Edit File: ftautoh.h
/***************************************************************************/ /* */ /* ftautoh.h */ /* */ /* FreeType API for controlling the auto-hinter (specification only). */ /* */ /* Copyright 2012-2017 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+A800 - U+A82F // Syloti Nagri * U+ABC0 - U+ABFF // Meetei Mayek * 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. * * This property can be set via the `FREETYPE_PROPERTIES' environment * variable (using values 1 and 0 for `on' and `off', respectively). * * 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. * * This property can be set via the `FREETYPE_PROPERTIES' environment * variable similar to the CFF driver. It can also be set per face * using @FT_Face_Properties with @FT_PARAM_TAG_STEM_DARKENING. * */ /************************************************************************** * * @constant: * FT_PARAM_TAG_STEM_DARKENING * * @description: * An @FT_Parameter tag to be used with @FT_Face_Properties. The * corresponding Boolean argument specifies whether to apply stem * darkening, overriding the global default values or the values set up * with @FT_Property_Set (see @no-stem-darkening[autofit] and * @no-stem-darkening[cff]). * * This is a passive setting that only takes effect if the font driver * or autohinter honors it, which the CFF driver always does, but the * autohinter only in `light' hinting mode (as of version 2.7.0). * */ #define FT_PARAM_TAG_STEM_DARKENING \ FT_MAKE_TAG( 'd', 'a', 'r', 'k' ) /************************************************************************** * * @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]. * * This property can be set via the `FREETYPE_PROPERTIES' environment * variable similar to the CFF driver. */ /* */ FT_END_HEADER #endif /* FTAUTOH_H_ */ /* END */