title: SceneKit, test if SCNNode completely visible
body: <p>I have a 2 SCNNode next to each other ( 1 big box and 1 small box ).</p>
  
  <p>I rotate its parent so that the small box sometimes is not visible any more in the camera, is it possible to know when the small box is not visible anymore because its behind the big box?</p>
  
  <p>my current structure</p>
  
  <pre><code>Scene - RootNode 
             - SCNNode (camera)
             - SCNNode (parent)
                  - SCNNode (Big box)
                  - SCNNode (Small box)
  </code></pre>