canvas.go
func PushClip() {
	c := rect{x: canvas.clipX, y: canvas.clipY, w: canvas.clipW, h: canvas.clipH}
	canvas.clipStack = append(canvas.clipStack, c)
}
func PushClip() {
	c := rect{x: canvas.clipX, y: canvas.clipY, w: canvas.clipW, h: canvas.clipH}
	canvas.clipStack = append(canvas.clipStack, c)
}
// PushClip saves the current clipping window