When using RealityView, why does it work in preview, but not in the Vision Pro simulator?

Question

This is my app code, trivial:

import SwiftUI

@main
struct LogicVisionApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }.windowStyle(.volumetric)
    }
}

This is my ContentView code:

import SwiftUI
import RealityKit
import RealityKitContent

struct ContentView: View {
    init() {
        // Register components
        DraggableComponent.registerComponent()
        [snip...]
        
        // Register systems
        TransmittableStaticInitSystem.registerSystem()
        [snip...]
        
        NSLog("I am running?!")
    }
    
    var body: some View {
        RealityView { content in
            // Add test entities
            let testWire = try! Entity.load(
                    named: "Wire",
                    in: realityKitContentBundle)
            content.add(testWire)

            [snip...]

            NSLog("I am running 2?!")
        }
        .gesture(DragGesture(coordinateSpace: .global)
            .targetedToEntity(
                where: QueryPredicate<Entity>.has(DraggableComponent.self))
            .onChanged { value in
                value.entity.position = value.convert(
                    value.location3D,
                    from: .global,
                    to: value.entity.parent!)
            }
        )
    }
}

#Preview {
    ContentView()
}

• It works as expected in Preview (except for the logs not showing up).
• When the app launches in Simulator, nothing appears in the volumetric window.
  • It prints:
    • "I am running?!"
    • "I am running 2?!"
    • (A log stating that the system update is running as expected)
    • (A log stating that the system update found an entity with the proper components for 1 frame, but that log doesn't appear on any other frame [maybe they despawned?])

Answer 1

I suspect the volumetric window is clipping your content. Try adding the .fixedSize() modifier to the RealityView.

Alternatively you can add a .defaultSize(width: height: depth: in:) to the Volumetric WindowGroup in order to scale it to the appropriate size to fit the RealityView's content. ie.

.defaultSize(width: 2.0, height: 2.0, depth: 2.0, in: .meters)

You should be able to get logs from preview content, in Xcode next at the bottom of the log window is a "Previews" toggle which should give you logs from the preview.