buffered: Bug fix: Copying pixels failed for the delayed commands

Fixes #1082

internal/buffered/image.go

@@ -199,9 +199,9 @@ func (i *Image) ReplacePixels(pix []byte) {
 	defer delayedCommandsM.Unlock()
 
 	if needsToDelayCommands {
+		copied := make([]byte, len(pix))
+		copy(copied, pix)
 		delayedCommands = append(delayedCommands, func() error {
-			copied := make([]byte, len(pix))
-			copy(copied, pix)
 			i.ReplacePixels(copied)
 			return nil
 		})
@@ -246,6 +246,9 @@ func (i *Image) drawImage(src *Image, bounds image.Rectangle, g *mipmap.GeoM, co
 	i.img.DrawImage(src.img, bounds, g, colorm, mode, filter)
 }
 
+// DrawTriangles draws the src image with the given vertices.
+//
+// Copying vertices and indices is the caller's responsibility.
 func (i *Image) DrawTriangles(src *Image, vertices []float32, indices []uint16, colorm *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address) {
 	if i == src {
 		panic("buffered: Image.DrawTriangles: src must be different from the receiver")
@@ -256,6 +259,7 @@ func (i *Image) DrawTriangles(src *Image, vertices []float32, indices []uint16,
 
 	if needsToDelayCommands {
 		delayedCommands = append(delayedCommands, func() error {
+			// Arguments are not copied. Copying is the caller's responsibility.
 			i.DrawTriangles(src, vertices, indices, colorm, mode, filter, address)
 			return nil
 		})

internal/buffered/image_test.go

@@ -246,3 +246,43 @@ func TestSetAndReplacePixelsBeforeMain(t *testing.T) {
 		t.Errorf("got: %v, want: %v", got, want)
 	}
 }
+
+var testReplacePixelsAndModifyBeforeMainResult = func() testResult {
+	img, _ := ebiten.NewImage(16, 16, ebiten.FilterDefault)
+	pix := make([]byte, 4*16*16)
+	for i := 0; i < len(pix)/4; i++ {
+		pix[4*i] = 1
+		pix[4*i+1] = 2
+		pix[4*i+2] = 3
+		pix[4*i+3] = 4
+	}
+	img.ReplacePixels(pix)
+	// After calling ReplacePixels, modifying pix must not affect the result.
+	for i := 0; i < len(pix)/4; i++ {
+		pix[4*i] = 5
+		pix[4*i+1] = 6
+		pix[4*i+2] = 7
+		pix[4*i+3] = 8
+	}
+
+	ch := make(chan color.RGBA, 1)
+	go func() {
+		runOnMainThread(func() {
+			ch <- img.At(0, 0).(color.RGBA)
+		})
+	}()
+
+	return testResult{
+		want: color.RGBA{1, 2, 3, 4},
+		got:  ch,
+	}
+}()
+
+func TestReplacePixelsAndModifyBeforeMain(t *testing.T) {
+	got := <-testReplacePixelsAndModifyBeforeMainResult.got
+	want := testReplacePixelsAndModifyBeforeMainResult.want
+
+	if got != want {
+		t.Errorf("got: %v, want: %v", got, want)
+	}
+}