title: adding a border around SceneKit node
body: <p>i am trying to highlight a selected node in SceneKit with a tap gesture. Unfortunately, I have not been able to accomplish it. The best thing I could do was to change the material when the node is tapped. </p>
  
  <pre><code>let material = key.geometry!.firstMaterial!
  material.emission.contents = UIColor.blackColor()
  </code></pre>
  
  <p>Can someone suggest a way I can go about to just add a border or outline around the object instead of changing the color of the entire node?</p>