78 lines
2.7 KiB
Plaintext
78 lines
2.7 KiB
Plaintext
// The Position object provides utility methods to manipulate
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// the GPOS position table.
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import Layout from './layout';
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/**
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* @exports opentype.Position
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* @class
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* @extends opentype.Layout
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* @param {opentype.Font}
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* @constructor
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*/
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function Position(font) {
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Layout.call(this, font, 'gpos');
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}
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Position.prototype = Layout.prototype;
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/**
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* Init some data for faster and easier access later.
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*/
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Position.prototype.init = function() {
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const script = this.getDefaultScriptName();
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this.defaultKerningTables = this.getKerningTables(script);
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};
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/**
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* Find a glyph pair in a list of lookup tables of type 2 and retrieve the xAdvance kerning value.
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*
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* @param {integer} leftIndex - left glyph index
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* @param {integer} rightIndex - right glyph index
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* @returns {integer}
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*/
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Position.prototype.getKerningValue = function(kerningLookups, leftIndex, rightIndex) {
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for (let i = 0; i < kerningLookups.length; i++) {
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const subtables = kerningLookups[i].subtables;
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for (let j = 0; j < subtables.length; j++) {
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const subtable = subtables[j];
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const covIndex = this.getCoverageIndex(subtable.coverage, leftIndex);
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if (covIndex < 0) continue;
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switch (subtable.posFormat) {
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case 1:
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// Search Pair Adjustment Positioning Format 1
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let pairSet = subtable.pairSets[covIndex];
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for (let k = 0; k < pairSet.length; k++) {
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let pair = pairSet[k];
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if (pair.secondGlyph === rightIndex) {
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return pair.value1 && pair.value1.xAdvance || 0;
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}
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}
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break; // left glyph found, not right glyph - try next subtable
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case 2:
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// Search Pair Adjustment Positioning Format 2
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const class1 = this.getGlyphClass(subtable.classDef1, leftIndex);
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const class2 = this.getGlyphClass(subtable.classDef2, rightIndex);
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const pair = subtable.classRecords[class1][class2];
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return pair.value1 && pair.value1.xAdvance || 0;
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}
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}
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}
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return 0;
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};
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/**
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* List all kerning lookup tables.
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*
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* @param {string} [script='DFLT'] - use font.position.getDefaultScriptName() for a better default value
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* @param {string} [language='dflt']
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* @return {object[]} The list of kerning lookup tables (may be empty), or undefined if there is no GPOS table (and we should use the kern table)
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*/
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Position.prototype.getKerningTables = function(script, language) {
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if (this.font.tables.gpos) {
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return this.getLookupTables(script, language, 'kern', 2);
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}
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};
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export default Position;
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