Creating a fog effect using scene depth

At a glance

Project structure

Source bundle/
├── ARDepthDataExample/
│   ├── Renderer.swift
│   ├── AppDelegate.swift
│   ├── ViewController.swift
│   ├── ARDepthDataExampleSwift-Bridging-Header.h
│   ├── ShaderTypes.h
│   ├── Shaders.metal
│   ├── Base.lproj/
│   │   └── Main.storyboard
│   └── Info.plist
├── ARDepthDataExample.xcodeproj/
│   ├── .xcodesamplecode.plist
│   └── project.pbxproj
└── Configuration/
    └── SampleCode.xcconfig

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 5 project/configuration file(s) and 4 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["RenderDestinationProvider"]
    N4["ARKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

ARDepthDataExample/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.supportsFrameSemantics(.sceneDepth) ||
            !ARWorldTrackingConfiguration.supportsFrameSemantics(.smoothedSceneDepth) {
            // Ensure that the device supports scene depth and present
            //  an error-message view controller, if not.
            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
    Renderer *-- Int : kMaxBuffersInFlight
    Renderer *-- Array : kImagePlaneVertexData
    Renderer o-- ARSession : session
    Renderer o-- MTLDevice : device

Ownership evidence

ARDepthDataExample/Renderer.swift:22 — stored dependency or nearest verified ownership anchor

let kMaxBuffersInFlight: Int = 3

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

ARDepthDataExample/Renderer.swift:35 — representative execution boundary

class Renderer {
    // ...
    let inFlightSemaphore = DispatchSemaphore(value: kMaxBuffersInFlight)
    // ...
}

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

ARDepthDataExample/Renderer.swift:14 — representative type boundary

protocol RenderDestinationProvider {
    var currentRenderPassDescriptor: MTLRenderPassDescriptor? { get }
    var currentDrawable: CAMetalDrawable? { get }
    var colorPixelFormat: MTLPixelFormat { get set }
    var sampleCount: Int { get set }
}

The source explicitly defines local protocol relationships: MTKView → RenderDestinationProvider.

Access control

Reference code

ARDepthDataExample/Renderer.swift:226 — representative boundary

    fileprivate func setMTLPixelFormat(_ texturePixelFormat: inout MTLPixelFormat?, basedOn pixelBuffer: CVPixelBuffer!) {
        // ...
            texturePixelFormat = .r32Float
        // ...
    }

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; Provider: RenderDestinationProvider; Renderer: Renderer.
• Protocols: RenderDestinationProvider.
• Methods: drawRectResized, update, loadMetal, updateAppState, updateCameraImageTextures, setMTLPixelFormat, updateARDepthTexures, createTexture.
• Files: ARDepthDataExample/Renderer.swift, ARDepthDataExample/AppDelegate.swift, ARDepthDataExample/ViewController.swift.

Architecture takeaways

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