ndx) => {
      const speed = 1 + ndx * .1;
      const rot = time * speed;
      cube.rotation.x = rot;
      cube.rotation.y = rot;
    });

    // draw render target scene to render target
    renderer.setRenderTarget(renderTarget);
    renderer.render(rtScene, rtCamera);
    renderer.setRenderTarget(null);

    // rotate the cube in the scene
    cube.rotation.x = time;
    cube.rotation.y = time * 1.1;

    // render the scene to the canvas
    renderer.render(scene, camera);

    requestAnimationFrame