}
	dx := r.Min.X - orig.X
	dy := r.Min.Y - orig.Y
	if dx == 0 && dy == 0 {
		return
	}
	sp.X += dx
	sp.Y += dy
	if mp != nil {
		mp.X += dx
		mp.Y += dy
	}
}

func processBackward(dst image.Image, r image.Rectangle, src image.Image, sp image.Point) bool {
	return dst == src &&
		r.Overlaps(r.Add(sp.Sub(r.Min))) &&
		(sp.Y < r.Min.Y || (sp.Y == r.Min.Y && sp.X < r.Min.X))
}