title: Sprite Particle System animation in viewController
body: <p>I create a macOS single window application and add a Sprite Particle System file with template <code>Stars</code>. and the visual effect just like this:
  <a href="https://i.stack.imgur.com/pdSWG.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pdSWG.gif" alt="enter image description here"></a></p>
  
  <p>And I want to add it to my viewController, as the guide of this <a href="https://stackoverflow.com/a/32848302/1096059">answer</a>, I got the result like this, and it was not which I desired:</p>
  
  <pre>
      override func viewDidLoad() {
          super.viewDidLoad()
  
          let scene = SCNScene()
          let particlesNode = SCNNode()
          let particleSystem = SCNParticleSystem(named: "Welcome", inDirectory: "")
          particlesNode.addParticleSystem(particleSystem!)
          scene.rootNode.addChildNode(particlesNode)
          skView.backgroundColor = .black
          skView.scene = scene
      }
  </pre>
  
  <p><a href="https://i.stack.imgur.com/UGsYo.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UGsYo.gif" alt="enter image description here"></a></p>
  
  <p>So, I'm wondering what's wrong and what should I do?</p>
  
  <p>Here is the demo repo: <a href="https://gitlab.com/hamguy/StarAnimationDemo" rel="nofollow noreferrer">Link Here</a></p>
  
  <p>The particle system itself is the standard "star" SceneKit particle system available in Xcode, with no changes.</p>