Canyon Crosser: Building a volumetric hike-planning app

At a glance

Project structure

Source bundle/
├── CanyonCrosser/
│   ├── CanyonCrosserApp.swift
│   ├── Views/
│   │   ├── Progress Slider/
│   │   │   └── WeatherOrTimeView.swift
│   │   └── Carousel/
│   │       └── CarouselLabelView.swift
│   ├── Models/
│   │   ├── AppModel/
│   │   │   └── AppModel.swift
│   │   ├── AppPhaseModel.swift
│   │   └── CarouselModel.swift
│   └── ECS/
│       ├── ClippingMarginPercentageComponent.swift
│       └── FeatheringSystem.swift
└── Packages/
    └── RealityKitContent/
        └── Sources/
            └── RealityKitContent/
                ├── TimeOfDayLightComponent.swift
                ├── TimeOfDayLightSystem.swift
                ├── TimeOfDayMaterialComponent.swift
                └── TimeOfDayMaterialSystem.swift

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 5 project/configuration file(s) and 90 source declaration(s).

Overall architecture

flowchart LR
    N1["CanyonCrosserApp"]
    N2["ContentView"]
    N3["AppModel"]
    N4["ClippingMarginPercentageSystem"]
    N5["SwiftUI / RealityKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

CanyonCrosser/CanyonCrosserApp.swift:11 — architecture anchor

@main
struct CanyonCrosserApp: App {
    @State private var appModel: AppModel = AppModel()
    @State private var appPhaseModel: AppPhaseModel = AppPhaseModel()

    init() {
        ClippingMarginPercentageSystem.registerSystem()
        FeatheringSystem.registerSystem()
        HikeSystem.registerSystem()
        LightRotationSystem.registerSystem()
        TimeOfDayLightSystem.registerSystem()
        TimeOfDayMaterialSystem.registerSystem()
        TimeOfDaySystem.registerSystem()
    }

    var body: some Scene {
        WindowGroup() {
            ContentView()
                .environment(appModel)
                .environment(appPhaseModel)
        }
        .defaultSize(width: 2.0 * 0.74, height: 2.0 * 0.74, depth: 2.0, in: .meters)
        .windowResizability(.contentMinSize)
        .windowStyle(.volumetric)
    }
}

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 visionOS.

Ownership and state

classDiagram
    CanyonCrosserApp *-- AppModel : appModel
    CanyonCrosserApp *-- AppPhaseModel : appPhaseModel
    AppModel o-- ClippingMarginPercentageComponent : clippingMarginEnvironment
    AppModel *-- Entity : root

Ownership evidence

CanyonCrosser/CanyonCrosserApp.swift:13 — stored dependency or nearest verified ownership anchor

@main
struct CanyonCrosserApp: App {
    @State private var appModel: AppModel = AppModel()
    // ...
}

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

CanyonCrosser/ECS/HikeSystem.swift:63 — representative execution boundary

    @MainActor
    private func animateHiker(deltaTime: TimeInterval, entity: Entity) -> Bool {
        let animationTime: TimeInterval = 0.2
        // ...
    }

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

Packages/RealityKitContent/Sources/RealityKitContent/ValueGradient.swift:8 — representative type boundary

protocol Interpolatable<Interpolator> {
    associatedtype Interpolator: BinaryFloatingPoint
    static func *(lhs: Self, rhs: Interpolator) -> Self
    static func *(lhs: Interpolator, rhs: Self) -> Self
    static func +(lhs: Self, rhs: Self) -> Self
}

The source explicitly defines local protocol relationships: Double → Interpolatable, Float → Interpolatable, SIMD3<Float> → Interpolatable, SIMD4<Float> → Interpolatable.

Access control

Reference code

CanyonCrosser/CanyonCrosserApp.swift:13 — representative boundary

@main
struct CanyonCrosserApp: App {
    @State private var appModel: AppModel = AppModel()
    // ...
}

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

Main application flow

sequenceDiagram
    participant AppModel
    participant Entity
    participant root
    participant grandCanyonEntity
    AppModel->>Entity: Entity()
    AppModel->>AppModel: rootScene()
    AppModel->>root: findAndLoadEntity()
    AppModel->>AppModel: findAndLoadEntity()
    AppModel->>root: findAndLoadEntity()
    AppModel->>root: findAndLoadEntity()
    AppModel->>grandCanyonEntity: findAndLoadEntity()
    AppModel->>AppModel: loadHikeAssets()

Reference code

CanyonCrosser/Models/AppModel/AppModel+Loading.swift:26 — prepareAssets()

    func prepareAssets() async throws {
        defer { doAllSetup() }
        // Load the root entity, the Grand Canyon scene.
        async let rootScene = try await Entity(named: EntityName.grandCanyonScene.rawValue, in: realityKitContentBundle)
        root = try await rootScene

        grandCanyonEntity = try await root.findAndLoadEntity(named: .grandCanyonEntity, error: .grandCanyon)

        let terrainEntity = try await self.grandCanyonEntity.findAndLoadEntity(named: .terrain, error: .terrain)
        self.terrainEntityBaseExtents = (terrainEntity.visualBounds(relativeTo: nil).extents) / terrainEntity.scale(relativeTo: nil)

        sunlight = try await root.findAndLoadEntity(named: .sunlight, error: .sunlight)

        birdsEntity = try await root.findAndLoadEntity(named: .birds, error: .birds)

        cloudsEntity = try await grandCanyonEntity.findAndLoadEntity(named: .clouds, error: .clouds)

        hikerEntity = try await grandCanyonEntity.findAndLoadEntity(named: .hiker, error: .hiker)

        hikeEntities = hikes.reduce(into: [Hike: [Entity]]()) { partialResult, hike in
            partialResult[hike] = []
        }
        await loadHikeAssets()
    }

Naming conventions

• Types: App: CanyonCrosserApp; Component: ClippingMarginPercentageComponent, FadingCloudComponent, HikePlaybackStateComponent, HikeTimingComponent, HikerDragStateComponent; Model: AppModel, AppPhaseModel, CarouselModel; System: ClippingMarginPercentageSystem, FeatheringSystem, HikeSystem, LightRotationSystem, TimeOfDayLightSystem; View: BackButtonView, CarouselBodyView, CarouselLabelView, CarouselView, CompactControlsView.
• Protocols: Interpolatable.
• Methods: fadeInClouds, fadeOutClouds, getHikerAnimationPlaybackController, setHikerVisibility, updateNormalizedZPositions, interpolateColor, interpolateIntensity.
• Files: CanyonCrosser/CanyonCrosserApp.swift, CanyonCrosser/Views/Progress Slider/WeatherOrTimeView.swift, CanyonCrosser/Models/AppModel/AppModel.swift, CanyonCrosser/Models/AppPhaseModel.swift, CanyonCrosser/ECS/ClippingMarginPercentageComponent.swift, CanyonCrosser/Views/Carousel/CarouselLabelView.swift.

Architecture takeaways

• CanyonCrosserApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, RealityKit, RealityKitContent, CoreGraphics 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