title: Poor FPS performance with antialias:true in Threejs
body: <p>Whenever I enable antialias on the WebGL renderer, the FPS goes from 60 to about 25.</p>
  
  <pre><code>this.renderer = new THREE.WebGLRenderer({
      antialias: true
  });
  </code></pre>
  
  <p>This seemed to start occurring after I added multiple scenes and had to manually clear the depth. Of note I also hit 60 FPS on mobile safari just fine but not desktop or chrome.</p>
  
  <p>What might cause this?</p>