graphicscommand: Remove CopyPixels command

This is an optimization. This change enables to avoid reading
pixels from GPU when extending an image.

Updates #897

internal/graphicscommand/command.go

@@ -361,45 +361,6 @@ func (c *replacePixelsCommand) CanMerge(dst, src *Image, color *affine.ColorM, m
 	return false
 }
 
-type copyPixelsCommand struct {
-	dst *Image
-	src *Image
-}
-
-func (c *copyPixelsCommand) String() string {
-	return fmt.Sprintf("copy-pixels: dst: %p <- src: %p", c.dst, c.src)
-}
-
-func (c *copyPixelsCommand) Exec(indexOffset int) error {
-	p, err := c.src.image.Pixels()
-	if err != nil {
-		return err
-	}
-	if c.dst.width < c.src.width || c.dst.height < c.src.height {
-		return fmt.Errorf("graphicscommand: the destination size (%d, %d) must include the source size (%d, %d)", c.dst.width, c.dst.height, c.src.width, c.src.height)
-	}
-	c.dst.image.ReplacePixels(p, 0, 0, c.src.width, c.src.height)
-	return nil
-}
-
-func (c *copyPixelsCommand) NumVertices() int {
-	return 0
-}
-
-func (c *copyPixelsCommand) NumIndices() int {
-	return 0
-}
-
-func (c *copyPixelsCommand) AddNumVertices(n int) {
-}
-
-func (c *copyPixelsCommand) AddNumIndices(n int) {
-}
-
-func (c *copyPixelsCommand) CanMerge(dst, src *Image, color *affine.ColorM, mode driver.CompositeMode, filter driver.Filter, address driver.Address) bool {
-	return false
-}
-
 type pixelsCommand struct {
 	result []byte
 	img    *Image

internal/graphicscommand/image.go

@@ -145,24 +145,6 @@ func (i *Image) ReplacePixels(p []byte, x, y, width, height int) {
 	i.lastCommand = lastCommandReplacePixels
 }
 
-// CopyPixels is basically same as Pixels and ReplacePixels, but reading pixels from GPU is done lazily.
-func (i *Image) CopyPixels(src *Image) {
-	if i.lastCommand == lastCommandDrawTriangles {
-		if i.width != src.width || i.height != src.height {
-			panic("graphicscommand: Copy for a part after DrawTriangles is forbidden")
-		}
-	}
-
-	c := &copyPixelsCommand{
-		dst: i,
-		src: src,
-	}
-	theCommandQueue.Enqueue(c)
-
-	// The execution is basically same as replacing pixels.
-	i.lastCommand = lastCommandReplacePixels
-}
-
 func (i *Image) IsInvalidated() bool {
 	if i.screen {
 		// The screen image might not have a texture, and in this case it is impossible to detect whether

internal/restorable/image.go

@@ -158,9 +158,9 @@ func (i *Image) Extend(width, height int) *Image {
 
 	newImg := NewImage(width, height)
 
-	// Do not use DrawTriangles here. ReplacePixels will be called on a part of newImg later, and it looked like
-	// ReplacePixels on a part of image deletes other region that are rendered by DrawTriangles (#593, #758).
-	newImg.image.CopyPixels(i.image)
+	if i.basePixels != nil && i.basePixels.pixels != nil {
+		newImg.image.ReplacePixels(i.basePixels.pixels, 0, 0, w, h)
+	}
 
 	// Copy basePixels.
 	newImg.basePixels = &Pixels{
@@ -359,6 +359,9 @@ func (i *Image) ReplacePixels(pixels []byte, x, y, width, height int) {
 		return
 	}
 
+	// It looked like ReplacePixels on a part of image deletes other region that are rendered by DrawTriangles
+	// (#593, #758).
+
 	if len(i.drawTrianglesHistory) > 0 {
 		panic("restorable: ReplacePixels for a part after DrawTriangles is forbidden")
 	}