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freetype2/include/freetype/ftautoh.h

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/***************************************************************************/
/* */
/* ftautoh.h */
/* */
/* FreeType API for controlling the auto-hinter (specification only). */
/* */
/* Copyright 2012-2016 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
/* modified, and distributed under the terms of the FreeType project */
/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
/* this file you indicate that you have read the license and */
/* understand and accept it fully. */
/* */
/***************************************************************************/
#ifndef FTAUTOH_H_
#define FTAUTOH_H_
#include <ft2build.h>
#include FT_FREETYPE_H
#ifdef FREETYPE_H
#error "freetype.h of FreeType 1 has been loaded!"
#error "Please fix the directory search order for header files"
#error "so that freetype.h of FreeType 2 is found first."
#endif
FT_BEGIN_HEADER
/**************************************************************************
*
* @section:
* auto_hinter
*
* @title:
* The auto-hinter
*
* @abstract:
* Controlling the auto-hinting module.
*
* @description:
* While FreeType's auto-hinter doesn't expose API functions by itself,
* it is possible to control its behaviour with @FT_Property_Set and
* @FT_Property_Get. The following lists the available properties
* together with the necessary macros and structures.
*
* Note that the auto-hinter's module name is `autofitter' for
* historical reasons.
*
*/
/**************************************************************************
*
* @property:
* glyph-to-script-map
*
* @description:
* *Experimental* *only*
*
* The auto-hinter provides various script modules to hint glyphs.
* Examples of supported scripts are Latin or CJK. Before a glyph is
* auto-hinted, the Unicode character map of the font gets examined, and
* the script is then determined based on Unicode character ranges, see
* below.
*
* OpenType fonts, however, often provide much more glyphs than
* character codes (small caps, superscripts, ligatures, swashes, etc.),
* to be controlled by so-called `features'. Handling OpenType features
* can be quite complicated and thus needs a separate library on top of
* FreeType.
*
* The mapping between glyph indices and scripts (in the auto-hinter
* sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an
* array with `num_glyphs' elements, as found in the font's @FT_Face
* structure. The `glyph-to-script-map' property returns a pointer to
* this array, which can be modified as needed. Note that the
* modification should happen before the first glyph gets processed by
* the auto-hinter so that the global analysis of the font shapes
* actually uses the modified mapping.
*
* The following example code demonstrates how to access it (omitting
* the error handling).
*
* {
* FT_Library library;
* FT_Face face;
* FT_Prop_GlyphToScriptMap prop;
*
*
* FT_Init_FreeType( &library );
* FT_New_Face( library, "foo.ttf", 0, &face );
*
* prop.face = face;
*
* FT_Property_Get( library, "autofitter",
* "glyph-to-script-map", &prop );
*
* // adjust `prop.map' as needed right here
*
* FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
* }
*
*/
/**************************************************************************
*
* @enum:
* FT_AUTOHINTER_SCRIPT_XXX
*
* @description:
* *Experimental* *only*
*
* A list of constants used for the @glyph-to-script-map property to
* specify the script submodule the auto-hinter should use for hinting a
* particular glyph.
*
* @values:
* FT_AUTOHINTER_SCRIPT_NONE ::
* Don't auto-hint this glyph.
*
* FT_AUTOHINTER_SCRIPT_LATIN ::
* Apply the latin auto-hinter. For the auto-hinter, `latin' is a
* very broad term, including Cyrillic and Greek also since characters
* from those scripts share the same design constraints.
*
* By default, characters from the following Unicode ranges are
* assigned to this submodule.
*
* {
* U+0020 - U+007F // Basic Latin (no control characters)
* U+00A0 - U+00FF // Latin-1 Supplement (no control characters)
* U+0100 - U+017F // Latin Extended-A
* U+0180 - U+024F // Latin Extended-B
* U+0250 - U+02AF // IPA Extensions
* U+02B0 - U+02FF // Spacing Modifier Letters
* U+0300 - U+036F // Combining Diacritical Marks
* U+0370 - U+03FF // Greek and Coptic
* U+0400 - U+04FF // Cyrillic
* U+0500 - U+052F // Cyrillic Supplement
* U+1D00 - U+1D7F // Phonetic Extensions
* U+1D80 - U+1DBF // Phonetic Extensions Supplement
* U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement
* U+1E00 - U+1EFF // Latin Extended Additional
* U+1F00 - U+1FFF // Greek Extended
* U+2000 - U+206F // General Punctuation
* U+2070 - U+209F // Superscripts and Subscripts
* U+20A0 - U+20CF // Currency Symbols
* U+2150 - U+218F // Number Forms
* U+2460 - U+24FF // Enclosed Alphanumerics
* U+2C60 - U+2C7F // Latin Extended-C
* U+2DE0 - U+2DFF // Cyrillic Extended-A
* U+2E00 - U+2E7F // Supplemental Punctuation
* U+A640 - U+A69F // Cyrillic Extended-B
* U+A720 - U+A7FF // Latin Extended-D
* U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures)
* U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
* U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
* }
*
* FT_AUTOHINTER_SCRIPT_CJK ::
* Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
* Vietnamese, and some other scripts.
*
* By default, characters from the following Unicode ranges are
* assigned to this submodule.
*
* {
* U+1100 - U+11FF // Hangul Jamo
* U+2E80 - U+2EFF // CJK Radicals Supplement
* U+2F00 - U+2FDF // Kangxi Radicals
* U+2FF0 - U+2FFF // Ideographic Description Characters
* U+3000 - U+303F // CJK Symbols and Punctuation
* U+3040 - U+309F // Hiragana
* U+30A0 - U+30FF // Katakana
* U+3100 - U+312F // Bopomofo
* U+3130 - U+318F // Hangul Compatibility Jamo
* U+3190 - U+319F // Kanbun
* U+31A0 - U+31BF // Bopomofo Extended
* U+31C0 - U+31EF // CJK Strokes
* U+31F0 - U+31FF // Katakana Phonetic Extensions
* U+3200 - U+32FF // Enclosed CJK Letters and Months
* U+3300 - U+33FF // CJK Compatibility
* U+3400 - U+4DBF // CJK Unified Ideographs Extension A
* U+4DC0 - U+4DFF // Yijing Hexagram Symbols
* U+4E00 - U+9FFF // CJK Unified Ideographs
* U+A960 - U+A97F // Hangul Jamo Extended-A
* U+AC00 - U+D7AF // Hangul Syllables
* U+D7B0 - U+D7FF // Hangul Jamo Extended-B
* U+F900 - U+FAFF // CJK Compatibility Ideographs
* U+FE10 - U+FE1F // Vertical forms
* U+FE30 - U+FE4F // CJK Compatibility Forms
* U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms
* U+1B000 - U+1B0FF // Kana Supplement
* U+1D300 - U+1D35F // Tai Xuan Hing Symbols
* U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
* U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
* U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
* U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
* U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
* }
*
* FT_AUTOHINTER_SCRIPT_INDIC ::
* Apply the indic auto-hinter, covering all major scripts from the
* Indian sub-continent and some other related scripts like Thai, Lao,
* or Tibetan.
*
* By default, characters from the following Unicode ranges are
* assigned to this submodule.
*
* {
* U+0900 - U+0DFF // Indic Range
* U+0F00 - U+0FFF // Tibetan
* U+1900 - U+194F // Limbu
* U+1B80 - U+1BBF // Sundanese
* U+1C80 - U+1CDF // Meetei Mayak
* U+A800 - U+A82F // Syloti Nagri
* U+11800 - U+118DF // Sharada
* }
*
* Note that currently Indic support is rudimentary only, missing blue
* zone support.
*
*/
#define FT_AUTOHINTER_SCRIPT_NONE 0
#define FT_AUTOHINTER_SCRIPT_LATIN 1
#define FT_AUTOHINTER_SCRIPT_CJK 2
#define FT_AUTOHINTER_SCRIPT_INDIC 3
/**************************************************************************
*
* @struct:
* FT_Prop_GlyphToScriptMap
*
* @description:
* *Experimental* *only*
*
* The data exchange structure for the @glyph-to-script-map property.
*
*/
typedef struct FT_Prop_GlyphToScriptMap_
{
FT_Face face;
FT_UShort* map;
} FT_Prop_GlyphToScriptMap;
/**************************************************************************
*
* @property:
* fallback-script
*
* @description:
* *Experimental* *only*
*
* If no auto-hinter script module can be assigned to a glyph, a
* fallback script gets assigned to it (see also the
* @glyph-to-script-map property). By default, this is
* @FT_AUTOHINTER_SCRIPT_CJK. Using the `fallback-script' property,
* this fallback value can be changed.
*
* {
* FT_Library library;
* FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter",
* "fallback-script", &fallback_script );
* }
*
* @note:
* This property can be used with @FT_Property_Get also.
*
* It's important to use the right timing for changing this value: The
* creation of the glyph-to-script map that eventually uses the
* fallback script value gets triggered either by setting or reading a
* face-specific property like @glyph-to-script-map, or by auto-hinting
* any glyph from that face. In particular, if you have already created
* an @FT_Face structure but not loaded any glyph (using the
* auto-hinter), a change of the fallback script will affect this face.
*
*/
/**************************************************************************
*
* @property:
* default-script
*
* @description:
* *Experimental* *only*
*
* If FreeType gets compiled with FT_CONFIG_OPTION_USE_HARFBUZZ to make
* the HarfBuzz library access OpenType features for getting better
* glyph coverages, this property sets the (auto-fitter) script to be
* used for the default (OpenType) script data of a font's GSUB table.
* Features for the default script are intended for all scripts not
* explicitly handled in GSUB; an example is a `dlig' feature,
* containing the combination of the characters `T', `E', and `L' to
* form a `TEL' ligature.
*
* By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the
* `default-script' property, this default value can be changed.
*
* {
* FT_Library library;
* FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter",
* "default-script", &default_script );
* }
*
* @note:
* This property can be used with @FT_Property_Get also.
*
* It's important to use the right timing for changing this value: The
* creation of the glyph-to-script map that eventually uses the
* default script value gets triggered either by setting or reading a
* face-specific property like @glyph-to-script-map, or by auto-hinting
* any glyph from that face. In particular, if you have already created
* an @FT_Face structure but not loaded any glyph (using the
* auto-hinter), a change of the default script will affect this face.
*
*/
/**************************************************************************
*
* @property:
* increase-x-height
*
* @description:
* For ppem values in the range 6~<= ppem <= `increase-x-height', round
* up the font's x~height much more often than normally. If the value
* is set to~0, which is the default, this feature is switched off. Use
* this property to improve the legibility of small font sizes if
* necessary.
*
* {
* FT_Library library;
* FT_Face face;
* FT_Prop_IncreaseXHeight prop;
*
*
* FT_Init_FreeType( &library );
* FT_New_Face( library, "foo.ttf", 0, &face );
* FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
*
* prop.face = face;
* prop.limit = 14;
*
* FT_Property_Set( library, "autofitter",
* "increase-x-height", &prop );
* }
*
* @note:
* This property can be used with @FT_Property_Get also.
*
* Set this value right after calling @FT_Set_Char_Size, but before
* loading any glyph (using the auto-hinter).
*
*/
/**************************************************************************
*
* @struct:
* FT_Prop_IncreaseXHeight
*
* @description:
* The data exchange structure for the @increase-x-height property.
*
*/
typedef struct FT_Prop_IncreaseXHeight_
{
FT_Face face;
FT_UInt limit;
} FT_Prop_IncreaseXHeight;
/**************************************************************************
*
* @property:
* warping
*
* @description:
* *Experimental* *only*
*
* If FreeType gets compiled with option AF_CONFIG_OPTION_USE_WARPER to
* activate the warp hinting code in the auto-hinter, this property
* switches warping on and off.
*
* Warping only works in `light' auto-hinting mode. The idea of the
* code is to slightly scale and shift a glyph along the non-hinted
* dimension (which is usually the horizontal axis) so that as much of
* its segments are aligned (more or less) to the grid. To find out a
* glyph's optimal scaling and shifting value, various parameter
* combinations are tried and scored.
*
* By default, warping is off. The example below shows how to switch on
* warping (omitting the error handling).
*
* {
* FT_Library library;
* FT_Bool warping = 1;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter",
* "warping", &warping );
* }
*
* @note:
* This property can be used with @FT_Property_Get also.
*
* The warping code can also change advance widths. Have a look at the
* `lsb_delta' and `rsb_delta' fields in the @FT_GlyphSlotRec structure
* for details on improving inter-glyph distances while rendering.
*
* Since warping is a global property of the auto-hinter it is best to
* change its value before rendering any face. Otherwise, you should
* reload all faces that get auto-hinted in `light' hinting mode.
*
*/
/**************************************************************************
*
* @property:
* no-stem-darkening[autofit]
*
* @description:
* *Experimental* *only,* *requires* *linear* *alpha* *blending* *and*
* *gamma* *correction*
*
* Stem darkening emboldens glyphs at smaller sizes to make them more
* readable on common low-DPI screens when using linear alpha blending
* and gamma correction, see @FT_Render_Glyph. When not using linear
* alpha blending and gamma correction, glyphs will appear heavy and
* fuzzy!
*
* Gamma correction essentially lightens fonts since shades of grey are
* shifted to higher pixel values (=~higher brightness) to match the
* original intention to the reality of our screens. The side-effect is
* that glyphs `thin out'. Mac OS~X and Adobe's proprietary font
* rendering library implement a counter-measure: stem darkening at
* smaller sizes where shades of gray dominate. By emboldening a glyph
* slightly in relation to its pixel size, individual pixels get higher
* coverage of filled-in outlines and are therefore `blacker'. This
* counteracts the `thinning out' of glyphs, making text remain readable
* at smaller sizes. All glyphs that pass through the auto-hinter will
* be emboldened unless this property is set to TRUE.
*
* See the description of the CFF driver for algorithmic details. Total
* consistency with the CFF driver is currently not achieved because the
* emboldening method differs and glyphs must be scaled down on the
* Y-axis to keep outline points inside their precomputed blue zones.
* The smaller the size (especially 9ppem and down), the higher the loss
* of emboldening versus the CFF driver.
*
*/
/**************************************************************************
*
* @property:
* darkening-parameters[autofit]
*
* @description:
* *Experimental* *only*
*
* See the description of the CFF driver for details. This
* implementation appropriates the
* CFF_CONFIG_OPTION_DARKENING_PARAMETER_* #defines for consistency.
* Note the differences described in @no-stem-darkening[autofit].
*
*/
/* */
FT_END_HEADER
#endif /* FTAUTOH_H_ */
/* END */
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