title: NSVisualEffectView with mask has jagged corners
body: <p>In one of the WWDC 2014 talks on the new Yosemite UI, it says to avoid the use of <code>NSVisualEffectView</code> in masked layers. Unfortunately my view's layer does have a shape mask, and as a result the visual effect view in it has an ugly jagged edge effect:</p>
  
  <p><img src="https://i.stack.imgur.com/SUmfa.png" alt="gross"></p>
  
  <p>However I know it must be somehow possible to create a masked visual effect view, partly due to 2 reasons:</p>
  
  <ul>
  <li>The image mask property on <code>NSVisualEffectView</code> produces a smooth, anti-alised mask (but requires an unmasked background behind it, and not just an unmasked parent view)</li>
  <li><code>NSPopover</code> and <code>NSMenu</code> seem to be able to achieve a smooth mask that changes with dimensions:</li>
  </ul>
  
  <p><img src="https://i.stack.imgur.com/Uio26.png" alt="Smooth"></p>
  
  <p><img src="https://i.stack.imgur.com/aRCfu.png" alt="Also smooth"></p>
  
  <p>Although it is doubtable as to wether or not they use <code>NSVisualEffectView</code>, and not a custom blurred view.</p>
  
  <p>Is there any way I can achieve this smooth mask that doesn't rely on a mask image but rather a path or shape layer?</p>