Combining user face-tracking and world tracking

At a glance

Project structure

Source bundle/
├── FaceAndWorldTrackingExample/
│   ├── AppDelegate.swift
│   ├── ViewController.swift
│   ├── RobotHead.swift
│   ├── MessageLabel.swift
│   ├── Utilities.swift
│   ├── ViewController+CoachingOverlay.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── FaceAndWorldTrackingExample.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 6 project/configuration file(s) and 6 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["ARKit APIs"]
    N1 --> N2
    N2 --> N3

Reference code

FaceAndWorldTrackingExample/AppDelegate.swift:11 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        if !ARWorldTrackingConfiguration.supportsUserFaceTracking {
            /*
             For this sample code, simultaneous world and face tracking is essential.
             If this feature is not supported, it replaces the AR view (the initial storyboard in the view controller)
             with an alternate view controller containing a static error message.
             */
            let storyboard = UIStoryboard(name: "Main", bundle: nil)
            window?.rootViewController = storyboard.instantiateViewController(withIdentifier: "unsupportedDeviceMessage")
        }
        return true
    }
}

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 ARKit.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    ViewController o-- ARView : arView
    ViewController o-- MessageLabel : messageLabel
    ViewController o-- UIButton : restartButton

Ownership evidence

FaceAndWorldTrackingExample/AppDelegate.swift:14 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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

FaceAndWorldTrackingExample/MessageLabel.swift:23 — representative execution boundary

            DispatchQueue.main.async {
                self.isHidden = true
                self.text = ""
            }

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

FaceAndWorldTrackingExample/AppDelegate.swift:12 — representative type boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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

Access control

Reference code

FaceAndWorldTrackingExample/RobotHead.swift:14 — representative boundary

class RobotHead: Entity, HasModel {
    // ...
    private let inactiveColor: SimpleMaterial.Color = .gray
    // ...
}

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: Controller: ViewController; Delegate: AppDelegate.
• Protocols: no local protocol declaration in the scanned source.
• Methods: application, viewDidLoad, viewWillAppear, handleTap, restartButtonPressed, resetTracking, displayErrorMessage, showInstruction.
• Files: FaceAndWorldTrackingExample/AppDelegate.swift, FaceAndWorldTrackingExample/ViewController.swift, FaceAndWorldTrackingExample/RobotHead.swift, FaceAndWorldTrackingExample/MessageLabel.swift.

Architecture takeaways

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