fontToSfntTable function

dynamic fontToSfntTable(dynamic font)

Implementation

function fontToSfntTable(font) {
    const xMins = [];
    const yMins = [];
    const xMaxs = [];
    const yMaxs = [];
    const advanceWidths = [];
    const leftSideBearings = [];
    const rightSideBearings = [];
    let firstCharIndex;
    let lastCharIndex = 0;
    let ulUnicodeRange1 = 0;
    let ulUnicodeRange2 = 0;
    let ulUnicodeRange3 = 0;
    let ulUnicodeRange4 = 0;

    for (let i = 0; i < font.glyphs.length; i += 1) {
        const glyph = font.glyphs.get(i);
        const unicode = glyph.unicode | 0;

        if (isNaN(glyph.advanceWidth)) {
            throw new Error('Glyph ' + glyph.name + ' (' + i + '): advanceWidth is not a number.');
        }

        if (firstCharIndex > unicode || firstCharIndex === undefined) {
            // ignore .notdef char
            if (unicode > 0) {
                firstCharIndex = unicode;
            }
        }

        if (lastCharIndex < unicode) {
            lastCharIndex = unicode;
        }

        const position = os2.getUnicodeRange(unicode);
        if (position < 32) {
            ulUnicodeRange1 |= 1 << position;
        } else if (position < 64) {
            ulUnicodeRange2 |= 1 << position - 32;
        } else if (position < 96) {
            ulUnicodeRange3 |= 1 << position - 64;
        } else if (position < 123) {
            ulUnicodeRange4 |= 1 << position - 96;
        } else {
            throw new Error('Unicode ranges bits > 123 are reserved for internal usage');
        }
        // Skip non-important characters.
        if (glyph.name === '.notdef') continue;
        const metrics = glyph.getMetrics();
        xMins.push(metrics.xMin);
        yMins.push(metrics.yMin);
        xMaxs.push(metrics.xMax);
        yMaxs.push(metrics.yMax);
        leftSideBearings.push(metrics.leftSideBearing);
        rightSideBearings.push(metrics.rightSideBearing);
        advanceWidths.push(glyph.advanceWidth);
    }

    const globals = {
        xMin: Math.min.apply(null, xMins),
        yMin: Math.min.apply(null, yMins),
        xMax: Math.max.apply(null, xMaxs),
        yMax: Math.max.apply(null, yMaxs),
        advanceWidthMax: Math.max.apply(null, advanceWidths),
        advanceWidthAvg: average(advanceWidths),
        minLeftSideBearing: Math.min.apply(null, leftSideBearings),
        maxLeftSideBearing: Math.max.apply(null, leftSideBearings),
        minRightSideBearing: Math.min.apply(null, rightSideBearings)
    };
    globals.ascender = font.ascender;
    globals.descender = font.descender;

    const headTable = head.make({
        flags: 3, // 00000011 (baseline for font at y=0; left sidebearing point at x=0)
        unitsPerEm: font.unitsPerEm,
        xMin: globals.xMin,
        yMin: globals.yMin,
        xMax: globals.xMax,
        yMax: globals.yMax,
        lowestRecPPEM: 3,
        createdTimestamp: font.createdTimestamp
    });

    const hheaTable = hhea.make({
        ascender: globals.ascender,
        descender: globals.descender,
        advanceWidthMax: globals.advanceWidthMax,
        minLeftSideBearing: globals.minLeftSideBearing,
        minRightSideBearing: globals.minRightSideBearing,
        xMaxExtent: globals.maxLeftSideBearing + (globals.xMax - globals.xMin),
        numberOfHMetrics: font.glyphs.length
    });

    const maxpTable = maxp.make(font.glyphs.length);

    const os2Table = os2.make(Object.assign({
        xAvgCharWidth: Math.round(globals.advanceWidthAvg),
        usFirstCharIndex: firstCharIndex,
        usLastCharIndex: lastCharIndex,
        ulUnicodeRange1: ulUnicodeRange1,
        ulUnicodeRange2: ulUnicodeRange2,
        ulUnicodeRange3: ulUnicodeRange3,
        ulUnicodeRange4: ulUnicodeRange4,
        // See http://typophile.com/node/13081 for more info on vertical metrics.
        // We get metrics for typical characters (such as "x" for xHeight).
        // We provide some fallback characters if characters are unavailable: their
        // ordering was chosen experimentally.
        sTypoAscender: globals.ascender,
        sTypoDescender: globals.descender,
        sTypoLineGap: 0,
        usWinAscent: globals.yMax,
        usWinDescent: Math.abs(globals.yMin),
        ulCodePageRange1: 1, // FIXME: hard-code Latin 1 support for now
        sxHeight: metricsForChar(font, 'xyvw', {yMax: Math.round(globals.ascender / 2)}).yMax,
        sCapHeight: metricsForChar(font, 'HIKLEFJMNTZBDPRAGOQSUVWXY', globals).yMax,
        usDefaultChar: font.hasChar(' ') ? 32 : 0, // Use space as the default character, if available.
        usBreakChar: font.hasChar(' ') ? 32 : 0, // Use space as the break character, if available.
    }, font.tables.os2));

    const hmtxTable = hmtx.make(font.glyphs);
    const cmapTable = cmap.make(font.glyphs);

    const englishFamilyName = font.getEnglishName('fontFamily');
    const englishStyleName = font.getEnglishName('fontSubfamily');
    const englishFullName = englishFamilyName + ' ' + englishStyleName;
    let postScriptName = font.getEnglishName('postScriptName');
    if (!postScriptName) {
        postScriptName = englishFamilyName.replace(/\s/g, '') + '-' + englishStyleName;
    }

    const names = {};
    for (let n in font.names) {
        names[n] = font.names[n];
    }

    if (!names.uniqueID) {
        names.uniqueID = {en: font.getEnglishName('manufacturer') + ':' + englishFullName};
    }

    if (!names.postScriptName) {
        names.postScriptName = {en: postScriptName};
    }

    if (!names.preferredFamily) {
        names.preferredFamily = font.names.fontFamily;
    }

    if (!names.preferredSubfamily) {
        names.preferredSubfamily = font.names.fontSubfamily;
    }

    const languageTags = [];
    const nameTable = _name.make(names, languageTags);
    const ltagTable = (languageTags.length > 0 ? ltag.make(languageTags) : undefined);

    const postTable = post.make();
    const cffTable = cff.make(font.glyphs, {
        version: font.getEnglishName('version'),
        fullName: englishFullName,
        familyName: englishFamilyName,
        weightName: englishStyleName,
        postScriptName: postScriptName,
        unitsPerEm: font.unitsPerEm,
        fontBBox: [0, globals.yMin, globals.ascender, globals.advanceWidthMax]
    });

    const metaTable = (font.metas && Object.keys(font.metas).length > 0) ? meta.make(font.metas) : undefined;

    // The order does not matter because makeSfntTable() will sort them.
    const tables = [headTable, hheaTable, maxpTable, os2Table, nameTable, cmapTable, postTable, cffTable, hmtxTable];
    if (ltagTable) {
        tables.push(ltagTable);
    }
    // Optional tables
    if (font.tables.gsub) {
        tables.push(gsub.make(font.tables.gsub));
    }
    if (metaTable) {
        tables.push(metaTable);
    }

    const sfntTable = makeSfntTable(tables);

    // Compute the font's checkSum and store it in head.checkSumAdjustment.
    const bytes = sfntTable.encode();
    const checkSum = computeCheckSum(bytes);
    const tableFields = sfntTable.fields;
    let checkSumAdjusted = false;
    for (let i = 0; i < tableFields.length; i += 1) {
        if (tableFields[i].name === 'head table') {
            tableFields[i].value.checkSumAdjustment = 0xB1B0AFBA - checkSum;
            checkSumAdjusted = true;
            break;
        }
    }

    if (!checkSumAdjusted) {
        throw new Error('Could not find head table with checkSum to adjust.');
    }

    return sfntTable;
}