freetype/truetype: load vertical metrics from the OS/2 table.

R=bsiegert
CC=golang-dev, remyoudompheng
https://codereview.appspot.com/34700043

freetype/truetype/glyph.go

@@ -377,12 +377,12 @@ func (g *GlyphBuf) loadCompound(recursion int32, b Bounds, uhm HMetric, i Index,
 
 func (g *GlyphBuf) addPhantomsAndScale(b Bounds, uhm HMetric, i Index, np0 int, simple bool) {
 	// Add the four phantom points.
-	uvm := g.font.unscaledVMetric(i)
+	uvm := g.font.unscaledVMetric(i, b.YMax)
 	g.Point = append(g.Point,
 		Point{X: b.XMin - uhm.LeftSideBearing},
 		Point{X: b.XMin - uhm.LeftSideBearing + uhm.AdvanceWidth},
-		Point{Y: b.YMax + uvm.TopSideBearing},
-		Point{Y: b.YMax + uvm.TopSideBearing - uvm.AdvanceHeight},
+		Point{X: uhm.AdvanceWidth / 2, Y: b.YMax + uvm.TopSideBearing},
+		Point{X: uhm.AdvanceWidth / 2, Y: b.YMax + uvm.TopSideBearing - uvm.AdvanceHeight},
 	)
 	// Scale the points.
 	if simple && g.hinter != nil {

freetype/truetype/truetype.go

@@ -98,7 +98,7 @@ type cm struct {
 type Font struct {
 	// Tables sliced from the TTF data. The different tables are documented
 	// at http://developer.apple.com/fonts/TTRefMan/RM06/Chap6.html
-	cmap, cvt, fpgm, glyf, head, hhea, hmtx, kern, loca, maxp, prep, vmtx []byte
+	cmap, cvt, fpgm, glyf, head, hhea, hmtx, kern, loca, maxp, os2, prep, vmtx []byte
 
 	cmapIndexes []byte
 
@@ -373,8 +373,8 @@ func (f *Font) HMetric(scale int32, i Index) HMetric {
 }
 
 // unscaledVMetric returns the unscaled vertical metrics for the glyph with
-// the given index.
-func (f *Font) unscaledVMetric(i Index) (v VMetric) {
+// the given index. yMax is the top of the glyph's bounding box.
+func (f *Font) unscaledVMetric(i Index, yMax int32) (v VMetric) {
 	j := int(i)
 	if j < 0 || f.nGlyph <= j {
 		return VMetric{}
@@ -385,6 +385,19 @@ func (f *Font) unscaledVMetric(i Index) (v VMetric) {
 			TopSideBearing: int32(int16(u16(f.vmtx, 4*j+2))),
 		}
 	}
+	// The OS/2 table has grown over time.
+	// https://developer.apple.com/fonts/TTRefMan/RM06/Chap6OS2.html
+	// says that it was originally 68 bytes. Optional fields, including
+	// the ascender and descender, are described at
+	// http://www.microsoft.com/typography/otspec/os2.htm
+	if len(f.os2) >= 72 {
+		sTypoAscender := int32(int16(u16(f.os2, 68)))
+		sTypoDescender := int32(int16(u16(f.os2, 70)))
+		return VMetric{
+			AdvanceHeight:  sTypoAscender - sTypoDescender,
+			TopSideBearing: sTypoAscender - yMax,
+		}
+	}
 	return VMetric{
 		AdvanceHeight:  f.fUnitsPerEm,
 		TopSideBearing: 0,
@@ -393,7 +406,8 @@ func (f *Font) unscaledVMetric(i Index) (v VMetric) {
 
 // VMetric returns the vertical metrics for the glyph with the given index.
 func (f *Font) VMetric(scale int32, i Index) VMetric {
-	v := f.unscaledVMetric(i)
+	// TODO: should 0 be bounds.YMax?
+	v := f.unscaledVMetric(i, 0)
 	v.AdvanceHeight = f.scale(scale * v.AdvanceHeight)
 	v.TopSideBearing = f.scale(scale * v.TopSideBearing)
 	return v
@@ -500,6 +514,8 @@ func parse(ttf []byte, offset int) (font *Font, err error) {
 			f.loca, err = readTable(ttf, ttf[x+8:x+16])
 		case "maxp":
 			f.maxp, err = readTable(ttf, ttf[x+8:x+16])
+		case "OS/2":
+			f.os2, err = readTable(ttf, ttf[x+8:x+16])
 		case "prep":
 			f.prep, err = readTable(ttf, ttf[x+8:x+16])
 		case "vmtx":

freetype/truetype/truetype_test.go

@@ -261,22 +261,6 @@ var scalingTestCases = []struct {
 	{"x-times-new-roman", 13, 0},
 }
 
-var scalingExceptions = map[string]map[int]bool{
-	// TODO: fix these exceptions now that C Freetype version 2.5.1 is released:
-	// see http://lists.nongnu.org/archive/html/freetype/2013-11/msg00004.html
-	"x-deja-vu-sans-oblique": map[int]bool{
-		269:  true,
-		733:  true,
-		734:  true,
-		2071: true,
-		2072: true,
-		2077: true,
-		2078: true,
-		2171: true,
-		2172: true,
-	},
-}
-
 // TODO: also test bounding boxes, not just points.
 
 func testScaling(t *testing.T, hinter *Hinter) {
@@ -329,7 +313,6 @@ func testScaling(t *testing.T, hinter *Hinter) {
 			continue
 		}
 
-		exceptions := scalingExceptions[tc.name]
 		glyphBuf := NewGlyphBuf()
 		for i, want := range wants {
 			// TODO: completely implement hinting. For now, only the first
@@ -338,10 +321,6 @@ func testScaling(t *testing.T, hinter *Hinter) {
 				break
 			}
 
-			if exceptions != nil && exceptions[i] {
-				continue
-			}
-
 			if err = glyphBuf.Load(font, tc.size*64, Index(i), hinter); err != nil {
 				t.Errorf("%s: glyph #%d: Load: %v", tc.name, i, err)
 				continue