freetype/truetype: variable sized bytecode interpreter stack/store.

R=bsiegert
CC=golang-dev
http://codereview.appspot.com/6343091

freetype/truetype/hint.go

@@ -13,11 +13,7 @@ import (
 )
 
 type hinter struct {
-	// TODO: variable sized stack and store slices based on the maxp section?
-	// Should the arrays for the stack and store be combined? For now, fixed
-	// maximum sizes seem to work in practice.
-	stack [800]int32
-	store [128]int32
+	stack, store []int32
 
 	// The fields below constitue the graphics state, which is described at
 	// https://developer.apple.com/fonts/TTRefMan/RM04/Chap4.html
@@ -32,6 +28,19 @@ type hinter struct {
 	roundPeriod, roundPhase, roundThreshold f26dot6
 }
 
+func (h *hinter) init(f *Font) {
+	if x := int(f.maxStackElements); x > len(h.stack) {
+		x += 255
+		x &^= 255
+		h.stack = make([]int32, x)
+	}
+	if x := int(f.maxStorage); x > len(h.store) {
+		x += 15
+		x &^= 15
+		h.store = make([]int32, x)
+	}
+}
+
 func (h *hinter) run(program []byte) error {
 	// The default vectors are along the X axis.
 	h.pv = [2]f2dot14{0x4000, 0}

freetype/truetype/hint_test.go

@@ -489,6 +489,10 @@ func TestBytecode(t *testing.T) {
 
 	for _, tc := range testCases {
 		h := &hinter{}
+		h.init(&Font{
+			maxStorage:       32,
+			maxStackElements: 100,
+		})
 		err, errStr := h.run(tc.prog), ""
 		if err != nil {
 			errStr = err.Error()

freetype/truetype/truetype.go

@@ -98,6 +98,8 @@ type Font struct {
 	nGlyph, nHMetric, nKern int
 	unitsPerEm              int
 	bounds                  Bounds
+	// Values from the maxp section.
+	maxTwilightPoints, maxStorage, maxFunctionDefs, maxStackElements uint16
 }
 
 func (f *Font) parseCmap() error {
@@ -254,6 +256,10 @@ func (f *Font) parseMaxp() error {
 		return FormatError(fmt.Sprintf("bad maxp length: %d", len(f.maxp)))
 	}
 	f.nGlyph = int(u16(f.maxp, 4))
+	f.maxTwilightPoints = u16(f.maxp, 16)
+	f.maxStorage = u16(f.maxp, 18)
+	f.maxFunctionDefs = u16(f.maxp, 20)
+	f.maxStackElements = u16(f.maxp, 24)
 	return nil
 }