Tracking and visualizing faces

At a glance

Project structure

Source bundle/
├── ARKitFaceExample/
│   ├── AppDelegate.swift
│   ├── ViewController.swift
│   ├── Face Overlay Content/
│   │   ├── VirtualContent.swift
│   │   ├── BlendShapeCharacter.swift
│   │   ├── FaceOcclusionOverlay.swift
│   │   ├── TexturedFace.swift
│   │   ├── TransformVisualization.swift
│   │   └── VideoTexturedFace.swift
│   ├── Utilities.swift
│   └── Base.lproj/
│       └── Main.storyboard
└── ARKitFaceExample.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 9 source declaration(s).

Overall architecture

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

Reference code

ARKitFaceExample/AppDelegate.swift:11 — architecture anchor

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

    func application(_ application: UIApplication, willFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
        if !ARFaceTrackingConfiguration.isSupported {
            /*
             Shipping apps cannot require a face-tracking-compatible device, and thus must
             offer face tracking AR as a secondary feature. In a shipping app, use the
             `isSupported` property to determine whether to offer face tracking AR features.
             This sample code has no features other than a demo of ARKit face tracking, so
             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-- ARSCNView : sceneView
    ViewController o-- UITabBar : tabBar
    ViewController *-- Dictionary : faceAnchorsAndContentControllers

Ownership evidence

ARKitFaceExample/AppDelegate.swift:13 — 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

ARKitFaceExample/ViewController.swift:84 — representative execution boundary

        DispatchQueue.main.async {
            self.displayErrorMessage(title: "The AR session failed.", message: errorMessage)
        }

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

ARKitFaceExample/Face Overlay Content/VirtualContent.swift:31 — representative type boundary

protocol VirtualContentController: ARSCNViewDelegate {
    // ...
    var contentNode: SCNNode? { get set }
    // ...
}

The source explicitly defines local protocol relationships: BlendShapeCharacter → VirtualContentController, FaceOcclusionOverlay → VirtualContentController, TexturedFace → VirtualContentController, TransformVisualization → VirtualContentController.

Access control

Reference code

ARKitFaceExample/Face Overlay Content/BlendShapeCharacter.swift:17 — representative boundary

class BlendShapeCharacter: NSObject, VirtualContentController {
    // ...
    private var originalJawY: Float = 0
    // ...
}

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, VirtualContentController; Delegate: AppDelegate.
• Protocols: VirtualContentController.
• Methods: application, viewDidLoad, viewDidAppear, session, resetTracking, displayErrorMessage, tabBar, renderer.
• Files: ARKitFaceExample/AppDelegate.swift, ARKitFaceExample/ViewController.swift, ARKitFaceExample/Face Overlay Content/BlendShapeCharacter.swift, ARKitFaceExample/Face Overlay Content/FaceOcclusionOverlay.swift, ARKitFaceExample/Face Overlay Content/TexturedFace.swift, ARKitFaceExample/Face Overlay Content/TransformVisualization.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches ARKit, SceneKit, UIKit 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.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation