70 lines
2.3 KiB
Plaintext
70 lines
2.3 KiB
Plaintext
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// The `kern` table contains kerning pairs.
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// Note that some fonts use the GPOS OpenType layout table to specify kerning.
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// https://www.microsoft.com/typography/OTSPEC/kern.htm
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import check from '../check';
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import parse from '../parse';
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function parseWindowsKernTable(p) {
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const pairs = {};
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// Skip nTables.
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p.skip('uShort');
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const subtableVersion = p.parseUShort();
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check.argument(subtableVersion === 0, 'Unsupported kern sub-table version.');
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// Skip subtableLength, subtableCoverage
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p.skip('uShort', 2);
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const nPairs = p.parseUShort();
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// Skip searchRange, entrySelector, rangeShift.
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p.skip('uShort', 3);
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for (let i = 0; i < nPairs; i += 1) {
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const leftIndex = p.parseUShort();
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const rightIndex = p.parseUShort();
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const value = p.parseShort();
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pairs[leftIndex + ',' + rightIndex] = value;
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}
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return pairs;
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}
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function parseMacKernTable(p) {
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const pairs = {};
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// The Mac kern table stores the version as a fixed (32 bits) but we only loaded the first 16 bits.
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// Skip the rest.
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p.skip('uShort');
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const nTables = p.parseULong();
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//check.argument(nTables === 1, 'Only 1 subtable is supported (got ' + nTables + ').');
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if (nTables > 1) {
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console.warn('Only the first kern subtable is supported.');
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}
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p.skip('uLong');
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const coverage = p.parseUShort();
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const subtableVersion = coverage & 0xFF;
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p.skip('uShort');
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if (subtableVersion === 0) {
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const nPairs = p.parseUShort();
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// Skip searchRange, entrySelector, rangeShift.
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p.skip('uShort', 3);
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for (let i = 0; i < nPairs; i += 1) {
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const leftIndex = p.parseUShort();
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const rightIndex = p.parseUShort();
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const value = p.parseShort();
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pairs[leftIndex + ',' + rightIndex] = value;
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}
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}
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return pairs;
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}
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// Parse the `kern` table which contains kerning pairs.
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function parseKernTable(data, start) {
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const p = new parse.Parser(data, start);
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const tableVersion = p.parseUShort();
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if (tableVersion === 0) {
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return parseWindowsKernTable(p);
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} else if (tableVersion === 1) {
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return parseMacKernTable(p);
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} else {
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throw new Error('Unsupported kern table version (' + tableVersion + ').');
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}
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}
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export default { parse: parseKernTable };
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