addLigature top-level property

Null Function(dynamic feature, dynamic ligature, dynamic script, dynamic language) addLigature

Implementation

Substitution.prototype.addLigature = function(feature, ligature, script, language) {
    const lookupTable = this.getLookupTables(script, language, feature, 4, true)[0];
    let subtable = lookupTable.subtables[0];
    if (!subtable) {
        subtable = {                // lookup type 4 subtable, format 1, coverage format 1
            substFormat: 1,
            coverage: { format: 1, glyphs: [] },
            ligatureSets: []
        };
        lookupTable.subtables[0] = subtable;
    }
    check.assert(subtable.coverage.format === 1, 'Ligature: unable to modify coverage table format ' + subtable.coverage.format);
    const coverageGlyph = ligature.sub[0];
    const ligComponents = ligature.sub.slice(1);
    const ligatureTable = {
        ligGlyph: ligature.by,
        components: ligComponents
    };
    let pos = this.binSearch(subtable.coverage.glyphs, coverageGlyph);
    if (pos >= 0) {
        // ligatureSet already exists
        const ligatureSet = subtable.ligatureSets[pos];
        for (let i = 0; i < ligatureSet.length; i++) {
            // If ligature already exists, return.
            if (arraysEqual(ligatureSet[i].components, ligComponents)) {
                return;
            }
        }
        // ligature does not exist: add it.
        ligatureSet.push(ligatureTable);
    } else {
        // Create a new ligatureSet and add coverage for the first glyph.
        pos = -1 - pos;
        subtable.coverage.glyphs.splice(pos, 0, coverageGlyph);
        subtable.ligatureSets.splice(pos, 0, [ligatureTable]);
    }
};