addAlternate top-level property

Null Function(dynamic feature, dynamic substitution, dynamic script, dynamic language) addAlternate

Implementation

Substitution.prototype.addAlternate = function(feature, substitution, script, language) {
    const lookupTable = this.getLookupTables(script, language, feature, 3, true)[0];
    const subtable = getSubstFormat(lookupTable, 1, {                // lookup type 3 subtable, format 1, coverage format 1
        substFormat: 1,
        coverage: {format: 1, glyphs: []},
        alternateSets: []
    });
    check.assert(subtable.coverage.format === 1, 'Alternate: unable to modify coverage table format ' + subtable.coverage.format);
    const coverageGlyph = substitution.sub;
    let pos = this.binSearch(subtable.coverage.glyphs, coverageGlyph);
    if (pos < 0) {
        pos = -1 - pos;
        subtable.coverage.glyphs.splice(pos, 0, coverageGlyph);
        subtable.alternateSets.splice(pos, 0, 0);
    }
    subtable.alternateSets[pos] = substitution.by;
};