title: What is the performance impact of using multisampled anti-aliasing on iOS?
body: <p>I've been experimenting with using multisampling to do full-scene anti-aliasing on the iPhone and iPad on iOS 4.  The general mechanism uses Apple's APPLE_framebuffer_multisample extension (<a href="http://www.khronos.org/registry/gles/extensions/APPLE/APPLE_framebuffer_multisample.txt" rel="nofollow noreferrer">http://www.khronos.org/registry/gles/extensions/APPLE/APPLE_framebuffer_multisample.txt</a>) and is described in the answer to this question: <a href="https://stackoverflow.com/questions/3340189/how-do-you-activate-multisampling-in-opengl-es-on-the-iphone">How do you activate multisampling in OpenGL ES on the iPhone?</a> and documented by Apple in their OpenGL ES Programming Guide.</p>
  
  <p>It works as described, but the drawing performance of my test application suffers by about 50% when I set the number of samples to be 2.  I'm primarily testing on an iPhone 4, using a non-retina-enabled application.  I am using the other performance suggestions offered by Apple in their documentation (using glDiscardFramebufferEXT to discard the renderbuffers attached to the multisample framebuffer, using glClear to clear the entire framebuffer at the start of the frame, etc.).</p>
  
  <p>The performance overhead of enabling multisampling in this manner seems surprisingly large to me.  Are you guys seeing similar results or does this suggest that I'm doing something incorrectly?</p>