RealityKit – ARView raycasting returns 0 results

Question

I have a subclass of RealityKit's ARView that has the following function for making a Raycast:

func makeRaycastQuery(alignmentType: ARRaycastQuery.TargetAlignment) -> simd_float4x4? {
    let results = self.raycast(from: self.center,
                           // Better for pinning to planes
                           allowing: .estimatedPlane,
                          alignment: alignmentType)

    // We don't care about changing scale on raycast so keep it the same
    guard var result = results.first?.worldTransform else { return nil }
    result.scale = SCNVector3(1, 1, 1)
    return result
}

However, my results array is always empty. Is there some sort of other configuration I need to do when setting up an ARView to enable raycasting?

Answer 1

Try this code (I've written it for iPad's Playgrounds):

import RealityKit
import SwiftUI
import ARKit
import PlaygroundSupport

struct ContentView : View {
    
    @State private var arView = ARView(frame: .zero)
    
    var body: some View {
        return ARContainer(arView: $arView)
            .gesture(
                TapGesture()
                    .onEnded { _ in
                        raycasting(arView: arView)
                    }
            )
    }        
    func raycasting(arView: ARView) {
        guard let query = arView.makeRaycastQuery(from: arView.center, 
                                              allowing: .estimatedPlane, 
                                             alignment: .any)
        else { fatalError() }
            
        guard let result = arView.session.raycast(query).first
        else { fatalError() }
            
        let entity = ModelEntity(mesh: .generateSphere(radius: 0.1))
        let anchor = AnchorEntity(raycastResult: result)
        anchor.addChild(entity)
        arView.scene.anchors.append(anchor)
    }
}

---

struct ARContainer : UIViewRepresentable {
    
    @Binding var arView: ARView
    
    func makeUIView(context: Context) -> ARView {
        arView.cameraMode = .ar
        return arView
    }   
    func updateUIView(_ view: ARView, context: Context) { }
}

---

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.setLiveView(ContentView())

P. S.

This version works in UIKit app.