title: OpenGL framebuffer post processing
body: <p>I'm trying to apply a simple vignette effect to my scene using a framebuffer and offscreen rendering. I was able to get the FBO and the effect working but for some reason my scene is not appearing at all. When the scene loads I can see the objects for a split second then it just goes "blank" (check attached gif). My understanding is that the scene is rendered into the FBO correctly (otherwise it wouldn't be visible at all, not even for a short time), but for some reason it is wiped out by something.</p>
  
  <p>Source files: gist.github.com/morcmarc/31a02dbbd9aad2955f47</p>
  
  <p><a href="http://postimg.org/image/wvhuestr3/" rel="nofollow">http://postimg.org/image/wvhuestr3/</a></p>
  
  <p>For comparison, this is how it looks rendered directly onto the built-in framebuffer. Just to show the scene seems to be rendering properly.</p>
  
  <p><a href="http://postimg.org/image/jegkle3z9/" rel="nofollow">http://postimg.org/image/jegkle3z9/</a></p>