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import {binarySearch} from '../utils';
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export default class KernProcessor {
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constructor(font) {
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this.kern = font.kern;
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}
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process(glyphs, positions) {
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for (let glyphIndex = 0; glyphIndex < glyphs.length - 1; glyphIndex++) {
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let left = glyphs[glyphIndex].id;
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let right = glyphs[glyphIndex + 1].id;
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positions[glyphIndex].xAdvance += this.getKerning(left, right);
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}
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}
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getKerning(left, right) {
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let res = 0;
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for (let table of this.kern.tables) {
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if (table.coverage.crossStream) {
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continue;
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}
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switch (table.version) {
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case 0:
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if (!table.coverage.horizontal) {
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continue;
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}
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break;
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case 1:
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if (table.coverage.vertical || table.coverage.variation) {
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continue;
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}
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break;
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default:
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throw new Error(`Unsupported kerning table version ${table.version}`);
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}
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let val = 0;
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let s = table.subtable;
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switch (table.format) {
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case 0:
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let pairIdx = binarySearch(s.pairs, function (pair) {
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return (left - pair.left) || (right - pair.right);
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});
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if (pairIdx >= 0) {
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val = s.pairs[pairIdx].value;
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}
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break;
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case 2:
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let leftOffset = 0, rightOffset = 0;
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if (left >= s.leftTable.firstGlyph && left < s.leftTable.firstGlyph + s.leftTable.nGlyphs) {
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leftOffset = s.leftTable.offsets[left - s.leftTable.firstGlyph];
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} else {
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leftOffset = s.array.off;
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}
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if (right >= s.rightTable.firstGlyph && right < s.rightTable.firstGlyph + s.rightTable.nGlyphs) {
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rightOffset = s.rightTable.offsets[right - s.rightTable.firstGlyph];
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}
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let index = (leftOffset + rightOffset - s.array.off) / 2;
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val = s.array.values.get(index);
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break;
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case 3:
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if (left >= s.glyphCount || right >= s.glyphCount) {
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return 0;
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}
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val = s.kernValue[s.kernIndex[s.leftClass[left] * s.rightClassCount + s.rightClass[right]]];
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break;
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default:
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throw new Error(`Unsupported kerning sub-table format ${table.format}`);
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}
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// Microsoft supports the override flag, which resets the result
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// Otherwise, the sum of the results from all subtables is returned
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if (table.coverage.override) {
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res = val;
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} else {
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res += val;
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}
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}
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return res;
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}
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}
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