Placing entities using head and device transform

At a glance

Project structure

Source bundle/
├── HeadTracking/
│   ├── HeadTrackingApp.swift
│   ├── AppModel.swift
│   ├── FollowSystemAndComponent/
│   │   ├── FollowComponent.swift
│   │   └── FollowSystem.swift
│   ├── ImmersiveView.swift
│   ├── TogglePanel.swift
│   └── Info.plist
├── Packages/
│   └── RealityKitContent/
│       ├── Sources/
│       │   └── RealityKitContent/
│       │       └── RealityKitContent.swift
│       └── Package.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── HeadTracking.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 4 project/configuration file(s) and 7 source declaration(s).

Overall architecture

flowchart LR
    N1["HeadTrackingApp"]
    N2["ImmersiveView"]
    N3["AppModel"]
    N4["FollowSystem"]
    N5["SwiftUI / ARKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

HeadTracking/HeadTrackingApp.swift:10 — architecture anchor

@main
struct HeadTrackingApp: App {
    @State private var appModel: AppModel = AppModel()
    @Environment(\.openImmersiveSpace) var openImmersiveSpace

    // Register the system and the component.
    init() {
        FollowSystem.registerSystem()
        FollowComponent.registerComponent()
    }
    var body: some Scene {
        WindowGroup {
            TogglePanel()
                .environment(appModel)
        }
        .defaultSize(CGSize(width: 400, height: 200))

        ImmersiveSpace(id: "immersiveSpace") {
            ImmersiveView()
                .environment(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
    HeadTrackingApp *-- AppModel : appModel
    AppModel o-- HeadTrackState : headTrackState
    AppModel *-- Bool : isImmersiveSpaceOpen
    FollowSystem *-- EntityQuery : query

Ownership evidence

HeadTracking/HeadTrackingApp.swift:12 — stored dependency or nearest verified ownership anchor

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

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

HeadTracking/AppModel.swift:13 — representative execution boundary

@MainActor
@Observable
class AppModel {
    // ...
    var headTrackState: HeadTrackState = .headPosition
    // ...
}

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

HeadTracking/HeadTrackingApp.swift:11 — representative type boundary

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

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

Access control

Reference code

HeadTracking/FollowSystemAndComponent/FollowSystem.swift:15 — representative boundary

public struct FollowSystem: System {
    // ...
    private let arkitSession = ARKitSession()
    // ...
}

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

Naming conventions

• Types: App: HeadTrackingApp; Component: FollowComponent; Model: AppModel; System: FollowSystem; View: ImmersiveView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: runSession, update, startFollowMode, startHeadPositionMode, toggleHeadPositionModeOrFollowMode, playHummingbirdAnimation.
• Files: HeadTracking/HeadTrackingApp.swift, HeadTracking/AppModel.swift, HeadTracking/FollowSystemAndComponent/FollowComponent.swift, HeadTracking/FollowSystemAndComponent/FollowSystem.swift, HeadTracking/ImmersiveView.swift, HeadTracking/TogglePanel.swift.

Architecture takeaways

• HeadTrackingApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, ARKit, RealityKit, PackageDescription 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