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1 /***************************************************************************/
2 /*                                                                         */
3 /*  ftdriver.h                                                             */
4 /*                                                                         */
5 /*    FreeType API for controlling driver modules (specification only).    */
6 /*                                                                         */
7 /*  Copyright 2017-2018 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
54    *   historical 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,
78    *   it 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
105    *   designed for the font.  This makes the screen display as close as it
106    *   can be to the result one would get with infinite resolution, while
107    *   preserving what is considered the key characteristics of each glyph.
108    *   Note that the distances between unhinted and grid-fitted positions at
109    *   small sizes are comparable to kerning values and thus would be
110    *   noticeable (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
114    *   vertical sub-pixels as the eye moves horizontally across each visible
115    *   pixel.  On devices where we can be certain this characteristic is
116    *   present a rasterizer can take advantage of the sub-pixels to add
117    *   increments of weight.  In Western writing systems this turns out to
118    *   be the more critical direction anyway; the weights and spacing of
119    *   vertical stems (see above) are central to Armenian, Cyrillic, Greek,
120    *   and Latin type designs.  Even when the rasterizer uses greyscale
121    *   antialiasing instead of color (a necessary compromise when one
122    *   doesn't know the screen characteristics), the unhinted vertical
123    *   features preserve the design's weight and spacing much better than
124    *   aliased type would.
125    *
126    *   2) Alignment in the vertical direction: Weights and spacing along the
127    *   y~axis are less critical; what is much more important is the visual
128    *   alignment of related features (like cap-height and x-height).  The
129    *   sense of alignment for these is enhanced by the sharpness of grid-fit
130    *   edges, while the cruder vertical resolution (full pixels instead of
131    *   1/3 pixels) is less of a problem.
132    *
133    *   On the technical side, horizontal alignment zones for ascender,
134    *   x-height, and other important height values (traditionally called
135    *   `blue zones') as defined in the font are positioned independently,
136    *   each being rounded to the nearest pixel edge, taking care of
137    *   overshoot suppression at small sizes, stem darkening, and scaling.
138    *
139    *   Hstems (this is, hint values defined in the font to help align
140    *   horizontal features) that fall within a blue zone are said to be
141    *   `captured' and are aligned to that zone.  Uncaptured stems are moved
142    *   in one of four ways, top edge up or down, bottom edge up or down.
143    *   Unless there are conflicting hstems, the smallest movement is taken
144    *   to minimize distortion.
145    *
146    */
147 
148 
149   /**************************************************************************
150    *
151    * @section:
152    *   pcf_driver
153    *
154    * @title:
155    *   The PCF driver
156    *
157    * @abstract:
158    *   Controlling the PCF driver module.
159    *
160    * @description:
161    *   While FreeType's PCF driver doesn't expose API functions by itself,
162    *   it is possible to control its behaviour with @FT_Property_Set and
163    *   @FT_Property_Get.  Right now, there is a single property
164    *   @no-long-family-names available if FreeType is compiled with
165    *   PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
166    *
167    *   The PCF driver's module name is `pcf'.
168    *
169    */
170 
171 
172   /**************************************************************************
173    *
174    * @section:
175    *   t1_cid_driver
176    *
177    * @title:
178    *   The Type 1 and CID drivers
179    *
180    * @abstract:
181    *   Controlling the Type~1 and CID driver modules.
182    *
183    * @description:
184    *   It is possible to control the behaviour of FreeType's Type~1 and
185    *   Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
186    *
187    *   Behind the scenes, both drivers use the Adobe CFF engine for hinting;
188    *   however, the used properties must be specified separately.
189    *
190    *   The Type~1 driver's module name is `type1'; the CID driver's module
191    *   name is `t1cid'.
192    *
193    *   Available properties are @hinting-engine, @no-stem-darkening,
194    *   @darkening-parameters, and @random-seed, as documented in the
195    *   @properties section.
196    *
197    *   Please see the @cff_driver section for more details on the new
198    *   hinting engine.
199    *
200    */
201 
202 
203   /**************************************************************************
204    *
205    * @section:
206    *   tt_driver
207    *
208    * @title:
209    *   The TrueType driver
210    *
211    * @abstract:
212    *   Controlling the TrueType driver module.
213    *
214    * @description:
215    *   While FreeType's TrueType driver doesn't expose API functions by
216    *   itself, it is possible to control its behaviour with @FT_Property_Set
217    *   and @FT_Property_Get.  The following lists the available properties
218    *   together with the necessary macros and structures.
219    *
220    *   The TrueType driver's module name is `truetype'.
221    *
222    *   A single property @interpreter-version is available, as documented in
223    *   the @properties section.
224    *
225    *   We start with a list of definitions, kindly provided by Greg
226    *   Hitchcock.
227    *
228    *   _Bi-Level_ _Rendering_
229    *
230    *   Monochromatic rendering, exclusively used in the early days of
231    *   TrueType by both Apple and Microsoft.  Microsoft's GDI interface
232    *   supported hinting of the right-side bearing point, such that the
233    *   advance width could be non-linear.  Most often this was done to
234    *   achieve some level of glyph symmetry.  To enable reasonable
235    *   performance (e.g., not having to run hinting on all glyphs just to
236    *   get the widths) there was a bit in the head table indicating if the
237    *   side bearing was hinted, and additional tables, `hdmx' and `LTSH', to
238    *   cache hinting widths across multiple sizes and device aspect ratios.
239    *
240    *   _Font_ _Smoothing_
241    *
242    *   Microsoft's GDI implementation of anti-aliasing.  Not traditional
243    *   anti-aliasing as the outlines were hinted before the sampling.  The
244    *   widths matched the bi-level rendering.
245    *
246    *   _ClearType_ _Rendering_
247    *
248    *   Technique that uses physical subpixels to improve rendering on LCD
249    *   (and other) displays.  Because of the higher resolution, many methods
250    *   of improving symmetry in glyphs through hinting the right-side
251    *   bearing were no longer necessary.  This lead to what GDI calls
252    *   `natural widths' ClearType, see
253    *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec21.  Since hinting
254    *   has extra resolution, most non-linearity went away, but it is still
255    *   possible for hints to change the advance widths in this mode.
256    *
257    *   _ClearType_ _Compatible_ _Widths_
258    *
259    *   One of the earliest challenges with ClearType was allowing the
260    *   implementation in GDI to be selected without requiring all UI and
261    *   documents to reflow.  To address this, a compatible method of
262    *   rendering ClearType was added where the font hints are executed once
263    *   to determine the width in bi-level rendering, and then re-run in
264    *   ClearType, with the difference in widths being absorbed in the font
265    *   hints for ClearType (mostly in the white space of hints); see
266    *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec20.  Somewhat by
267    *   definition, compatible width ClearType allows for non-linear widths,
268    *   but only when the bi-level version has non-linear widths.
269    *
270    *   _ClearType_ _Subpixel_ _Positioning_
271    *
272    *   One of the nice benefits of ClearType is the ability to more crisply
273    *   display fractional widths; unfortunately, the GDI model of integer
274    *   bitmaps did not support this.  However, the WPF and Direct Write
275    *   frameworks do support fractional widths.  DWrite calls this `natural
276    *   mode', not to be confused with GDI's `natural widths'.  Subpixel
277    *   positioning, in the current implementation of Direct Write,
278    *   unfortunately does not support hinted advance widths, see
279    *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec22.  Note that the
280    *   TrueType interpreter fully allows the advance width to be adjusted in
281    *   this mode, just the DWrite client will ignore those changes.
282    *
283    *   _ClearType_ _Backward_ _Compatibility_
284    *
285    *   This is a set of exceptions made in the TrueType interpreter to
286    *   minimize hinting techniques that were problematic with the extra
287    *   resolution of ClearType; see
288    *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec1 and
289    *   https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
290    *   This technique is not to be confused with ClearType compatible
291    *   widths.  ClearType backward compatibility has no direct impact on
292    *   changing advance widths, but there might be an indirect impact on
293    *   disabling some deltas.  This could be worked around in backward
294    *   compatibility mode.
295    *
296    *   _Native_ _ClearType_ _Mode_
297    *
298    *   (Not to be confused with `natural widths'.)  This mode removes all
299    *   the exceptions in the TrueType interpreter when running with
300    *   ClearType.  Any issues on widths would still apply, though.
301    *
302    */
303 
304 
305   /**************************************************************************
306    *
307    * @section:
308    *   properties
309    *
310    * @title:
311    *   Driver properties
312    *
313    * @abstract:
314    *   Controlling driver modules.
315    *
316    * @description:
317    *   Driver modules can be controlled by setting and unsetting properties,
318    *   using the functions @FT_Property_Set and @FT_Property_Get.  This
319    *   section documents the available properties, together with auxiliary
320    *   macros and structures.
321    *
322    */
323 
324 
325   /**************************************************************************
326    *
327    * @enum:
328    *   FT_HINTING_XXX
329    *
330    * @description:
331    *   A list of constants used for the @hinting-engine property to
332    *   select the hinting engine for CFF, Type~1, and CID fonts.
333    *
334    * @values:
335    *   FT_HINTING_FREETYPE ::
336    *     Use the old FreeType hinting engine.
337    *
338    *   FT_HINTING_ADOBE ::
339    *     Use the hinting engine contributed by Adobe.
340    *
341    * @since:
342    *   2.9
343    *
344    */
345 #define FT_HINTING_FREETYPE  0
346 #define FT_HINTING_ADOBE     1
347 
348   /* these constants (introduced in 2.4.12) are deprecated */
349 #define FT_CFF_HINTING_FREETYPE  FT_HINTING_FREETYPE
350 #define FT_CFF_HINTING_ADOBE     FT_HINTING_ADOBE
351 
352 
353   /**************************************************************************
354    *
355    * @property:
356    *   hinting-engine
357    *
358    * @description:
359    *   Thanks to Adobe, which contributed a new hinting (and parsing)
360    *   engine, an application can select between `freetype' and `adobe' if
361    *   compiled with CFF_CONFIG_OPTION_OLD_ENGINE.  If this configuration
362    *   macro isn't defined, `hinting-engine' does nothing.
363    *
364    *   The same holds for the Type~1 and CID modules if compiled with
365    *   T1_CONFIG_OPTION_OLD_ENGINE.
366    *
367    *   For the `cff' module, the default engine is `freetype' if
368    *   CFF_CONFIG_OPTION_OLD_ENGINE is defined, and `adobe' otherwise.
369    *
370    *   For both the `type1' and `t1cid' modules, the default engine is
371    *   `freetype' if T1_CONFIG_OPTION_OLD_ENGINE is defined, and `adobe'
372    *   otherwise.
373    *
374    *   The following example code demonstrates how to select Adobe's hinting
375    *   engine for the `cff' module (omitting the error handling).
376    *
377    *   {
378    *     FT_Library  library;
379    *     FT_UInt     hinting_engine = FT_CFF_HINTING_ADOBE;
380    *
381    *
382    *     FT_Init_FreeType( &library );
383    *
384    *     FT_Property_Set( library, "cff",
385    *                               "hinting-engine", &hinting_engine );
386    *   }
387    *
388    * @note:
389    *   This property can be used with @FT_Property_Get also.
390    *
391    *   This property can be set via the `FREETYPE_PROPERTIES' environment
392    *   variable (using values `adobe' or `freetype').
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
409    *   unless this property is set to TRUE.  The same is true for the CFF,
410    *   Type~1, and CID font modules if the `Adobe' engine is selected (which
411    *   is the 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
435    *   thus switched off by default (this is, `no-stem-darkening' is set to
436    *   TRUE by default).  Total consistency with the CFF driver is not
437    *   achieved right now because the emboldening method differs and glyphs
438    *   must be 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
443    *   set.
444    *
445    *   {
446    *     FT_Library  library;
447    *     FT_Bool     no_stem_darkening = TRUE;
448    *
449    *
450    *     FT_Init_FreeType( &library );
451    *
452    *     FT_Property_Set( library, "cff",
453    *                               "no-stem-darkening", &no_stem_darkening );
454    *   }
455    *
456    * @note:
457    *   This property can be used with @FT_Property_Get also.
458    *
459    *   This property can be set via the `FREETYPE_PROPERTIES' environment
460    *   variable (using values 1 and 0 for `on' and `off', respectively).
461    *   It can also be set per face using @FT_Face_Properties with
462    *   @FT_PARAM_TAG_STEM_DARKENING.
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
482    *   `no-stem-darkening' 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, as the following
496    *   example demonstrates for the Type~1 driver.
497    *
498    *   {
499    *     FT_Library  library;
500    *     FT_Int      darken_params[8] = {  500, 300,   // x1, y1
501    *                                      1000, 200,   // x2, y2
502    *                                      1500, 100,   // x3, y3
503    *                                      2000,   0 }; // x4, y4
504    *
505    *
506    *     FT_Init_FreeType( &library );
507    *
508    *     FT_Property_Set( library, "type1",
509    *                               "darkening-parameters", darken_params );
510    *   }
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
515    *   y~values must be monotonically decreasing and smaller than or
516    *   equal to 500 (corresponding to half a pixel); the slope of each
517    *   linear piece must 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    * @since:
535    *   2.5.1 (for `cff' module)
536    *
537    *   2.6.2 (for `autofitter' module)
538    *
539    *   2.9 (for `type1' and `t1cid' modules)
540    *
541    */
542 
543 
544   /**************************************************************************
545    *
546    * @property:
547    *   random-seed
548    *
549    * @description:
550    *   By default, the seed value for the CFF `random' operator and the
551    *   similar `0 28 callothersubr pop' command for the Type~1 and CID
552    *   drivers is set to a random value.  However, mainly for debugging
553    *   purposes, it is often necessary to use a known value as a seed so
554    *   that the pseudo-random number sequences generated by `random' are
555    *   repeatable.
556    *
557    *   The `random-seed' property does that.  Its argument is a signed 32bit
558    *   integer; if the value is zero or negative, the seed given by the
559    *   `intitialRandomSeed' private DICT operator in a CFF file gets used
560    *   (or a default value if there is no such operator).  If the value is
561    *   positive, use it instead of `initialRandomSeed', which is
562    *   consequently ignored.
563    *
564    * @note:
565    *   This property can be set via the `FREETYPE_PROPERTIES' environment
566    *   variable.  It can also be set per face using @FT_Face_Properties with
567    *   @FT_PARAM_TAG_RANDOM_SEED.
568    *
569    * @since:
570    *   2.8 (for `cff' module)
571    *
572    *   2.9 (for `type1' and `t1cid' modules)
573    *
574    */
575 
576 
577   /**************************************************************************
578    *
579    * @property:
580    *   no-long-family-names
581    *
582    * @description:
583    *   If PCF_CONFIG_OPTION_LONG_FAMILY_NAMES is active while compiling
584    *   FreeType, the PCF driver constructs long family names.
585    *
586    *   There are many PCF fonts just called `Fixed' which look completely
587    *   different, and which have nothing to do with each other.  When
588    *   selecting `Fixed' in KDE or Gnome one gets results that appear rather
589    *   random, the style changes often if one changes the size and one
590    *   cannot select some fonts at all.  The improve this situation, the PCF
591    *   module prepends the foundry name (plus a space) to the family name.
592    *   It also checks whether there are `wide' characters; all put together,
593    *   family names like `Sony Fixed' or `Misc Fixed Wide' are constructed.
594    *
595    *   If `no-long-family-names' is set, this feature gets switched off.
596    *
597    *   {
598    *     FT_Library  library;
599    *     FT_Bool     no_long_family_names = TRUE;
600    *
601    *
602    *     FT_Init_FreeType( &library );
603    *
604    *     FT_Property_Set( library, "pcf",
605    *                               "no-long-family-names",
606    *                               &no_long_family_names );
607    *   }
608    *
609    * @note:
610    *   This property can be used with @FT_Property_Get also.
611    *
612    *   This property can be set via the `FREETYPE_PROPERTIES' environment
613    *   variable (using values 1 and 0 for `on' and `off', respectively).
614    *
615    * @since:
616    *   2.8
617    */
618 
619 
620   /**************************************************************************
621    *
622    * @enum:
623    *   TT_INTERPRETER_VERSION_XXX
624    *
625    * @description:
626    *   A list of constants used for the @interpreter-version property to
627    *   select the hinting engine for Truetype fonts.
628    *
629    *   The numeric value in the constant names represents the version
630    *   number as returned by the `GETINFO' bytecode instruction.
631    *
632    * @values:
633    *   TT_INTERPRETER_VERSION_35 ::
634    *     Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
635    *     Windows~98; only grayscale and B/W rasterizing is supported.
636    *
637    *   TT_INTERPRETER_VERSION_38 ::
638    *     Version~38 corresponds to MS rasterizer v.1.9; it is roughly
639    *     equivalent to the hinting provided by DirectWrite ClearType (as can
640    *     be found, for example, in the Internet Explorer~9 running on
641    *     Windows~7).  It is used in FreeType to select the `Infinality'
642    *     subpixel hinting code.  The code may be removed in a future
643    *     version.
644    *
645    *   TT_INTERPRETER_VERSION_40 ::
646    *     Version~40 corresponds to MS rasterizer v.2.1; it is roughly
647    *     equivalent to the hinting provided by DirectWrite ClearType (as can
648    *     be found, for example, in Microsoft's Edge Browser on Windows~10).
649    *     It is used in FreeType to select the `minimal' subpixel hinting
650    *     code, a stripped-down and higher performance version of the
651    *     `Infinality' code.
652    *
653    * @note:
654    *   This property controls the behaviour of the bytecode interpreter
655    *   and thus how outlines get hinted.  It does *not* control how glyph
656    *   get rasterized!  In particular, it does not control subpixel color
657    *   filtering.
658    *
659    *   If FreeType has not been compiled with the configuration option
660    *   TT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 or~40 causes
661    *   an `FT_Err_Unimplemented_Feature' error.
662    *
663    *   Depending on the graphics framework, Microsoft uses different
664    *   bytecode and rendering engines.  As a consequence, the version
665    *   numbers returned by a call to the `GETINFO' bytecode instruction are
666    *   more convoluted than desired.
667    *
668    *   Here are two tables that try to shed some light on the possible
669    *   values for the MS rasterizer engine, together with the additional
670    *   features introduced by it.
671    *
672    *   {
673    *     GETINFO framework               version feature
674    *     -------------------------------------------------------------------
675    *         3   GDI (Win 3.1),            v1.0  16-bit, first version
676    *             TrueImage
677    *        33   GDI (Win NT 3.1),         v1.5  32-bit
678    *             HP Laserjet
679    *        34   GDI (Win 95)              v1.6  font smoothing,
680    *                                             new SCANTYPE opcode
681    *        35   GDI (Win 98/2000)         v1.7  (UN)SCALED_COMPONENT_OFFSET
682    *                                               bits in composite glyphs
683    *        36   MGDI (Win CE 2)           v1.6+ classic ClearType
684    *        37   GDI (XP and later),       v1.8  ClearType
685    *             GDI+ old (before Vista)
686    *        38   GDI+ old (Vista, Win 7),  v1.9  subpixel ClearType,
687    *             WPF                             Y-direction ClearType,
688    *                                             additional error checking
689    *        39   DWrite (before Win 8)     v2.0  subpixel ClearType flags
690    *                                               in GETINFO opcode,
691    *                                             bug fixes
692    *        40   GDI+ (after Win 7),       v2.1  Y-direction ClearType flag
693    *             DWrite (Win 8)                    in GETINFO opcode,
694    *                                             Gray ClearType
695    *   }
696    *
697    *   The `version' field gives a rough orientation only, since some
698    *   applications provided certain features much earlier (as an example,
699    *   Microsoft Reader used subpixel and Y-direction ClearType already in
700    *   Windows 2000).  Similarly, updates to a given framework might include
701    *   improved hinting support.
702    *
703    *   {
704    *      version   sampling          rendering        comment
705    *               x        y       x           y
706    *     --------------------------------------------------------------
707    *       v1.0   normal  normal  B/W           B/W    bi-level
708    *       v1.6   high    high    gray          gray   grayscale
709    *       v1.8   high    normal  color-filter  B/W    (GDI) ClearType
710    *       v1.9   high    high    color-filter  gray   Color ClearType
711    *       v2.1   high    normal  gray          B/W    Gray ClearType
712    *       v2.1   high    high    gray          gray   Gray ClearType
713    *   }
714    *
715    *   Color and Gray ClearType are the two available variants of
716    *   `Y-direction ClearType', meaning grayscale rasterization along the
717    *   Y-direction; the name used in the TrueType specification for this
718    *   feature is `symmetric smoothing'.  `Classic ClearType' is the
719    *   original algorithm used before introducing a modified version in
720    *   Win~XP.  Another name for v1.6's grayscale rendering is `font
721    *   smoothing', and `Color ClearType' is sometimes also called `DWrite
722    *   ClearType'.  To differentiate between today's Color ClearType and the
723    *   earlier ClearType variant with B/W rendering along the vertical axis,
724    *   the latter is sometimes called `GDI ClearType'.
725    *
726    *   `Normal' and `high' sampling describe the (virtual) resolution to
727    *   access the rasterized outline after the hinting process.  `Normal'
728    *   means 1 sample per grid line (i.e., B/W).  In the current Microsoft
729    *   implementation, `high' means an extra virtual resolution of 16x16 (or
730    *   16x1) grid lines per pixel for bytecode instructions like `MIRP'.
731    *   After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
732    *   lines for color filtering if Color ClearType is activated.
733    *
734    *   Note that `Gray ClearType' is essentially the same as v1.6's
735    *   grayscale rendering.  However, the GETINFO instruction handles it
736    *   differently: v1.6 returns bit~12 (hinting for grayscale), while v2.1
737    *   returns bits~13 (hinting for ClearType), 18 (symmetrical smoothing),
738    *   and~19 (Gray ClearType).  Also, this mode respects bits 2 and~3 for
739    *   the version~1 gasp table exclusively (like Color ClearType), while
740    *   v1.6 only respects the values of version~0 (bits 0 and~1).
741    *
742    *   Keep in mind that the features of the above interpreter versions
743    *   might not map exactly to FreeType features or behavior because it is
744    *   a fundamentally different library with different internals.
745    *
746    */
747 #define TT_INTERPRETER_VERSION_35  35
748 #define TT_INTERPRETER_VERSION_38  38
749 #define TT_INTERPRETER_VERSION_40  40
750 
751 
752   /**************************************************************************
753    *
754    * @property:
755    *   interpreter-version
756    *
757    * @description:
758    *   Currently, three versions are available, two representing the
759    *   bytecode interpreter with subpixel hinting support (old `Infinality'
760    *   code and new stripped-down and higher performance `minimal' code) and
761    *   one without, respectively.  The default is subpixel support if
762    *   TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel support
763    *   otherwise (since it isn't available then).
764    *
765    *   If subpixel hinting is on, many TrueType bytecode instructions behave
766    *   differently compared to B/W or grayscale rendering (except if `native
767    *   ClearType' is selected by the font).  Microsoft's main idea is to
768    *   render at a much increased horizontal resolution, then sampling down
769    *   the created output to subpixel precision.  However, many older fonts
770    *   are not suited to this and must be specially taken care of by
771    *   applying (hardcoded) tweaks in Microsoft's interpreter.
772    *
773    *   Details on subpixel hinting and some of the necessary tweaks can be
774    *   found in Greg Hitchcock's whitepaper at
775    *   `https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
776    *   Note that FreeType currently doesn't really `subpixel hint' (6x1, 6x2,
777    *   or 6x5 supersampling) like discussed in the paper.  Depending on the
778    *   chosen interpreter, it simply ignores instructions on vertical stems
779    *   to arrive at very similar results.
780    *
781    *   The following example code demonstrates how to deactivate subpixel
782    *   hinting (omitting the error handling).
783    *
784    *   {
785    *     FT_Library  library;
786    *     FT_Face     face;
787    *     FT_UInt     interpreter_version = TT_INTERPRETER_VERSION_35;
788    *
789    *
790    *     FT_Init_FreeType( &library );
791    *
792    *     FT_Property_Set( library, "truetype",
793    *                               "interpreter-version",
794    *                               &interpreter_version );
795    *   }
796    *
797    * @note:
798    *   This property can be used with @FT_Property_Get also.
799    *
800    *   This property can be set via the `FREETYPE_PROPERTIES' environment
801    *   variable (using values `35', `38', or `40').
802    *
803    * @since:
804    *   2.5
805    */
806 
807 
808   /**************************************************************************
809    *
810    * @property:
811    *   glyph-to-script-map
812    *
813    * @description:
814    *   *Experimental* *only*
815    *
816    *   The auto-hinter provides various script modules to hint glyphs.
817    *   Examples of supported scripts are Latin or CJK.  Before a glyph is
818    *   auto-hinted, the Unicode character map of the font gets examined, and
819    *   the script is then determined based on Unicode character ranges, see
820    *   below.
821    *
822    *   OpenType fonts, however, often provide much more glyphs than
823    *   character codes (small caps, superscripts, ligatures, swashes, etc.),
824    *   to be controlled by so-called `features'.  Handling OpenType features
825    *   can be quite complicated and thus needs a separate library on top of
826    *   FreeType.
827    *
828    *   The mapping between glyph indices and scripts (in the auto-hinter
829    *   sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an
830    *   array with `num_glyphs' elements, as found in the font's @FT_Face
831    *   structure.  The `glyph-to-script-map' property returns a pointer to
832    *   this array, which can be modified as needed.  Note that the
833    *   modification should happen before the first glyph gets processed by
834    *   the auto-hinter so that the global analysis of the font shapes
835    *   actually uses the modified mapping.
836    *
837    *   The following example code demonstrates how to access it (omitting
838    *   the error handling).
839    *
840    *   {
841    *     FT_Library                library;
842    *     FT_Face                   face;
843    *     FT_Prop_GlyphToScriptMap  prop;
844    *
845    *
846    *     FT_Init_FreeType( &library );
847    *     FT_New_Face( library, "foo.ttf", 0, &face );
848    *
849    *     prop.face = face;
850    *
851    *     FT_Property_Get( library, "autofitter",
852    *                               "glyph-to-script-map", &prop );
853    *
854    *     // adjust `prop.map' as needed right here
855    *
856    *     FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
857    *   }
858    *
859    * @since:
860    *   2.4.11
861    *
862    */
863 
864 
865   /**************************************************************************
866    *
867    * @enum:
868    *   FT_AUTOHINTER_SCRIPT_XXX
869    *
870    * @description:
871    *   *Experimental* *only*
872    *
873    *   A list of constants used for the @glyph-to-script-map property to
874    *   specify the script submodule the auto-hinter should use for hinting a
875    *   particular glyph.
876    *
877    * @values:
878    *   FT_AUTOHINTER_SCRIPT_NONE ::
879    *     Don't auto-hint this glyph.
880    *
881    *   FT_AUTOHINTER_SCRIPT_LATIN ::
882    *     Apply the latin auto-hinter.  For the auto-hinter, `latin' is a
883    *     very broad term, including Cyrillic and Greek also since characters
884    *     from those scripts share the same design constraints.
885    *
886    *     By default, characters from the following Unicode ranges are
887    *     assigned to this submodule.
888    *
889    *     {
890    *       U+0020 - U+007F  // Basic Latin (no control characters)
891    *       U+00A0 - U+00FF  // Latin-1 Supplement (no control characters)
892    *       U+0100 - U+017F  // Latin Extended-A
893    *       U+0180 - U+024F  // Latin Extended-B
894    *       U+0250 - U+02AF  // IPA Extensions
895    *       U+02B0 - U+02FF  // Spacing Modifier Letters
896    *       U+0300 - U+036F  // Combining Diacritical Marks
897    *       U+0370 - U+03FF  // Greek and Coptic
898    *       U+0400 - U+04FF  // Cyrillic
899    *       U+0500 - U+052F  // Cyrillic Supplement
900    *       U+1D00 - U+1D7F  // Phonetic Extensions
901    *       U+1D80 - U+1DBF  // Phonetic Extensions Supplement
902    *       U+1DC0 - U+1DFF  // Combining Diacritical Marks Supplement
903    *       U+1E00 - U+1EFF  // Latin Extended Additional
904    *       U+1F00 - U+1FFF  // Greek Extended
905    *       U+2000 - U+206F  // General Punctuation
906    *       U+2070 - U+209F  // Superscripts and Subscripts
907    *       U+20A0 - U+20CF  // Currency Symbols
908    *       U+2150 - U+218F  // Number Forms
909    *       U+2460 - U+24FF  // Enclosed Alphanumerics
910    *       U+2C60 - U+2C7F  // Latin Extended-C
911    *       U+2DE0 - U+2DFF  // Cyrillic Extended-A
912    *       U+2E00 - U+2E7F  // Supplemental Punctuation
913    *       U+A640 - U+A69F  // Cyrillic Extended-B
914    *       U+A720 - U+A7FF  // Latin Extended-D
915    *       U+FB00 - U+FB06  // Alphab. Present. Forms (Latin Ligatures)
916    *      U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
917    *      U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
918    *     }
919    *
920    *   FT_AUTOHINTER_SCRIPT_CJK ::
921    *     Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
922    *     Vietnamese, and some other scripts.
923    *
924    *     By default, characters from the following Unicode ranges are
925    *     assigned to this submodule.
926    *
927    *     {
928    *       U+1100 - U+11FF  // Hangul Jamo
929    *       U+2E80 - U+2EFF  // CJK Radicals Supplement
930    *       U+2F00 - U+2FDF  // Kangxi Radicals
931    *       U+2FF0 - U+2FFF  // Ideographic Description Characters
932    *       U+3000 - U+303F  // CJK Symbols and Punctuation
933    *       U+3040 - U+309F  // Hiragana
934    *       U+30A0 - U+30FF  // Katakana
935    *       U+3100 - U+312F  // Bopomofo
936    *       U+3130 - U+318F  // Hangul Compatibility Jamo
937    *       U+3190 - U+319F  // Kanbun
938    *       U+31A0 - U+31BF  // Bopomofo Extended
939    *       U+31C0 - U+31EF  // CJK Strokes
940    *       U+31F0 - U+31FF  // Katakana Phonetic Extensions
941    *       U+3200 - U+32FF  // Enclosed CJK Letters and Months
942    *       U+3300 - U+33FF  // CJK Compatibility
943    *       U+3400 - U+4DBF  // CJK Unified Ideographs Extension A
944    *       U+4DC0 - U+4DFF  // Yijing Hexagram Symbols
945    *       U+4E00 - U+9FFF  // CJK Unified Ideographs
946    *       U+A960 - U+A97F  // Hangul Jamo Extended-A
947    *       U+AC00 - U+D7AF  // Hangul Syllables
948    *       U+D7B0 - U+D7FF  // Hangul Jamo Extended-B
949    *       U+F900 - U+FAFF  // CJK Compatibility Ideographs
950    *       U+FE10 - U+FE1F  // Vertical forms
951    *       U+FE30 - U+FE4F  // CJK Compatibility Forms
952    *       U+FF00 - U+FFEF  // Halfwidth and Fullwidth Forms
953    *      U+1B000 - U+1B0FF // Kana Supplement
954    *      U+1D300 - U+1D35F // Tai Xuan Hing Symbols
955    *      U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
956    *      U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
957    *      U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
958    *      U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
959    *      U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
960    *     }
961    *
962    *   FT_AUTOHINTER_SCRIPT_INDIC ::
963    *     Apply the indic auto-hinter, covering all major scripts from the
964    *     Indian sub-continent and some other related scripts like Thai, Lao,
965    *     or Tibetan.
966    *
967    *     By default, characters from the following Unicode ranges are
968    *     assigned to this submodule.
969    *
970    *     {
971    *       U+0900 - U+0DFF  // Indic Range
972    *       U+0F00 - U+0FFF  // Tibetan
973    *       U+1900 - U+194F  // Limbu
974    *       U+1B80 - U+1BBF  // Sundanese
975    *       U+A800 - U+A82F  // Syloti Nagri
976    *       U+ABC0 - U+ABFF  // Meetei Mayek
977    *      U+11800 - U+118DF // Sharada
978    *     }
979    *
980    *     Note that currently Indic support is rudimentary only, missing blue
981    *     zone support.
982    *
983    * @since:
984    *   2.4.11
985    *
986    */
987 #define FT_AUTOHINTER_SCRIPT_NONE   0
988 #define FT_AUTOHINTER_SCRIPT_LATIN  1
989 #define FT_AUTOHINTER_SCRIPT_CJK    2
990 #define FT_AUTOHINTER_SCRIPT_INDIC  3
991 
992 
993   /**************************************************************************
994    *
995    * @struct:
996    *   FT_Prop_GlyphToScriptMap
997    *
998    * @description:
999    *   *Experimental* *only*
1000    *
1001    *   The data exchange structure for the @glyph-to-script-map property.
1002    *
1003    * @since:
1004    *   2.4.11
1005    *
1006    */
1007   typedef struct  FT_Prop_GlyphToScriptMap_
1008   {
1009     FT_Face     face;
1010     FT_UShort*  map;
1011 
1012   } FT_Prop_GlyphToScriptMap;
1013 
1014 
1015   /**************************************************************************
1016    *
1017    * @property:
1018    *   fallback-script
1019    *
1020    * @description:
1021    *   *Experimental* *only*
1022    *
1023    *   If no auto-hinter script module can be assigned to a glyph, a
1024    *   fallback script gets assigned to it (see also the
1025    *   @glyph-to-script-map property).  By default, this is
1026    *   @FT_AUTOHINTER_SCRIPT_CJK.  Using the `fallback-script' property,
1027    *   this fallback value can be changed.
1028    *
1029    *   {
1030    *     FT_Library  library;
1031    *     FT_UInt     fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
1032    *
1033    *
1034    *     FT_Init_FreeType( &library );
1035    *
1036    *     FT_Property_Set( library, "autofitter",
1037    *                               "fallback-script", &fallback_script );
1038    *   }
1039    *
1040    * @note:
1041    *   This property can be used with @FT_Property_Get also.
1042    *
1043    *   It's important to use the right timing for changing this value: The
1044    *   creation of the glyph-to-script map that eventually uses the
1045    *   fallback script value gets triggered either by setting or reading a
1046    *   face-specific property like @glyph-to-script-map, or by auto-hinting
1047    *   any glyph from that face.  In particular, if you have already created
1048    *   an @FT_Face structure but not loaded any glyph (using the
1049    *   auto-hinter), a change of the fallback script will affect this face.
1050    *
1051    * @since:
1052    *   2.4.11
1053    *
1054    */
1055 
1056 
1057   /**************************************************************************
1058    *
1059    * @property:
1060    *   default-script
1061    *
1062    * @description:
1063    *   *Experimental* *only*
1064    *
1065    *   If FreeType gets compiled with FT_CONFIG_OPTION_USE_HARFBUZZ to make
1066    *   the HarfBuzz library access OpenType features for getting better
1067    *   glyph coverages, this property sets the (auto-fitter) script to be
1068    *   used for the default (OpenType) script data of a font's GSUB table.
1069    *   Features for the default script are intended for all scripts not
1070    *   explicitly handled in GSUB; an example is a `dlig' feature,
1071    *   containing the combination of the characters `T', `E', and `L' to
1072    *   form a `TEL' ligature.
1073    *
1074    *   By default, this is @FT_AUTOHINTER_SCRIPT_LATIN.  Using the
1075    *   `default-script' property, this default value can be changed.
1076    *
1077    *   {
1078    *     FT_Library  library;
1079    *     FT_UInt     default_script = FT_AUTOHINTER_SCRIPT_NONE;
1080    *
1081    *
1082    *     FT_Init_FreeType( &library );
1083    *
1084    *     FT_Property_Set( library, "autofitter",
1085    *                               "default-script", &default_script );
1086    *   }
1087    *
1088    * @note:
1089    *   This property can be used with @FT_Property_Get also.
1090    *
1091    *   It's important to use the right timing for changing this value: The
1092    *   creation of the glyph-to-script map that eventually uses the
1093    *   default script value gets triggered either by setting or reading a
1094    *   face-specific property like @glyph-to-script-map, or by auto-hinting
1095    *   any glyph from that face.  In particular, if you have already created
1096    *   an @FT_Face structure but not loaded any glyph (using the
1097    *   auto-hinter), a change of the default script will affect this face.
1098    *
1099    * @since:
1100    *   2.5.3
1101    *
1102    */
1103 
1104 
1105   /**************************************************************************
1106    *
1107    * @property:
1108    *   increase-x-height
1109    *
1110    * @description:
1111    *   For ppem values in the range 6~<= ppem <= `increase-x-height', round
1112    *   up the font's x~height much more often than normally.  If the value
1113    *   is set to~0, which is the default, this feature is switched off.  Use
1114    *   this property to improve the legibility of small font sizes if
1115    *   necessary.
1116    *
1117    *   {
1118    *     FT_Library               library;
1119    *     FT_Face                  face;
1120    *     FT_Prop_IncreaseXHeight  prop;
1121    *
1122    *
1123    *     FT_Init_FreeType( &library );
1124    *     FT_New_Face( library, "foo.ttf", 0, &face );
1125    *     FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
1126    *
1127    *     prop.face  = face;
1128    *     prop.limit = 14;
1129    *
1130    *     FT_Property_Set( library, "autofitter",
1131    *                               "increase-x-height", &prop );
1132    *   }
1133    *
1134    * @note:
1135    *   This property can be used with @FT_Property_Get also.
1136    *
1137    *   Set this value right after calling @FT_Set_Char_Size, but before
1138    *   loading any glyph (using the auto-hinter).
1139    *
1140    * @since:
1141    *   2.4.11
1142    *
1143    */
1144 
1145 
1146   /**************************************************************************
1147    *
1148    * @struct:
1149    *   FT_Prop_IncreaseXHeight
1150    *
1151    * @description:
1152    *   The data exchange structure for the @increase-x-height property.
1153    *
1154    */
1155   typedef struct  FT_Prop_IncreaseXHeight_
1156   {
1157     FT_Face  face;
1158     FT_UInt  limit;
1159 
1160   } FT_Prop_IncreaseXHeight;
1161 
1162 
1163   /**************************************************************************
1164    *
1165    * @property:
1166    *   warping
1167    *
1168    * @description:
1169    *   *Experimental* *only*
1170    *
1171    *   If FreeType gets compiled with option AF_CONFIG_OPTION_USE_WARPER to
1172    *   activate the warp hinting code in the auto-hinter, this property
1173    *   switches warping on and off.
1174    *
1175    *   Warping only works in `normal' auto-hinting mode replacing it.
1176    *   The idea of the code is to slightly scale and shift a glyph along
1177    *   the non-hinted dimension (which is usually the horizontal axis) so
1178    *   that as much of its segments are aligned (more or less) to the grid.
1179    *   To find out a glyph's optimal scaling and shifting value, various
1180    *   parameter combinations are tried and scored.
1181    *
1182    *   By default, warping is off.  The example below shows how to switch on
1183    *   warping (omitting the error handling).
1184    *
1185    *   {
1186    *     FT_Library  library;
1187    *     FT_Bool     warping = 1;
1188    *
1189    *
1190    *     FT_Init_FreeType( &library );
1191    *
1192    *     FT_Property_Set( library, "autofitter",
1193    *                               "warping", &warping );
1194    *   }
1195    *
1196    * @note:
1197    *   This property can be used with @FT_Property_Get also.
1198    *
1199    *   This property can be set via the `FREETYPE_PROPERTIES' environment
1200    *   variable (using values 1 and 0 for `on' and `off', respectively).
1201    *
1202    *   The warping code can also change advance widths.  Have a look at the
1203    *   `lsb_delta' and `rsb_delta' fields in the @FT_GlyphSlotRec structure
1204    *   for details on improving inter-glyph distances while rendering.
1205    *
1206    *   Since warping is a global property of the auto-hinter it is best to
1207    *   change its value before rendering any face.  Otherwise, you should
1208    *   reload all faces that get auto-hinted in `normal' hinting mode.
1209    *
1210    * @since:
1211    *   2.6
1212    *
1213    */
1214 
1215 
1216  /* */
1217 
1218 
1219 FT_END_HEADER
1220 
1221 
1222 #endif /* FTDRIVER_H_ */
1223 
1224 
1225 /* END */
1226