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