Implementing saliency-based image cropping in iOS and watchOS

At a glance

Project structure

Source bundle/
├── VisionWatchSample iOS/
│   ├── VisionWatchSampleApp.swift
│   ├── ContentView.swift
│   └── AnimalDetailView.swift
├── VisionWatchSample watchOS/
│   ├── VisionWatchSampleApp.swift
│   ├── AnimalDetailView.swift
│   ├── AnimalStore.swift
│   └── ContentView.swift
├── Shared/
│   ├── Vision/
│   │   └── SaliencyImageProcessor.swift
│   ├── Models/
│   │   └── Animal.swift
│   └── Views/
│       └── ImageLoadingPlaceholder.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── VisionWatchSample.xcodeproj/
    └── .xcodesamplecode.plist

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 3 project/configuration file(s) and 15 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["VisionWatchSample iOS"]
    V2["VisionWatchSample watchOS"]
    Boundary["SwiftUI / CoreGraphics APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

VisionWatchSample iOS/VisionWatchSampleApp.swift:10 — architecture anchor

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

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    VisionWatchSampleApp *-- AnimalStore : animalStore
    CroppedImageCache *-- CroppedImageCache : shared
    CroppedImageCache o-- Cache : cache
    ImageCrop *-- CGRect : rect

Ownership evidence

VisionWatchSample watchOS/VisionWatchSampleApp.swift:12 — stored dependency or nearest verified ownership anchor

@main
struct VisionWatchSampleApp: App {
    @State private var animalStore = AnimalStore()
    // ...
}

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

Shared/Vision/SaliencyImageProcessor.swift:21 — representative execution boundary

#if os(iOS)
private final class CroppedImageCache: @unchecked Sendable {
    static let shared = CroppedImageCache()
    // ...
}
#endif

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

VisionWatchSample iOS/VisionWatchSampleApp.swift:11 — representative type boundary

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

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

Access control

Reference code

Shared/Vision/SaliencyImageProcessor.swift:23 — representative boundary

#if os(iOS)
private final class CroppedImageCache: @unchecked Sendable {
    // ...
}
#endif

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: VisionWatchSampleApp; Processor: SaliencyImageProcessor; Store: AnimalStore; View: AnimalDetailView, ContentView, CroppedImageView, ThumbnailView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: image, store, imageSize, salientBoundingBox, generateThumbnail, crop, pad, squareCropRect.
• Files: VisionWatchSample iOS/VisionWatchSampleApp.swift, VisionWatchSample watchOS/VisionWatchSampleApp.swift, Shared/Vision/SaliencyImageProcessor.swift, VisionWatchSample iOS/ContentView.swift, VisionWatchSample watchOS/AnimalDetailView.swift, VisionWatchSample iOS/AnimalDetailView.swift.

Architecture takeaways

• VisionWatchSampleApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, CoreGraphics, ImageIO, 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation