title: iphone - How to control CALayer's shadow, exactly?
body: <p>I am very new to CALayer thing. I had a look at the documentation, but quite don't understand the meaning of those properties which can be used to control the shadow</p>
  
  <p><em>shadowOpacity</em></p>
  
  <p><em>shadowRadius</em></p>
  
  <p><em>shadowOffset</em></p>
  
  <p>I particularly don't understand the Offset &amp; Radius. </p>
  
  <p>Can anyone give me some lights to me, for this newbie question?</p>
  
  <p>Another question about the shadow is</p>
  
  <p>If the UIView view1's frame is CGRect(0, 0, 768, 40), if I apply shadow on it, will the shadow possibly be covered by another UIView which is just next to the bottom edge of view1?</p>
  
  <p>thanks</p>