diff --git a/draw/gen.go b/draw/gen.go
index 06080d8..a16bf84 100644
--- a/draw/gen.go
+++ b/draw/gen.go
@@ -26,8 +26,8 @@
 	w.WriteString("// generated by \"go run gen.go\". DO NOT EDIT.\n\n" +
 		"package draw\n\nimport (\n\"image\"\n\"image/color\"\n)\n")
 
-	gen(w, "nnScaler", codeNNLeaf)
-	gen(w, "ablScaler", codeABLLeaf)
+	gen(w, "nnInterpolator", codeNNLeaf)
+	gen(w, "ablInterpolator", codeABLLeaf)
 	genKernel(w)
 
 	if *debug {
@@ -181,7 +181,7 @@
 		default:
 			return ";"
 		case "*image.RGBA":
-			return "d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))"
+			return "d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))"
 		}
 
 	case "preKernelInner":
@@ -189,7 +189,7 @@
 		default:
 			return ";"
 		case "*image.RGBA":
-			return "d := dst.PixOffset(dp.X+int(dx), dp.Y+adr.Min.Y)"
+			return "d := dst.PixOffset(dr.Min.X+int(dx), dr.Min.Y+adr.Min.Y)"
 		}
 
 	case "blend":
@@ -222,7 +222,7 @@
 				"dstColorRGBA64.G = uint16(%sg)\n"+
 				"dstColorRGBA64.B = uint16(%sb)\n"+
 				"dstColorRGBA64.A = uint16(%sa)\n"+
-				"dst.Set(dp.X+int(%s), dp.Y+int(%s), dstColor)",
+				"dst.Set(dr.Min.X+int(%s), dr.Min.Y+int(%s), dstColor)",
 				args[2], args[2], args[2], args[2],
 				args[0], args[1],
 			)
@@ -251,7 +251,7 @@
 				"dstColorRGBA64.G = ftou(%sg * %s)\n"+
 				"dstColorRGBA64.B = ftou(%sb * %s)\n"+
 				"dstColorRGBA64.A = ftou(%sa * %s)\n"+
-				"dst.Set(dp.X+int(%s), dp.Y+int(%s), dstColor)",
+				"dst.Set(dr.Min.X+int(%s), dr.Min.Y+int(%s), dstColor)",
 				args[2], args[3], args[2], args[3], args[2], args[3], args[2], args[3],
 				args[0], args[1],
 			)
@@ -287,14 +287,14 @@
 			log.Fatalf("bad sType %q", d.sType)
 		case "image.Image", "*image.Gray", "*image.NRGBA", "*image.Uniform", "*image.YCbCr": // TODO: separate code for concrete types.
 			fmt.Fprintf(buf, "%sr%s, %sg%s, %sb%s, %sa%s := "+
-				"src.At(sp.X + int(%s), sp.Y+int(%s)).RGBA()\n",
+				"src.At(sr.Min.X + int(%s), sr.Min.Y+int(%s)).RGBA()\n",
 				lhs, tmp, lhs, tmp, lhs, tmp, lhs, tmp,
 				args[0], args[1],
 			)
 		case "*image.RGBA":
 			// TODO: there's no need to multiply by 0x101 if the next thing
 			// we're going to do is shift right by 8.
-			fmt.Fprintf(buf, "%si := src.PixOffset(sp.X + int(%s), sp.Y+int(%s))\n"+
+			fmt.Fprintf(buf, "%si := src.PixOffset(sr.Min.X + int(%s), sr.Min.Y+int(%s))\n"+
 				"%sr%s := uint32(src.Pix[%si+0]) * 0x101\n"+
 				"%sg%s := uint32(src.Pix[%si+1]) * 0x101\n"+
 				"%sb%s := uint32(src.Pix[%si+2]) * 0x101\n"+
@@ -407,34 +407,35 @@
 
 const (
 	codeRoot = `
-		func (z *$receiver) Scale(dst Image, dp image.Point, src image.Image, sp image.Point) {
-			if z.dw <= 0 || z.dh <= 0 || z.sw <= 0 || z.sh <= 0 {
-				return
-			}
-			// adr is the affected destination pixels, relative to dp.
-			adr := dst.Bounds().Sub(dp).Intersect(image.Rectangle{Max: image.Point{int(z.dw), int(z.dh)}})
-			if adr.Empty() {
+		func (z $receiver) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+			// adr is the affected destination pixels, relative to dr.Min.
+			adr := dst.Bounds().Intersect(dr).Sub(dr.Min)
+			if adr.Empty() || sr.Empty() {
 				return
 			}
 			// sr is the source pixels. If it extends beyond the src bounds,
 			// we cannot use the type-specific fast paths, as they access
 			// the Pix fields directly without bounds checking.
-			if sr := (image.Rectangle{sp, sp.Add(image.Point{int(z.sw), int(z.sh)})}); !sr.In(src.Bounds()) {
-				z.scale_Image_Image(dst, dp, adr, src, sp)
+			if !sr.In(src.Bounds()) {
+				z.scale_Image_Image(dst, dr, adr, src, sr)
 			} else {
-				$switch z.scale_$dTypeRN_$sTypeRN(dst, dp, adr, src, sp)
+				$switch z.scale_$dTypeRN_$sTypeRN(dst, dr, adr, src, sr)
 			}
 		}
 	`
 
 	codeNNLeaf = `
-		func (z *nnScaler) scale_$dTypeRN_$sTypeRN(dst $dType, dp image.Point, adr image.Rectangle, src $sType, sp image.Point) {
+		func (nnInterpolator) scale_$dTypeRN_$sTypeRN(dst $dType, dr, adr image.Rectangle, src $sType, sr image.Rectangle) {
+			dw2 := uint64(dr.Dx()) * 2
+			dh2 := uint64(dr.Dy()) * 2
+			sw := uint64(sr.Dx())
+			sh := uint64(sr.Dy())
 			$preOuter
 			for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-				sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
+				sy := (2*uint64(dy) + 1) * sh / dh2
 				$preInner
 				for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-					sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
+					sx := (2*uint64(dx) + 1) * sw / dw2
 					p := $srcu[sx, sy]
 					$outputu[dx, dy, p]
 				}
@@ -443,9 +444,11 @@
 	`
 
 	codeABLLeaf = `
-		func (z *ablScaler) scale_$dTypeRN_$sTypeRN(dst $dType, dp image.Point, adr image.Rectangle, src $sType, sp image.Point) {
-			yscale := float64(z.sh) / float64(z.dh)
-			xscale := float64(z.sw) / float64(z.dw)
+		func (ablInterpolator) scale_$dTypeRN_$sTypeRN(dst $dType, dr, adr image.Rectangle, src $sType, sr image.Rectangle) {
+			sw := int32(sr.Dx())
+			sh := int32(sr.Dy())
+			yscale := float64(sh) / float64(dr.Dy())
+			xscale := float64(sw) / float64(dr.Dx())
 			$preOuter
 			for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 				sy := (float64(dy)+0.5)*yscale - 0.5
@@ -456,7 +459,7 @@
 				if sy < 0 {
 					sy0, sy1 = 0, 0
 					yFrac0, yFrac1 = 0, 1
-				} else if sy1 >= z.sh {
+				} else if sy1 >= sh {
 					sy1 = sy0
 					yFrac0, yFrac1 = 1, 0
 				}
@@ -470,7 +473,7 @@
 					if sx < 0 {
 						sx0, sx1 = 0, 0
 						xFrac0, xFrac1 = 0, 1
-					} else if sx1 >= z.sw {
+					} else if sx1 >= sw {
 						sx1 = sx0
 						xFrac0, xFrac1 = 1, 0
 					}
@@ -488,13 +491,14 @@
 	`
 
 	codeKernelRoot = `
-		func (z *kernelScaler) Scale(dst Image, dp image.Point, src image.Image, sp image.Point) {
-			if z.dw <= 0 || z.dh <= 0 || z.sw <= 0 || z.sh <= 0 {
+		func (z *kernelScaler) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+			if z.dw != int32(dr.Dx()) || z.dh != int32(dr.Dy()) || z.sw != int32(sr.Dx()) || z.sh != int32(sr.Dy()) {
+				z.kernel.Scale(dst, dr, src, sr)
 				return
 			}
-			// adr is the affected destination pixels, relative to dp.
-			adr := dst.Bounds().Sub(dp).Intersect(image.Rectangle{Max: image.Point{int(z.dw), int(z.dh)}})
-			if adr.Empty() {
+			// adr is the affected destination pixels, relative to dr.Min.
+			adr := dst.Bounds().Intersect(dr).Sub(dr.Min)
+			if adr.Empty() || sr.Empty() {
 				return
 			}
 			// Create a temporary buffer:
@@ -506,18 +510,18 @@
 			// sr is the source pixels. If it extends beyond the src bounds,
 			// we cannot use the type-specific fast paths, as they access
 			// the Pix fields directly without bounds checking.
-			if sr := (image.Rectangle{sp, sp.Add(image.Point{int(z.sw), int(z.sh)})}); !sr.In(src.Bounds()) {
-				z.scaleX_Image(tmp, src, sp)
+			if !sr.In(src.Bounds()) {
+				z.scaleX_Image(tmp, src, sr)
 			} else {
-				$switchS z.scaleX_$sTypeRN(tmp, src, sp)
+				$switchS z.scaleX_$sTypeRN(tmp, src, sr)
 			}
 
-			$switchD z.scaleY_$dTypeRN(dst, dp, adr, tmp)
+			$switchD z.scaleY_$dTypeRN(dst, dr, adr, tmp)
 		}
 	`
 
 	codeKernelLeafX = `
-		func (z *kernelScaler) scaleX_$sTypeRN(tmp [][4]float64, src $sType, sp image.Point) {
+		func (z *kernelScaler) scaleX_$sTypeRN(tmp [][4]float64, src $sType, sr image.Rectangle) {
 			t := 0
 			for y := int32(0); y < z.sh; y++ {
 				for _, s := range z.horizontal.sources {
@@ -538,7 +542,7 @@
 	`
 
 	codeKernelLeafY = `
-		func (z *kernelScaler) scaleY_$dTypeRN(dst $dType, dp image.Point, adr image.Rectangle, tmp [][4]float64) {
+		func (z *kernelScaler) scaleY_$dTypeRN(dst $dType, dr, adr image.Rectangle, tmp [][4]float64) {
 			$preOuter
 			for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 				$preKernelInner
diff --git a/draw/impl.go b/draw/impl.go
index ccc0632..7a0a5bb 100644
--- a/draw/impl.go
+++ b/draw/impl.go
@@ -7,53 +7,54 @@
 	"image/color"
 )
 
-func (z *nnScaler) Scale(dst Image, dp image.Point, src image.Image, sp image.Point) {
-	if z.dw <= 0 || z.dh <= 0 || z.sw <= 0 || z.sh <= 0 {
-		return
-	}
-	// adr is the affected destination pixels, relative to dp.
-	adr := dst.Bounds().Sub(dp).Intersect(image.Rectangle{Max: image.Point{int(z.dw), int(z.dh)}})
-	if adr.Empty() {
+func (z nnInterpolator) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+	// adr is the affected destination pixels, relative to dr.Min.
+	adr := dst.Bounds().Intersect(dr).Sub(dr.Min)
+	if adr.Empty() || sr.Empty() {
 		return
 	}
 	// sr is the source pixels. If it extends beyond the src bounds,
 	// we cannot use the type-specific fast paths, as they access
 	// the Pix fields directly without bounds checking.
-	if sr := (image.Rectangle{sp, sp.Add(image.Point{int(z.sw), int(z.sh)})}); !sr.In(src.Bounds()) {
-		z.scale_Image_Image(dst, dp, adr, src, sp)
+	if !sr.In(src.Bounds()) {
+		z.scale_Image_Image(dst, dr, adr, src, sr)
 	} else {
 		switch dst := dst.(type) {
 		case *image.RGBA:
 			switch src := src.(type) {
 			case *image.Gray:
-				z.scale_RGBA_Gray(dst, dp, adr, src, sp)
+				z.scale_RGBA_Gray(dst, dr, adr, src, sr)
 			case *image.NRGBA:
-				z.scale_RGBA_NRGBA(dst, dp, adr, src, sp)
+				z.scale_RGBA_NRGBA(dst, dr, adr, src, sr)
 			case *image.RGBA:
-				z.scale_RGBA_RGBA(dst, dp, adr, src, sp)
+				z.scale_RGBA_RGBA(dst, dr, adr, src, sr)
 			case *image.Uniform:
-				z.scale_RGBA_Uniform(dst, dp, adr, src, sp)
+				z.scale_RGBA_Uniform(dst, dr, adr, src, sr)
 			case *image.YCbCr:
-				z.scale_RGBA_YCbCr(dst, dp, adr, src, sp)
+				z.scale_RGBA_YCbCr(dst, dr, adr, src, sr)
 			default:
-				z.scale_RGBA_Image(dst, dp, adr, src, sp)
+				z.scale_RGBA_Image(dst, dr, adr, src, sr)
 			}
 		default:
 			switch src := src.(type) {
 			default:
-				z.scale_Image_Image(dst, dp, adr, src, sp)
+				z.scale_Image_Image(dst, dr, adr, src, sr)
 			}
 		}
 	}
 }
 
-func (z *nnScaler) scale_RGBA_Gray(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.Gray, sp image.Point) {
+func (nnInterpolator) scale_RGBA_Gray(dst *image.RGBA, dr, adr image.Rectangle, src *image.Gray, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dst.Pix[d+0] = uint8(uint32(pr) >> 8)
 			dst.Pix[d+1] = uint8(uint32(pg) >> 8)
 			dst.Pix[d+2] = uint8(uint32(pb) >> 8)
@@ -63,13 +64,17 @@
 	}
 }
 
-func (z *nnScaler) scale_RGBA_NRGBA(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.NRGBA, sp image.Point) {
+func (nnInterpolator) scale_RGBA_NRGBA(dst *image.RGBA, dr, adr image.Rectangle, src *image.NRGBA, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dst.Pix[d+0] = uint8(uint32(pr) >> 8)
 			dst.Pix[d+1] = uint8(uint32(pg) >> 8)
 			dst.Pix[d+2] = uint8(uint32(pb) >> 8)
@@ -79,13 +84,17 @@
 	}
 }
 
-func (z *nnScaler) scale_RGBA_RGBA(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.RGBA, sp image.Point) {
+func (nnInterpolator) scale_RGBA_RGBA(dst *image.RGBA, dr, adr image.Rectangle, src *image.RGBA, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pi := src.PixOffset(sp.X+int(sx), sp.Y+int(sy))
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pi := src.PixOffset(sr.Min.X+int(sx), sr.Min.Y+int(sy))
 			pr := uint32(src.Pix[pi+0]) * 0x101
 			pg := uint32(src.Pix[pi+1]) * 0x101
 			pb := uint32(src.Pix[pi+2]) * 0x101
@@ -99,13 +108,17 @@
 	}
 }
 
-func (z *nnScaler) scale_RGBA_Uniform(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.Uniform, sp image.Point) {
+func (nnInterpolator) scale_RGBA_Uniform(dst *image.RGBA, dr, adr image.Rectangle, src *image.Uniform, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dst.Pix[d+0] = uint8(uint32(pr) >> 8)
 			dst.Pix[d+1] = uint8(uint32(pg) >> 8)
 			dst.Pix[d+2] = uint8(uint32(pb) >> 8)
@@ -115,13 +128,17 @@
 	}
 }
 
-func (z *nnScaler) scale_RGBA_YCbCr(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.YCbCr, sp image.Point) {
+func (nnInterpolator) scale_RGBA_YCbCr(dst *image.RGBA, dr, adr image.Rectangle, src *image.YCbCr, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dst.Pix[d+0] = uint8(uint32(pr) >> 8)
 			dst.Pix[d+1] = uint8(uint32(pg) >> 8)
 			dst.Pix[d+2] = uint8(uint32(pb) >> 8)
@@ -131,13 +148,17 @@
 	}
 }
 
-func (z *nnScaler) scale_RGBA_Image(dst *image.RGBA, dp image.Point, adr image.Rectangle, src image.Image, sp image.Point) {
+func (nnInterpolator) scale_RGBA_Image(dst *image.RGBA, dr, adr image.Rectangle, src image.Image, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		sy := (2*uint64(dy) + 1) * sh / dh2
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dst.Pix[d+0] = uint8(uint32(pr) >> 8)
 			dst.Pix[d+1] = uint8(uint32(pg) >> 8)
 			dst.Pix[d+2] = uint8(uint32(pb) >> 8)
@@ -147,66 +168,69 @@
 	}
 }
 
-func (z *nnScaler) scale_Image_Image(dst Image, dp image.Point, adr image.Rectangle, src image.Image, sp image.Point) {
+func (nnInterpolator) scale_Image_Image(dst Image, dr, adr image.Rectangle, src image.Image, sr image.Rectangle) {
+	dw2 := uint64(dr.Dx()) * 2
+	dh2 := uint64(dr.Dy()) * 2
+	sw := uint64(sr.Dx())
+	sh := uint64(sr.Dy())
 	dstColorRGBA64 := &color.RGBA64{}
 	dstColor := color.Color(dstColorRGBA64)
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
-		sy := (2*uint64(dy) + 1) * uint64(z.sh) / (2 * uint64(z.dh))
+		sy := (2*uint64(dy) + 1) * sh / dh2
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-			sx := (2*uint64(dx) + 1) * uint64(z.sw) / (2 * uint64(z.dw))
-			pr, pg, pb, pa := src.At(sp.X+int(sx), sp.Y+int(sy)).RGBA()
+			sx := (2*uint64(dx) + 1) * sw / dw2
+			pr, pg, pb, pa := src.At(sr.Min.X+int(sx), sr.Min.Y+int(sy)).RGBA()
 			dstColorRGBA64.R = uint16(pr)
 			dstColorRGBA64.G = uint16(pg)
 			dstColorRGBA64.B = uint16(pb)
 			dstColorRGBA64.A = uint16(pa)
-			dst.Set(dp.X+int(dx), dp.Y+int(dy), dstColor)
+			dst.Set(dr.Min.X+int(dx), dr.Min.Y+int(dy), dstColor)
 		}
 	}
 }
 
-func (z *ablScaler) Scale(dst Image, dp image.Point, src image.Image, sp image.Point) {
-	if z.dw <= 0 || z.dh <= 0 || z.sw <= 0 || z.sh <= 0 {
-		return
-	}
-	// adr is the affected destination pixels, relative to dp.
-	adr := dst.Bounds().Sub(dp).Intersect(image.Rectangle{Max: image.Point{int(z.dw), int(z.dh)}})
-	if adr.Empty() {
+func (z ablInterpolator) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+	// adr is the affected destination pixels, relative to dr.Min.
+	adr := dst.Bounds().Intersect(dr).Sub(dr.Min)
+	if adr.Empty() || sr.Empty() {
 		return
 	}
 	// sr is the source pixels. If it extends beyond the src bounds,
 	// we cannot use the type-specific fast paths, as they access
 	// the Pix fields directly without bounds checking.
-	if sr := (image.Rectangle{sp, sp.Add(image.Point{int(z.sw), int(z.sh)})}); !sr.In(src.Bounds()) {
-		z.scale_Image_Image(dst, dp, adr, src, sp)
+	if !sr.In(src.Bounds()) {
+		z.scale_Image_Image(dst, dr, adr, src, sr)
 	} else {
 		switch dst := dst.(type) {
 		case *image.RGBA:
 			switch src := src.(type) {
 			case *image.Gray:
-				z.scale_RGBA_Gray(dst, dp, adr, src, sp)
+				z.scale_RGBA_Gray(dst, dr, adr, src, sr)
 			case *image.NRGBA:
-				z.scale_RGBA_NRGBA(dst, dp, adr, src, sp)
+				z.scale_RGBA_NRGBA(dst, dr, adr, src, sr)
 			case *image.RGBA:
-				z.scale_RGBA_RGBA(dst, dp, adr, src, sp)
+				z.scale_RGBA_RGBA(dst, dr, adr, src, sr)
 			case *image.Uniform:
-				z.scale_RGBA_Uniform(dst, dp, adr, src, sp)
+				z.scale_RGBA_Uniform(dst, dr, adr, src, sr)
 			case *image.YCbCr:
-				z.scale_RGBA_YCbCr(dst, dp, adr, src, sp)
+				z.scale_RGBA_YCbCr(dst, dr, adr, src, sr)
 			default:
-				z.scale_RGBA_Image(dst, dp, adr, src, sp)
+				z.scale_RGBA_Image(dst, dr, adr, src, sr)
 			}
 		default:
 			switch src := src.(type) {
 			default:
-				z.scale_Image_Image(dst, dp, adr, src, sp)
+				z.scale_Image_Image(dst, dr, adr, src, sr)
 			}
 		}
 	}
 }
 
-func (z *ablScaler) scale_RGBA_Gray(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.Gray, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_Gray(dst *image.RGBA, dr, adr image.Rectangle, src *image.Gray, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -216,11 +240,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -230,16 +254,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -248,12 +272,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -275,9 +299,11 @@
 	}
 }
 
-func (z *ablScaler) scale_RGBA_NRGBA(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.NRGBA, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_NRGBA(dst *image.RGBA, dr, adr image.Rectangle, src *image.NRGBA, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -287,11 +313,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -301,16 +327,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -319,12 +345,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -346,9 +372,11 @@
 	}
 }
 
-func (z *ablScaler) scale_RGBA_RGBA(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.RGBA, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_RGBA(dst *image.RGBA, dr, adr image.Rectangle, src *image.RGBA, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -358,11 +386,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -372,11 +400,11 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00i := src.PixOffset(sp.X+int(sx0), sp.Y+int(sy0))
+			s00i := src.PixOffset(sr.Min.X+int(sx0), sr.Min.Y+int(sy0))
 			s00ru := uint32(src.Pix[s00i+0]) * 0x101
 			s00gu := uint32(src.Pix[s00i+1]) * 0x101
 			s00bu := uint32(src.Pix[s00i+2]) * 0x101
@@ -385,7 +413,7 @@
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10i := src.PixOffset(sp.X+int(sx1), sp.Y+int(sy0))
+			s10i := src.PixOffset(sr.Min.X+int(sx1), sr.Min.Y+int(sy0))
 			s10ru := uint32(src.Pix[s10i+0]) * 0x101
 			s10gu := uint32(src.Pix[s10i+1]) * 0x101
 			s10bu := uint32(src.Pix[s10i+2]) * 0x101
@@ -398,7 +426,7 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01i := src.PixOffset(sp.X+int(sx0), sp.Y+int(sy1))
+			s01i := src.PixOffset(sr.Min.X+int(sx0), sr.Min.Y+int(sy1))
 			s01ru := uint32(src.Pix[s01i+0]) * 0x101
 			s01gu := uint32(src.Pix[s01i+1]) * 0x101
 			s01bu := uint32(src.Pix[s01i+2]) * 0x101
@@ -407,7 +435,7 @@
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11i := src.PixOffset(sp.X+int(sx1), sp.Y+int(sy1))
+			s11i := src.PixOffset(sr.Min.X+int(sx1), sr.Min.Y+int(sy1))
 			s11ru := uint32(src.Pix[s11i+0]) * 0x101
 			s11gu := uint32(src.Pix[s11i+1]) * 0x101
 			s11bu := uint32(src.Pix[s11i+2]) * 0x101
@@ -433,9 +461,11 @@
 	}
 }
 
-func (z *ablScaler) scale_RGBA_Uniform(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.Uniform, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_Uniform(dst *image.RGBA, dr, adr image.Rectangle, src *image.Uniform, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -445,11 +475,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -459,16 +489,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -477,12 +507,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -504,9 +534,11 @@
 	}
 }
 
-func (z *ablScaler) scale_RGBA_YCbCr(dst *image.RGBA, dp image.Point, adr image.Rectangle, src *image.YCbCr, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_YCbCr(dst *image.RGBA, dr, adr image.Rectangle, src *image.YCbCr, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -516,11 +548,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -530,16 +562,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -548,12 +580,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -575,9 +607,11 @@
 	}
 }
 
-func (z *ablScaler) scale_RGBA_Image(dst *image.RGBA, dp image.Point, adr image.Rectangle, src image.Image, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_RGBA_Image(dst *image.RGBA, dr, adr image.Rectangle, src image.Image, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
 		sy := (float64(dy)+0.5)*yscale - 0.5
 		sy0 := int32(sy)
@@ -587,11 +621,11 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
-		d := dst.PixOffset(dp.X+adr.Min.X, dp.Y+int(dy))
+		d := dst.PixOffset(dr.Min.X+adr.Min.X, dr.Min.Y+int(dy))
 		for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
 			sx := (float64(dx)+0.5)*xscale - 0.5
 			sx0 := int32(sx)
@@ -601,16 +635,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -619,12 +653,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -646,9 +680,11 @@
 	}
 }
 
-func (z *ablScaler) scale_Image_Image(dst Image, dp image.Point, adr image.Rectangle, src image.Image, sp image.Point) {
-	yscale := float64(z.sh) / float64(z.dh)
-	xscale := float64(z.sw) / float64(z.dw)
+func (ablInterpolator) scale_Image_Image(dst Image, dr, adr image.Rectangle, src image.Image, sr image.Rectangle) {
+	sw := int32(sr.Dx())
+	sh := int32(sr.Dy())
+	yscale := float64(sh) / float64(dr.Dy())
+	xscale := float64(sw) / float64(dr.Dx())
 	dstColorRGBA64 := &color.RGBA64{}
 	dstColor := color.Color(dstColorRGBA64)
 	for dy := int32(adr.Min.Y); dy < int32(adr.Max.Y); dy++ {
@@ -660,7 +696,7 @@
 		if sy < 0 {
 			sy0, sy1 = 0, 0
 			yFrac0, yFrac1 = 0, 1
-		} else if sy1 >= z.sh {
+		} else if sy1 >= sh {
 			sy1 = sy0
 			yFrac0, yFrac1 = 1, 0
 		}
@@ -673,16 +709,16 @@
 			if sx < 0 {
 				sx0, sx1 = 0, 0
 				xFrac0, xFrac1 = 0, 1
-			} else if sx1 >= z.sw {
+			} else if sx1 >= sw {
 				sx1 = sx0
 				xFrac0, xFrac1 = 1, 0
 			}
-			s00ru, s00gu, s00bu, s00au := src.At(sp.X+int(sx0), sp.Y+int(sy0)).RGBA()
+			s00ru, s00gu, s00bu, s00au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy0)).RGBA()
 			s00r := float64(s00ru)
 			s00g := float64(s00gu)
 			s00b := float64(s00bu)
 			s00a := float64(s00au)
-			s10ru, s10gu, s10bu, s10au := src.At(sp.X+int(sx1), sp.Y+int(sy0)).RGBA()
+			s10ru, s10gu, s10bu, s10au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy0)).RGBA()
 			s10r := float64(s10ru)
 			s10g := float64(s10gu)
 			s10b := float64(s10bu)
@@ -691,12 +727,12 @@
 			s10g = xFrac1*s00g + xFrac0*s10g
 			s10b = xFrac1*s00b + xFrac0*s10b
 			s10a = xFrac1*s00a + xFrac0*s10a
-			s01ru, s01gu, s01bu, s01au := src.At(sp.X+int(sx0), sp.Y+int(sy1)).RGBA()
+			s01ru, s01gu, s01bu, s01au := src.At(sr.Min.X+int(sx0), sr.Min.Y+int(sy1)).RGBA()
 			s01r := float64(s01ru)
 			s01g := float64(s01gu)
 			s01b := float64(s01bu)
 			s01a := float64(s01au)
-			s11ru, s11gu, s11bu, s11au := src.At(sp.X+int(sx1), sp.Y+int(sy1)).RGBA()
+			s11ru, s11gu, s11bu, s11au := src.At(sr.Min.X+int(sx1), sr.Min.Y+int(sy1)).RGBA()
 			s11r := float64(s11ru)
 			s11g := float64(s11gu)
 			s11b := float64(s11bu)
@@ -713,18 +749,19 @@
 			dstColorRGBA64.G = uint16(s11g)
 			dstColorRGBA64.B = uint16(s11b)
 			dstColorRGBA64.A = uint16(s11a)
-			dst.Set(dp.X+int(dx), dp.Y+int(dy), dstColor)
+			dst.Set(dr.Min.X+int(dx), dr.Min.Y+int(dy), dstColor)
 		}
 	}
 }
 
-func (z *kernelScaler) Scale(dst Image, dp image.Point, src image.Image, sp image.Point) {
-	if z.dw <= 0 || z.dh <= 0 || z.sw <= 0 || z.sh <= 0 {
+func (z *kernelScaler) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+	if z.dw != int32(dr.Dx()) || z.dh != int32(dr.Dy()) || z.sw != int32(sr.Dx()) || z.sh != int32(sr.Dy()) {
+		z.kernel.Scale(dst, dr, src, sr)
 		return
 	}
-	// adr is the affected destination pixels, relative to dp.
-	adr := dst.Bounds().Sub(dp).Intersect(image.Rectangle{Max: image.Point{int(z.dw), int(z.dh)}})
-	if adr.Empty() {
+	// adr is the affected destination pixels, relative to dr.Min.
+	adr := dst.Bounds().Intersect(dr).Sub(dr.Min)
+	if adr.Empty() || sr.Empty() {
 		return
 	}
 	// Create a temporary buffer:
@@ -736,40 +773,40 @@
 	// sr is the source pixels. If it extends beyond the src bounds,
 	// we cannot use the type-specific fast paths, as they access
 	// the Pix fields directly without bounds checking.
-	if sr := (image.Rectangle{sp, sp.Add(image.Point{int(z.sw), int(z.sh)})}); !sr.In(src.Bounds()) {
-		z.scaleX_Image(tmp, src, sp)
+	if !sr.In(src.Bounds()) {
+		z.scaleX_Image(tmp, src, sr)
 	} else {
 		switch src := src.(type) {
 		case *image.Gray:
-			z.scaleX_Gray(tmp, src, sp)
+			z.scaleX_Gray(tmp, src, sr)
 		case *image.NRGBA:
-			z.scaleX_NRGBA(tmp, src, sp)
+			z.scaleX_NRGBA(tmp, src, sr)
 		case *image.RGBA:
-			z.scaleX_RGBA(tmp, src, sp)
+			z.scaleX_RGBA(tmp, src, sr)
 		case *image.Uniform:
-			z.scaleX_Uniform(tmp, src, sp)
+			z.scaleX_Uniform(tmp, src, sr)
 		case *image.YCbCr:
-			z.scaleX_YCbCr(tmp, src, sp)
+			z.scaleX_YCbCr(tmp, src, sr)
 		default:
-			z.scaleX_Image(tmp, src, sp)
+			z.scaleX_Image(tmp, src, sr)
 		}
 	}
 
 	switch dst := dst.(type) {
 	case *image.RGBA:
-		z.scaleY_RGBA(dst, dp, adr, tmp)
+		z.scaleY_RGBA(dst, dr, adr, tmp)
 	default:
-		z.scaleY_Image(dst, dp, adr, tmp)
+		z.scaleY_Image(dst, dr, adr, tmp)
 	}
 }
 
-func (z *kernelScaler) scaleX_Gray(tmp [][4]float64, src *image.Gray, sp image.Point) {
+func (z *kernelScaler) scaleX_Gray(tmp [][4]float64, src *image.Gray, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pru, pgu, pbu, pau := src.At(sp.X+int(c.coord), sp.Y+int(y)).RGBA()
+				pru, pgu, pbu, pau := src.At(sr.Min.X+int(c.coord), sr.Min.Y+int(y)).RGBA()
 				pr += float64(pru) * c.weight
 				pg += float64(pgu) * c.weight
 				pb += float64(pbu) * c.weight
@@ -786,13 +823,13 @@
 	}
 }
 
-func (z *kernelScaler) scaleX_NRGBA(tmp [][4]float64, src *image.NRGBA, sp image.Point) {
+func (z *kernelScaler) scaleX_NRGBA(tmp [][4]float64, src *image.NRGBA, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pru, pgu, pbu, pau := src.At(sp.X+int(c.coord), sp.Y+int(y)).RGBA()
+				pru, pgu, pbu, pau := src.At(sr.Min.X+int(c.coord), sr.Min.Y+int(y)).RGBA()
 				pr += float64(pru) * c.weight
 				pg += float64(pgu) * c.weight
 				pb += float64(pbu) * c.weight
@@ -809,13 +846,13 @@
 	}
 }
 
-func (z *kernelScaler) scaleX_RGBA(tmp [][4]float64, src *image.RGBA, sp image.Point) {
+func (z *kernelScaler) scaleX_RGBA(tmp [][4]float64, src *image.RGBA, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pi := src.PixOffset(sp.X+int(c.coord), sp.Y+int(y))
+				pi := src.PixOffset(sr.Min.X+int(c.coord), sr.Min.Y+int(y))
 				pru := uint32(src.Pix[pi+0]) * 0x101
 				pgu := uint32(src.Pix[pi+1]) * 0x101
 				pbu := uint32(src.Pix[pi+2]) * 0x101
@@ -836,13 +873,13 @@
 	}
 }
 
-func (z *kernelScaler) scaleX_Uniform(tmp [][4]float64, src *image.Uniform, sp image.Point) {
+func (z *kernelScaler) scaleX_Uniform(tmp [][4]float64, src *image.Uniform, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pru, pgu, pbu, pau := src.At(sp.X+int(c.coord), sp.Y+int(y)).RGBA()
+				pru, pgu, pbu, pau := src.At(sr.Min.X+int(c.coord), sr.Min.Y+int(y)).RGBA()
 				pr += float64(pru) * c.weight
 				pg += float64(pgu) * c.weight
 				pb += float64(pbu) * c.weight
@@ -859,13 +896,13 @@
 	}
 }
 
-func (z *kernelScaler) scaleX_YCbCr(tmp [][4]float64, src *image.YCbCr, sp image.Point) {
+func (z *kernelScaler) scaleX_YCbCr(tmp [][4]float64, src *image.YCbCr, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pru, pgu, pbu, pau := src.At(sp.X+int(c.coord), sp.Y+int(y)).RGBA()
+				pru, pgu, pbu, pau := src.At(sr.Min.X+int(c.coord), sr.Min.Y+int(y)).RGBA()
 				pr += float64(pru) * c.weight
 				pg += float64(pgu) * c.weight
 				pb += float64(pbu) * c.weight
@@ -882,13 +919,13 @@
 	}
 }
 
-func (z *kernelScaler) scaleX_Image(tmp [][4]float64, src image.Image, sp image.Point) {
+func (z *kernelScaler) scaleX_Image(tmp [][4]float64, src image.Image, sr image.Rectangle) {
 	t := 0
 	for y := int32(0); y < z.sh; y++ {
 		for _, s := range z.horizontal.sources {
 			var pr, pg, pb, pa float64
 			for _, c := range z.horizontal.contribs[s.i:s.j] {
-				pru, pgu, pbu, pau := src.At(sp.X+int(c.coord), sp.Y+int(y)).RGBA()
+				pru, pgu, pbu, pau := src.At(sr.Min.X+int(c.coord), sr.Min.Y+int(y)).RGBA()
 				pr += float64(pru) * c.weight
 				pg += float64(pgu) * c.weight
 				pb += float64(pbu) * c.weight
@@ -905,9 +942,9 @@
 	}
 }
 
-func (z *kernelScaler) scaleY_RGBA(dst *image.RGBA, dp image.Point, adr image.Rectangle, tmp [][4]float64) {
+func (z *kernelScaler) scaleY_RGBA(dst *image.RGBA, dr, adr image.Rectangle, tmp [][4]float64) {
 	for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
-		d := dst.PixOffset(dp.X+int(dx), dp.Y+adr.Min.Y)
+		d := dst.PixOffset(dr.Min.X+int(dx), dr.Min.Y+adr.Min.Y)
 		for _, s := range z.vertical.sources[adr.Min.Y:adr.Max.Y] {
 			var pr, pg, pb, pa float64
 			for _, c := range z.vertical.contribs[s.i:s.j] {
@@ -926,7 +963,7 @@
 	}
 }
 
-func (z *kernelScaler) scaleY_Image(dst Image, dp image.Point, adr image.Rectangle, tmp [][4]float64) {
+func (z *kernelScaler) scaleY_Image(dst Image, dr, adr image.Rectangle, tmp [][4]float64) {
 	dstColorRGBA64 := &color.RGBA64{}
 	dstColor := color.Color(dstColorRGBA64)
 	for dx := int32(adr.Min.X); dx < int32(adr.Max.X); dx++ {
@@ -943,7 +980,7 @@
 			dstColorRGBA64.G = ftou(pg * s.invTotalWeight)
 			dstColorRGBA64.B = ftou(pb * s.invTotalWeight)
 			dstColorRGBA64.A = ftou(pa * s.invTotalWeight)
-			dst.Set(dp.X+int(dx), dp.Y+int(adr.Min.Y+dy), dstColor)
+			dst.Set(dr.Min.X+int(dx), dr.Min.Y+int(adr.Min.Y+dy), dstColor)
 		}
 	}
 }
diff --git a/draw/scale.go b/draw/scale.go
index 53ec801..9f8cdd4 100644
--- a/draw/scale.go
+++ b/draw/scale.go
@@ -6,16 +6,25 @@
 
 package draw
 
-// TODO: should Scale and NewScaler also take an Op argument?
+// TODO: add an Options type a la
+// https://groups.google.com/forum/#!topic/golang-dev/fgn_xM0aeq4
 
 import (
 	"image"
 	"math"
 )
 
-// Scale scales the part of the source image defined by src and sr and writes
+// Scaler scales the part of the source image defined by src and sr and writes
 // to the part of the destination image defined by dst and dr.
 //
+// A Scaler is safe to use concurrently.
+type Scaler interface {
+	Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle)
+}
+
+// Interpolator is an interpolation algorithm, when dst and src pixels don't
+// have a 1:1 correspondance.
+//
 // Of the interpolators provided by this package:
 //	- NearestNeighbor is fast but usually looks worst.
 //	- CatmullRom is slow but usually looks best.
@@ -24,23 +33,9 @@
 // The time taken depends on the size of dr. For kernel interpolators, the
 // speed also depends on the size of sr, and so are often slower than
 // non-kernel interpolators, especially when scaling down.
-func Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle, q Interpolator) {
-	q.NewScaler(int32(dr.Dx()), int32(dr.Dy()), int32(sr.Dx()), int32(sr.Dy())).Scale(dst, dr.Min, src, sr.Min)
-}
-
-// Scaler scales part of a source image, starting from sp, and writes to a
-// destination image, starting from dp. The destination and source width and
-// heights are pre-determined, as part of the Scaler.
-//
-// A Scaler is safe to use concurrently.
-type Scaler interface {
-	Scale(dst Image, dp image.Point, src image.Image, sp image.Point)
-}
-
-// Interpolator creates scalers for a given destination and source width and
-// heights.
 type Interpolator interface {
-	NewScaler(dw, dh, sw, sh int32) Scaler
+	Scaler
+	// TODO: Transformer
 }
 
 // Kernel is an interpolator that blends source pixels weighted by a symmetric
@@ -54,15 +49,22 @@
 	At func(t float64) float64
 }
 
-// NewScaler implements the Interpolator interface.
-func (k *Kernel) NewScaler(dw, dh, sw, sh int32) Scaler {
+// Scale implements the Scaler interface.
+func (k *Kernel) Scale(dst Image, dr image.Rectangle, src image.Image, sr image.Rectangle) {
+	k.NewScaler(dr.Dx(), dr.Dy(), sr.Dx(), sr.Dy()).Scale(dst, dr, src, sr)
+}
+
+// NewScaler returns a Scaler that is optimized for scaling multiple times with
+// the same fixed destination and source width and height.
+func (k *Kernel) NewScaler(dw, dh, sw, sh int) Scaler {
 	return &kernelScaler{
-		dw:         dw,
-		dh:         dh,
-		sw:         sw,
-		sh:         sh,
-		horizontal: newDistrib(k, dw, sw),
-		vertical:   newDistrib(k, dh, sh),
+		kernel:     k,
+		dw:         int32(dw),
+		dh:         int32(dh),
+		sw:         int32(sw),
+		sh:         int32(sh),
+		horizontal: newDistrib(k, int32(dw), int32(sw)),
+		vertical:   newDistrib(k, int32(dh), int32(sh)),
 	}
 }
 
@@ -107,21 +109,10 @@
 
 type nnInterpolator struct{}
 
-func (nnInterpolator) NewScaler(dw, dh, sw, sh int32) Scaler { return &nnScaler{dw, dh, sw, sh} }
-
-type nnScaler struct {
-	dw, dh, sw, sh int32
-}
-
 type ablInterpolator struct{}
 
-func (ablInterpolator) NewScaler(dw, dh, sw, sh int32) Scaler { return &ablScaler{dw, dh, sw, sh} }
-
-type ablScaler struct {
-	dw, dh, sw, sh int32
-}
-
 type kernelScaler struct {
+	kernel               *Kernel
 	dw, dh, sw, sh       int32
 	horizontal, vertical distrib
 }
diff --git a/draw/scale_test.go b/draw/scale_test.go
index c7c6ef2..8bc5a4b 100644
--- a/draw/scale_test.go
+++ b/draw/scale_test.go
@@ -47,7 +47,7 @@
 		gotFilename := fmt.Sprintf("../testdata/go-turns-two-%s-%s.png", direction, name)
 
 		got := image.NewRGBA(image.Rect(0, 0, w, h))
-		Scale(got, got.Bounds(), src, src.Bounds(), q)
+		q.Scale(got, got.Bounds(), src, src.Bounds())
 		if *genScaleFiles {
 			g, err := os.Create(gotFilename)
 			if err != nil {
@@ -112,12 +112,12 @@
 		}
 
 		// Scale then clip.
-		Scale(dst0, outer, src, src.Bounds(), q)
+		q.Scale(dst0, outer, src, src.Bounds())
 		dst0 = dst0.SubImage(inner).(*image.RGBA)
 
 		// Clip then scale.
 		dst1 = dst1.SubImage(inner).(*image.RGBA)
-		Scale(dst1, outer, src, src.Bounds(), q)
+		q.Scale(dst1, outer, src, src.Bounds())
 
 	loop:
 		for y := inner.Min.Y; y < inner.Max.Y; y++ {
@@ -187,8 +187,8 @@
 					dst1 := image.NewRGBA(drs[0])
 					Draw(dst0, dst0.Bounds(), blue, image.Point{}, Src)
 					Draw(dstWrapper{dst1}, dst1.Bounds(), srcWrapper{blue}, image.Point{}, Src)
-					Scale(dst0, dr, src, sr, q)
-					Scale(dstWrapper{dst1}, dr, srcWrapper{src}, sr, q)
+					q.Scale(dst0, dr, src, sr)
+					q.Scale(dstWrapper{dst1}, dr, srcWrapper{src}, sr)
 					if !bytes.Equal(dst0.Pix, dst1.Pix) {
 						t.Errorf("pix differ for dr=%v, src=%T, sr=%v, q=%T", dr, src, sr, q)
 					}
@@ -260,11 +260,16 @@
 		b.Fatal(err)
 	}
 	dr, sr := dst.Bounds(), src.Bounds()
-	scaler := q.NewScaler(int32(dr.Dx()), int32(dr.Dy()), int32(sr.Dx()), int32(sr.Dy()))
+	scaler := Scaler(q)
+	if n, ok := q.(interface {
+		NewScaler(int, int, int, int) Scaler
+	}); ok {
+		scaler = n.NewScaler(dr.Dx(), dr.Dy(), sr.Dx(), sr.Dy())
+	}
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		scaler.Scale(dst, dr.Min, src, sr.Min)
+		scaler.Scale(dst, dr, src, sr)
 	}
 }