title: SceneKit - Threads - What to do on which thread?
body: <p>When using SceneKit, the update method:</p>
  
  <pre><code>func renderer(aRenderer: SCNSceneRenderer, updateAtTime time: NSTimeInterval)    
  </code></pre>
  
  <p>is not called on the main thead, but on some other thread.</p>
  
  <p>What am I supposed to do on the main thread, and what has to be done on this "SceneKit thread"?</p>
  
  <p>Where should I add new nodes / geometry?</p>
  
  <p>Where is it safe to modify position / etc of these objects?</p>