Petite Asteroids: Building a volumetric visionOS game

At a glance

Project structure

Source bundle/
├── PetiteAsteroids/
│   ├── PetiteAsteroids.swift
│   ├── AppModel.swift
│   ├── ECS/
│   │   ├── Camera/
│   │   │   └── RotationalCameraFollowComponent.swift
│   │   └── Character/
│   │       ├── CharacterMovementComponent.swift
│   │       └── CharacterProgressComponent.swift
│   └── Views/
│       └── FriendsView.swift
└── Packages/
    └── RealityKitContent/
        └── Sources/
            └── RealityKitContent/
                ├── CompoundCollisionMarkerComponent.swift
                ├── BakedDirectionalLightSourceComponent.swift
                ├── CharacterSpawnPointComponent.swift
                ├── CheckpointComponent.swift
                ├── DirectionalLightFaderComponent.swift
                └── DropShadowReceiverComponent.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Metal, Swift.
• The verified tree contains 4 project/configuration file(s) and 123 source declaration(s).

Overall architecture

flowchart LR
    N1["PetiteAsteroids"]
    N2["ContentView"]
    N3["AppModel"]
    N4["AudioCueSystem"]
    N5["RealityKit / RealityKitContent APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

PetiteAsteroids/PetiteAsteroids.swift:12 — architecture anchor

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

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into visionOS.

Ownership and state

classDiagram
    GameAssetContainer *-- Dictionary : levels
    GameAssetContainer o-- Entity : characterAnimationRoot
    AssetIdentifier *-- String : name
    AssetIdentifier o-- AssetType : type

Ownership evidence

PetiteAsteroids/AppModel.swift:13 — stored dependency or nearest verified ownership anchor

struct GameAssetContainer: Component {
    let levels: [GameLevel: Entity]
    let characterAnimationRoot: Entity
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

Packages/RealityKitContent/Sources/RealityKitContent/SpeechBubbleTriggerComponent.swift:10 — representative execution boundary

@MainActor
public struct SpeechBubbleTriggerComponent: Component, Codable {
    public var characterText: String = "Update the text..."
    public var timer: Float = 5.0
    // ...
}

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

PetiteAsteroids/AppModel.swift:76 — representative type boundary

@MainActor
@Observable
class AppModel {
    // ...
    var isDifficultyHard: Bool = false
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

Packages/RealityKitContent/Sources/RealityKitContent/BakedDirectionalLightSourceComponent.swift:11 — representative boundary

    public init() {
    }

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Main application flow

sequenceDiagram
    participant AppModel
    participant Entity
    participant AudioResourcesComponent
    participant LoadResult
    AppModel->>AppModel: withTaskGroup()
    AppModel->>Entity: Entity()
    AppModel->>AudioResourcesComponent: load()
    AppModel->>LoadResult: LoadResult()
    AppModel->>AppModel: prepareGameAssets()

Reference code

PetiteAsteroids/AppModel+LoadAssets.swift:30 — loadGameAssets()

    func loadGameAssets() async {
        // ...
        root.components.set(GamePlayStateComponent.loadingAssets)
        await withTaskGroup(of: LoadResult.self) { loadAssetsTaskGroup in
            for asset in assetsToLoad {
                loadAssetsTaskGroup.addTask {
                    switch asset.type {
                        case .level, .character, .inputVisualizer:
                            guard let entity = try? await Entity(named: asset.name, in: realityKitContentBundle) else {
                                fatalError("Attempted to load entity \(asset.name), but failed.")
                            }
                            return LoadResult(entity: entity, type: asset.type)
                        case .audio:
                        do {
                            let audioResourcesComponent = try await AudioResourcesComponent.load()
                            return await LoadResult(entity: Entity(components: [audioResourcesComponent]), type: asset.type)
                        } catch {
                            fatalError("Attempted to load audio resources, but failed.")
                        }
                    }
                }
            }
            let (levels, characterAnimationRoot) = await prepareGameAssets(loadAssetsTaskGroup: loadAssetsTaskGroup)
            guard let characterAnimationRoot else {
                fatalError("Failed to load character animation root.")
            }
            let assetContainerComponent = GameAssetContainer(levels: levels,
                                                             characterAnimationRoot: characterAnimationRoot)
            root.components.set(assetContainerComponent)
        }
        root.components.set(GamePlayStateComponent.assetsLoaded)
    }

Naming conventions

• Types: Component: AudioCueStorageComponent, AudioEventComponent, AudioResourcesComponent, BakedDirectionalLightSourceComponent, ButteAmbienceBlendComponent; Model: AppModel; System: AudioCueSystem, AudioEventSystem, BakedDirectionalLightShadowSystem, ButteAmbienceBlendSystem, CharacterAnimationSystem; View: ContentView, FriendView, FriendsView, HighScoreView, LoadingView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: registerSystems, registerComponents, playLevel, updateAnimationTime.
• Files: PetiteAsteroids/PetiteAsteroids.swift, PetiteAsteroids/AppModel.swift, Packages/RealityKitContent/Sources/RealityKitContent/CompoundCollisionMarkerComponent.swift, PetiteAsteroids/ECS/Camera/RotationalCameraFollowComponent.swift, PetiteAsteroids/ECS/Character/CharacterMovementComponent.swift, PetiteAsteroids/ECS/Character/CharacterProgressComponent.swift.

Architecture takeaways

• PetiteAsteroids is the main source-visible entry or composition anchor for this sample.
• Framework work reaches RealityKit, RealityKitContent, SwiftUI, CoreMedia through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation