glyph-to-script-map

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 );

FT_AUTOHINTER_SCRIPT_XXX

Defined in FT_AUTOHINTER_H (freetype/ftautoh.h).

#define FT_AUTOHINTER_SCRIPT_NONE   0
#define FT_AUTOHINTER_SCRIPT_LATIN  1
#define FT_AUTOHINTER_SCRIPT_CJK    2
#define FT_AUTOHINTER_SCRIPT_INDIC  3

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

  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

  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

  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

FT_Prop_GlyphToScriptMap

Defined in FT_AUTOHINTER_H (freetype/ftautoh.h).

  typedef struct  FT_Prop_GlyphToScriptMap_
  {
    FT_Face     face;
    FT_UShort*  map;

  } FT_Prop_GlyphToScriptMap;

Experimental only

The data exchange structure for the glyph-to-script-map property.

fallback-script

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.

default-script

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.

increase-x-height

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).

FT_Prop_IncreaseXHeight

Defined in FT_AUTOHINTER_H (freetype/ftautoh.h).

  typedef struct  FT_Prop_IncreaseXHeight_
  {
    FT_Face  face;
    FT_UInt  limit;

  } FT_Prop_IncreaseXHeight;

The data exchange structure for the increase-x-height property.

warping

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.