AVCamFilter: Applying filters to a capture stream

At a glance

Project structure

Source bundle/
└── AVCamFilter/
    ├── AppDelegate.swift
    ├── CameraViewController.swift
    ├── DepthToGrayscaleConverter.swift
    ├── PreviewMetalView.swift
    ├── FilterRenderer.swift
    ├── RosyCIRenderer.swift
    ├── RosyMetalRenderer.swift
    ├── Shaders/
    │   ├── Mixer.metal
    │   ├── DepthToGrayscale.metal
    │   └── PassThrough.metal
    ├── VideoMixer.swift
    └── AVCamFilter-Bridging-Header.h

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, Objective-C, Swift.
• The verified tree contains 6 project/configuration file(s) and 16 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["CameraViewController"]
    N3["FilterRenderer"]
    N4["CoreMedia / CoreVideo APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

AVCamFilter/AppDelegate.swift:10 — architecture anchor

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

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 AVFoundation.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    CameraViewController *-- Bool : videoFilterOn
    CameraViewController *-- Bool : depthVisualizationOn
    CameraViewController *-- Bool : depthSmoothingOn

Ownership evidence

AVCamFilter/AppDelegate.swift:12 — 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

AVCamFilter/CameraViewController.swift:67 — representative execution boundary

class CameraViewController: UIViewController, AVCapturePhotoCaptureDelegate, AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureDepthDataOutputDelegate, AVCaptureDataOutputSynchronizerDelegate {
    // ...
    private let sessionQueue = DispatchQueue(label: "SessionQueue", attributes: [], autoreleaseFrequency: .workItem)
    // ...
}

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

AVCamFilter/FilterRenderer.swift:10 — representative type boundary

protocol FilterRenderer: AnyObject {
    // ...
    var description: String { get }
    // ...
}

The source explicitly defines local protocol relationships: DepthToGrayscaleConverter → FilterRenderer, RosyCIRenderer → FilterRenderer, RosyMetalRenderer → FilterRenderer.

Access control

Reference code

AVCamFilter/CameraViewController.swift:32 — representative boundary

class CameraViewController: UIViewController, AVCapturePhotoCaptureDelegate, AVCaptureVideoDataOutputSampleBufferDelegate, AVCaptureDepthDataOutputDelegate, AVCaptureDataOutputSynchronizerDelegate {
    // ...
    private var videoFilterOn: Bool = false
    // ...
}

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: CameraViewController; Converter: DepthToGrayscaleConverter; Delegate: AppDelegate; Renderer: FilterRenderer, RosyCIRenderer, RosyMetalRenderer; View: PreviewMetalView.
• Protocols: FilterRenderer.
• Methods: viewDidLoad, viewWillAppear, viewWillDisappear, didEnterBackground, willEnterForground, thermalStateChanged, showThermalState, viewWillTransition.
• Files: AVCamFilter/AppDelegate.swift, AVCamFilter/CameraViewController.swift, AVCamFilter/DepthToGrayscaleConverter.swift, AVCamFilter/PreviewMetalView.swift, AVCamFilter/FilterRenderer.swift, AVCamFilter/RosyCIRenderer.swift.

Architecture takeaways

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