title: glAccum (blur effect) working with with one graphics card but not the other
body: <p>I am trying to create a "blur" effect in my OpenGL game, whereby in certain sections I enable the following code and the vision blurs for a bit...</p>
  
  <pre><code>if(world-&gt;blur) {
      glAccum(GL_MULT, 0.85);
      glAccum(GL_ACCUM, 1- 0.85);
      glAccum(GL_RETURN, 1.0);
      glFlush();
  }
  </code></pre>
  
  <p>Which works fine when I am using my laptop's integrated chip, which often results in lower framerate, but if I enable the ATI gpu which gives me faster performance then the effect is not visible...</p>
  
  <p>I am using a fixed-time clock on my game:</p>
  
  <pre><code>tickTime += dt;
  if(tickTime &gt;= 1/DESIRED_FRAME_RATE) {
      level-&gt;update(tickTime);
      world-&gt;update(tickTime);
      renderer-&gt;drawScene(tickTime);
      tickTime = 0;
  }
  </code></pre>
  
  <p>Is there some obvious reason why this happens?</p>