AR anchor shared across multiple immersive scenes

Hi @tomires

It was great connecting with you on Wednesday. If I understand correctly, you want to transition from mixed immersion to full immersion while maintaining the real-world position of an AR anchor. This is possible. Here's how.

• Instead of closing the old space then opening the new one, conditionally render views in a single immersive space. The former changes the scene's origin and the latter does not.
• Use a state variable to change the immersion style of the current immersive space.

Here's a code snippet. To create and run the app, create a new project then replace the generated code with the snippets below.

AppModel.swift

// Define an enum with entries for each immersive scene.
enum Scenes : String, CaseIterable, Identifiable {
    case red
    case green
    
    var id: Self { self }
}

//...

class AppModel {
    
    // Add a variable to store the current scene.
    var currentScene = Scenes.red
}

<YourAppName>App.swift

//...
// Set the immersion style based on the current scene.
let immersionStyle:ImmersionStyle = appModel.currentScene == .red ? .mixed : .full

ImmersiveSpace(id: appModel.immersiveSpaceID) {
    ImmersiveView()
 	//...
}
.immersionStyle(selection: .constant(immersionStyle), in: .mixed, .full)

ContentView.swift

// Display a picker to transition between scenes.
struct ContentView: View {
    @Environment(AppModel.self) private var appModel

    var body: some View {
        @Bindable var appModel = appModel

        VStack {
            Picker("Scene", selection: $appModel.currentScene) {
                ForEach(Scenes.allCases) {
                    Text($0.rawValue)
                }
            }

            ToggleImmersiveSpaceButton()
        }
        .padding()
    }
}

ImmersiveView.swift

struct ImmersiveView: View {
    @Environment(AppModel.self) private var appModel
    @State private var session = ARKitSession()
    @State private var anchorTransform:Transform?
    
    var body: some View {
        @Bindable var appModel = appModel
        
        VStack {
        	// Render the view for the current scene and pass it the anchor's transform.
            if let anchorTransform {
                switch appModel.currentScene {
                case .red:
                    RedView(anchorTransform: anchorTransform)
                case .green:
                    GreenView(anchorTransform: anchorTransform)
                }
            }
        }
        .task {
            guard ImageTrackingProvider.isSupported else {
                print("Image tracking is not supported.")
                return
            }
            
            let referenceImages = ReferenceImage.loadReferenceImages(inGroupNamed: "AR Resources")
            let imageTrackingProvider = ImageTrackingProvider(referenceImages: referenceImages)
            
            try? await session.run([imageTrackingProvider])
            
            for await update in imageTrackingProvider.anchorUpdates {
                
                if update.event == .added || update.event == .removed {
                    anchorTransform = Transform(matrix: update.anchor.originFromAnchorTransform)
                }
                
                // TODO handle remove
            }
        }

    }
}

struct RedView: View {
    let anchorTransform:Transform
    
    var body: some View {
        RealityView { content in
            let entity = ModelEntity(mesh: .generateSphere(radius: 0.2), materials: [SimpleMaterial(color: .red, isMetallic: false)])
            entity.transform = anchorTransform

            content.add(entity)
        }
    }
}

struct GreenView: View {
    let anchorTransform:Transform
    
    var body: some View {
        RealityView { content in
            let entity = ModelEntity(mesh: .generateSphere(radius: 0.2), materials: [SimpleMaterial(color: .green, isMetallic: false)])
            entity.transform = anchorTransform

            content.add(entity)
        }
    }
}