pub struct Plane {
    pub p0: Point,
    pub normal: Vector3,
    pub color: Color,
}

pub enum Element {
    Sphere(Sphere),
    Plane(Plane),
}
impl Element {
    pub fn color(&self) -> &Color {
        match *self {
            Element::Sphere(ref s) => &s.color,
            Element::Plane(ref p) => &p.color,
        }
    }
}
impl Intersectable for Element {
    fn intersect(&self, ray: &Ray) -> Option<f64> {
        match *self {
            Element::Sphere(ref s) => s.intersect(ray),
            Element::Plane(ref p) => p.intersect(ray),
        }
    }
}
impl Intersectable for Plane {
    fn intersect(&self, ray: &Ray) -> Option<f64> {
        None
    }
}