title: Ignore color output from within the shader
body: <p>Is it possible from within the shader to ignore colour output all together for a particular FBO color attachment?</p>
  
  <p>Something like this for example:</p>
  
  <pre><code>#version 330
  
  layout (location = 0) out vec4 output_A;    
  layout (location = 1) out vec4 output_B;
  
  uniform float isGlass;
  
  void main(void)
  {
      if (isGlass = 0)
      {
          output_A = vec4(1,1,1,1);
          output_B = vec4(1,1,1,1);
      }
      else
      {
          output_A = vec4(1,1,1,1);
          output_B = NULL;
      }   
  }
  </code></pre>