title: Make part of UIView visible
body: <p>I want to add a "shadow" image on my view, but, i want part of my view to still be "visible". You better understand what i want to do, when look on screenshot:<a href="https://i.stack.imgur.com/VcrSL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VcrSL.png" alt="enter image description here"></a></p>
  
  <p>I can add a <code>UIView</code> above my superview, but how could i make specific point "visible"? That actually mean make specific area of a view with different colour or opaque.</p>