title: printf in GLSL?
body: <p>In C, I can debug code like:</p>
  
  <pre><code>fprintf(stderr, "blah: %f", some_var);
  </code></pre>
  
  <p>in GLSL ... is there anyway for me to just dump out a value in a Vertex or Fragment shader? I don't care if it's slow; I just want to dump out the value. Ideally, I want a setup like the following:</p>
  
  <ul>
  <li>normal state = run GLSL shader normally</li>
  <li>press key 'd' = next frame is generated in <em>ULTRA</em> slow mode, where the "printfs" in the
  Vertex/Fragment shader are executed and dumped out.</li>
  </ul>
  
  <p>Is this feasible? (I don't care about performance; I just want to do this for one frame).</p>
  
  <p>Thanks!</p>