Controlling Entity Collisions in RealityKit

At a glance

Project structure

Source bundle/
└── RealityKitCollisionGroups/
    ├── ViewController.swift  # ViewController
    ├── Custom Entities/
    │   ├── Entities.swift  # MovableEntity, BoxEntity, BeveledBoxEntity
    │   └── PlaneEntity.swift  # PlaneEntity
    └── AppDelegate.swift  # AppDelegate

Structure observations

• The runtime boundary is UIApplicationDelegate + UIViewController; 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
    AppDelegate_1["AppDelegate"]
    UIApplicationDelegate___UIViewController_2["UIApplicationDelegate + UIViewController"]
    ViewController_3["ViewController"]
    RealityKit_entity_graph_4["RealityKit entity graph"]
    RealityKit_collision_filters_events_5["RealityKit collision filters/events"]
    AppDelegate_1 --> UIApplicationDelegate___UIViewController_2
    UIApplicationDelegate___UIViewController_2 --> ViewController_3
    ViewController_3 --> RealityKit_entity_graph_4
    RealityKit_entity_graph_4 --> RealityKit_collision_filters_events_5

Reference code

RealityKitCollisionGroups/AppDelegate.swift:11 — executable or app-lifecycle anchor.

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

}

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
    ViewController *-- BoxEntity : cube1
    ViewController *-- BoxEntity : cube2
    ViewController *-- BoxEntity : cube3
    ViewController *-- SphereEntity : sphere1

Ownership evidence

RealityKitCollisionGroups/ViewController.swift:44 — representative stored state or nearest verified lifecycle anchor.

    let cube1 = BoxEntity(size: 0.05, color: .green, roughness: 0.0)
    let cube2 = BoxEntity(size: 0.05, color: .green, roughness: 0.0)
    let cube3 = BoxEntity(size: 0.05, color: .green, roughness: 0.0)
    
    let sphere1 = SphereEntity(size: 0.05, color: .orange, roughness: 1.0)
    let sphere2 = SphereEntity(size: 0.05, color: .orange, roughness: 1.0)
    let sphere3 = SphereEntity(size: 0.05, color: .orange, roughness: 1.0)

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), public, open; declarations without a modifier are internal.

Reference code

RealityKitCollisionGroups/ViewController.swift:169 — representative visibility boundary.

    fileprivate func configureEntityAccessibility() {
        // ...
    }

Logic ownership and placement

Design patterns

Naming conventions

• Role suffixes are evidence, not decoration: Controller: ViewController.
• Protocols: no app-defined protocol in the reviewed source.
• Commands use verb-led methods: tappedResetButton, toggleDebugDrawing, viewDidLoad, setInitialTransforms, setPhysicsModeAll, setCollisionFilters, configureEntityAccessibility, setScene.
• 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 AppDelegate 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.

Source map

• Official Apple documentation