func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

    guard let planeAnchor = anchor as? ARPlaneAnchor else { return }
    DispatchQueue.main.async {

      let planeNode = self.createARPlaneNode(planeAnchor: planeAnchor,
                                             color: UIColor.yellow.withAlphaComponent(0.5))
      node.addChildNode(planeNode)
    }
  }

/*------------------------------------------------------------*/

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
    DispatchQueue.main.async {
      if let planeAnchor = anchor as? ARPlaneAnchor, !self.isPortalPlaced {
        #if DEBUG
          let debugPlaneNode = createPlaneNode(
            center: planeAnchor.center,
            extent: planeAnchor.extent)
          node.addChildNode(debugPlaneNode)
          self.debugPlanes.append(debugPlaneNode)
        #endif
        self.messageLabel?.alpha = 1.0
        self.messageLabel?.text = "Tap on the detected horizontal plane to place the portal"
      }
      else if !self.isPortalPlaced {

        self.portalNode = self.makePortal()
        if let portal = self.portalNode {
          node.addChildNode(portal)
          self.isPortalPlaced = true

          self.removeDebugPlanes()
          self.sceneView?.debugOptions = []

          DispatchQueue.main.async {
            self.messageLabel?.text = ""
            self.messageLabel?.alpha = 0
          }
        }

      }
    }
  }