freetype/truetype: propagate the useMyMetrics flag to nested components.

Also increase the maximum recursion depth from 4 to 8, since some
x-deja-vu-sans-oblique glyphs are actually depth 4. It's an arbitrary
limit. The C Freetype code doesn't seem to limit recursion (below
whatever the font says it needs), but it seems safer to have a limit.

R=bsiegert
CC=golang-dev
https://codereview.appspot.com/14494062

freetype/truetype/glyph.go

@@ -94,7 +94,8 @@ func (g *GlyphBuf) Load(f *Font, scale int32, i Index, h *Hinter) error {
 }
 
 func (g *GlyphBuf) load(recursion int32, i Index, useMyMetrics bool) (err error) {
-	if recursion >= 4 {
+	// The recursion limit here is arbitrary, but defends against malformed glyphs.
+	if recursion >= 32 {
 		return UnsupportedError("excessive compound glyph recursion")
 	}
 	// Find the relevant slice of g.font.glyf.
@@ -126,7 +127,7 @@ func (g *GlyphBuf) load(recursion int32, i Index, useMyMetrics bool) (err error)
 			return UnsupportedError("negative number of contours")
 		}
 		pp1x = g.font.scale(g.scale * (b.XMin - uhm.LeftSideBearing))
-		if err := g.loadCompound(recursion, glyf); err != nil {
+		if err := g.loadCompound(recursion, glyf, useMyMetrics); err != nil {
 			return err
 		}
 	} else {
@@ -267,7 +268,7 @@ func (g *GlyphBuf) loadSimple(glyf []byte, ne int) (program []byte) {
 	return program
 }
 
-func (g *GlyphBuf) loadCompound(recursion int32, glyf []byte) error {
+func (g *GlyphBuf) loadCompound(recursion int32, glyf []byte, useMyMetrics bool) error {
 	// Flags for decoding a compound glyph. These flags are documented at
 	// http://developer.apple.com/fonts/TTRefMan/RM06/Chap6glyf.html.
 	const (
@@ -319,7 +320,8 @@ func (g *GlyphBuf) loadCompound(recursion int32, glyf []byte) error {
 			}
 		}
 		np0 := len(g.Point)
-		if err := g.load(recursion+1, component, flags&flagUseMyMetrics != 0); err != nil {
+		componentUMM := useMyMetrics && (flags&flagUseMyMetrics != 0)
+		if err := g.load(recursion+1, component, componentUMM); err != nil {
 			return err
 		}
 		if hasTransform {

freetype/truetype/truetype_test.go

@@ -252,10 +252,8 @@ var scalingTestCases = []struct {
 	hintingBrokenAt int
 }{
 	{"luxisr", 12, -1},
-	// TODO: uncomment the fonts below, once they get past Parse and
-	// GlyphBuf.Load, and the unhinted values match C Freetype.
 	{"x-arial-bold", 11, 0},
-	//{"x-deja-vu-sans-oblique", 17, 0},
+	{"x-deja-vu-sans-oblique", 17, 0},
 	{"x-droid-sans-japanese", 9, 0},
 	{"x-times-new-roman", 13, 0},
 }