Detecting human body poses in 3D with Vision

At a glance

Project structure

Source bundle/
├── HumanBodyPose3DApp/
│   ├── HumanBodyPose3DApp.swift
│   ├── Models/
│   │   ├── HumanBodyPoseImageModel.swift
│   │   └── HumanBodyPose3DDetector.swift
│   ├── Views/
│   │   ├── PhotoSelectionView.swift
│   │   ├── ContentView.swift
│   │   ├── HumanBodySkeletonRenderer.swift
│   │   ├── SkeletonSceneView.swift
│   │   └── HumanBodyPoseImage.swift
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── HumanBodyPose3DApp.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 14 source declaration(s).

Overall architecture

flowchart LR
    N1["HumanBodyPose3DApp"]
    N2["ContentView"]
    N3["HumanBodyPoseImageModel"]
    N4["HumanBodySkeletonRenderer"]
    N5["Vision APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

HumanBodyPose3DApp/HumanBodyPose3DApp.swift:11 — architecture anchor

@main
struct HumanBodyPose3DApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

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 Vision.

Ownership and state

classDiagram
    HumanBodyPoseImage o-- Image : image
    HumanBodyPoseImage o-- PHAsset : selectedAsset
    HumanBodyPoseImage o-- ImageState : imageState
    HumanBodyPoseImage o-- PhotosPickerItem : imageSelection

Ownership evidence

HumanBodyPose3DApp/Models/HumanBodyPoseImageModel.swift:29 — stored dependency or nearest verified ownership anchor

    struct HumanBodyPoseImage: Transferable {
        let image: Image
        // ...
    }

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

HumanBodyPose3DApp/Models/HumanBodyPose3DDetector.swift:42 — representative execution boundary

    public func runHumanBodyPose3DRequestOnImage(fileURL: URL?) async {
        // ...
            guard let assetURL = fileURL else {
                return
            }
        // ...
    }

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

HumanBodyPose3DApp/HumanBodyPose3DApp.swift:12 — representative type boundary

@main
struct HumanBodyPose3DApp: App {
    // ...
            ContentView()
    // ...
}

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

Access control

Reference code

HumanBodyPose3DApp/Models/HumanBodyPose3DDetector.swift:21 — representative boundary

    public func calculateLocalAngleToParent(joint: VNHumanBodyPose3DObservation.JointName) -> simd_float3 {
        var angleVector: simd_float3 = simd_float3()
        // ...
    }

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: HumanBodyPose3DApp; Model: HumanBodyPoseImageModel; Renderer: HumanBodySkeletonRenderer; Scene: SkeletonScene; View: ContentView, PersonPlaceholderImageView, PhotoSelectionView, PhotoSelectorView, SelectablePersonPhotoView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: loadOriginalFileURL, getAssetFileURL, loadAssetFromID, loadTransferable, requestAuthorization, relate3DSkeletonProportionToImagePlane, computeOffsetOfRoot, createInputImage2DNode.
• Files: HumanBodyPose3DApp/HumanBodyPose3DApp.swift, HumanBodyPose3DApp/Models/HumanBodyPoseImageModel.swift, HumanBodyPose3DApp/Views/PhotoSelectionView.swift, HumanBodyPose3DApp/Views/ContentView.swift, HumanBodyPose3DApp/Views/HumanBodySkeletonRenderer.swift, HumanBodyPose3DApp/Models/HumanBodyPose3DDetector.swift.

Architecture takeaways

• HumanBodyPose3DApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, Vision, SceneKit, PhotosUI 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