harfbuzz-feature-map.md

Feature mappings in HarfBuzz

The font features described by OpenType, AAT, and Graphite are not indentical. However, in many cases there is a clear mapping between them.

The OpenType shaping library HarfBuzz supports a mapping between AAT and OpenType features that covers most, but not all of the AAT codes.

The first thing to note is that the AAT codes tend to be more granular. So, for example, the c2sc OpenType feature, which means "capitals to small caps," maps to a set of two AAT selectors taken together: kUpperCaseSmallCapsSelector + kDefaultUpperCaseSelector.

The other thing to note is that there are several AAT codes not currently supported in this mapping. Excluding deprecated code and the codes that are exclusively tied to script-shaping features, they are:

• kRequiredLigaturesOnSelector Required Ligatures
• kRebusPicturesOnSelector Rebus Pictures
• kDiphthongLigaturesOnSelector Diphthong Ligatures
• kSquaredLigaturesOnSelector Squared Ligatures
• kAbbrevSquaredLigaturesOnSelector Squared Ligatures, Abbreviated
• kSymbolLigaturesOnSelector Symbol Ligatures
• kWordInitialSwashesOnSelector Word Initial Swashes
• kWordFinalSwashesOnSelector Word Final Swashes
• kShowDiacriticsSelector Show Diacritics
• kHideDiacriticsSelector Hide Diacritics
• kDecomposeDiacriticsSelector Decompose Diacritics
• kVerticalFractionsSelector Vertical Fractions
• kNoOrnamentsSelector None
• kDingbatsSelector Dingbats
• kPiCharactersSelector Pi Characters
• kFleuronsSelector Fleurons
• kDecorativeBordersSelector Decorative Borders
• kInternationalSymbolsSelector International Symbols
• kMathSymbolsSelector Math Symbols
• kCharacterAlternatives Character Alternatives
• kDesignLevel1Selector Design Level 1
• kDesignLevel2Selector Design Level 2
• kDesignLevel3Selector Design Level 3
• kDesignLevel4Selector Design Level 4
• kDesignLevel5Selector Design Level 5
• kDisplayTextSelector Display Text
• kEngravedTextSelector Engraved Text
• kIlluminatedCapsSelector Illuminated Caps
• kTallCapsSelector Tall Caps
• kNoAnnotationSelector No Annotation
• kBoxAnnotationSelector Box Annotation
• kRoundedBoxAnnotationSelector Rounded Box Annotation
• kCircleAnnotationSelector Circle Annotation
• kInvertedCircleAnnotationSelector Inverted Circle Annotation
• kParenthesisAnnotationSelector Parenthesis Annotation
• kPeriodAnnotationSelector Period Annotation
• kRomanNumeralAnnotationSelector Roman Numeral Annotation
• kDiamondAnnotationSelector Diamond Annotation
• kInvertedBoxAnnotationSelector Inverted Box Annotation
• kInvertedRoundedBoxAnnotationSelector Inverted Rounded Box Annotation