title: Android masking background with round gradient shape
body: <p>I need to implement following component, but not sure where to start.</p>
  
  <p>I have two fragments stacked. Top fragment has gradient background and other content as well. Fragment below that has also own content and you should be able to see below content.</p>
  
  <p>Following picture demonstrates the situation and the white round should be movable, so user can see below content on certain position.</p>
  
  <p><img src="https://i.stack.imgur.com/OcTp6.png" alt="enter image description here"></p>