RealityKit – updateHandler of trackedRaycast not called - swift

Question

I call trackedRaycast() from startTracing() which is called from viewDidLoad(). My goal is to have the AR content be placed wherever the raycast from the camera hits a horizontal surface and that it updates when the raycast intersects a different location. When the user taps the screen the updates stop.
The updateHandler closure of the function trackedRaycast is never executed.
import RealityKit
import ARKit
class ViewController: UIViewController {
#IBOutlet var arView: ARView!
var gameAnchor: Experience.PreviewBoard!
var raycast: ARTrackedRaycast?
var gameIsPlaced = false
override func viewDidLoad() {
super.viewDidLoad()
setupARConfiguration()
loadGameBoard()
startTracing()
let tapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(handleTap(recognizer:)))
arView.addGestureRecognizer(tapGestureRecognizer)
}
func setupARConfiguration() {
arView.automaticallyConfigureSession = false
let config = ARWorldTrackingConfiguration()
config.planeDetection = [.horizontal]
config.isCollaborationEnabled = true
config.environmentTexturing = .automatic
arView.session.run(config)
}
func loadGameBoard() {
gameAnchor = try! Experience.loadPreviewBoard()
arView.scene.addAnchor(gameAnchor)
}
func startTracing() {
raycast = arView.trackedRaycast(from: view.center, allowing: .estimatedPlane, alignment: .horizontal) { results in
print("This is never executed")
// Refine the game position with raycast update
if let result = results.first {
self.gameAnchor.setTransformMatrix(result.worldTransform, relativeTo: nil)
}
}
}
func stopTracing() {
print("raycast has stopped")
raycast?.stopTracking()
}
#objc func handleTap(recognizer: UITapGestureRecognizer) {
if !gameIsPlaced {
gameIsPlaced = true
stopTracing()
}
}
}
What could be the issue?

Answer 1

There appears to be some kind of lag when the view is initialized, leading to the tracked raycast not being initialized from the usual lifecycle methods. When I tried initializing it via a tap on the screen, it worked as intended. You can check this with the following code:
var r : ARTrackedRaycast? {
didSet {
print("Raycast initialized")
}
}
r = self.arView.trackedRaycast(from: self.view.center, allowing: .existingPlaneInfinite, alignment: .any) { result in
print("Callback received")
}
If you initialize your raycast from viewDidLoad() or viewDidAppear() even, the setter is never called.
The solution for me was to delay the raycast's initialization by a few seconds, like so:
DispatchQueue.main.asyncAfter(deadline: .now() + 5) {
r = self.arView.trackedRaycast(from: self.view.center, allowing: .existingPlaneInfinite, alignment: .any) { result in
print("Callback received")
}
This is, obviously, far from ideal, but right now I'm not sure how to go about solving that issue any differently.