Petite Asteroids: Building a volumetric visionOS game

At a glance

Project structure

Source bundle/
├── PetiteAsteroids/PetiteAsteroids.swift  # PetiteAsteroids
├── PetiteAsteroids/AppModel.swift  # GameAssetContainer, GameLevel, AssetType
├── Packages/RealityKitContent/Sources/RealityKitContent/CompoundCollisionMarkerComponent.swift  # GameCollisionGroup, GameCollisionMask, CompoundCollisionMarkerComponent
├── PetiteAsteroids/ECS/Camera/RotationalCameraFollowComponent.swift  # RotationalCameraFollowComponent, CameraParameterAnimation, CameraPoint
├── PetiteAsteroids/ContentView.swift  # ContentView
├── Packages/RealityKitContent/Sources/RealityKitContent/BakedDirectionalLightSourceComponent.swift  # BakedDirectionalLightSourceComponent
├── Packages/RealityKitContent/Sources/RealityKitContent/CharacterSpawnPointComponent.swift  # CharacterSpawnPointComponent
├── Packages/RealityKitContent/Sources/RealityKitContent/CheckpointComponent.swift  # CheckpointComponent
└── Packages/RealityKitContent/Package.realitycomposerpro/ProjectData/main.json  # authored RealityKit content

Structure observations

• The runtime boundary is WindowGroup + volumetric window; the pruned tree lists only files that explain lifecycle, state, or framework integration.
• App code is split into role-named views, models, managers, providers, components, or systems.
• Authored .reality or Reality Composer Pro content is a real implementation boundary; Swift loads or drives it rather than reproducing its entity graph.

Overall architecture

flowchart LR
    PetiteAsteroids_1["PetiteAsteroids"]
    WindowGroup___volumetric_window_2["WindowGroup + volumetric window"]
    ContentView_3["ContentView"]
    AppModel_4["AppModel"]
    RealityView_entity_graph_5["RealityView entity graph"]
    RealityKit_components_and_systems_6["RealityKit components and systems"]
    PetiteAsteroids_1 --> WindowGroup___volumetric_window_2
    WindowGroup___volumetric_window_2 --> ContentView_3
    ContentView_3 --> AppModel_4
    AppModel_4 --> RealityView_entity_graph_5
    RealityView_entity_graph_5 --> RealityKit_components_and_systems_6

Reference code

PetiteAsteroids/PetiteAsteroids.swift:13 — the app or executable entry declares the outer scene lifecycle.

struct PetiteAsteroids: App {
    // ...
}

The diagram is a responsibility flow, not a claim that every adjacent node directly calls the next. It keeps scene ownership, shared state, RealityKit content, and framework-provider work at separate levels.

Ownership and state

classDiagram
    PetiteAsteroids *-- AppModel : appModel
    ContentView o-- AppModel : appModel
    AppModel *-- Entity : root
    AppModel *-- Entity : levelRoot

Ownership evidence

PetiteAsteroids/PetiteAsteroids.swift:15 — representative stored state or the nearest verified lifecycle anchor.

@main
struct PetiteAsteroids: App {
    // ...
    @State private var appModel = AppModel()
    // ...
}

Ownership here is deliberately narrow: @Environment and weak references are shared links, initialized @State or stored services are lifecycle ownership, and a RealityView content closure owns additions to its entity graph without making the SwiftUI view a reference-type owner.

Class and protocol design

The source defines no local substitution protocol in the reviewed boundary. Its protocol use is framework-facing (App, View, RealityKit/ARKit protocols, or platform adapters), so this document does not label the whole app protocol-oriented.

Access control

No reviewed declaration uses fileprivate, private(set), open; unmodified Swift declarations are internal.

Reference code

PetiteAsteroids/ContentView.swift:13 — representative visibility boundary.

    @Environment(AppModel.self) private var appModel
    @Environment(\.dismissWindow) private var dismissWindow
    @Environment(\.openWindow) private var openWindow
    
    private static let menuAttachmentID = "MenuAttachment"

Logic ownership and placement

Design patterns

Naming conventions

• Role suffixes are evidence, not decoration: Model: AppModel; View: ContentView, FriendView, FriendsView, HighScoreView, LoadingView.
• ECS names pair data and behavior: components BakedDirectionalLightSourceComponent, CharacterSpawnPointComponent, CheckpointComponent, CompoundCollisionMarkerComponent; systems AudioCueSystem, AudioEventSystem, ButteAmbienceBlendSystem, RotationalCameraFollowSystem.
• Protocols: no app-defined protocol in the reviewed source.
• Commands use verb-led methods: registerSystems, registerComponents, playLevel, updateAnimationTime.
• Files generally match their primary type; Views, Models, Managers, Providers, Components, Systems, and Packages folders describe architectural roles where present.

Architecture takeaways

• Treat PetiteAsteroids as the owner of scene declarations, not as the owner of every RealityKit entity created later.
• Keep view-local interaction in SwiftUI, but move provider sessions, playback resources, shared game state, or transport state into a stable owner when their lifetime exceeds one render pass.
• Use RealityKit components for per-entity data and systems for repeated simulation instead of a monolithic view model.

Source map

• Official Apple documentation