Demo demonstrating physics joints breaking in RealityKit

PhysicsTestApp.swift

// put the following code into a new VisionOS 2 beta project and run it
// inside a real device (hand tracking will fail in the simulator)

// interacting with the door on the hinge will separate it from the hinge

import SwiftUI
import RealityKit
import ARKit

let mat1 = UnlitMaterial(color: .blue)
let mat2 = UnlitMaterial(color: .yellow)
let mat3 = UnlitMaterial(color: .red)
let thickness = Float(0.005)
let width = Float(0.1)

let trackingProvider = HandTrackingProvider()
let arKitSession = ARKitSession()

@main
struct PhysicsTestApp: App {
    var body: some SwiftUI.Scene {
        ImmersiveSpace { ImmersiveView() }
        .immersionStyle(selection: .constant(.mixed), in: .mixed)
    }
}

struct ImmersiveView: View {
    @State var handRoot = Entity()
    @State var parts: [String: Entity] = [:]
    var body: some View {
        RealityView { content in
            
            let hingeEntity = ModelEntity(mesh: .generateCylinder(height: width, radius: thickness / 1.5), materials: [mat2])
            hingeEntity.generateCollisionShapes(recursive: false)
            hingeEntity.components.set(PhysicsBodyComponent(mode: .kinematic))
            hingeEntity.components.set(OpacityComponent(opacity: 0.5))
            hingeEntity.transform.rotation = .init(angle: .pi / 2, axis: [0, 0, 1])
            hingeEntity.position = [0, 1, -0.5 - width / 2]
            content.add(hingeEntity)
            
            let doorEntity = ModelEntity(mesh: .generateBox(size: [width, thickness, width]), materials: [mat1])
            doorEntity.generateCollisionShapes(recursive: false)
            doorEntity.components.set(PhysicsBodyComponent(mode: .dynamic))
            doorEntity.components.set(OpacityComponent(opacity: 0.5))
            doorEntity.position = [0, 1, -0.5]
            content.add(doorEntity)
            
            let hingePin = hingeEntity.pins.set(named: "Hinge", orientation: .init(angle: .pi / 2, axis: [0, 0, 1]))
            let doorPin = doorEntity.pins.set(named: "Door", position: [0, 0, width / -2])
            let doorHingeJoint = PhysicsRevoluteJoint(pin0: hingePin, pin1: doorPin)
            try! doorHingeJoint.addToSimulation()
            
            content.add(handRoot)
        }
        .task {
            try! await arKitSession.run([trackingProvider])
            for await update in trackingProvider.anchorUpdates {
                let anchor = update.anchor
                guard anchor.isTracked else { continue }
                guard let handSkeleton = update.anchor.handSkeleton else { continue }
                for joint in handSkeleton.allJoints.filter({ $0.isTracked }) {
                    let partID = "\(joint.name)-\(anchor.chirality)"
                    var part = parts[partID]
                    if part == nil {
                        part = ModelEntity(mesh: .generateSphere(radius: 0.01), materials: [mat3])
                        part!.generateCollisionShapes(recursive: false)
                        part!.components.set(PhysicsBodyComponent(mode: .kinematic))
                        part!.components.set(OpacityComponent(opacity: 0.5))
                        handRoot.addChild(part!)
                        parts[partID] = part
                    }
                    let transform = anchor.originFromAnchorTransform * joint.anchorFromJointTransform
                    part!.setTransformMatrix(transform, relativeTo: nil)
                }
            }
        }
    }
}