinting
1131 * any glyph from that face. In particular, if you have already created
1132 * an @FT_Face structure but not loaded any glyph (using the
1133 * auto-hinter), a change of the default script will affect this face.
1134 *
1135 * @example:
1136 * ```
1137 * FT_Library library;
1138 * FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
1139 *
1140 *
1141 * FT_Init_FreeType( &library );
1142 *
1143 * FT_Property_Set( library, "autofitter",
1144 * "default-script", &default_script );
1145 * ```
1146 *
1147 * @since:
1148 * 2.5.3
1149 *
1150 */
1151
1152
1153 /**************************************************************************
1154 *
1155 * @property:
1156 * increase-x-height
1157 *
1158 * @description:
1159 * For ppem values in the range 6~<= ppem <= `increase-x-height`, round
1160 * up the font's x~height much more often than normally. If the value is
1161 * set to~0, which is the default, this feature is switched off. Use
1162 * this property to improve the legibility of small font sizes if
1163 * necessary.
1164 *
1165 * @note:
1166 * This property can be used with @FT_Property_Get also.
1167 *
1168 * Set this value right after calling @FT_Set_Char_Size, but before
1169 * loading any glyph (using the auto-hinter).
1170 *
1171 * @example:
1172 * ```
1173 * FT_Library library;
1174 * FT_Face face;
1175 * FT_Prop_IncreaseXHeight prop;
1176 *
1177 *
1178 * FT_Init_FreeType( &library );
1179 * FT_New_Face( library, "foo.ttf", 0, &face );
1180 * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
1181 *
1182 * prop.face = face;
1183 * prop.limit = 14;
1184 *
1185 * FT_Property_Set( library, "autofitter",
1186 * "increase-x-height", &prop );
1187 * ```
1188 *
1189 * @since:
1190 * 2.4.11
1191 *
1192 */
1193
1194
1195 /**************************************************************************
1196 *
1197 * @struct:
1198 * FT_Prop_IncreaseXHeight
1199 *
1200 * @description:
1201 * The data exchange structure for the @increase-x-height property.
1202 *
1203 */
1204 typedef struct FT_Prop_IncreaseXHeight_
1205 {
1206 FT_Face face;
1207 FT_UInt limit;
1208
1209 } FT_Prop_IncreaseXHeight;
1210
1211
1212 /**************************************************************************
1213 *
1214 * @property:
1215 * warping
1216 *
1217 * @description:
1218 * **Obsolete**
1219 *
1220 * This property was always experimental and probably never worked
1221 * correctly. It was entirely removed from the FreeType~2 sources. This
1222 * entry is only here for historical reference.
1223 *
1224 * Warping only worked in 'normal' auto-hinting mode replacing it. The
1225 * idea of the code was to slightly scale and shift a glyph along the
1226 * non-hinted dimension (which is usually the horizontal axis) so that as
1227 * much of its segments were aligned (more or less) to the grid. To find
1228 * out a glyph's optimal scaling and shifting value, various parameter
1229 * combinations were tried and scored.
1230 *
1231 * @since:
1232 * 2.6
1233 *
1234 */
1235
1236
1237 /* */
1238
1239
1240 FT_END_HEADER
1241
1242
1243 #endif /* FTDRIVER_H_ */
1244
1245
1246 /* END */