title: How can UIVisualEffectView be used inside of a circle?
body: <p>I'm making a custom control circle. Part of the circle may be transparent. It would make more visual sense and look better if it was translucent instead of transparent.</p>
  
  <p>Because views are rectangular, and I only want the circle to be translucent, not the rest of the rectangle, this is a problem.</p>
  
  <p>The <code>UIVisualEffectView</code> is behind the custom control.</p>
  
  <p><img src="https://i.stack.imgur.com/PETia.png" alt="enter image description here"></p>
  
  <p>(Without anything rendered inside of the circle for debugging purposes)</p>
  
  <p>As you can see, the view is blurring things outside of the circle.</p>
  
  <p>I don't know how to blur inside only the view, and the prerelease documentation is <a href="https://developer.apple.com/library/prerelease/ios/documentation/UIKit/Reference/UIVisualEffectView/index.html" rel="noreferrer">practically empty</a>. My only thought is to create many 1x1 views to cover the circle, but this seems like it would not really work, and even if it did it would be a slow and ugly solution. <strong>How can I blur the content inside the view, without blurring anything outside it?</strong></p>