title: Forge Viewer rendering pipeline
body: <p>In the latest release of <code>THREE.js</code>, Mesh can implement following callback in order to hook into the rendering pipeline: </p>
  
  <pre><code>this.onBeforeRender = function (renderer, scene, camera ) {
     ..
  }
  </code></pre>
  
  <p>Is there any way to achieve a similar logic in the current implementation of the viewer?</p>