javascript - 提取ttf字体连字映射

我有一个现存的ttf font，我希望将所有Ligature映射提取为以下形式:

{
    "calendar_today": "E935",
    "calendar_view_day": "E936",
    ...
}

我在此脚本中使用fontkit:

const fontkit = require('fontkit');
let font = fontkit.openSync('./MaterialIcons-Regular.ttf');
let lookupList = font.GSUB.lookupList.toArray();
let lookupListIndexes = font.GSUB.featureList[0].feature.lookupListIndexes;

lookupListIndexes.forEach(index => {
    let subTable = lookupList[index].subTables[0];
    let ligatureSets = subTable.ligatureSets.toArray();

    ligatureSets.forEach(ligatureSet => {
        ligatureSet.forEach(ligature => {
            let character = font.stringsForGlyph(ligature.glyph)[0];
            let characterCode = character.charCodeAt(0).toString(16).toUpperCase();

            let ligatureText = ligature
                .components
                .map(x => font.stringsForGlyph(x)[0])
                .join('');

            console.log(`${ligatureText} -> ${characterCode}`);
        });
    });
});

但是，我没有完整的Ligature名称。输出:

...
alendar_today -> E935
rop_portrait -> E3C5
ontact_phone -> E0CF
ontrol_point -> E3BA
hevron_right -> E5CC
...

我究竟做错了什么？根据FontForge的分析判断，字体的Ligature名称不缺少任何字符。

最佳答案

如here所述，根据覆盖范围记录计算第一个字符。

首先，计算主角

let leadingCharacters = [];
subTable.coverage.rangeRecords.forEach((coverage) => {
    for (let i = coverage.start; i <= coverage.end; i++) {
        let character = font.stringsForGlyph(i)[0];
        leadingCharacters.push(character);
    }
});

然后，通过子表的索引访问这些字符

let ligatureSets = subTable.ligatureSets.toArray();
ligatureSets.forEach((ligatureSet, ligatureSetIndex) => {

    let leadingCharacter = leadingCharacters[ligatureSetIndex];

    ligatureSet.forEach(ligature => {
        let character = font.stringsForGlyph(ligature.glyph)[0];
        let characterCode = character.charCodeAt(0).toString(16).toUpperCase();

        let ligatureText = ligature
            .components
            .map(x => font.stringsForGlyph(x)[0])
            .join('');

        ligatureText = leadingCharacter + ligatureText;

        console.log(`${ligatureText} -> ${characterCode}`);
    });
});