Composing interactive 3D content with RealityKit and Reality Composer Pro

At a glance

Project structure

Source bundle/
├── RealityKitAnimation/RealityKitAnimation/AppModel.swift  # ImmersiveSpaceState, AppModel
├── RealityKitAnimation/RealityKitAnimation/ImmersiveView.swift  # ImmersiveView
├── RealityKitAnimation/RealityKitAnimation/RealityKitAnimationApp.swift  # RealityKitAnimationApp
├── RealityKitAnimation/Packages/RealityKitContent/Sources/RealityKitContent/HeroRobotComponent.swift  # HeroRobotState, RobotTravelHomeAction, RobotMoveToHomeComplete
├── RealityKitAnimation/Packages/RealityKitContent/Sources/RealityKitContent/EntityMoverComponent.swift  # EntityMoverComponent, EntityMoverRuntimeComponent, EntityMoverSystem
├── RealityKitAnimation/Packages/RealityKitContent/Sources/RealityKitContent/HeroPlantComponent.swift  # PlantState, HeroPlantComponent, HeroPlantRuntimeComponent
├── RealityKitAnimation/Packages/RealityKitContent/Sources/RealityKitContent/StationaryRobotComponent.swift  # StationaryRobotComponent, StationaryRobotRuntimeComponent, StationaryRobotSystem
└── RealityKitAnimation/Packages/RealityKitContent/Package.realitycomposerpro/ProjectData/main.json  # authored RealityKit content

Structure observations

• The runtime boundary is WindowGroup + volumetric window + ImmersiveSpace; 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.
• Authored .reality, .rkassets, or Reality Composer Pro content is an implementation boundary; Swift loads or drives it rather than reproducing its entity graph.

Overall architecture

flowchart LR
    RealityKitAnimationApp_1["RealityKitAnimationApp"]
    WindowGroup___volumetric_window___ImmersiveSpace_2["WindowGroup + volumetric window + ImmersiveSpace"]
    ImmersiveView_3["ImmersiveView"]
    AppModel_4["AppModel"]
    EntityMoverSystem_5["EntityMoverSystem"]
    RealityKit_entity_graph_6["RealityKit entity graph"]
    authored_RealityKit_content___ECS_7["authored RealityKit content + ECS"]
    RealityKitAnimationApp_1 --> WindowGroup___volumetric_window___ImmersiveSpace_2
    WindowGroup___volumetric_window___ImmersiveSpace_2 --> ImmersiveView_3
    ImmersiveView_3 --> AppModel_4
    AppModel_4 --> EntityMoverSystem_5
    EntityMoverSystem_5 --> RealityKit_entity_graph_6
    RealityKit_entity_graph_6 --> authored_RealityKit_content___ECS_7

Reference code

RealityKitAnimation/RealityKitAnimation/RealityKitAnimationApp.swift:11 — executable or app-lifecycle anchor.

struct RealityKitAnimationApp: App {
    // ...
}

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
    RealityKitAnimationApp *-- AppModel : appModel
    ImmersiveView o-- AppModel : appModel
    AppModel --> ImmersiveSpaceState : immersiveSpaceState
    HeroPlantRuntimeComponent --> AnimationPlaybackController : wiltingPlaybackController

Ownership evidence

RealityKitAnimation/RealityKitAnimation/RealityKitAnimationApp.swift:13 — representative stored state or nearest verified lifecycle anchor.

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

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 fileprivate, private(set), open; declarations without a modifier are internal.

Reference code

RealityKitAnimation/Packages/RealityKitContent/Sources/RealityKitContent/EntityMoverComponent.swift:31 — representative visibility boundary.

    private var settingsSource: EntityMoverComponent? = nil

    // The x, y, z extent of movement for the current frame.
    private var currentExtentX: Float = 0.0
    private var currentExtentY: Float = 0.0
    private var currentExtentZ: Float = 0.0

Logic ownership and placement

Design patterns

Naming conventions

• Role suffixes are evidence, not decoration: App: RealityKitAnimationApp; Model: AppModel; System: EntityMoverSystem, HeroPlantSystem, HeroRobotSystem, StationaryRobotSystem; Component: EntityMoverComponent, EntityMoverRuntimeComponent, HeroPlantComponent, HeroPlantRuntimeComponent, HeroRobotComponent; View: ContentView, ImmersiveView.
• ECS names pair data and behavior: components EntityMoverComponent, EntityMoverRuntimeComponent, HeroPlantComponent, HeroPlantRuntimeComponent, HeroRobotComponent; systems EntityMoverSystem, HeroPlantSystem, HeroRobotSystem, StationaryRobotSystem.
• Protocols: no app-defined protocol in the reviewed source.
• Commands use verb-led methods: getHeroRobotIfAvailable, getHeroRobot, isPlantUnhealthy, isAvailable, setState, enableIK, calculateReachPosition, initialize.
• 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 RealityKitAnimationApp 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.
• Count authored Reality Composer Pro assets as implementation; the Swift shell is not the complete architecture.

Source map

• Official Apple documentation