504 lines
18 KiB
C
504 lines
18 KiB
C
/***************************************************************************/
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/* */
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/* ftautoh.h */
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/* */
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/* FreeType API for controlling the auto-hinter (specification only). */
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/* */
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/* Copyright 2012-2016 by */
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/* David Turner, Robert Wilhelm, and Werner Lemberg. */
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/* */
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/* This file is part of the FreeType project, and may only be used, */
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/* modified, and distributed under the terms of the FreeType project */
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/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
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/* this file you indicate that you have read the license and */
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/* understand and accept it fully. */
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/* */
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/***************************************************************************/
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#ifndef FTAUTOH_H_
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#define FTAUTOH_H_
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#ifdef FREETYPE_H
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#error "freetype.h of FreeType 1 has been loaded!"
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#error "Please fix the directory search order for header files"
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#error "so that freetype.h of FreeType 2 is found first."
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#endif
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* auto_hinter
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*
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* @title:
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* The auto-hinter
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*
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* @abstract:
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* Controlling the auto-hinting module.
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*
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* @description:
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* While FreeType's auto-hinter doesn't expose API functions by itself,
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* it is possible to control its behaviour with @FT_Property_Set and
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* @FT_Property_Get. The following lists the available properties
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* together with the necessary macros and structures.
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*
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* Note that the auto-hinter's module name is `autofitter' for
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* historical reasons.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* glyph-to-script-map
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*
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* @description:
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* *Experimental* *only*
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*
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* The auto-hinter provides various script modules to hint glyphs.
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* Examples of supported scripts are Latin or CJK. Before a glyph is
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* auto-hinted, the Unicode character map of the font gets examined, and
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* the script is then determined based on Unicode character ranges, see
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* below.
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*
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* OpenType fonts, however, often provide much more glyphs than
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* character codes (small caps, superscripts, ligatures, swashes, etc.),
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* to be controlled by so-called `features'. Handling OpenType features
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* can be quite complicated and thus needs a separate library on top of
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* FreeType.
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*
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* The mapping between glyph indices and scripts (in the auto-hinter
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* sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an
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* array with `num_glyphs' elements, as found in the font's @FT_Face
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* structure. The `glyph-to-script-map' property returns a pointer to
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* this array, which can be modified as needed. Note that the
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* modification should happen before the first glyph gets processed by
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* the auto-hinter so that the global analysis of the font shapes
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* actually uses the modified mapping.
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*
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* The following example code demonstrates how to access it (omitting
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* the error handling).
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*
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* {
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* FT_Library library;
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* FT_Face face;
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* FT_Prop_GlyphToScriptMap prop;
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*
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*
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* FT_Init_FreeType( &library );
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* FT_New_Face( library, "foo.ttf", 0, &face );
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*
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* prop.face = face;
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*
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* FT_Property_Get( library, "autofitter",
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* "glyph-to-script-map", &prop );
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*
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* // adjust `prop.map' as needed right here
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*
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* FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
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* }
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*
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*/
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/**************************************************************************
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*
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* @enum:
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* FT_AUTOHINTER_SCRIPT_XXX
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*
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* @description:
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* *Experimental* *only*
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*
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* A list of constants used for the @glyph-to-script-map property to
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* specify the script submodule the auto-hinter should use for hinting a
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* particular glyph.
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*
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* @values:
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* FT_AUTOHINTER_SCRIPT_NONE ::
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* Don't auto-hint this glyph.
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*
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* FT_AUTOHINTER_SCRIPT_LATIN ::
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* Apply the latin auto-hinter. For the auto-hinter, `latin' is a
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* very broad term, including Cyrillic and Greek also since characters
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* from those scripts share the same design constraints.
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*
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* By default, characters from the following Unicode ranges are
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* assigned to this submodule.
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*
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* {
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* U+0020 - U+007F // Basic Latin (no control characters)
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* U+00A0 - U+00FF // Latin-1 Supplement (no control characters)
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* U+0100 - U+017F // Latin Extended-A
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* U+0180 - U+024F // Latin Extended-B
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* U+0250 - U+02AF // IPA Extensions
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* U+02B0 - U+02FF // Spacing Modifier Letters
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* U+0300 - U+036F // Combining Diacritical Marks
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* U+0370 - U+03FF // Greek and Coptic
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* U+0400 - U+04FF // Cyrillic
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* U+0500 - U+052F // Cyrillic Supplement
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* U+1D00 - U+1D7F // Phonetic Extensions
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* U+1D80 - U+1DBF // Phonetic Extensions Supplement
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* U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement
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* U+1E00 - U+1EFF // Latin Extended Additional
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* U+1F00 - U+1FFF // Greek Extended
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* U+2000 - U+206F // General Punctuation
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* U+2070 - U+209F // Superscripts and Subscripts
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* U+20A0 - U+20CF // Currency Symbols
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* U+2150 - U+218F // Number Forms
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* U+2460 - U+24FF // Enclosed Alphanumerics
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* U+2C60 - U+2C7F // Latin Extended-C
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* U+2DE0 - U+2DFF // Cyrillic Extended-A
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* U+2E00 - U+2E7F // Supplemental Punctuation
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* U+A640 - U+A69F // Cyrillic Extended-B
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* U+A720 - U+A7FF // Latin Extended-D
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* U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures)
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* U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
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* U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
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* }
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*
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* FT_AUTOHINTER_SCRIPT_CJK ::
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* Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
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* Vietnamese, and some other scripts.
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*
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* By default, characters from the following Unicode ranges are
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* assigned to this submodule.
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*
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* {
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* U+1100 - U+11FF // Hangul Jamo
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* U+2E80 - U+2EFF // CJK Radicals Supplement
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* U+2F00 - U+2FDF // Kangxi Radicals
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* U+2FF0 - U+2FFF // Ideographic Description Characters
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* U+3000 - U+303F // CJK Symbols and Punctuation
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* U+3040 - U+309F // Hiragana
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* U+30A0 - U+30FF // Katakana
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* U+3100 - U+312F // Bopomofo
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* U+3130 - U+318F // Hangul Compatibility Jamo
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* U+3190 - U+319F // Kanbun
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* U+31A0 - U+31BF // Bopomofo Extended
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* U+31C0 - U+31EF // CJK Strokes
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* U+31F0 - U+31FF // Katakana Phonetic Extensions
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* U+3200 - U+32FF // Enclosed CJK Letters and Months
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* U+3300 - U+33FF // CJK Compatibility
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* U+3400 - U+4DBF // CJK Unified Ideographs Extension A
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* U+4DC0 - U+4DFF // Yijing Hexagram Symbols
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* U+4E00 - U+9FFF // CJK Unified Ideographs
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* U+A960 - U+A97F // Hangul Jamo Extended-A
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* U+AC00 - U+D7AF // Hangul Syllables
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* U+D7B0 - U+D7FF // Hangul Jamo Extended-B
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* U+F900 - U+FAFF // CJK Compatibility Ideographs
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* U+FE10 - U+FE1F // Vertical forms
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* U+FE30 - U+FE4F // CJK Compatibility Forms
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* U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms
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* U+1B000 - U+1B0FF // Kana Supplement
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* U+1D300 - U+1D35F // Tai Xuan Hing Symbols
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* U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
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* U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
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* U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
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* U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
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* U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
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* }
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*
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* FT_AUTOHINTER_SCRIPT_INDIC ::
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* Apply the indic auto-hinter, covering all major scripts from the
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* Indian sub-continent and some other related scripts like Thai, Lao,
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* or Tibetan.
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*
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* By default, characters from the following Unicode ranges are
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* assigned to this submodule.
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*
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* {
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* U+0900 - U+0DFF // Indic Range
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* U+0F00 - U+0FFF // Tibetan
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* U+1900 - U+194F // Limbu
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* U+1B80 - U+1BBF // Sundanese
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* U+A800 - U+A82F // Syloti Nagri
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* U+ABC0 - U+ABFF // Meetei Mayek
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* U+11800 - U+118DF // Sharada
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* }
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*
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* Note that currently Indic support is rudimentary only, missing blue
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* zone support.
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*
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*/
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#define FT_AUTOHINTER_SCRIPT_NONE 0
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#define FT_AUTOHINTER_SCRIPT_LATIN 1
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#define FT_AUTOHINTER_SCRIPT_CJK 2
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#define FT_AUTOHINTER_SCRIPT_INDIC 3
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/**************************************************************************
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*
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* @struct:
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* FT_Prop_GlyphToScriptMap
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*
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* @description:
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* *Experimental* *only*
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*
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* The data exchange structure for the @glyph-to-script-map property.
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*
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*/
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typedef struct FT_Prop_GlyphToScriptMap_
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{
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FT_Face face;
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FT_UShort* map;
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} FT_Prop_GlyphToScriptMap;
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/**************************************************************************
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*
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* @property:
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* fallback-script
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*
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* @description:
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* *Experimental* *only*
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*
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* If no auto-hinter script module can be assigned to a glyph, a
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* fallback script gets assigned to it (see also the
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* @glyph-to-script-map property). By default, this is
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* @FT_AUTOHINTER_SCRIPT_CJK. Using the `fallback-script' property,
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* this fallback value can be changed.
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*
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* {
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* FT_Library library;
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* FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "autofitter",
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* "fallback-script", &fallback_script );
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* }
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* It's important to use the right timing for changing this value: The
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* creation of the glyph-to-script map that eventually uses the
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* fallback script value gets triggered either by setting or reading a
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* face-specific property like @glyph-to-script-map, or by auto-hinting
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* any glyph from that face. In particular, if you have already created
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* an @FT_Face structure but not loaded any glyph (using the
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* auto-hinter), a change of the fallback script will affect this face.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* default-script
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*
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* @description:
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* *Experimental* *only*
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*
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* If FreeType gets compiled with FT_CONFIG_OPTION_USE_HARFBUZZ to make
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* the HarfBuzz library access OpenType features for getting better
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* glyph coverages, this property sets the (auto-fitter) script to be
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* used for the default (OpenType) script data of a font's GSUB table.
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* Features for the default script are intended for all scripts not
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* explicitly handled in GSUB; an example is a `dlig' feature,
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* containing the combination of the characters `T', `E', and `L' to
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* form a `TEL' ligature.
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*
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* By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the
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* `default-script' property, this default value can be changed.
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*
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* {
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* FT_Library library;
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* FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "autofitter",
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* "default-script", &default_script );
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* }
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* It's important to use the right timing for changing this value: The
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* creation of the glyph-to-script map that eventually uses the
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* default script value gets triggered either by setting or reading a
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* face-specific property like @glyph-to-script-map, or by auto-hinting
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* any glyph from that face. In particular, if you have already created
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* an @FT_Face structure but not loaded any glyph (using the
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* auto-hinter), a change of the default script will affect this face.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* increase-x-height
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*
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* @description:
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* For ppem values in the range 6~<= ppem <= `increase-x-height', round
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* up the font's x~height much more often than normally. If the value
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* is set to~0, which is the default, this feature is switched off. Use
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* this property to improve the legibility of small font sizes if
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* necessary.
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*
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* {
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* FT_Library library;
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* FT_Face face;
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* FT_Prop_IncreaseXHeight prop;
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*
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*
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* FT_Init_FreeType( &library );
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* FT_New_Face( library, "foo.ttf", 0, &face );
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* FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
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*
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* prop.face = face;
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* prop.limit = 14;
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*
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* FT_Property_Set( library, "autofitter",
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* "increase-x-height", &prop );
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* }
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* Set this value right after calling @FT_Set_Char_Size, but before
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* loading any glyph (using the auto-hinter).
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*
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*/
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/**************************************************************************
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*
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* @struct:
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* FT_Prop_IncreaseXHeight
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*
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* @description:
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* The data exchange structure for the @increase-x-height property.
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*
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*/
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typedef struct FT_Prop_IncreaseXHeight_
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{
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FT_Face face;
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FT_UInt limit;
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} FT_Prop_IncreaseXHeight;
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/**************************************************************************
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*
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* @property:
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* warping
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*
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* @description:
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* *Experimental* *only*
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*
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* If FreeType gets compiled with option AF_CONFIG_OPTION_USE_WARPER to
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* activate the warp hinting code in the auto-hinter, this property
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* switches warping on and off.
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*
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* Warping only works in `light' auto-hinting mode. The idea of the
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* code is to slightly scale and shift a glyph along the non-hinted
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* dimension (which is usually the horizontal axis) so that as much of
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* its segments are aligned (more or less) to the grid. To find out a
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* glyph's optimal scaling and shifting value, various parameter
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* combinations are tried and scored.
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*
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* By default, warping is off. The example below shows how to switch on
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* warping (omitting the error handling).
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*
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* {
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* FT_Library library;
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* FT_Bool warping = 1;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "autofitter",
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* "warping", &warping );
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* }
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* The warping code can also change advance widths. Have a look at the
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* `lsb_delta' and `rsb_delta' fields in the @FT_GlyphSlotRec structure
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* for details on improving inter-glyph distances while rendering.
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*
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* Since warping is a global property of the auto-hinter it is best to
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* change its value before rendering any face. Otherwise, you should
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* reload all faces that get auto-hinted in `light' hinting mode.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* no-stem-darkening[autofit]
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*
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* @description:
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* *Experimental* *only,* *requires* *linear* *alpha* *blending* *and*
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* *gamma* *correction*
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*
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* Stem darkening emboldens glyphs at smaller sizes to make them more
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* readable on common low-DPI screens when using linear alpha blending
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* and gamma correction, see @FT_Render_Glyph. When not using linear
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* alpha blending and gamma correction, glyphs will appear heavy and
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* fuzzy!
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*
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* Gamma correction essentially lightens fonts since shades of grey are
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* shifted to higher pixel values (=~higher brightness) to match the
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* original intention to the reality of our screens. The side-effect is
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* that glyphs `thin out'. Mac OS~X and Adobe's proprietary font
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* rendering library implement a counter-measure: stem darkening at
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* smaller sizes where shades of gray dominate. By emboldening a glyph
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* slightly in relation to its pixel size, individual pixels get higher
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* coverage of filled-in outlines and are therefore `blacker'. This
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* counteracts the `thinning out' of glyphs, making text remain readable
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* at smaller sizes. All glyphs that pass through the auto-hinter will
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* be emboldened unless this property is set to TRUE.
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*
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* See the description of the CFF driver for algorithmic details. Total
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* consistency with the CFF driver is currently not achieved because the
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* emboldening method differs and glyphs must be scaled down on the
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* Y-axis to keep outline points inside their precomputed blue zones.
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* The smaller the size (especially 9ppem and down), the higher the loss
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* of emboldening versus the CFF driver.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* darkening-parameters[autofit]
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*
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* @description:
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* *Experimental* *only*
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*
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* See the description of the CFF driver for details. This
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* implementation appropriates the
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* CFF_CONFIG_OPTION_DARKENING_PARAMETER_* #defines for consistency.
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* Note the differences described in @no-stem-darkening[autofit].
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*
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*/
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/* */
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FT_END_HEADER
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#endif /* FTAUTOH_H_ */
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/* END */
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