Respect useTypoMetrics

README.md

@@ -83,6 +83,7 @@ The following properties describe the general metrics of the font. See [here](ht
 * `underlinePosition` - the offset from the normal underline position that should be used
 * `underlineThickness` - the weight of the underline that should be used
 * `italicAngle` - if this is an italic font, the angle the cursor should be drawn at to match the font design
+* `lineHeight` - is the vertical space between adjacent lines (their baselines) of text, also known as leading. See [here](https://en.wikipedia.org/wiki/Leading) for more details.
 * `capHeight` - the height of capital letters above the baseline. See [here](http://en.wikipedia.org/wiki/Cap_height) for more details.
 * `xHeight`- the height of lower case letters. See [here](http://en.wikipedia.org/wiki/X-height) for more details.
 * `bbox` - the font’s bounding box, i.e. the box that encloses all glyphs in the font

src/TTFFont.js

@@ -91,6 +91,44 @@ export default class TTFFont {
     return result;
   }
 
+  _getMetrics() {
+    if (this._metrics) { return this._metrics; }
+
+    let { 'OS/2': os2, hhea } = this;
+    let useTypoMetrics = os2.fsSelection.useTypoMetrics;
+    let ascent, descent, lineGap, lineHeight;
+
+    // Use the same approach as FreeType
+    // https://gitlab.freedesktop.org/freetype/freetype/-/blob/4d8db130ea4342317581bab65fc96365ce806b77/src/sfnt/sfobjs.c#L1310
+
+    if (useTypoMetrics) {
+      ascent = os2.typoAscender;
+      descent = os2.typoDescender;
+      lineGap = os2.typoLineGap;
+      lineHeight = ascent - descent + lineGap;
+    } else {
+      ascent = hhea.ascent;
+      descent = hhea.descent;
+      lineGap = hhea.lineGap;
+      lineHeight = ascent - descent + lineGap;
+    }
+
+    if (!ascent || !descent) {
+      if (os2.typoAscender || os2.typoDescender) {
+        ascent = os2.typoAscender;
+        descent = os2.typoDescender;
+        lineGap = os2.typoLineGap;
+        lineHeight = ascent - descent + lineGap;
+      } else {
+        ascent = os2.winAscent;
+        descent = -os2.winDescent;
+        lineHeight = ascent - descent;
+      }
+    }
+
+    return this._metrics = {ascent, descent, lineGap, lineHeight};
+  }
+
   /**
    * Gets a string from the font's `name` table
    * `lang` is a BCP-47 language code.
@@ -166,23 +204,23 @@ export default class TTFFont {
    * @type {number}
    */
   get ascent() {
-    return this.hhea.ascent;
+    return this._getMetrics().ascent;
   }
 
   /**
    * The font’s [descender](https://en.wikipedia.org/wiki/Descender)
    * @type {number}
    */
   get descent() {
-    return this.hhea.descent;
+    return this._getMetrics().descent;
   }
 
   /**
    * The amount of space that should be included between lines
    * @type {number}
    */
   get lineGap() {
-    return this.hhea.lineGap;
+    return this._getMetrics().lineGap;
   }
 
   /**
@@ -209,6 +247,15 @@ export default class TTFFont {
     return this.post.italicAngle;
   }
 
+  /**
+   * The vertical space between adjacent lines (their baselines) of text.
+   * See [here](https://en.wikipedia.org/wiki/Leading) for more details.
+   * @type {number}
+   */
+  get lineHeight() {
+    return this._getMetrics().lineHeight;
+  }
+
   /**
    * The height of capital letters above the baseline.
    * See [here](https://en.wikipedia.org/wiki/Cap_height) for more details.

src/glyph/Glyph.js

@@ -64,23 +64,13 @@ export default class Glyph {
 
     let {advance:advanceWidth, bearing:leftBearing} = this._getTableMetrics(this._font.hmtx);
 
-    // For vertical metrics, use vmtx if available, or fall back to global data from OS/2 or hhea
+    // For vertical metrics, use vmtx if available, or fall back to global data
     if (this._font.vmtx) {
       var {advance:advanceHeight, bearing:topBearing} = this._getTableMetrics(this._font.vmtx);
-
     } else {
-      let os2;
       if (typeof cbox === 'undefined' || cbox === null) { ({ cbox } = this); }
-
-      if ((os2 = this._font['OS/2']) && os2.version > 0) {
-        var advanceHeight = Math.abs(os2.typoAscender - os2.typoDescender);
-        var topBearing = os2.typoAscender - cbox.maxY;
-
-      } else {
-        let { hhea } = this._font;
-        var advanceHeight = Math.abs(hhea.ascent - hhea.descent);
-        var topBearing = hhea.ascent - cbox.maxY;
-      }
+      var advanceHeight = Math.abs(this._font.ascent - this._font.descent);
+      var topBearing = this._font.ascent - cbox.maxY;
     }
 
     if (this._font._variationProcessor && this._font.HVAR) {

src/glyph/Path.js

@@ -63,6 +63,14 @@ export default class Path {
         }
       }
 
+      if (this.commands.length === 0) {
+        // No content, put 0 instead of Infinity
+        cbox.minX = 0;
+        cbox.minY = 0;
+        cbox.maxX = 0;
+        cbox.maxY = 0;
+      }
+
       this._cbox = Object.freeze(cbox);
     }
 
@@ -172,6 +180,14 @@ export default class Path {
       }
     }
 
+    if (this.commands.length === 0) {
+      // No content, put 0 instead of Infinity
+      bbox.minX = 0;
+      bbox.minY = 0;
+      bbox.maxX = 0;
+      bbox.maxY = 0;
+    }
+
     return this._bbox = Object.freeze(bbox);
   }
 

src/glyph/TTFGlyph.js

@@ -74,8 +74,16 @@ export default class TTFGlyph extends Glyph {
       return this.path.cbox;
     }
 
+    let glyfPos = this._font.loca.offsets[this.id];
+    let nextPos = this._font.loca.offsets[this.id + 1];
+
+    // No data for this glyph (space?)
+    if (glyfPos === nextPos) {
+      return super._getCBox();
+    }
+
     let stream = this._font._getTableStream('glyf');
-    stream.pos += this._font.loca.offsets[this.id];
+    stream.pos += glyfPos;
     let glyph = GlyfHeader.decode(stream);
 
     let cbox = new BBox(glyph.xMin, glyph.yMin, glyph.xMax, glyph.yMax);

src/tables/maxp.js

@@ -1,8 +1,9 @@
 import * as r from 'restructure';
+import { version16Dot16 } from '../utils';
 
 // maxiumum profile
 export default new r.Struct({
-  version:                r.int32,
+  version:                version16Dot16,
   numGlyphs:              r.uint16,  // The number of glyphs in the font
   maxPoints:              r.uint16,  // Maximum points in a non-composite glyph
   maxContours:            r.uint16,  // Maximum contours in a non-composite glyph

src/tables/post.js

@@ -1,7 +1,8 @@
 import * as r from 'restructure';
+import { version16Dot16 } from '../utils';
 
 // PostScript information
-export default new r.VersionedStruct(r.fixed32, {
+export default new r.VersionedStruct(version16Dot16, {
   header: { // these fields exist at the top of all versions
     italicAngle:        r.fixed32, // Italic angle in counter-clockwise degrees from the vertical.
     underlinePosition:  r.int16,   // Suggested distance of the top of the underline from the baseline

src/tables/vhea.js

@@ -1,8 +1,9 @@
 import * as r from 'restructure';
+import { version16Dot16 } from '../utils';
 
 // Vertical Header Table
 export default new r.Struct({
-  version:                r.uint16,  // Version number of the Vertical Header Table
+  version:                version16Dot16,
   ascent:                 r.int16,   // The vertical typographic ascender for this font
   descent:                r.int16,   // The vertical typographic descender for this font
   lineGap:                r.int16,   // The vertical typographic line gap for this font

src/utils.js

@@ -1,3 +1,5 @@
+import { DecodeStream, EncodeStream } from 'restructure';
+
 export function binarySearch(arr, cmp) {
   let min = 0;
   let max = arr.length - 1;
@@ -60,3 +62,37 @@ export function decodeBase64(base64) {
 
   return bytes;
 }
+
+export class Version16Dot16 {
+  fromBuffer(buffer) {
+    let stream = new DecodeStream(buffer);
+    return this.decode(stream);
+  }
+
+  toBuffer(value) {
+    let size = this.size(value);
+    let buffer = new Uint8Array(size);
+    let stream = new EncodeStream(buffer);
+    this.encode(stream, value);
+    return buffer;
+  }
+
+  size() {
+    return 4;
+  }
+
+  decode(stream) {
+    let major = stream.readUInt16BE();
+    let minor = stream.readUInt16BE() >> 12;
+    return major + minor / 10;
+  }
+
+  encode(stream, val) {
+    let major = Math.trunc(val);
+    let minor = (val - major) * 10;
+    stream.writeUInt16BE(major);
+    return stream.writeUInt16BE(minor << 12);
+  }
+}
+
+export const version16Dot16 = new Version16Dot16();