colorm.go
func (c *ColorM) Scale(r, g, b, a float64) {
	c.impl = c.impl.Scale(float32(r), float32(g), float32(b), float32(a))
}
func (c *ColorM) Scale(r, g, b, a float64) {
	c.impl = c.impl.Scale(float32(r), float32(g), float32(b), float32(a))
}
// Scale scales the matrix by (r, g, b, a).