graphicscommand: Remove copying pixels

Now ReplacePixels takes the ownership.

Updates #983

internal/graphicscommand/image.go

@@ -155,15 +155,17 @@ func (i *Image) Pixels() []byte {
 	return c.result
 }
 
-func (i *Image) ReplacePixels(p []byte, x, y, width, height int) {
+// ReplacePixels replaces the pixels on the given region.
+//
+// ReplacePixels takes the ownership of pixels. This means that pixels must not be modified after calling
+// ReplacePixels.
+func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 	// ReplacePixels for a part might invalidate the current image that are drawn by DrawTriangles (#593, #738).
 	if i.lastCommand == lastCommandDrawTriangles {
 		if x != 0 || y != 0 || i.width != width || i.height != height {
 			panic("graphicscommand: ReplacePixels for a part after DrawTriangles is forbidden")
 		}
 	}
-	pixels := make([]byte, len(p))
-	copy(pixels, p)
 	c := &replacePixelsCommand{
 		dst:    i,
 		pixels: pixels,

internal/restorable/image.go

@@ -328,6 +328,13 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 	// For this purpuse, images should remember which part of that is used for DrawTriangles.
 	theImages.makeStaleIfDependingOn(i)
 
+	// pixels are taken by graphicscommand.Image. Copy it for the later usage.
+	var copied []byte
+	if needsRestoring() && pixels != nil {
+		copied = make([]byte, len(pixels))
+		copy(copied, pixels)
+	}
+
 	if pixels != nil {
 		i.image.ReplacePixels(pixels, x, y, width, height)
 	} else {
@@ -337,14 +344,20 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 		i.image.ReplacePixels(make([]byte, 4*width*height), x, y, width, height)
 	}
 
+	// pixels are no longer available. Use copied when necessary.
+
 	if x == 0 && y == 0 && width == w && height == h {
+		i.drawTrianglesHistory = nil
+		i.stale = false
 		if pixels != nil {
-			i.basePixels.AddOrReplace(pixels, 0, 0, w, h)
+			if needsRestoring() {
+				i.basePixels.AddOrReplace(copied, 0, 0, w, h)
+			} else {
+				i.makeStale()
+			}
 		} else {
 			i.basePixels.Remove(0, 0, w, h)
 		}
-		i.drawTrianglesHistory = nil
-		i.stale = false
 		return
 	}
 
@@ -361,7 +374,11 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 	}
 
 	if pixels != nil {
-		i.basePixels.AddOrReplace(pixels, x, y, width, height)
+		if needsRestoring() {
+			i.basePixels.AddOrReplace(copied, x, y, width, height)
+		} else {
+			i.makeStale()
+		}
 	} else {
 		i.basePixels.Remove(x, y, width, height)
 	}

internal/restorable/images_test.go

@@ -829,3 +829,70 @@ func TestMutateSlices(t *testing.T) {
 		}
 	}
 }
+
+func TestReplacePixelsAndModify(t *testing.T) {
+	const w, h = 16, 16
+	img := NewImage(w, h, false)
+
+	pix := make([]byte, 4*w*h)
+	for i := 0; i < w*h; i++ {
+		pix[4*i] = byte(i)
+		pix[4*i+1] = byte(i)
+		pix[4*i+2] = byte(i)
+		pix[4*i+3] = byte(i)
+	}
+	img.ReplacePixels(pix, 0, 0, w, h)
+
+	// Modify pix after ReplacePixels
+	for i := 0; i < w*h; i++ {
+		pix[4*i] = 0
+		pix[4*i+1] = 0
+		pix[4*i+2] = 0
+		pix[4*i+3] = 0
+	}
+
+	for i := 0; i < w*h; i++ {
+		want := color.RGBA{byte(i), byte(i), byte(i), byte(i)}
+		r, g, b, a := img.At(i%w, i/w)
+		got := color.RGBA{r, g, b, a}
+		if got != want {
+			t.Errorf("At(%d, %d): got: %v, want: %v", i%w, i/w, got, want)
+		}
+	}
+}
+
+func TestReplacePixelsPartAndModify(t *testing.T) {
+	const w, h = 16, 16
+	const w2, h2 = 8, 8
+	img := NewImage(w, h, false)
+
+	pix := make([]byte, 4*w2*h2)
+	for i := 0; i < w2*h2; i++ {
+		pix[4*i] = byte(i)
+		pix[4*i+1] = byte(i)
+		pix[4*i+2] = byte(i)
+		pix[4*i+3] = byte(i)
+	}
+	img.ReplacePixels(pix, 4, 4, w2, h2)
+
+	// Modify pix after ReplacePixels
+	for i := 0; i < w2*h2; i++ {
+		pix[4*i] = 0
+		pix[4*i+1] = 0
+		pix[4*i+2] = 0
+		pix[4*i+3] = 0
+	}
+
+	idx := 0
+	for j := 4; j < 4+h2; j++ {
+		for i := 4; i < 4+w2; i++ {
+			want := color.RGBA{byte(idx), byte(idx), byte(idx), byte(idx)}
+			r, g, b, a := img.At(i, j)
+			got := color.RGBA{r, g, b, a}
+			if got != want {
+				t.Errorf("At(%d, %d): got: %v, want: %v", i, j, got, want)
+			}
+			idx++
+		}
+	}
+}

internal/restorable/rect.go

@@ -28,6 +28,7 @@ type rectToPixels struct {
 	lastPix []byte
 }
 
+// addOrReplace takes the ownership of pixels.
 func (rtp *rectToPixels) addOrReplace(pixels []byte, x, y, width, height int) {
 	if len(pixels) != 4*width*height {
 		panic(fmt.Sprintf("restorable: len(pixels) must be %d but %d", 4*width*height, len(pixels)))
@@ -37,16 +38,13 @@ func (rtp *rectToPixels) addOrReplace(pixels []byte, x, y, width, height int) {
 		rtp.m = map[image.Rectangle][]byte{}
 	}
 
-	copied := make([]byte, len(pixels))
-	copy(copied, pixels)
-
 	newr := image.Rect(x, y, x+width, y+height)
 	for r := range rtp.m {
 		if r == newr {
 			// Replace the region.
-			rtp.m[r] = copied
+			rtp.m[r] = pixels
 			if r == rtp.lastR {
-				rtp.lastPix = copied
+				rtp.lastPix = pixels
 			}
 			return
 		}
@@ -56,9 +54,9 @@ func (rtp *rectToPixels) addOrReplace(pixels []byte, x, y, width, height int) {
 	}
 
 	// Add the region.
-	rtp.m[newr] = copied
+	rtp.m[newr] = pixels
 	if newr == rtp.lastR {
-		rtp.lastPix = copied
+		rtp.lastPix = pixels
 	}
 }