title: use core-image in 3d
body: <p>i have a working <code>Core Video</code> setup (a frame captured from a USB camera via <code>QTKit</code>) and the current frame is rendered as a texture on an arbitary plane in 3d space in a subclassed <code>NSOpenGLView</code>. so far so good but i would like to use some <code>Core Image</code> filter on this frame.
  i now have the basic code setup and it renders my unprocessed video frame like before, but the final processed output <code>CIImage</code> is rendererd as a screen aligned quad into the view. it feels like a image blitted over my 3d rendering. this is what i do not want!</p>
  
  <p>i am looking for a way to process my video frame (a <code>CVOpenGLTextureRef</code>) with <code>Core Image</code> and just render the resulting image on my plane in 3d.
  do i have to use offscreen rendering (store viewport, set new viewport and modelview and perspective matrices and render into a FBO) or is there any easier way?</p>
  
  <p>thanks in advance!</p>