Simulating particles in your visionOS app

At a glance

Project structure

Source bundle/
├── Particle Emitter/
│   ├── MainView.swift  # MainView
│   ├── EmitterView.swift  # EmitterView
│   ├── ParticleEmitterApp.swift  # ParticleEmitterApp
│   └── EmitterSettings.swift  # EmitterSettings, EmitterPresets, ColorSetting
└── Packages/
    └── RealityGestures/
        └── Sources/
            └── RealityGestures/
                ├── RealityDragComponent.swift  # RealityDragComponent, MoveConstraint, DragComponentType
                ├── GeneralGoalComponent.swift  # GeneralGoalComponent, GeneralGoal, GeneralGoalSystem
                └── RealityTapComponent.swift  # RealityTapComponent

Structure observations

• The runtime boundary is WindowGroup; the tree is pruned to lifecycle, state, framework, rendering, and ECS files.
• The source is Swift; role-named types and feature folders separate the major responsibilities.

Overall architecture

flowchart LR
    ParticleEmitterApp_1["ParticleEmitterApp"]
    WindowGroup_2["WindowGroup"]
    MainView_3["MainView"]
    GeneralGoalSystem_4["GeneralGoalSystem"]
    RealityKit_entity_graph_5["RealityKit entity graph"]
    ParticleEmitterComponent_6["ParticleEmitterComponent"]
    ParticleEmitterApp_1 --> WindowGroup_2
    WindowGroup_2 --> MainView_3
    MainView_3 --> GeneralGoalSystem_4
    GeneralGoalSystem_4 --> RealityKit_entity_graph_5
    RealityKit_entity_graph_5 --> ParticleEmitterComponent_6

Reference code

Particle Emitter/ParticleEmitterApp.swift:11 — executable or app-lifecycle anchor.

struct ParticleEmitterApp: App {
    /// Stores settings for the particle emitter.
    @ObservedObject public var emitterSettings = EmitterSettings()

    var body: some Scene {
        WindowGroup {
            MainView()
        }.environment(emitterSettings)
    }
}

The diagram is a responsibility flow, not a claim that every adjacent node directly calls the next. It separates lifecycle, presentation, stable state, framework/session work, and the RealityKit entity graph.

Ownership and state

classDiagram
    ParticleEmitterApp o-- EmitterSettings : emitterSettings
    EmitterSettings *-- Entity : emitterEntity
    MainView o-- EmitterSettings : emitterSettings
    GeneralGoalSystem *-- EntityQuery : generalGoalQuery

Ownership evidence

Particle Emitter/ParticleEmitterApp.swift:13 — representative stored state or nearest verified lifecycle anchor.

@main
struct ParticleEmitterApp: App {
    // ...
    @ObservedObject public var emitterSettings = EmitterSettings()
    // ...
}

Ownership is intentionally narrow: environment, bindings, observed objects, weak links, and delegate callbacks do not prove lifetime ownership. Initialized stored services and wrapper-managed state do; entities added inside a RealityKit content closure belong to that entity graph.

Class and protocol design

The reviewed source defines no local substitution protocol. Its App, View, delegate, renderer, ARKit, and RealityKit conformances are framework-facing contracts, so this document does not label the whole app protocol-oriented.

Access control

No reviewed Swift access example uses private(set), open; declarations without a modifier are internal.

Reference code

Packages/RealityGestures/Sources/RealityGestures/SwiftUI+RealityGestures.swift:35 — representative visibility boundary.

public struct RealityDragGesture: Gesture {
    // ...
    private var updated: ((EntityTargetValue<DragGesture.Value>, RealityDragComponent.DragStatus) -> Void)?
    // ...
}

Logic ownership and placement

Design patterns

Naming conventions

• Role suffixes are evidence, not decoration: App: ParticleEmitterApp; System: GeneralGoalSystem; Component: GeneralGoalComponent, RealityDragComponent, RealityTapComponent; View: EmitterView, MainView.
• ECS names pair data and behavior: components GeneralGoalComponent, RealityDragComponent, RealityTapComponent; systems GeneralGoalSystem.
• Protocols: no app-defined protocol in the reviewed source.
• Commands use verb-led methods: buildEmitterContent, updateEmitterBounds, getCollisionPoints, getClampedPosition, getClampedRotation, handleMoveState, handleRotationState, closestPoint.
• Files and folders use primary-type or responsibility names such as Views, Models, Rendering, Components, Systems, Packages, or feature names where those boundaries exist.

Architecture takeaways

• Treat ParticleEmitterApp as the owner of executable or scene lifecycle, not automatically as the owner of every entity created later.
• Keep view/controller input near presentation, but move sessions, reconstruction, capture, rendering, shared game state, or documents into stable owners when their lifetime exceeds one callback or render pass.
• Use components for per-entity data and systems for repeated simulation instead of centralizing every update in a view model or controller.

Source map

• Official Apple documentation