fn rect_to_verts(rect: &Rect) -> [Vec2; 4] {
    [
        Vec2::new(rect.left(), rect.top()),
        Vec2::new(rect.right(), rect.top()),
        Vec2::new(rect.right(), rect.bottom()),
        Vec2::new(rect.left(), rect.bottom()),
    ]
}

fn build_shadow_mesh(walls: &[Rect], pov: Vec2) -> Mesh{
let mut meshbuilder = MeshBuilder::new();
for w in walls.iter(){
        for v in rect_to_verts(w).iter()
    }
}