Detect touch on SCNNode in ARKit

Question

I have placed a SCNNode (a plane) at the location of a recognized image in ARKit 1.5 beta. I would like to print a message to the console when the plane is tapped on. So far I have this code:

// MARK: - ARSCNViewDelegate (Image detection results)
    /// - Tag: ARImageAnchor-Visualizing
    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

        guard let imageAnchor = anchor as? ARImageAnchor else { return }
        let referenceImage = imageAnchor.referenceImage
        updateQueue.async {

            // Create a plane to visualize the initial position of the detected image.
            let plane = SCNPlane(width: referenceImage.physicalSize.width,
                                 height: referenceImage.physicalSize.height)
            let planeNode = SCNNode(geometry: plane)
            planeNode.opacity = 0.25

            /*
             `SCNPlane` is vertically oriented in its local coordinate space, but
             `ARImageAnchor` assumes the image is horizontal in its local space, so
             rotate the plane to match.
             */
            planeNode.eulerAngles.x = -.pi / 2

            /*
             Image anchors are not tracked after initial detection, so create an
             animation that limits the duration for which the plane visualization appears.
             */
            //planeNode.runAction(self.imageHighlightAction)

            // Add the plane visualization to the scene.
            node.addChildNode(planeNode)
        }

        DispatchQueue.main.async {
            let imageName = referenceImage.name ?? ""
            self.statusViewController.cancelAllScheduledMessages()
            self.statusViewController.showMessage("Detected image “\(imageName)”")
        }
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        let touch = touches.first as! UITouch
        if(touch.view == self.sceneView){
            print("touch working")
            let viewTouchLocation:CGPoint = touch.location(in: sceneView)
            guard let result = sceneView.hitTest(viewTouchLocation, options: nil).first else {
                return
            }
            if let planeNode = planeNode, planeNode == result.node {
                print("match")
            }

        }
    }

But I'm getting an 'unresolved identifier' error on this line: if let planeNode = planeNode, planeNode == result.node {, which I understand because planeNode is defined in the Renderer function above and is not in the right scope. My question is how to fix this, because I dont believe I can return the value in Renderer, nor can I put the touchesBegan function in the Renderer function so its in the right scope. Can anyone give me any ideas on how to fix this? Thanks!

Answer 1

To solve this problem declare a global variable in your ViewController

class ViewController: UIViewController, ARSCNViewDelegate {

    @IBOutlet var sceneView: ARSCNView!

    var planeNode : SCNNode? = nil

    .....

}

Then use the planeNode variable just declared and assign it to your actual planeNode in the renderer method

func renderer(_ renderer: SCNSceneRenderer, nodeFor anchor: ARAnchor) -> SCNNode? {

     .........

     let planeNode = SCNNode(geometry: plane)
     self.planeNode = planeNode
}

This way you can access the planeNode from anywhere inside the class

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    let touch = touches.first as! UITouch
    if(touch.view == self.sceneView){
        print("touch working")
        let viewTouchLocation:CGPoint = touch.location(in: sceneView)
        guard let result = sceneView.hitTest(viewTouchLocation, options: nil).first else {
            return
        }
        if let planeNode = planeNode, planeNode == result.node {
            print("match")
        }

    }
}

Answer 2

// Add a gesture recognizer
 let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTap))
    self.sceneView.addGestureRecognizer(tapGestureRecognizer)
    tapGestureRecognizer.cancelsTouchesInView = false 

@objc func handleTap(sender:UITapGestureRecognizer) {

    guard let sceneView = sender.view as? ARSCNView else {return}
    let touchLcoation = sender.location(in: sceneView)
    let hitTestResult = sceneView.hitTest(touchLcoation, types: .existingPlaneUsingExtent)

    if !hitTestResult.isEmpty {
        // add something to scene 
        // e.g self.sceneView.scene.rootNode.addChildNode(yourNode!)
    }
}