title: efficient texel access in OpenGL
body: <p>I'm working on a game in OpenGL and here's what I'd like to do:</p>
  
  <ol>
  <li>During an iteration of game logic, access texels of a texture for computations.</li>
  <li>Still during the same logic interation, possibly modify the texels of the texture.</li>
  <li>Render the game scene with the current version of the texture.</li>
  <li>Start another iteration with similar access to texel data.</li>
  </ol>
  
  <p>I'm having trouble using glGetTexImage() in that the call crashes my program, and I'm not entirely sure this is what I want to be using anyway.</p>
  
  <p>The only straightforward way I can see to do this is to have a buffer in system memory with texel information that I can mess around with, and generate a new OpenGL texture from it every iteration.  That seems like a bad move.</p>
  
  <p>Any help?</p>