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!

To fix this you need to understand the difference between local and global variables: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Properties.html#//apple_ref/doc/uid/TP40014097-CH14-ID263 which is not related to Scenekit or ARkit but very basic programming. Or try this one: https://www.youtube.com/watch?v=qRZAdbAgj3c — Xartec, Feb 19 '18 at 19:59

fannolo · Answer 1 · 2018-08-18T09:59:45.970

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")
        }

    }
}

Hey, how to add new scnnode when user touch the plane? – PvDev Aug 30 '18 at 10:29 — PvDev, Aug 30 '18 at 10:29

score 0 · Answer 2 · answered Sep 25 '18 at 11:28

// 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!)
    }
}

Detect touch on SCNNode in ARKit

2 Answers2

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