title: Special case for deferred rendering
body: <p>I wonder if the following is possible:</p>
  
  <p>I want to render a scene in two passes. On the first pass detect the fragments that are actually visible and only those that are visible (i.e if I only have a single triangle that get's rasterized, any pixel not contained in the rasterization of the triangle is considered non visible).</p>
  
  <p>I then want to use this information on a second pass to produce a more complex image.</p>
  
  <p>The point here being, that not only do I want to ommit occluded fragments from the computation, I want to ommit anything that is not the result of rasterization.</p>
  
  <p>The end goal is simple, abuse this kind of shader to render a  geometry containing opaque and transparent geometry. The opaque geometry is considered non-existentt in the first pass and discarded.</p>
  
  <p>Generating a fragment map of only the first visible transparent fragments.</p>
  
  <p>I then use this information on a second pass to generate ray-traced colors based on the transparency.</p>
  
  <p>The goal being to reduce the number of fragments to only be the strict minimum necessary to actually trace the transparent geometry.</p>