fn voxel_aabb(v:Pnt3i)->(Pnt3f,Pnt3f) {
        ((v.cast().unwrap()-Vec3f::new(-0.5,-0.5,-0.5))*GRID_SIZE,
        (v.cast().unwrap()+Vec3f::new(0.5,0.5,0.5))*GRID_SIZE)
    }