image: add type-specific Set methods and use them when decoding PNG.

This speeds up PNG decode about 20% by avoiding per-pixel interface conversions.

R=nigeltao, rsc
CC=golang-dev
https://golang.org/cl/4428080

src/pkg/image/image.go

@@ -51,6 +51,13 @@ func (p *RGBA) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toRGBAColor(c).(RGBAColor)
 }
 
+func (p *RGBA) SetRGBA(x, y int, c RGBAColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA) Opaque() bool {
 	if p.Rect.Empty() {
@@ -103,6 +110,13 @@ func (p *RGBA64) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toRGBA64Color(c).(RGBA64Color)
 }
 
+func (p *RGBA64) SetRGBA64(x, y int, c RGBA64Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *RGBA64) Opaque() bool {
 	if p.Rect.Empty() {
@@ -155,6 +169,13 @@ func (p *NRGBA) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toNRGBAColor(c).(NRGBAColor)
 }
 
+func (p *NRGBA) SetNRGBA(x, y int, c NRGBAColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA) Opaque() bool {
 	if p.Rect.Empty() {
@@ -207,6 +228,13 @@ func (p *NRGBA64) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toNRGBA64Color(c).(NRGBA64Color)
 }
 
+func (p *NRGBA64) SetNRGBA64(x, y int, c NRGBA64Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *NRGBA64) Opaque() bool {
 	if p.Rect.Empty() {
@@ -252,11 +280,11 @@ func (p *Alpha) At(x, y int) Color {
 	return p.Pix[y*p.Stride+x]
 }
 
-func (p *Alpha) Set(x, y int, c Color) {
+func (p *Alpha) SetAlpha(x, y int, c AlphaColor) {
 	if !p.Rect.Contains(Point{x, y}) {
 		return
 	}
-	p.Pix[y*p.Stride+x] = toAlphaColor(c).(AlphaColor)
+	p.Pix[y*p.Stride+x] = c
 }
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
@@ -311,6 +339,13 @@ func (p *Alpha16) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toAlpha16Color(c).(Alpha16Color)
 }
 
+func (p *Alpha16) SetAlpha16(x, y int, c Alpha16Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Alpha16) Opaque() bool {
 	if p.Rect.Empty() {
@@ -363,6 +398,13 @@ func (p *Gray) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toGrayColor(c).(GrayColor)
 }
 
+func (p *Gray) SetGray(x, y int, c GrayColor) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Gray) Opaque() bool {
 	return true
@@ -401,6 +443,13 @@ func (p *Gray16) Set(x, y int, c Color) {
 	p.Pix[y*p.Stride+x] = toGray16Color(c).(Gray16Color)
 }
 
+func (p *Gray16) SetGray16(x, y int, c Gray16Color) {
+	if !p.Rect.Contains(Point{x, y}) {
+		return
+	}
+	p.Pix[y*p.Stride+x] = c
+}
+
 // Opaque scans the entire image and returns whether or not it is fully opaque.
 func (p *Gray16) Opaque() bool {
 	return true

src/pkg/image/png/reader.go

@@ -378,7 +378,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 8 {
 				b := cdat[x/8]
 				for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 7) * 0xff})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 7) * 0xff})
 					b <<= 1
 				}
 			}
@@ -386,7 +386,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 4 {
 				b := cdat[x/4]
 				for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 6) * 0x55})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 6) * 0x55})
 					b <<= 2
 				}
 			}
@@ -394,22 +394,22 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			for x := 0; x < d.width; x += 2 {
 				b := cdat[x/2]
 				for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
-					gray.Set(x+x2, y, image.GrayColor{(b >> 4) * 0x11})
+					gray.SetGray(x+x2, y, image.GrayColor{(b >> 4) * 0x11})
 					b <<= 4
 				}
 			}
 		case cbG8:
 			for x := 0; x < d.width; x++ {
-				gray.Set(x, y, image.GrayColor{cdat[x]})
+				gray.SetGray(x, y, image.GrayColor{cdat[x]})
 			}
 		case cbGA8:
 			for x := 0; x < d.width; x++ {
 				ycol := cdat[2*x+0]
-				nrgba.Set(x, y, image.NRGBAColor{ycol, ycol, ycol, cdat[2*x+1]})
+				nrgba.SetNRGBA(x, y, image.NRGBAColor{ycol, ycol, ycol, cdat[2*x+1]})
 			}
 		case cbTC8:
 			for x := 0; x < d.width; x++ {
-				rgba.Set(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
+				rgba.SetRGBA(x, y, image.RGBAColor{cdat[3*x+0], cdat[3*x+1], cdat[3*x+2], 0xff})
 			}
 		case cbP1:
 			for x := 0; x < d.width; x += 8 {
@@ -456,25 +456,25 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 			}
 		case cbTCA8:
 			for x := 0; x < d.width; x++ {
-				nrgba.Set(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
+				nrgba.SetNRGBA(x, y, image.NRGBAColor{cdat[4*x+0], cdat[4*x+1], cdat[4*x+2], cdat[4*x+3]})
 			}
 		case cbG16:
 			for x := 0; x < d.width; x++ {
 				ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
-				gray16.Set(x, y, image.Gray16Color{ycol})
+				gray16.SetGray16(x, y, image.Gray16Color{ycol})
 			}
 		case cbGA16:
 			for x := 0; x < d.width; x++ {
 				ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
 				acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
-				nrgba64.Set(x, y, image.NRGBA64Color{ycol, ycol, ycol, acol})
+				nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{ycol, ycol, ycol, acol})
 			}
 		case cbTC16:
 			for x := 0; x < d.width; x++ {
 				rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
 				gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
 				bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
-				rgba64.Set(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
+				rgba64.SetRGBA64(x, y, image.RGBA64Color{rcol, gcol, bcol, 0xffff})
 			}
 		case cbTCA16:
 			for x := 0; x < d.width; x++ {
@@ -482,7 +482,7 @@ func (d *decoder) idatReader(idat io.Reader) (image.Image, os.Error) {
 				gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
 				bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
 				acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
-				nrgba64.Set(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
+				nrgba64.SetNRGBA64(x, y, image.NRGBA64Color{rcol, gcol, bcol, acol})
 			}
 		}