title: Getting a bitmap from CALayers, any alternative to renderInContext
body: <p>I have many CALayers which are created on the fly while my app is running, and I need to be able to produce a single bitmap of these, which will later be masked. </p>
  
  <p>When I need to create the mask, the CALayers are already drawn to the background (also using shouldRasterize = YES) , and using renderInContext I am able to get a bitmap. However, as the amount of CAlayers increases, the pause caused by renderInContext gets longer and longer. Is there an alternative I can use to renderInContext, or an alternative way I can use it to stop my app temporarily freezing? </p>
  
  <p>The ideal would be to access the already drawn pixel data directly from memory/buffer/cache  without using OpenGL, but I am unsure if this is possible with CoreAnimation. </p>
  
  <p>Thanks, any additional information at all would be very useful! </p>