ebiten: Remove copying pixels from ReplacePixels and copyImage (renamed to imageToBytes)

This optimization utilizes the fact that copying happens in the
'shareable' package to add paddings.

Updates #1222

export_test.go

@@ -15,5 +15,5 @@
 package ebiten
 
 var (
-	CopyImage = copyImage
+	ImageToBytes = imageToBytes
 )

image.go

@@ -540,7 +540,7 @@ func (i *Image) Dispose() error {
 // When the image is disposed, ReplacePixels does nothing.
 //
 // ReplacePixels always returns nil as of 1.5.0.
-func (i *Image) ReplacePixels(pix []byte) error {
+func (i *Image) ReplacePixels(pixels []byte) error {
 	i.copyCheck()
 
 	if i.isDisposed() {
@@ -548,12 +548,10 @@ func (i *Image) ReplacePixels(pix []byte) error {
 	}
 	r := i.Bounds()
 
-	// Copy the pixels as restorable package might reuse the pixels later.
-	// TODO: Would it be possible to avoid copying? (#1222)
-	copied := make([]byte, len(pix))
-	copy(copied, pix)
-
-	if err := i.buffered.ReplacePixels(copied, r.Min.X, r.Min.Y, r.Dx(), r.Dy()); err != nil {
+	// Do not need to copy pixels here.
+	// * In internal/buffered, pixels are copied when necessary.
+	// * In internal/shareable, pixels are copied to make its paddings.
+	if err := i.buffered.ReplacePixels(pixels, r.Min.X, r.Min.Y, r.Dx(), r.Dy()); err != nil {
 		theUIContext.setError(err)
 	}
 	return nil
@@ -637,10 +635,7 @@ func NewImageFromImage(source image.Image, filter Filter) (*Image, error) {
 	}
 	i.addr = i
 
-	// Call (*buffered.Image).ReplacePixels directly to avoid copying.
-	if err := i.buffered.ReplacePixels(copyImage(source), 0, 0, width, height); err != nil {
-		theUIContext.setError(err)
-	}
+	i.ReplacePixels(imageToBytes(source))
 	return i, nil
 }
 

imagetobytes.go

@@ -20,17 +20,20 @@ import (
 	"image/draw"
 )
 
-// copyImage copies img to a new RGBA image.
+// imageToBytes gets RGBA bytes from img.
 //
-// Basically copyImage just calls draw.Draw.
+// Basically imageToBytes just calls draw.Draw.
 // If img is a paletted image, an optimized copying method is used.
-func copyImage(img image.Image) []byte {
+//
+// If img is *image.RGBA and its length is same as 4*width*height, imageToBytes returns its Pix.
+func imageToBytes(img image.Image) []byte {
 	size := img.Bounds().Size()
 	w, h := size.X, size.Y
-	bs := make([]byte, 4*w*h)
 
 	switch img := img.(type) {
 	case *image.Paletted:
+		bs := make([]byte, 4*w*h)
+
 		b := img.Bounds()
 		x0 := b.Min.X
 		y0 := b.Min.Y
@@ -61,13 +64,27 @@ func copyImage(img image.Image) []byte {
 			}
 			idx0 += d
 		}
-	default:
-		dstImg := &image.RGBA{
-			Pix:    bs,
-			Stride: 4 * w,
-			Rect:   image.Rect(0, 0, w, h),
+		return bs
+	case *image.RGBA:
+		if len(img.Pix) == 4*w*h {
+			return img.Pix
 		}
-		draw.Draw(dstImg, image.Rect(0, 0, w, h), img, img.Bounds().Min, draw.Src)
+		return imageToBytesSlow(img)
+	default:
+		return imageToBytesSlow(img)
 	}
+}
+
+func imageToBytesSlow(img image.Image) []byte {
+	size := img.Bounds().Size()
+	w, h := size.X, size.Y
+	bs := make([]byte, 4*w*h)
+
+	dstImg := &image.RGBA{
+		Pix:    bs,
+		Stride: 4 * w,
+		Rect:   image.Rect(0, 0, w, h),
+	}
+	draw.Draw(dstImg, image.Rect(0, 0, w, h), img, img.Bounds().Min, draw.Src)
 	return bs
 }

imagetobytes_test.go

@@ -24,7 +24,7 @@ import (
 	. "github.com/hajimehoshi/ebiten"
 )
 
-func TestCopyImage(t *testing.T) {
+func TestImageToBytes(t *testing.T) {
 	pal := make(color.Palette, 256)
 	for i := range pal {
 		pal[i] = color.White
@@ -93,7 +93,7 @@ func TestCopyImage(t *testing.T) {
 		},
 	}
 	for i, c := range cases {
-		got := CopyImage(c.In)
+		got := ImageToBytes(c.In)
 		want := c.Out
 		if !bytes.Equal(got, want) {
 			t.Errorf("Test %d: got: %v, want: %v", i, got, want)
@@ -101,26 +101,26 @@ func TestCopyImage(t *testing.T) {
 	}
 }
 
-func BenchmarkCopyImageRGBA(b *testing.B) {
+func BenchmarkImageToBytesRGBA(b *testing.B) {
 	img := image.NewRGBA(image.Rect(0, 0, 4096, 4096))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		CopyImage(img)
+		ImageToBytes(img)
 	}
 }
 
-func BenchmarkCopyImageNRGBA(b *testing.B) {
+func BenchmarkImageToBytesNRGBA(b *testing.B) {
 	img := image.NewNRGBA(image.Rect(0, 0, 4096, 4096))
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		CopyImage(img)
+		ImageToBytes(img)
 	}
 }
 
-func BenchmarkCopyImagePaletted(b *testing.B) {
+func BenchmarkImageToBytesPaletted(b *testing.B) {
 	img := image.NewPaletted(image.Rect(0, 0, 4096, 4096), palette.Plan9)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		CopyImage(img)
+		ImageToBytes(img)
 	}
 }

internal/buffered/image.go

@@ -192,8 +192,10 @@ func (i *Image) ReplacePixels(pix []byte, x, y, width, height int) error {
 	}
 
 	if maybeCanAddDelayedCommand() {
+		copied := make([]byte, len(pix))
+		copy(copied, pix)
 		if tryAddDelayedCommand(func() error {
-			i.ReplacePixels(pix, x, y, width, height)
+			i.ReplacePixels(copied, x, y, width, height)
 			return nil
 		}) {
 			return nil