Add vhea and vmtx parsing

Author: opengraphica

README.md

@@ -442,8 +442,10 @@ A Glyph is an individual mark that often corresponds to a character. Some glyphs
 * `unicode`: The primary unicode value of this glyph (can be `undefined`).
 * `unicodes`: The list of unicode values for this glyph (most of the time this will be `1`, can also be empty).
 * `index`: The index number of the glyph.
-* `advanceWidth`: The width to advance the pen when drawing this glyph.
+* `advanceWidth`: The width to advance the pen when drawing this glyph horizontally.
 * `leftSideBearing`: The horizontal distance from the previous character to the origin (`0, 0`); a negative value indicates an overhang
+* `advanceHeight`: The height to advance the pen when drawing this glyph vertically.
+* `topSideBearing`: The vertical distance from the previous character to the origin (`0, 0`); a negative value indicates an overhang
 * `xMin`, `yMin`, `xMax`, `yMax`: The bounding box of the glyph.
 * `path`: The raw, unscaled path of the glyph.
 

src/glyph.mjs

@@ -37,6 +37,8 @@ function getPathDefinition(glyph, path) {
  * @property {number} [yMax]
  * @property {number} [advanceWidth]
  * @property {number} [leftSideBearing]
+ * @property {number} [advanceHeight]
+ * @property {number} [topSideBearing]
  */
 
 // A Glyph is an individual mark that often corresponds to a character.
@@ -103,6 +105,14 @@ Glyph.prototype.bindConstructorValues = function(options) {
         this.leftSideBearing = options.leftSideBearing;
     }
 
+    if ('advanceHeight' in options) {
+        this.advanceHeight = options.advanceHeight;
+    }
+
+    if ('topSideBearing' in options) {
+        this.topSideBearing = options.topSideBearing;
+    }
+
     if ('points' in options) {
         this.points = options.points;
     }
@@ -324,7 +334,8 @@ Glyph.prototype.getMetrics = function() {
         yMin: Math.min.apply(null, yCoords),
         xMax: Math.max.apply(null, xCoords),
         yMax: Math.max.apply(null, yCoords),
-        leftSideBearing: this.leftSideBearing
+        leftSideBearing: this.leftSideBearing,
+        topSideBearing: this.topSideBearing
     };
 
     if (!isFinite(metrics.xMin)) {
@@ -344,6 +355,9 @@ Glyph.prototype.getMetrics = function() {
     }
 
     metrics.rightSideBearing = this.advanceWidth - metrics.leftSideBearing - (metrics.xMax - metrics.xMin);
+    metrics.bottomSideBearing = metrics.topSideBearing != null
+        ? this.advanceHeight - metrics.topSideBearing - (metrics.yMax - metrics.yMin)
+        : undefined;
     return metrics;
 };
 

src/glyphset.mjs

@@ -88,6 +88,10 @@ GlyphSet.prototype.get = function(index) {
 
         this.glyphs[index].advanceWidth = this.font._hmtxTableData[index].advanceWidth;
         this.glyphs[index].leftSideBearing = this.font._hmtxTableData[index].leftSideBearing;
+        if (this.font._vmtxTableData) {
+            this.glyphs[index].advanceHeight = this.font._vmtxTableData[index].advanceHeight;
+            this.glyphs[index].topSideBearing = this.font._vmtxTableData[index].topSideBearing;
+        }
     } else {
         if (typeof this.glyphs[index] === 'function') {
             this.glyphs[index] = this.glyphs[index]();

src/opentype.mjs

@@ -26,7 +26,9 @@ import gpos from './tables/gpos.mjs';
 import gsub from './tables/gsub.mjs';
 import head from './tables/head.mjs';
 import hhea from './tables/hhea.mjs';
+import vhea from './tables/vhea.mjs';
 import hmtx from './tables/hmtx.mjs';
+import vmtx from './tables/vmtx.mjs';
 import kern from './tables/kern.mjs';
 import ltag from './tables/ltag.mjs';
 import loca from './tables/loca.mjs';
@@ -189,6 +191,7 @@ function parseBuffer(buffer, opt={}) {
     let gsubTableEntry;
     let hmtxTableEntry;
     let hvarTableEntry;
+    let vmtxTableEntry;
     let kernTableEntry;
     let locaTableEntry;
     let nameTableEntry;
@@ -248,6 +251,16 @@ function parseBuffer(buffer, opt={}) {
             case 'hmtx':
                 hmtxTableEntry = tableEntry;
                 break;
+            case 'vhea':
+                table = uncompressTable(data, tableEntry);
+                font.tables.vhea = vhea.parse(table.data, table.offset);
+                font.vertTypoAscender = font.tables.vhea.vertTypoAscender;
+                font.vertTypoDescender = font.tables.vhea.vertTypoDescender;
+                font.numOfLongVerMetrics = font.tables.vhea.numOfLongVerMetrics;
+                break;
+            case 'vmtx':
+                vmtxTableEntry = tableEntry;
+                break;
             case 'ltag':
                 table = uncompressTable(data, tableEntry);
                 ltagTable = ltag.parse(table.data, table.offset);
@@ -343,8 +356,14 @@ function parseBuffer(buffer, opt={}) {
         throw new Error('Font doesn\'t contain TrueType, CFF or CFF2 outlines.');
     }
 
-    const hmtxTable = uncompressTable(data, hmtxTableEntry);
-    hmtx.parse(font, hmtxTable.data, hmtxTable.offset, font.numberOfHMetrics, font.numGlyphs, font.glyphs, opt);
+    if (hmtxTableEntry) {
+        const hmtxTable = uncompressTable(data, hmtxTableEntry);
+        hmtx.parse(font, hmtxTable.data, hmtxTable.offset, font.numberOfHMetrics, font.numGlyphs, font.glyphs, opt);
+    }
+    if (vmtxTableEntry) {
+        const vmtxTable = uncompressTable(data, vmtxTableEntry);
+        vmtx.parse(font, vmtxTable.data, vmtxTable.offset, font.numOfLongVerMetrics, font.numGlyphs, font.glyphs, opt);
+    }
     addGlyphNames(font, opt);
 
     if (kernTableEntry) {

src/tables/vhea.mjs

@@ -0,0 +1,53 @@
+// The `vhea` table contains information for vertical layout.
+// https://learn.microsoft.com/en-us/typography/opentype/spec/vhea
+
+import parse from '../parse.mjs';
+import table from '../table.mjs';
+
+// Parse the vertical header `vhea` table
+function parseVheaTable(data, start) {
+    const vhea = {};
+    const p = new parse.Parser(data, start);
+    vhea.version = p.parseVersion();
+    vhea.ascent = p.parseShort(); // v1.0
+    vhea.vertTypoAscender = vhea.ascent; // v1.1
+    vhea.descent = p.parseShort(); // v1.0
+    vhea.vertTypoDescender = vhea.descent; // v1.1
+    vhea.lineGap = p.parseShort(); // v1.0
+    vhea.vertTypoLineGap = vhea.lineGap; // v1.1
+    vhea.advanceHeightMax = p.parseUShort();
+    vhea.minTopSideBearing = p.parseShort();
+    vhea.minBottomSideBearing = p.parseShort();
+    vhea.yMaxExtent = p.parseShort();
+    vhea.caretSlopeRise = p.parseShort();
+    vhea.caretSlopeRun = p.parseShort();
+    vhea.caretOffset = p.parseShort();
+    p.relativeOffset += 8;
+    vhea.metricDataFormat = p.parseShort();
+    vhea.numOfLongVerMetrics = p.parseUShort();
+    return vhea;
+}
+
+function makeVheaTable(options) {
+    return new table.Table('vhea', [
+        {name: 'version', type: 'FIXED', value: 0x00010000},
+        {name: 'ascent', type: 'FWORD', value: 0},
+        {name: 'descent', type: 'FWORD', value: 0},
+        {name: 'lineGap', type: 'FWORD', value: 0},
+        {name: 'advanceHeightMax', type: 'UFWORD', value: 0},
+        {name: 'minTopSideBearing', type: 'FWORD', value: 0},
+        {name: 'minBottomSideBearing', type: 'FWORD', value: 0},
+        {name: 'yMaxExtent', type: 'FWORD', value: 0},
+        {name: 'caretSlopeRise', type: 'SHORT', value: 1},
+        {name: 'caretSlopeRun', type: 'SHORT', value: 0},
+        {name: 'caretOffset', type: 'SHORT', value: 0},
+        {name: 'reserved1', type: 'SHORT', value: 0},
+        {name: 'reserved2', type: 'SHORT', value: 0},
+        {name: 'reserved3', type: 'SHORT', value: 0},
+        {name: 'reserved4', type: 'SHORT', value: 0},
+        {name: 'metricDataFormat', type: 'SHORT', value: 0},
+        {name: 'numOfLongVerMetrics', type: 'USHORT', value: 0}
+    ], options);
+}
+
+export default { parse: parseVheaTable, make: makeVheaTable };

src/tables/vmtx.mjs

@@ -0,0 +1,66 @@
+// The `vmtx` table contains the vertical metrics for all glyphs.
+// https://learn.microsoft.com/en-us/typography/opentype/spec/vmtx
+
+import parse from '../parse.mjs';
+import table from '../table.mjs';
+
+function parseVmtxTableAll(data, start, numMetrics, numGlyphs, glyphs) {
+    let advanceHeight;
+    let topSideBearing;
+    const p = new parse.Parser(data, start);
+    for (let i = 0; i < numGlyphs; i += 1) {
+        // If the font is monospaced, only one entry is needed. This last entry applies to all subsequent glyphs.
+        if (i < numMetrics) {
+            advanceHeight = p.parseUShort();
+            topSideBearing = p.parseShort();
+        }
+
+        const glyph = glyphs.get(i);
+        glyph.advanceHeight = advanceHeight;
+        glyph.topSideBearing = topSideBearing;
+    }
+}
+
+function parseVmtxTableOnLowMemory(font, data, start, numMetrics, numGlyphs) {
+    font._vmtxTableData = {};
+
+    let advanceHeight;
+    let topSideBearing;
+    const p = new parse.Parser(data, start);
+    for (let i = 0; i < numGlyphs; i += 1) {
+        // If the font is monospaced, only one entry is needed. This last entry applies to all subsequent glyphs.
+        if (i < numMetrics) {
+            advanceHeight = p.parseUShort();
+            topSideBearing = p.parseShort();
+        }
+
+        font._vmtxTableData[i] = {
+            advanceHeight: advanceHeight,
+            topSideBearing: topSideBearing
+        };
+    }
+}
+
+// Parse the `vmtx` table, which contains the horizontal metrics for all glyphs.
+// This function augments the glyph array, adding the advanceHeight and topSideBearing to each glyph.
+function parseVmtxTable(font, data, start, numMetrics, numGlyphs, glyphs, opt) {
+    if (opt.lowMemory)
+        parseVmtxTableOnLowMemory(font, data, start, numMetrics, numGlyphs);
+    else
+        parseVmtxTableAll(data, start, numMetrics, numGlyphs, glyphs);
+}
+
+function makeVmtxTable(glyphs) {
+    const t = new table.Table('vmtx', []);
+    for (let i = 0; i < glyphs.length; i += 1) {
+        const glyph = glyphs.get(i);
+        const advanceHeight = glyph.advanceHeight || 0;
+        const topSideBearing = glyph.topSideBearing || 0;
+        t.fields.push({name: 'advanceHeight_' + i, type: 'USHORT', value: advanceHeight});
+        t.fields.push({name: 'topSideBearing_' + i, type: 'SHORT', value: topSideBearing});
+    }
+
+    return t;
+}
+
+export default { parse: parseVmtxTable, make: makeVmtxTable };

test/fonts/NotoSansJP-Medium.ttf

@@ -0,0 +1,35 @@
+import assert from 'assert';
+import { parse } from '../../src/opentype.mjs';
+import { readFileSync } from 'fs';
+const loadSync = (url, opt) => parse(readFileSync(url), opt);
+
+describe('tables/vhea.mjs', function() {
+    const fonts = {
+        notoSansJp: loadSync('./test/fonts/NotoSansJP-Medium.ttf'),
+    };
+    it('correctly parses the vertical header table', function() {
+        // tests for all fonts
+        const { notoSansJp } = fonts;
+        assert.equal(notoSansJp.tables.vhea.version, 1.1);
+        assert.equal(notoSansJp.tables.vhea.ascent, 500);
+        assert.equal(notoSansJp.tables.vhea.vertTypoAscender, 500);
+        assert.equal(notoSansJp.tables.vhea.descent, -500);
+        assert.equal(notoSansJp.tables.vhea.vertTypoDescender, -500);
+        assert.equal(notoSansJp.tables.vhea.lineGap, 0);
+        assert.equal(notoSansJp.tables.vhea.vertTypoLineGap, 0);
+        assert.equal(notoSansJp.tables.vhea.advanceHeightMax, 3000);
+        assert.equal(notoSansJp.tables.vhea.minTopSideBearing, -224);
+        assert.equal(notoSansJp.tables.vhea.minBottomSideBearing, -689);
+        assert.equal(notoSansJp.tables.vhea.yMaxExtent, 2927);
+        assert.equal(notoSansJp.tables.vhea.caretSlopeRise, 0);
+        assert.equal(notoSansJp.tables.vhea.caretSlopeRun, 1);
+        assert.equal(notoSansJp.tables.vhea.caretOffset, 0);
+        assert.equal(notoSansJp.tables.vhea.metricDataFormat, 0);
+        assert.equal(notoSansJp.tables.vhea.numOfLongVerMetrics, 17481);
+
+        // Directly exposed equivalents to ascender, descender, numberOfHMetrics
+        assert.equal(notoSansJp.vertTypoAscender, 500);
+        assert.equal(notoSansJp.vertTypoDescender, -500);
+        assert.equal(notoSansJp.numOfLongVerMetrics, 17481);
+    });
+});

test/tables/vhea.spec.mjs

@@ -0,0 +1,35 @@
+import assert from 'assert';
+import { parse } from '../../src/opentype.mjs';
+import { readFileSync } from 'fs';
+const loadSync = (url, opt) => parse(readFileSync(url), opt);
+
+describe('tables/vmtx.mjs', function() {
+    const fonts = {
+        notoSansJp: loadSync('./test/fonts/NotoSansJP-Medium.ttf'),
+        notoSansJpLowMemory: loadSync('./test/fonts/NotoSansJP-Medium.ttf', { lowMemory: true }),
+    };
+
+    it('correctly parses the vertical metrics table - high memory', function() {
+        // tests for all fonts
+        const { notoSansJp } = fonts;
+
+        const a = notoSansJp.charToGlyph('あ');
+        assert.equal(a.topSideBearing, 80);
+        assert.equal(a.advanceHeight, 1000);
+        const aMetrics = a.getMetrics();
+        assert.equal(aMetrics.topSideBearing, 80);
+        assert.equal(aMetrics.bottomSideBearing, 64);
+    });
+
+    it('correctly parses the vertical metrics table - low memory', function() {
+        // tests for all fonts
+        const { notoSansJpLowMemory } = fonts;
+
+        const a = notoSansJpLowMemory.charToGlyph('あ');
+        assert.equal(a.topSideBearing, 80);
+        assert.equal(a.advanceHeight, 1000);
+        const aMetrics = a.getMetrics();
+        assert.equal(aMetrics.topSideBearing, 80);
+        assert.equal(aMetrics.bottomSideBearing, 64);
+    });
+});