title: Static subview background image effect
body: <p>In the latest Expedia app for iOS, they have a very interesting effect that I am trying to wrap my head around. The have two columns of infinitely scrolling subviews which I know can be accomplished with 2 scrollviews. The interesting part is that the overall scrollview appears to have a linen background that stays static and can be seen in the gap between each of the subview cells. The really cool part is that the subviews have a different background that stays in place. In the screenshot below it is city skyline image. When the subviews scroll, the city image can only be seen behind the subview cells. It appears to be some sort of masking trick but I can't quite figure out how the effect is done. How can I achieve the same result? </p>
  
  <p>Essentially, how can you show a static background behind subviews that act as little windows and not show the linen. The linen should only be shown around the cells.</p>
  
  <p>You can download the app, hit airplane mode and try it for yourself.</p>
  
  <p>Here is a screenshot:<img src="https://i.stack.imgur.com/7PXtl.png" alt="enter image description here"></p>
  
  <p>Here is another to show that the cells scrolled but the city stays the same:</p>
  
  <p><img src="https://i.stack.imgur.com/e8gwH.png" alt="enter image description here"></p>