Function parsePairPosSubTable

libraries/p5.js:4742–4826

(data, start)

// Parse a pair adjustment positioning subtable, format 1 or format 2
// The subtable is returned in the form of a lookup function.
function parsePairPosSubTable(data, start) {
    var p = new parse.Parser(data, start);
    // This part is common to format 1 and format 2 subtables
    var format = p.parseUShort();
    var coverageOffset = p.parseUShort();
    var coverage = parseCoverageTable(data, start + coverageOffset);
    // valueFormat 4: XAdvance only, 1: XPlacement only, 0: no ValueRecord for second glyph
    // Only valueFormat1=4 and valueFormat2=0 is supported.
    var valueFormat1 = p.parseUShort();
    var valueFormat2 = p.parseUShort();
    var value1;
    var value2;
    if (valueFormat1 !== 4 || valueFormat2 !== 0) return;
    var sharedPairSets = {};
    if (format === 1) {
        // Pair Positioning Adjustment: Format 1
        var pairSetCount = p.parseUShort();
        var pairSet = [];
        // Array of offsets to PairSet tables-from beginning of PairPos subtable-ordered by Coverage Index
        var pairSetOffsets = p.parseOffset16List(pairSetCount);
        for (var firstGlyph = 0; firstGlyph < pairSetCount; firstGlyph++) {
            var pairSetOffset = pairSetOffsets[firstGlyph];
            var sharedPairSet = sharedPairSets[pairSetOffset];
            if (!sharedPairSet) {
                // Parse a pairset table in a pair adjustment subtable format 1
                sharedPairSet = {};
                p.relativeOffset = pairSetOffset;
                var pairValueCount = p.parseUShort();
                for (; pairValueCount--;) {
                    var secondGlyph = p.parseUShort();
                    if (valueFormat1) value1 = p.parseShort();
                    if (valueFormat2) value2 = p.parseShort();
                    // We only support valueFormat1 = 4 and valueFormat2 = 0,
                    // so value1 is the XAdvance and value2 is empty.
                    sharedPairSet[secondGlyph] = value1;
                }
            }

            pairSet[coverage[firstGlyph]] = sharedPairSet;
        }

        return function(leftGlyph, rightGlyph) {
            var pairs = pairSet[leftGlyph];
            if (pairs) return pairs[rightGlyph];
        };
    }
    else if (format === 2) {
        // Pair Positioning Adjustment: Format 2
        var classDef1Offset = p.parseUShort();
        var classDef2Offset = p.parseUShort();
        var class1Count = p.parseUShort();
        var class2Count = p.parseUShort();
        var getClass1 = parseClassDefTable(data, start + classDef1Offset);
        var getClass2 = parseClassDefTable(data, start + classDef2Offset);

        // Parse kerning values by class pair.
        var kerningMatrix = [];
        for (var i = 0; i < class1Count; i++) {