title: SKPhysicsBody avoid collision Swift/SpriteKit
body: <p>I have 3 SKSpriteNodes in my Scene. One <strong>bird</strong>, one <strong>coin</strong> and a <strong>border</strong> around the scene. I don't want the <strong>coin</strong> and the <strong>bird</strong> to collide with each other but withe the <strong>border</strong>.
  I assign a different collisionBitMask and categoryBitMask to every node:</p>
  
  <pre><code>enum CollisionType:UInt32{
      case Bird  = 1
      case Coin = 2
      case Border = 3 
  }
  </code></pre>
  
  <p>Like so:</p>
  
  <pre><code>bird.physicsBody!.categoryBitMask = CollisionType.Bird.rawValue
  bird.physicsBody!.collisionBitMask = CollisionType.Border.rawValue
  
  coin.physicsBody!.categoryBitMask = CollisionType.Coin.rawValue
  coin.physicsBody!.collisionBitMask = CollisionType.Border.rawValue
  </code></pre>
  
  <p>But the <strong>coin</strong> and the <strong>bird</strong> still collide with each other.
  What am I doing wrong?</p>