Implementing special rendering effects with RealityKit postprocessing

At a glance

Project structure

Source bundle/
└── RealityKitPostProcessing/
    ├── RealityView/
    │   ├── RealityView.swift  # RealityView
    │   ├── RealityViewContainer.swift  # RealityViewContainer, Coordinator
    │   └── RealityView+CoachingView.swift
    ├── AppDelegate.swift  # AppDelegate
    ├── ContentView.swift  # ContentView, SelectionCell, ContentView_Previews
    └── Application State/
        ├── ApplicationState+Enums.swift  # CategoryEntry, ModeEntry, Category
        └── ApplicationState.swift  # ApplicationState

Structure observations

• The runtime boundary is SwiftUI/UIKit host; the tree is pruned to lifecycle, state, framework, rendering, and ECS files.
• The source is C/Objective-C header, Metal, Swift; role-named types and feature folders separate the major responsibilities.

Overall architecture

flowchart LR
    AppDelegate_1["AppDelegate"]
    SwiftUI_UIKit_host_2["SwiftUI/UIKit host"]
    RealityView_3["RealityView"]
    Coordinator_4["Coordinator"]
    RealityKit_entity_graph_5["RealityKit entity graph"]
    ARView_postprocess___GPU_effects_6["ARView postprocess + GPU effects"]
    AppDelegate_1 --> SwiftUI_UIKit_host_2
    SwiftUI_UIKit_host_2 --> RealityView_3
    RealityView_3 --> Coordinator_4
    Coordinator_4 --> RealityKit_entity_graph_5
    RealityKit_entity_graph_5 --> ARView_postprocess___GPU_effects_6

Reference code

RealityKitPostProcessing/AppDelegate.swift:12 — executable or app-lifecycle anchor.

class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
}

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
    RealityView --> SKRenderer : skRenderer
    AppDelegate --> UIWindow : window
    RealityView --> MTLTexture : alphaTexture
    RealityView --> MTLTexture : bloomTexture

Ownership evidence

RealityKitPostProcessing/RealityView/RealityView.swift:48 — representative stored state or nearest verified lifecycle anchor.

    var skRenderer: SKRenderer!
    
    // MARK: - Initializers
    
    required init(frame: CGRect) {
        super.init(frame: frame)
    }

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.

Objective-C/C header and implementation visibility is documented separately from Swift lexical access control.

Reference code

RealityKitPostProcessing/RealityView/RealityView+Metal.swift:105 — representative visibility boundary.

    private func postProcessUsingMetalShader(context: ARView.PostProcessContext,
                                             pipeline: MTLComputePipelineState,
                                             parameterHandler: MetalParameterSetup?) {
        // ...
    }

Logic ownership and placement

Design patterns

Naming conventions

• Role suffixes are evidence, not decoration: Coordinator: Coordinator; View: ContentView, RealityView.
• Protocols: no app-defined protocol in the reviewed source.
• Commands use verb-led methods: postProcessSetupCallback, configureWorldTracking, setUpCoachingOverlay, loadScene, setupPostProcessing, postProcess, postEffectNone, application.
• 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