code: function animate() {
      // render
      controls.update();
  
      if (ready) {
        renderer.render(sceneRTT, camera, rtTexture, true);
        renderer.render(sceneScreen, camera);
      }
  
      stats.update();
  
      // request new frame
      requestAnimationFrame(function() {
        animate();
      });
    }
docs: this function is executed on each animation frame