func PopAttributes() {
	if len(canvas.attrStack) == 0 {
		return
	}
	a := canvas.attrStack[len(canvas.attrStack)-1]
	canvas.attrStack = canvas.attrStack[:len(canvas.attrStack)-1]
	SetTextColor(a.text)
	SetBackColor(a.back)
}
func PopAttributes() {
	if len(canvas.attrStack) == 0 {
		return
	}
	a := canvas.attrStack[len(canvas.attrStack)-1]
	canvas.attrStack = canvas.attrStack[:len(canvas.attrStack)-1]
	SetTextColor(a.text)
	SetBackColor(a.back)
}
// PopAttributes restores saved with PushAttributes colors. Function does
// nothing if there is no saved colors