title: How to mask a UIView to highlight a selection?
body: <p>The problem that I am facing is simple (and less abstract than the question itself). I am looking for a solution to highlight an area of an image (the selection) while the rest of the image is faded or grayed out. You can compare the effect with the interface you see in, for example, Photoshop when you crop an image. The image is grayed out and the the area that will be cropped is clear.</p>
  
  <p>My initial idea was to use masking for this (hence the question), but I am not sure if this is a viable approach and, if it is, how to proceed.</p>