Function parseCmapTable

libraries/p5.js:4020–4098

(data, start)

// There are many available formats, but we only support the Windows format 4.
// This function returns a `CmapEncoding` object or null if no supported format could be found.
function parseCmapTable(data, start) {
    var i;
    var cmap = {};
    cmap.version = parse.getUShort(data, start);
    check.argument(cmap.version === 0, 'cmap table version should be 0.');

    // The cmap table can contain many sub-tables, each with their own format.
    // We're only interested in a "platform 3" table. This is a Windows format.
    cmap.numTables = parse.getUShort(data, start + 2);
    var offset = -1;
    for (i = 0; i < cmap.numTables; i += 1) {
        var platformId = parse.getUShort(data, start + 4 + (i * 8));
        var encodingId = parse.getUShort(data, start + 4 + (i * 8) + 2);
        if (platformId === 3 && (encodingId === 1 || encodingId === 0)) {
            offset = parse.getULong(data, start + 4 + (i * 8) + 4);
            break;
        }
    }

    if (offset === -1) {
        // There is no cmap table in the font that we support, so return null.
        // This font will be marked as unsupported.
        return null;
    }

    var p = new parse.Parser(data, start + offset);
    cmap.format = p.parseUShort();
    check.argument(cmap.format === 4, 'Only format 4 cmap tables are supported.');

    // Length in bytes of the sub-tables.
    cmap.length = p.parseUShort();
    cmap.language = p.parseUShort();

    // segCount is stored x 2.
    var segCount;
    cmap.segCount = segCount = p.parseUShort() >> 1;

    // Skip searchRange, entrySelector, rangeShift.
    p.skip('uShort', 3);

    // The "unrolled" mapping from character codes to glyph indices.
    cmap.glyphIndexMap = {};

    var endCountParser = new parse.Parser(data, start + offset + 14);
    var startCountParser = new parse.Parser(data, start + offset + 16 + segCount * 2);
    var idDeltaParser = new parse.Parser(data, start + offset + 16 + segCount * 4);
    var idRangeOffsetParser = new parse.Parser(data, start + offset + 16 + segCount * 6);
    var glyphIndexOffset = start + offset + 16 + segCount * 8;
    for (i = 0; i < segCount - 1; i += 1) {
        var glyphIndex;
        var endCount = endCountParser.parseUShort();
        var startCount = startCountParser.parseUShort();
        var idDelta = idDeltaParser.parseShort();
        var idRangeOffset = idRangeOffsetParser.parseUShort();
        for (var c = startCount; c <= endCount; c += 1) {
            if (idRangeOffset !== 0) {
                // The idRangeOffset is relative to the current position in the idRangeOffset array.
                // Take the current offset in the idRangeOffset array.