var trackerNode:SCNNode!
    var gameHasStarted = false
    var foundSurface = false
    var gamePos = SCNVector3(0.0, 0.0, 0.0)
    
    
    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
            guard !gameHasStarted else { return }
            guard let hitTest = sceneView.hitTest(CGPoint(x: view.frame.midX, y: view.frame.midY), types: [.existingPlane, .featurePoint, .estimatedHorizontalPlane]).last else { return }
            
            let trans = SCNMatrix4(hitTest.worldTransform)
            gamePos = SCNVector3Make(trans.m41, trans.m42, trans.m43)
            
            if !foundSurface {
                let trackerPlane = SCNPlane(width: 0.3, height: 0.3)
            
                trackerPlane.firstMaterial?.diffuse.contents = #imageLiteral(resourceName: "surface.png")
                
                trackerNode = SCNNode(geometry: trackerPlane)
                trackerNode.eulerAngles.x = .pi * -0.5
                
                sceneView.scene.rootNode.addChildNode(trackerNode)
            }
            
        trackerNode.position = gamePos
            foundSurface = true
        }