Function parseClassDefTable

libraries/p5.js:4695–4738

(data, start)

// Parse a Class Definition Table in a GSUB, GPOS or GDEF table.
// Returns a function that gets a class value from a glyph ID.
function parseClassDefTable(data, start) {
    var p = new parse.Parser(data, start);
    var format = p.parseUShort();
    if (format === 1) {
        // Format 1 specifies a range of consecutive glyph indices, one class per glyph ID.
        var startGlyph = p.parseUShort();
        var glyphCount = p.parseUShort();
        var classes = p.parseUShortList(glyphCount);
        return function(glyphID) {
            return classes[glyphID - startGlyph] || 0;
        };
    }
    else if (format === 2) {
        // Format 2 defines multiple groups of glyph indices that belong to the same class.
        var rangeCount = p.parseUShort();
        var startGlyphs = [];
        var endGlyphs = [];
        var classValues = [];
        for (var i = 0; i < rangeCount; i++) {
            startGlyphs[i] = p.parseUShort();
            endGlyphs[i] = p.parseUShort();
            classValues[i] = p.parseUShort();
        }

        return function(glyphID) {
            var l = 0;
            var r = startGlyphs.length - 1;
            while (l < r) {
                var c = (l + r + 1) >> 1;
                if (glyphID < startGlyphs[c]) {
                    r = c - 1;
                } else {
                    l = c;
                }
            }

            if (startGlyphs[l] <= glyphID && glyphID <= endGlyphs[l]) {
                return classValues[l] || 0;
            }

            return 0;
        };
    }
}

// Parse a pair adjustment positioning subtable, format 1 or format 2
// The subtable is returned in the form of a lookup function.