From 2a5cbfd47e3e23d75bcbe4e4e0e1d3ae3c20620e Mon Sep 17 00:00:00 2001
From: Nigel Tao <nigeltao@golang.org>
Date: Tue, 18 Aug 2015 16:30:37 +1000
Subject: [PATCH] Use the fixed.Int26_6 type in package truetype.

---
 example/freetype/main.go  |  4 +--
 example/truetype/main.go  |  3 +-
 freetype.go               | 10 +++---
 truetype/glyph.go         | 76 +++++++++++++++++++++------------------
 truetype/hint.go          | 46 ++++++++++++------------
 truetype/hint_test.go     |  4 ++-
 truetype/truetype.go      | 61 +++++++++++++++----------------
 truetype/truetype_test.go | 16 +++++----
 8 files changed, 117 insertions(+), 103 deletions(-)

diff --git a/example/freetype/main.go b/example/freetype/main.go
index e20800e..d5e60f9 100644
--- a/example/freetype/main.go
+++ b/example/freetype/main.go
@@ -116,14 +116,14 @@ func main() {
 	}
 
 	// Draw the text.
-	pt := freetype.Pt(10, 10+int(c.PointToFix32(*size)>>6))
+	pt := freetype.Pt(10, 10+int(c.PointToFixed(*size)>>6))
 	for _, s := range text {
 		_, err = c.DrawString(s, pt)
 		if err != nil {
 			log.Println(err)
 			return
 		}
-		pt.Y += c.PointToFix32(*size * *spacing)
+		pt.Y += c.PointToFixed(*size * *spacing)
 	}
 
 	// Save that RGBA image to disk.
diff --git a/example/truetype/main.go b/example/truetype/main.go
index bca1755..93ea5d0 100644
--- a/example/truetype/main.go
+++ b/example/truetype/main.go
@@ -17,6 +17,7 @@ import (
 	"log"
 
 	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/math/fixed"
 )
 
 var fontfile = flag.String("fontfile", "../../testdata/luxisr.ttf", "filename of the ttf font")
@@ -56,7 +57,7 @@ func main() {
 		log.Println(err)
 		return
 	}
-	fupe := font.FUnitsPerEm()
+	fupe := fixed.Int26_6(font.FUnitsPerEm())
 	printBounds(font.Bounds(fupe))
 	fmt.Printf("FUnitsPerEm:%d\n\n", fupe)
 
diff --git a/freetype.go b/freetype.go
index 291935d..221485f 100644
--- a/freetype.go
+++ b/freetype.go
@@ -78,15 +78,15 @@ type Context struct {
 	// fontSize and dpi are used to calculate scale. scale is the number of
 	// 26.6 fixed point units in 1 em. hinting is the hinting policy.
 	fontSize, dpi float64
-	scale         int32
+	scale         fixed.Int26_6
 	hinting       Hinting
 	// cache is the glyph cache.
 	cache [nGlyphs * nXFractions * nYFractions]cacheEntry
 }
 
-// PointToFix32 converts the given number of points (as in ``a 12 point font'')
-// into fixed point units.
-func (c *Context) PointToFix32(x float64) fixed.Int26_6 {
+// PointToFixed converts the given number of points (as in ``a 12 point font'')
+// into a 26.6 fixed point number of pixels.
+func (c *Context) PointToFixed(x float64) fixed.Int26_6 {
 	return fixed.Int26_6(x * float64(c.dpi) * (64.0 / 72.0))
 }
 
@@ -269,7 +269,7 @@ func (c *Context) DrawString(s string, p fixed.Point26_6) (fixed.Point26_6, erro
 // recalc recalculates scale and bounds values from the font size, screen
 // resolution and font metrics, and invalidates the glyph cache.
 func (c *Context) recalc() {
-	c.scale = int32(c.fontSize * c.dpi * (64.0 / 72.0))
+	c.scale = fixed.Int26_6(c.fontSize * c.dpi * (64.0 / 72.0))
 	if c.font == nil {
 		c.r.SetBounds(0, 0)
 	} else {
diff --git a/truetype/glyph.go b/truetype/glyph.go
index b5f3278..7fbc4ef 100644
--- a/truetype/glyph.go
+++ b/truetype/glyph.go
@@ -5,8 +5,12 @@
 
 package truetype
 
+import (
+	"golang.org/x/image/math/fixed"
+)
+
 // Hinting is the policy for snapping a glyph's contours to pixel boundaries.
-type Hinting int32
+type Hinting uint32
 
 const (
 	// NoHinting means to not perform any hinting.
@@ -20,7 +24,7 @@ const (
 // A Point is a co-ordinate pair plus whether it is ``on'' a contour or an
 // ``off'' control point.
 type Point struct {
-	X, Y int32
+	X, Y fixed.Int26_6
 	// The Flags' LSB means whether or not this Point is ``on'' the contour.
 	// Other bits are reserved for internal use.
 	Flags uint32
@@ -30,7 +34,7 @@ type Point struct {
 // series of glyphs from a Font.
 type GlyphBuf struct {
 	// AdvanceWidth is the glyph's advance width.
-	AdvanceWidth int32
+	AdvanceWidth fixed.Int26_6
 	// B is the glyph's bounding box.
 	B Bounds
 	// Point contains all Points from all contours of the glyph. If
@@ -45,7 +49,7 @@ type GlyphBuf struct {
 	End []int
 
 	font    *Font
-	scale   int32
+	scale   fixed.Int26_6
 	hinting Hinting
 	hinter  hinter
 	// phantomPoints are the co-ordinates of the synthetic phantom points
@@ -54,7 +58,7 @@ type GlyphBuf struct {
 	// pp1x is the X co-ordinate of the first phantom point. The '1' is
 	// using 1-based indexing; pp1x is almost always phantomPoints[0].X.
 	// TODO: eliminate this and consistently use phantomPoints[0].X.
-	pp1x int32
+	pp1x fixed.Int26_6
 	// metricsSet is whether the glyph's metrics have been set yet. For a
 	// compound glyph, a sub-glyph may override the outer glyph's metrics.
 	metricsSet bool
@@ -84,10 +88,10 @@ const (
 	flagThisYIsSame = flagPositiveYShortVector
 )
 
-// Load loads a glyph's contours from a Font, overwriting any previously
-// loaded contours for this GlyphBuf. scale is the number of 26.6 fixed point
-// units in 1 em, i is the glyph index, and h is the hinting policy.
-func (g *GlyphBuf) Load(f *Font, scale int32, i Index, h Hinting) error {
+// Load loads a glyph's contours from a Font, overwriting any previously loaded
+// contours for this GlyphBuf. scale is the number of 26.6 fixed point units in
+// 1 em, i is the glyph index, and h is the hinting policy.
+func (g *GlyphBuf) Load(f *Font, scale fixed.Int26_6, i Index, h Hinting) error {
 	g.Point = g.Point[:0]
 	g.Unhinted = g.Unhinted[:0]
 	g.InFontUnits = g.InFontUnits[:0]
@@ -125,8 +129,8 @@ func (g *GlyphBuf) Load(f *Font, scale int32, i Index, h Hinting) error {
 		if len(f.hdmx) >= 8 {
 			if n := u32(f.hdmx, 4); n > 3+uint32(i) {
 				for hdmx := f.hdmx[8:]; uint32(len(hdmx)) >= n; hdmx = hdmx[n:] {
-					if int32(hdmx[0]) == scale>>6 {
-						advanceWidth = int32(hdmx[2+i]) << 6
+					if fixed.Int26_6(hdmx[0]) == scale>>6 {
+						advanceWidth = fixed.Int26_6(hdmx[2+i]) << 6
 						break
 					}
 				}
@@ -175,7 +179,7 @@ func (g *GlyphBuf) Load(f *Font, scale int32, i Index, h Hinting) error {
 	return nil
 }
 
-func (g *GlyphBuf) load(recursion int32, i Index, useMyMetrics bool) (err error) {
+func (g *GlyphBuf) load(recursion uint32, i Index, useMyMetrics bool) (err error) {
 	// The recursion limit here is arbitrary, but defends against malformed glyphs.
 	if recursion >= 32 {
 		return UnsupportedError("excessive compound glyph recursion")
@@ -193,16 +197,16 @@ func (g *GlyphBuf) load(recursion int32, i Index, useMyMetrics bool) (err error)
 	// Decode the contour count and nominal bounding box, from the first
 	// 10 bytes of the glyf data. boundsYMin and boundsXMax, at offsets 4
 	// and 6, are unused.
-	glyf, ne, boundsXMin, boundsYMax := []byte(nil), 0, int32(0), int32(0)
+	glyf, ne, boundsXMin, boundsYMax := []byte(nil), 0, fixed.Int26_6(0), fixed.Int26_6(0)
 	if g0+10 <= g1 {
 		glyf = g.font.glyf[g0:g1]
 		ne = int(int16(u16(glyf, 0)))
-		boundsXMin = int32(int16(u16(glyf, 2)))
-		boundsYMax = int32(int16(u16(glyf, 8)))
+		boundsXMin = fixed.Int26_6(int16(u16(glyf, 2)))
+		boundsYMax = fixed.Int26_6(int16(u16(glyf, 8)))
 	}
 
 	// Create the phantom points.
-	uhm, pp1x := g.font.unscaledHMetric(i), int32(0)
+	uhm, pp1x := g.font.unscaledHMetric(i), fixed.Int26_6(0)
 	uvm := g.font.unscaledVMetric(i, boundsYMax)
 	g.phantomPoints = [4]Point{
 		{X: boundsXMin - uhm.LeftSideBearing},
@@ -322,7 +326,7 @@ func (g *GlyphBuf) loadSimple(glyf []byte, ne int) (program []byte) {
 			x += int16(u16(glyf, offset))
 			offset += 2
 		}
-		g.Point[i].X = int32(x)
+		g.Point[i].X = fixed.Int26_6(x)
 	}
 	var y int16
 	for i := np0; i < np1; i++ {
@@ -339,13 +343,13 @@ func (g *GlyphBuf) loadSimple(glyf []byte, ne int) (program []byte) {
 			y += int16(u16(glyf, offset))
 			offset += 2
 		}
-		g.Point[i].Y = int32(y)
+		g.Point[i].Y = fixed.Int26_6(y)
 	}
 
 	return program
 }
 
-func (g *GlyphBuf) loadCompound(recursion int32, uhm HMetric, i Index,
+func (g *GlyphBuf) loadCompound(recursion uint32, uhm HMetric, i Index,
 	glyf []byte, useMyMetrics bool) error {
 
 	// Flags for decoding a compound glyph. These flags are documented at
@@ -368,14 +372,14 @@ func (g *GlyphBuf) loadCompound(recursion int32, uhm HMetric, i Index,
 	for {
 		flags := u16(glyf, offset)
 		component := Index(u16(glyf, offset+2))
-		dx, dy, transform, hasTransform := int32(0), int32(0), [4]int32{}, false
+		dx, dy, transform, hasTransform := fixed.Int26_6(0), fixed.Int26_6(0), [4]int16{}, false
 		if flags&flagArg1And2AreWords != 0 {
-			dx = int32(int16(u16(glyf, offset+4)))
-			dy = int32(int16(u16(glyf, offset+6)))
+			dx = fixed.Int26_6(int16(u16(glyf, offset+4)))
+			dy = fixed.Int26_6(int16(u16(glyf, offset+6)))
 			offset += 8
 		} else {
-			dx = int32(int16(int8(glyf[offset+4])))
-			dy = int32(int16(int8(glyf[offset+5])))
+			dx = fixed.Int26_6(int16(int8(glyf[offset+4])))
+			dy = fixed.Int26_6(int16(int8(glyf[offset+5])))
 			offset += 6
 		}
 		if flags&flagArgsAreXYValues == 0 {
@@ -385,18 +389,18 @@ func (g *GlyphBuf) loadCompound(recursion int32, uhm HMetric, i Index,
 			hasTransform = true
 			switch {
 			case flags&flagWeHaveAScale != 0:
-				transform[0] = int32(int16(u16(glyf, offset+0)))
+				transform[0] = int16(u16(glyf, offset+0))
 				transform[3] = transform[0]
 				offset += 2
 			case flags&flagWeHaveAnXAndYScale != 0:
-				transform[0] = int32(int16(u16(glyf, offset+0)))
-				transform[3] = int32(int16(u16(glyf, offset+2)))
+				transform[0] = int16(u16(glyf, offset+0))
+				transform[3] = int16(u16(glyf, offset+2))
 				offset += 4
 			case flags&flagWeHaveATwoByTwo != 0:
-				transform[0] = int32(int16(u16(glyf, offset+0)))
-				transform[1] = int32(int16(u16(glyf, offset+2)))
-				transform[2] = int32(int16(u16(glyf, offset+4)))
-				transform[3] = int32(int16(u16(glyf, offset+6)))
+				transform[0] = int16(u16(glyf, offset+0))
+				transform[1] = int16(u16(glyf, offset+2))
+				transform[2] = int16(u16(glyf, offset+4))
+				transform[3] = int16(u16(glyf, offset+6))
 				offset += 8
 			}
 		}
@@ -412,10 +416,12 @@ func (g *GlyphBuf) loadCompound(recursion int32, uhm HMetric, i Index,
 		if hasTransform {
 			for j := np0; j < len(g.Point); j++ {
 				p := &g.Point[j]
-				newX := int32((int64(p.X)*int64(transform[0])+1<<13)>>14) +
-					int32((int64(p.Y)*int64(transform[2])+1<<13)>>14)
-				newY := int32((int64(p.X)*int64(transform[1])+1<<13)>>14) +
-					int32((int64(p.Y)*int64(transform[3])+1<<13)>>14)
+				newX := 0 +
+					fixed.Int26_6((int64(p.X)*int64(transform[0])+1<<13)>>14) +
+					fixed.Int26_6((int64(p.Y)*int64(transform[2])+1<<13)>>14)
+				newY := 0 +
+					fixed.Int26_6((int64(p.X)*int64(transform[1])+1<<13)>>14) +
+					fixed.Int26_6((int64(p.Y)*int64(transform[3])+1<<13)>>14)
 				p.X, p.Y = newX, newY
 			}
 		}
diff --git a/truetype/hint.go b/truetype/hint.go
index 26c6314..d967bd9 100644
--- a/truetype/hint.go
+++ b/truetype/hint.go
@@ -11,6 +11,8 @@ package truetype
 import (
 	"errors"
 	"math"
+
+	"golang.org/x/image/math/fixed"
 )
 
 const (
@@ -47,7 +49,7 @@ type hinter struct {
 	// Changing the font will require running the new font's fpgm bytecode.
 	// Changing either will require running the font's prep bytecode.
 	font  *Font
-	scale int32
+	scale fixed.Int26_6
 
 	// gs and defaultGS are the current and default graphics state. The
 	// default graphics state is the global default graphics state after
@@ -113,7 +115,7 @@ func resetTwilightPoints(f *Font, p []Point) []Point {
 	return p
 }
 
-func (h *hinter) init(f *Font, scale int32) error {
+func (h *hinter) init(f *Font, scale fixed.Int26_6) error {
 	h.points[twilightZone][0] = resetTwilightPoints(f, h.points[twilightZone][0])
 	h.points[twilightZone][1] = resetTwilightPoints(f, h.points[twilightZone][1])
 	h.points[twilightZone][2] = resetTwilightPoints(f, h.points[twilightZone][2])
@@ -315,8 +317,8 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 					mulDiv(int64(dy), int64(dbx), 0x40)
 				rx := mulDiv(val, int64(dax), discriminant)
 				ry := mulDiv(val, int64(day), discriminant)
-				p.X = a0.X + int32(rx)
-				p.Y = a0.Y + int32(ry)
+				p.X = a0.X + fixed.Int26_6(rx)
+				p.Y = a0.Y + fixed.Int26_6(ry)
 			} else {
 				p.X = (a0.X + a1.X + b0.X + b1.X) / 4
 				p.Y = (a0.Y + a1.Y + b0.Y + b1.Y) / 4
@@ -379,7 +381,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 
 		case opSSW:
 			top--
-			h.gs.singleWidth = f26dot6(h.font.scale(h.scale * h.stack[top]))
+			h.gs.singleWidth = f26dot6(h.font.scale(h.scale * fixed.Int26_6(h.stack[top])))
 
 		case opDUP:
 			if top >= len(h.stack) {
@@ -711,8 +713,8 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 			if h.gs.zp[0] == 0 {
 				p := h.point(0, unhinted, i)
 				q := h.point(0, current, i)
-				p.X = int32((int64(distance) * int64(h.gs.fv[0])) >> 14)
-				p.Y = int32((int64(distance) * int64(h.gs.fv[1])) >> 14)
+				p.X = fixed.Int26_6((int64(distance) * int64(h.gs.fv[0])) >> 14)
+				p.Y = fixed.Int26_6((int64(distance) * int64(h.gs.fv[1])) >> 14)
 				*q = *p
 			}
 			p := h.point(0, current, i)
@@ -809,7 +811,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 			}
 			d := int32(dotProduct(f26dot6(p.X-q.X), f26dot6(p.Y-q.Y), v))
 			if scale {
-				d = int32(int64(d*h.scale) / int64(h.font.fUnitsPerEm))
+				d = int32(int64(d*int32(h.scale)) / int64(h.font.fUnitsPerEm))
 			}
 			h.stack[top-1] = d
 
@@ -818,7 +820,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 				return errors.New("truetype: hinting: stack overflow")
 			}
 			// For MPS, point size should be irrelevant; we return the PPEM.
-			h.stack[top] = h.scale >> 6
+			h.stack[top] = int32(h.scale) >> 6
 			top++
 
 		case opFLIPON, opFLIPOFF:
@@ -935,7 +937,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 
 		case opWCVTF:
 			top -= 2
-			h.setScaledCVT(h.stack[top], f26dot6(h.font.scale(h.scale*h.stack[top+1])))
+			h.setScaledCVT(h.stack[top], f26dot6(h.font.scale(h.scale*fixed.Int26_6(h.stack[top+1]))))
 
 		case opDELTAP2, opDELTAP3, opDELTAC1, opDELTAC2, opDELTAC3:
 			goto delta
@@ -1144,7 +1146,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 					p0 := h.point(1, inFontUnits, i)
 					p1 := h.point(0, inFontUnits, h.gs.rp[0])
 					oldDist = dotProduct(f26dot6(p0.X-p1.X), f26dot6(p0.Y-p1.Y), h.gs.dv)
-					oldDist = f26dot6(h.font.scale(h.scale * int32(oldDist)))
+					oldDist = f26dot6(h.font.scale(h.scale * fixed.Int26_6(oldDist)))
 				}
 
 				// Single-width cut-in test.
@@ -1358,7 +1360,7 @@ func (h *hinter) run(program []byte, pCurrent, pUnhinted, pInFontUnits []Point,
 					c += 32
 				}
 				c += h.gs.deltaBase
-				if ppem := (h.scale + 1<<5) >> 6; ppem != c {
+				if ppem := (int32(h.scale) + 1<<5) >> 6; ppem != c {
 					continue
 				}
 				b = (b & 0x0f) - 8
@@ -1399,7 +1401,7 @@ func (h *hinter) initializeScaledCVT() {
 	}
 	for i := range h.scaledCVT {
 		unscaled := uint16(h.font.cvt[2*i])<<8 | uint16(h.font.cvt[2*i+1])
-		h.scaledCVT[i] = f26dot6(h.font.scale(h.scale * int32(int16(unscaled))))
+		h.scaledCVT[i] = f26dot6(h.font.scale(h.scale * fixed.Int26_6(int16(unscaled))))
 	}
 }
 
@@ -1437,7 +1439,7 @@ func (h *hinter) move(p *Point, distance f26dot6, touch bool) {
 	fvx := int64(h.gs.fv[0])
 	pvx := int64(h.gs.pv[0])
 	if fvx == 0x4000 && pvx == 0x4000 {
-		p.X += int32(distance)
+		p.X += fixed.Int26_6(distance)
 		if touch {
 			p.Flags |= flagTouchedX
 		}
@@ -1447,7 +1449,7 @@ func (h *hinter) move(p *Point, distance f26dot6, touch bool) {
 	fvy := int64(h.gs.fv[1])
 	pvy := int64(h.gs.pv[1])
 	if fvy == 0x4000 && pvy == 0x4000 {
-		p.Y += int32(distance)
+		p.Y += fixed.Int26_6(distance)
 		if touch {
 			p.Flags |= flagTouchedY
 		}
@@ -1457,14 +1459,14 @@ func (h *hinter) move(p *Point, distance f26dot6, touch bool) {
 	fvDotPv := (fvx*pvx + fvy*pvy) >> 14
 
 	if fvx != 0 {
-		p.X += int32(mulDiv(fvx, int64(distance), fvDotPv))
+		p.X += fixed.Int26_6(mulDiv(fvx, int64(distance), fvDotPv))
 		if touch {
 			p.Flags |= flagTouchedX
 		}
 	}
 
 	if fvy != 0 {
-		p.Y += int32(mulDiv(fvy, int64(distance), fvDotPv))
+		p.Y += fixed.Int26_6(mulDiv(fvy, int64(distance), fvDotPv))
 		if touch {
 			p.Flags |= flagTouchedY
 		}
@@ -1480,7 +1482,7 @@ func (h *hinter) iupInterp(interpY bool, p1, p2, ref1, ref2 int) {
 		return
 	}
 
-	var ifu1, ifu2 int32
+	var ifu1, ifu2 fixed.Int26_6
 	if interpY {
 		ifu1 = h.points[glyphZone][inFontUnits][ref1].Y
 		ifu2 = h.points[glyphZone][inFontUnits][ref2].Y
@@ -1493,7 +1495,7 @@ func (h *hinter) iupInterp(interpY bool, p1, p2, ref1, ref2 int) {
 		ref1, ref2 = ref2, ref1
 	}
 
-	var unh1, unh2, delta1, delta2 int32
+	var unh1, unh2, delta1, delta2 fixed.Int26_6
 	if interpY {
 		unh1 = h.points[glyphZone][unhinted][ref1].Y
 		unh2 = h.points[glyphZone][unhinted][ref2].Y
@@ -1506,7 +1508,7 @@ func (h *hinter) iupInterp(interpY bool, p1, p2, ref1, ref2 int) {
 		delta2 = h.points[glyphZone][current][ref2].X - unh2
 	}
 
-	var xy, ifuXY int32
+	var xy, ifuXY fixed.Int26_6
 	if ifu1 == ifu2 {
 		for i := p1; i <= p2; i++ {
 			if interpY {
@@ -1555,7 +1557,7 @@ func (h *hinter) iupInterp(interpY bool, p1, p2, ref1, ref2 int) {
 			} else {
 				numer -= 0x8000
 			}
-			xy = unh1 + delta1 + int32(numer/0x10000)
+			xy = unh1 + delta1 + fixed.Int26_6(numer/0x10000)
 		}
 
 		if interpY {
@@ -1567,7 +1569,7 @@ func (h *hinter) iupInterp(interpY bool, p1, p2, ref1, ref2 int) {
 }
 
 func (h *hinter) iupShift(interpY bool, p1, p2, p int) {
-	var delta int32
+	var delta fixed.Int26_6
 	if interpY {
 		delta = h.points[glyphZone][current][p].Y - h.points[glyphZone][unhinted][p].Y
 	} else {
diff --git a/truetype/hint_test.go b/truetype/hint_test.go
index c8b8d60..7eb43dd 100644
--- a/truetype/hint_test.go
+++ b/truetype/hint_test.go
@@ -9,6 +9,8 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
+	"golang.org/x/image/math/fixed"
 )
 
 func TestBytecode(t *testing.T) {
@@ -589,7 +591,7 @@ func TestMove(t *testing.T) {
 	h, p := hinter{}, Point{}
 	testCases := []struct {
 		pvX, pvY, fvX, fvY f2dot14
-		wantX, wantY       int32
+		wantX, wantY       fixed.Int26_6
 	}{
 		{+0x4000, +0x0000, +0x4000, +0x0000, +1000, +0},
 		{+0x4000, +0x0000, -0x4000, +0x0000, +1000, +0},
diff --git a/truetype/truetype.go b/truetype/truetype.go
index ce1678d..ebc36e6 100644
--- a/truetype/truetype.go
+++ b/truetype/truetype.go
@@ -9,10 +9,9 @@
 //
 // Some of a font's methods provide lengths or co-ordinates, e.g. bounds, font
 // metrics and control points. All these methods take a scale parameter, which
-// is the number of device units in 1 em. For example, if 1 em is 10 pixels and
-// 1 pixel is 64 units, then scale is 640. If the device space involves pixels,
-// 64 units per pixel is recommended, since that is what the bytecode hinter
-// uses when snapping point co-ordinates to the pixel grid.
+// is the number of pixels in 1 em, expressed as a 26.6 fixed point value. For
+// example, if 1 em is 10 pixels then scale is fixed.I(10), which is equal to
+// fixed.Int26_6(10 << 6).
 //
 // To measure a TrueType font in ideal FUnit space, use scale equal to
 // font.FUnitsPerEm().
@@ -20,6 +19,8 @@ package truetype // import "github.com/golang/freetype/truetype"
 
 import (
 	"fmt"
+
+	"golang.org/x/image/math/fixed"
 )
 
 // An Index is a Font's index of a rune.
@@ -28,17 +29,17 @@ type Index uint16
 // A Bounds holds the co-ordinate range of one or more glyphs.
 // The endpoints are inclusive.
 type Bounds struct {
-	XMin, YMin, XMax, YMax int32
+	XMin, YMin, XMax, YMax fixed.Int26_6
 }
 
 // An HMetric holds the horizontal metrics of a single glyph.
 type HMetric struct {
-	AdvanceWidth, LeftSideBearing int32
+	AdvanceWidth, LeftSideBearing fixed.Int26_6
 }
 
 // A VMetric holds the vertical metrics of a single glyph.
 type VMetric struct {
-	AdvanceHeight, TopSideBearing int32
+	AdvanceHeight, TopSideBearing fixed.Int26_6
 }
 
 // A FormatError reports that the input is not a valid TrueType font.
@@ -226,10 +227,10 @@ func (f *Font) parseHead() error {
 		return FormatError(fmt.Sprintf("bad head length: %d", len(f.head)))
 	}
 	f.fUnitsPerEm = int32(u16(f.head, 18))
-	f.bounds.XMin = int32(int16(u16(f.head, 36)))
-	f.bounds.YMin = int32(int16(u16(f.head, 38)))
-	f.bounds.XMax = int32(int16(u16(f.head, 40)))
-	f.bounds.YMax = int32(int16(u16(f.head, 42)))
+	f.bounds.XMin = fixed.Int26_6(int16(u16(f.head, 36)))
+	f.bounds.YMin = fixed.Int26_6(int16(u16(f.head, 38)))
+	f.bounds.XMax = fixed.Int26_6(int16(u16(f.head, 40)))
+	f.bounds.YMax = fixed.Int26_6(int16(u16(f.head, 42)))
 	switch i := u16(f.head, 50); i {
 	case 0:
 		f.locaOffsetFormat = locaOffsetFormatShort
@@ -306,17 +307,17 @@ func (f *Font) parseMaxp() error {
 }
 
 // scale returns x divided by f.fUnitsPerEm, rounded to the nearest integer.
-func (f *Font) scale(x int32) int32 {
+func (f *Font) scale(x fixed.Int26_6) fixed.Int26_6 {
 	if x >= 0 {
-		x += f.fUnitsPerEm / 2
+		x += fixed.Int26_6(f.fUnitsPerEm) / 2
 	} else {
-		x -= f.fUnitsPerEm / 2
+		x -= fixed.Int26_6(f.fUnitsPerEm) / 2
 	}
-	return x / f.fUnitsPerEm
+	return x / fixed.Int26_6(f.fUnitsPerEm)
 }
 
 // Bounds returns the union of a Font's glyphs' bounds.
-func (f *Font) Bounds(scale int32) Bounds {
+func (f *Font) Bounds(scale fixed.Int26_6) Bounds {
 	b := f.bounds
 	b.XMin = f.scale(scale * b.XMin)
 	b.YMin = f.scale(scale * b.YMin)
@@ -360,18 +361,18 @@ func (f *Font) unscaledHMetric(i Index) (h HMetric) {
 	if j >= f.nHMetric {
 		p := 4 * (f.nHMetric - 1)
 		return HMetric{
-			AdvanceWidth:    int32(u16(f.hmtx, p)),
-			LeftSideBearing: int32(int16(u16(f.hmtx, p+2*(j-f.nHMetric)+4))),
+			AdvanceWidth:    fixed.Int26_6(u16(f.hmtx, p)),
+			LeftSideBearing: fixed.Int26_6(int16(u16(f.hmtx, p+2*(j-f.nHMetric)+4))),
 		}
 	}
 	return HMetric{
-		AdvanceWidth:    int32(u16(f.hmtx, 4*j)),
-		LeftSideBearing: int32(int16(u16(f.hmtx, 4*j+2))),
+		AdvanceWidth:    fixed.Int26_6(u16(f.hmtx, 4*j)),
+		LeftSideBearing: fixed.Int26_6(int16(u16(f.hmtx, 4*j+2))),
 	}
 }
 
 // HMetric returns the horizontal metrics for the glyph with the given index.
-func (f *Font) HMetric(scale int32, i Index) HMetric {
+func (f *Font) HMetric(scale fixed.Int26_6, i Index) HMetric {
 	h := f.unscaledHMetric(i)
 	h.AdvanceWidth = f.scale(scale * h.AdvanceWidth)
 	h.LeftSideBearing = f.scale(scale * h.LeftSideBearing)
@@ -380,15 +381,15 @@ func (f *Font) HMetric(scale int32, i Index) HMetric {
 
 // unscaledVMetric returns the unscaled vertical metrics for the glyph with
 // the given index. yMax is the top of the glyph's bounding box.
-func (f *Font) unscaledVMetric(i Index, yMax int32) (v VMetric) {
+func (f *Font) unscaledVMetric(i Index, yMax fixed.Int26_6) (v VMetric) {
 	j := int(i)
 	if j < 0 || f.nGlyph <= j {
 		return VMetric{}
 	}
 	if 4*j+4 <= len(f.vmtx) {
 		return VMetric{
-			AdvanceHeight:  int32(u16(f.vmtx, 4*j)),
-			TopSideBearing: int32(int16(u16(f.vmtx, 4*j+2))),
+			AdvanceHeight:  fixed.Int26_6(u16(f.vmtx, 4*j)),
+			TopSideBearing: fixed.Int26_6(int16(u16(f.vmtx, 4*j+2))),
 		}
 	}
 	// The OS/2 table has grown over time.
@@ -397,21 +398,21 @@ func (f *Font) unscaledVMetric(i Index, yMax int32) (v VMetric) {
 	// 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)))
+		sTypoAscender := fixed.Int26_6(int16(u16(f.os2, 68)))
+		sTypoDescender := fixed.Int26_6(int16(u16(f.os2, 70)))
 		return VMetric{
 			AdvanceHeight:  sTypoAscender - sTypoDescender,
 			TopSideBearing: sTypoAscender - yMax,
 		}
 	}
 	return VMetric{
-		AdvanceHeight:  f.fUnitsPerEm,
+		AdvanceHeight:  fixed.Int26_6(f.fUnitsPerEm),
 		TopSideBearing: 0,
 	}
 }
 
 // VMetric returns the vertical metrics for the glyph with the given index.
-func (f *Font) VMetric(scale int32, i Index) VMetric {
+func (f *Font) VMetric(scale fixed.Int26_6, i Index) VMetric {
 	// TODO: should 0 be bounds.YMax?
 	v := f.unscaledVMetric(i, 0)
 	v.AdvanceHeight = f.scale(scale * v.AdvanceHeight)
@@ -420,7 +421,7 @@ func (f *Font) VMetric(scale int32, i Index) VMetric {
 }
 
 // Kerning returns the kerning for the given glyph pair.
-func (f *Font) Kerning(scale int32, i0, i1 Index) int32 {
+func (f *Font) Kerning(scale fixed.Int26_6, i0, i1 Index) fixed.Int26_6 {
 	if f.nKern == 0 {
 		return 0
 	}
@@ -434,7 +435,7 @@ func (f *Font) Kerning(scale int32, i0, i1 Index) int32 {
 		} else if ig > g {
 			hi = i
 		} else {
-			return f.scale(scale * int32(int16(u16(f.kern, 22+6*i))))
+			return f.scale(scale * fixed.Int26_6(int16(u16(f.kern, 22+6*i))))
 		}
 	}
 	return 0
diff --git a/truetype/truetype_test.go b/truetype/truetype_test.go
index 12cc7e9..568bec6 100644
--- a/truetype/truetype_test.go
+++ b/truetype/truetype_test.go
@@ -14,6 +14,8 @@ import (
 	"strconv"
 	"strings"
 	"testing"
+
+	"golang.org/x/image/math/fixed"
 )
 
 func parseTestdataFont(name string) (font *Font, testdataIsOptional bool, err error) {
@@ -40,7 +42,7 @@ func TestParse(t *testing.T) {
 	if got, want := font.FUnitsPerEm(), int32(2048); got != want {
 		t.Errorf("FUnitsPerEm: got %v, want %v", got, want)
 	}
-	fupe := font.FUnitsPerEm()
+	fupe := fixed.Int26_6(font.FUnitsPerEm())
 	if got, want := font.Bounds(fupe), (Bounds{-441, -432, 2024, 2033}); got != want {
 		t.Errorf("Bounds: got %v, want %v", got, want)
 	}
@@ -56,7 +58,7 @@ func TestParse(t *testing.T) {
 	if got, want := font.VMetric(fupe, i0), (VMetric{2465, 553}); got != want {
 		t.Errorf("VMetric: got %v, want %v", got, want)
 	}
-	if got, want := font.Kerning(fupe, i0, i1), int32(-144); got != want {
+	if got, want := font.Kerning(fupe, i0, i1), fixed.Int26_6(-144); got != want {
 		t.Errorf("Kerning: got %v, want %v", got, want)
 	}
 
@@ -196,7 +198,7 @@ func TestIndex(t *testing.T) {
 }
 
 type scalingTestData struct {
-	advanceWidth int32
+	advanceWidth fixed.Int26_6
 	bounds       Bounds
 	points       []Point
 }
@@ -205,13 +207,13 @@ type scalingTestData struct {
 // 213 -22 -111 236 555;-22 -111 1, 178 555 1, 236 555 1, 36 -111 1
 // The line will not have a trailing "\n".
 func scalingTestParse(line string) (ret scalingTestData) {
-	next := func(s string) (string, int32) {
+	next := func(s string) (string, fixed.Int26_6) {
 		t, i := "", strings.Index(s, " ")
 		if i != -1 {
 			s, t = s[:i], s[i+1:]
 		}
 		x, _ := strconv.Atoi(s)
-		return t, int32(x)
+		return t, fixed.Int26_6(x)
 	}
 
 	i := strings.Index(line, ";")
@@ -257,7 +259,7 @@ func scalingTestEquals(a, b []Point) (index int, equals bool) {
 
 var scalingTestCases = []struct {
 	name string
-	size int32
+	size int
 }{
 	{"luxisr", 12},
 	{"x-arial-bold", 11},
@@ -318,7 +320,7 @@ func testScaling(t *testing.T, h Hinting) {
 
 		glyphBuf := NewGlyphBuf()
 		for i, want := range wants {
-			if err = glyphBuf.Load(font, tc.size*64, Index(i), h); err != nil {
+			if err = glyphBuf.Load(font, fixed.I(tc.size), Index(i), h); err != nil {
 				t.Errorf("%s: glyph #%d: Load: %v", tc.name, i, err)
 				continue
 			}
-- 
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