title: How to render the same scene with different cameras in three.js?
body: <p>I had a scene set up and I want two cameras watch the same scene at a different angle, front &amp;  back. 
  I tried something like this:</p>
  
  <pre><code>renderer.setViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT/2);
  renderer.render(scene, camera);
  
  renderer.setViewport(0, SCREEN_HEIGHT/2, SCREEN_WIDTH, SCREEN_HEIGHT/2);
  renderer.render(scene, testcamera);
  </code></pre>
  
  <p>But the 2nd view which is back never showed up.
  Any idea why?</p>