title: cheap shadow in SceneKit
body: <p>Is it possible to cast a static shadow in SceneKit? Don't know if static is the right word. I would only like a smooth black circle underneath my object when it falls. The object moves in y- and x-direction. I know that I can use <code>sampleRadius</code> property but that has a significant impact on performance. I have seen such thing in other game engines and I am wondering if I can achieve it in SceneKit too.</p>
  
  <p>EDIT:</p>
  
  <p>I used this, but I only ge black scene with very little lightning. It looks like that floor is completely black. I have tried different gobo images, but no luck. What have I missed?</p>
  
  <pre><code>    let spotNode = scene.rootNode.childNodeWithName("spot", recursively: true)
      let spotlight = spotNode?.light
      spotlight?.categoryBitMask = 1
      spotlight!.shadowMode = SCNShadowMode.Modulated
      spotlight?.gobo?.contents = UIImage(named: "goboImage")
      floorNode?.categoryBitMask = 1
  </code></pre>
  
  <p>//Apple code:</p>
  
  <pre><code>// Use modulated mode
  light.shadowMode = SCNShadowModeModulated;
  
  // Configure the projected shadow 
  light.gobo.contents = aShadowImage;
  
  // Use bit masks to specify receivers 
  light.categoryBitMask = kProjectorLightMask; 
  floor.categoryBitMask = kProjectorLightMask;
  </code></pre>