RealityKit Development Guide

Purpose: Build 3D content, AR experiences, and spatial computing apps using RealityKit's Entity-Component-System architecture iOS Version: iOS 13+ (base), iOS 18+ (RealityView on iOS), visionOS 1.0+ Xcode: Xcode 15+

When to Use This Skill

Use this skill when:

Building any 3D experience (AR, games, visualization, spatial computing)
Creating SwiftUI apps with 3D content (RealityView, Model3D)
Implementing AR with anchors (world, image, face, body tracking)
Working with Entity-Component-System (ECS) architecture
Setting up physics, collisions, or spatial interactions
Building multiplayer or shared AR experiences
Migrating from SceneKit to RealityKit
Targeting visionOS

Do NOT use this skill for:

SceneKit maintenance (use
```
axiom-scenekit
```
)
2D games (use
```
axiom-spritekit
```
)
Metal shader programming (use
```
axiom-metal-migration-ref
```
)
Pure GPU compute (use Metal directly)

1. Mental Model: ECS vs Scene Graph

Scene Graph (SceneKit)

In SceneKit, nodes own their properties. A node IS a renderable, collidable, animated thing.

Entity-Component-System (RealityKit)

In RealityKit, entities are empty containers. Components add data. Systems process that data.

Entity (identity + hierarchy)
  ├── TransformComponent (position, rotation, scale)
  ├── ModelComponent (mesh + materials)
  ├── CollisionComponent (collision shapes)
  ├── PhysicsBodyComponent (mass, mode)
  └── [YourCustomComponent] (game-specific data)

System (processes entities with specific components each frame)

Why ECS matters:

Composition over inheritance: Combine any components on any entity
Data-oriented: Systems process arrays of components efficiently
Decoupled logic: Systems don't know about each other
Testable: Components are pure data, Systems are pure logic

The ECS Mental Shift

Scene Graph Thinking	ECS Thinking
"The player node moves"	"The movement system processes entities with MovementComponent"
"Add a method to the node subclass"	"Add a component, create a system"
"Override `update(_:)` in the node"	"Register a System that queries for components"
"The node knows its health"	"HealthComponent holds data, DamageSystem processes it"

2. Entity Hierarchy

Creating Entities

swift

// Empty entity
let entity = Entity()
entity.name = "player"

// Entity with components
let entity = Entity()
entity.components[ModelComponent.self] = ModelComponent(
    mesh: .generateBox(size: 0.1),
    materials: [SimpleMaterial(color: .blue, isMetallic: false)]
)

// ModelEntity convenience (has ModelComponent built in)
let box = ModelEntity(
    mesh: .generateBox(size: 0.1),
    materials: [SimpleMaterial(color: .red, isMetallic: true)]
)

Hierarchy Management

swift

// Parent-child
parent.addChild(child)
child.removeFromParent()

// Find entities
let found = root.findEntity(named: "player")

// Enumerate
for child in entity.children {
    // Process children
}

// Clone
let clone = entity.clone(recursive: true)

Transform

swift

// Local transform (relative to parent)
entity.position = SIMD3<Float>(0, 1, 0)
entity.orientation = simd_quatf(angle: .pi / 4, axis: SIMD3(0, 1, 0))
entity.scale = SIMD3<Float>(repeating: 2.0)

// World-space queries
let worldPos = entity.position(relativeTo: nil)
let worldTransform = entity.transform(relativeTo: nil)

// Set world-space transform
entity.setPosition(SIMD3(1, 0, 0), relativeTo: nil)

// Look at a point
entity.look(at: targetPosition, from: entity.position, relativeTo: nil)

3. Components

Built-in Components

Component	Purpose
`Transform`	Position, rotation, scale
`ModelComponent`	Mesh geometry + materials
`CollisionComponent`	Collision shapes for physics and interaction
`PhysicsBodyComponent`	Mass, physics mode (dynamic/static/kinematic)
`PhysicsMotionComponent`	Linear and angular velocity
`AnchoringComponent`	AR anchor attachment
`SynchronizationComponent`	Multiplayer sync
`PerspectiveCameraComponent`	Camera settings
`DirectionalLightComponent`	Directional light
`PointLightComponent`	Point light
`SpotLightComponent`	Spot light
`CharacterControllerComponent`	Character physics controller
`AudioMixGroupsComponent`	Audio mixing
`SpatialAudioComponent`	3D positional audio
`AmbientAudioComponent`	Non-positional audio
`ChannelAudioComponent`	Multi-channel audio
`OpacityComponent`	Entity transparency
`GroundingShadowComponent`	Contact shadow
`InputTargetComponent`	Gesture input (visionOS)
`HoverEffectComponent`	Hover highlight (visionOS)
`AccessibilityComponent`	VoiceOver support

Custom Components

swift

struct HealthComponent: Component {
    var current: Int
    var maximum: Int

    var percentage: Float {
        Float(current) / Float(maximum)
    }
}

// Register before use (typically in app init)
HealthComponent.registerComponent()

// Attach to entity
entity.components[HealthComponent.self] = HealthComponent(current: 100, maximum: 100)

// Read
if let health = entity.components[HealthComponent.self] {
    print(health.current)
}

// Modify
entity.components[HealthComponent.self]?.current -= 10

Component Lifecycle

Components are value types (structs). When you read a component, modify it, and write it back, you're replacing the entire component:

swift

// Read-modify-write pattern
var health = entity.components[HealthComponent.self]!
health.current -= damage
entity.components[HealthComponent.self] = health

Anti-pattern: Holding a reference to a component and expecting mutations to propagate. Components are copied on read.

4. Systems

System Protocol

swift

struct DamageSystem: System {
    // Define which components this system needs
    static let query = EntityQuery(where: .has(HealthComponent.self))

    init(scene: RealityKit.Scene) {
        // One-time setup
    }

    func update(context: SceneUpdateContext) {
        for entity in context.entities(matching: Self.query,
                                        updatingSystemWhen: .rendering) {
            var health = entity.components[HealthComponent.self]!
            if health.current <= 0 {
                entity.removeFromParent()
            }
        }
    }
}

// Register system
DamageSystem.registerSystem()

System Best Practices

One responsibility per system: MovementSystem, DamageSystem, RenderingSystem — not GameLogicSystem
Query filtering: Use precise queries to avoid processing irrelevant entities
Order matters: Systems run in registration order. Register dependencies first.
Avoid storing entity references: Query each frame instead. Entity references can become stale.

Event Handling

swift

// Subscribe to collision events
scene.subscribe(to: CollisionEvents.Began.self) { event in
    let entityA = event.entityA
    let entityB = event.entityB
    // Handle collision
}

// Subscribe to scene update
scene.subscribe(to: SceneEvents.Update.self) { event in
    let deltaTime = event.deltaTime
    // Per-frame logic
}

5. SwiftUI Integration

RealityView (iOS 18+, visionOS 1.0+)

swift

struct ContentView: View {
    var body: some View {
        RealityView { content in
            // make closure — called once
            let box = ModelEntity(
                mesh: .generateBox(size: 0.1),
                materials: [SimpleMaterial(color: .blue, isMetallic: false)]
            )
            content.add(box)

        } update: { content in
            // update closure — called when SwiftUI state changes
        }
    }
}

RealityView with Camera (iOS)

On iOS,

RealityView

provides a camera content parameter for configuring the AR or virtual camera:

swift

RealityView { content, attachments in
    // Load 3D content
    if let model = try? await ModelEntity(named: "scene") {
        content.add(model)
    }
}

Loading Content Asynchronously

swift

RealityView { content in
    // Load from bundle
    if let entity = try? await Entity(named: "MyScene", in: .main) {
        content.add(entity)
    }

    // Load from URL
    if let entity = try? await Entity(contentsOf: modelURL) {
        content.add(entity)
    }
}

Model3D (Simple Display)

swift

// Simple 3D model display (no interaction)
Model3D(named: "toy_robot") { model in
    model
        .resizable()
        .scaledToFit()
} placeholder: {
    ProgressView()
}

SwiftUI Attachments (visionOS)

swift

RealityView { content, attachments in
    let entity = ModelEntity(mesh: .generateSphere(radius: 0.1))
    content.add(entity)

    if let label = attachments.entity(for: "priceTag") {
        label.position = SIMD3(0, 0.15, 0)
        entity.addChild(label)
    }
} attachments: {
    Attachment(id: "priceTag") {
        Text("$9.99")
            .padding()
            .glassBackgroundEffect()
    }
}

State Binding Pattern

swift

struct GameView: View {
    @State private var score = 0

    var body: some View {
        VStack {
            Text("Score: \(score)")

            RealityView { content in
                let scene = try! await Entity(named: "GameScene")
                content.add(scene)
            } update: { content in
                // React to state changes
                // Note: update is called when SwiftUI state changes,
                // not every frame. Use Systems for per-frame logic.
            }
        }
    }
}

6. AR on iOS

AnchorEntity

swift

// Horizontal plane
let anchor = AnchorEntity(.plane(.horizontal, classification: .table,
                                  minimumBounds: SIMD2(0.2, 0.2)))

// Vertical plane
let anchor = AnchorEntity(.plane(.vertical, classification: .wall,
                                  minimumBounds: SIMD2(0.5, 0.5)))

// World position
let anchor = AnchorEntity(world: SIMD3<Float>(0, 0, -1))

// Image anchor
let anchor = AnchorEntity(.image(group: "AR Resources", name: "poster"))

// Face anchor (front camera)
let anchor = AnchorEntity(.face)

// Body anchor
let anchor = AnchorEntity(.body)

SpatialTrackingSession (iOS 18+)

swift

let session = SpatialTrackingSession()
let configuration = SpatialTrackingSession.Configuration(tracking: [.plane, .object])
let result = await session.run(configuration)

if let notSupported = result {
    // Handle unsupported tracking on this device
    for denied in notSupported.deniedTrackingModes {
        print("Not supported: \(denied)")
    }
}

AR Best Practices

Anchor entities to detected surfaces rather than world positions for stability
Use plane classification (
```
.table
```
,
```
.floor
```
,
```
.wall
```
) to place content appropriately
Start with horizontal plane detection — it's the most reliable
Test on real devices; simulator AR is limited
Provide visual feedback during surface detection (coaching overlay)

7. Interaction

ManipulationComponent (iOS, visionOS)

swift

// Enable drag, rotate, scale gestures
entity.components[ManipulationComponent.self] = ManipulationComponent(
    allowedModes: .all  // .translate, .rotate, .scale
)

// Also requires CollisionComponent for hit testing
entity.generateCollisionShapes(recursive: true)

InputTargetComponent (visionOS)

swift

// Required for visionOS gesture input
entity.components[InputTargetComponent.self] = InputTargetComponent()
entity.components[CollisionComponent.self] = CollisionComponent(
    shapes: [.generateBox(size: SIMD3(0.1, 0.1, 0.1))]
)

Gesture Integration with SwiftUI

swift

RealityView { content in
    let entity = ModelEntity(mesh: .generateBox(size: 0.1))
    entity.generateCollisionShapes(recursive: true)
    entity.components.set(InputTargetComponent())
    content.add(entity)
}
.gesture(
    TapGesture()
        .targetedToAnyEntity()
        .onEnded { value in
            let tappedEntity = value.entity
            // Handle tap
        }
)
.gesture(
    DragGesture()
        .targetedToAnyEntity()
        .onChanged { value in
            value.entity.position = value.convert(value.location3D,
                from: .local, to: .scene)
        }
)

Hit Testing

swift

// Ray-cast from screen point
if let result = arView.raycast(from: screenPoint,
                                allowing: .estimatedPlane,
                                alignment: .horizontal).first {
    let worldPosition = result.worldTransform.columns.3
    // Place entity at worldPosition
}

8. Materials and Rendering

Material Types

Material	Purpose	Customization
`SimpleMaterial`	Solid color or texture	Color, metallic, roughness
`PhysicallyBasedMaterial`	Full PBR	All PBR maps (base color, normal, metallic, roughness, AO, emissive)
`UnlitMaterial`	No lighting response	Color or texture, always fully lit
`OcclusionMaterial`	Invisible but occludes	AR content hiding behind real objects
`VideoMaterial`	Video playback on surface	AVPlayer-driven
`ShaderGraphMaterial`	Custom shader graph	Reality Composer Pro
`CustomMaterial`	Metal shader functions	Full Metal control

PhysicallyBasedMaterial

swift

var material = PhysicallyBasedMaterial()
material.baseColor = .init(tint: .white,
    texture: .init(try! .load(named: "albedo")))
material.metallic = .init(floatLiteral: 0.0)
material.roughness = .init(floatLiteral: 0.5)
material.normal = .init(texture: .init(try! .load(named: "normal")))
material.ambientOcclusion = .init(texture: .init(try! .load(named: "ao")))
material.emissiveColor = .init(color: .blue)
material.emissiveIntensity = 2.0

let entity = ModelEntity(
    mesh: .generateSphere(radius: 0.1),
    materials: [material]
)

OcclusionMaterial (AR)

swift

// Invisible plane that hides 3D content behind it
let occluder = ModelEntity(
    mesh: .generatePlane(width: 1, depth: 1),
    materials: [OcclusionMaterial()]
)
occluder.position = SIMD3(0, 0, 0)
anchor.addChild(occluder)

Environment Lighting

swift

// Image-based lighting
if let resource = try? await EnvironmentResource(named: "studio_lighting") {
    // Apply via RealityView content
}

9. Physics and Collision

Collision Shapes

swift

// Generate from mesh (accurate but expensive)
entity.generateCollisionShapes(recursive: true)

// Manual shapes (prefer for performance)
entity.components[CollisionComponent.self] = CollisionComponent(
    shapes: [
        .generateBox(size: SIMD3(0.1, 0.2, 0.1)),     // Box
        .generateSphere(radius: 0.1),                   // Sphere
        .generateCapsule(height: 0.3, radius: 0.05)     // Capsule
    ]
)

Physics Body

swift

// Dynamic — physics simulation controls movement
entity.components[PhysicsBodyComponent.self] = PhysicsBodyComponent(
    massProperties: .init(mass: 1.0),
    material: .generate(staticFriction: 0.5,
                        dynamicFriction: 0.3,
                        restitution: 0.4),
    mode: .dynamic
)

// Static — immovable collision surface
ground.components[PhysicsBodyComponent.self] = PhysicsBodyComponent(
    mode: .static
)

// Kinematic — code-controlled, participates in collisions
platform.components[PhysicsBodyComponent.self] = PhysicsBodyComponent(
    mode: .kinematic
)

Collision Groups and Filters

swift

// Define groups
let playerGroup = CollisionGroup(rawValue: 1 << 0)
let enemyGroup = CollisionGroup(rawValue: 1 << 1)
let bulletGroup = CollisionGroup(rawValue: 1 << 2)

// Filter: player collides with enemies and bullets
entity.components[CollisionComponent.self] = CollisionComponent(
    shapes: [.generateSphere(radius: 0.1)],
    filter: CollisionFilter(
        group: playerGroup,
        mask: enemyGroup | bulletGroup
    )
)

Collision Events

swift

// Subscribe in RealityView make closure or System
scene.subscribe(to: CollisionEvents.Began.self, on: playerEntity) { event in
    let otherEntity = event.entityA == playerEntity ? event.entityB : event.entityA
    handleCollision(with: otherEntity)
}

Applying Forces

swift

if var motion = entity.components[PhysicsMotionComponent.self] {
    motion.linearVelocity = SIMD3(0, 5, 0)  // Impulse up
    entity.components[PhysicsMotionComponent.self] = motion
}

10. Animation

Transform Animation

swift

// Animate to position over duration
entity.move(
    to: Transform(
        scale: SIMD3(repeating: 1.5),
        rotation: simd_quatf(angle: .pi, axis: SIMD3(0, 1, 0)),
        translation: SIMD3(0, 2, 0)
    ),
    relativeTo: entity.parent,
    duration: 2.0,
    timingFunction: .easeInOut
)

Playing USD Animations

swift

if let entity = try? await Entity(named: "character") {
    // Play all available animations
    for animation in entity.availableAnimations {
        entity.playAnimation(animation.repeat())
    }
}

Animation Playback Control

swift

let controller = entity.playAnimation(animation)
controller.pause()
controller.resume()
controller.speed = 2.0      // 2x playback speed
controller.blendFactor = 0.5 // Blend with current state

11. Audio

Spatial Audio

swift

// Load audio resource
let resource = try! AudioFileResource.load(named: "engine.wav",
    configuration: .init(shouldLoop: true))

// Create entity with spatial audio
let audioEntity = Entity()
audioEntity.components[SpatialAudioComponent.self] = SpatialAudioComponent()
let controller = audioEntity.playAudio(resource)

// Position the audio source in 3D space
audioEntity.position = SIMD3(2, 0, -1)

Ambient Audio

swift

entity.components[AmbientAudioComponent.self] = AmbientAudioComponent()
entity.playAudio(backgroundMusic)

12. Performance

Entity Count

Under 100 entities: No concerns
100-1000 entities: Monitor with RealityKit debugger
1000+ entities: Use instancing and LOD strategies

Instancing

swift

// Share mesh and material across many entities
let sharedMesh = MeshResource.generateSphere(radius: 0.01)
let sharedMaterial = SimpleMaterial(color: .white, isMetallic: false)

for i in 0..<1000 {
    let entity = ModelEntity(mesh: sharedMesh, materials: [sharedMaterial])
    entity.position = randomPosition()
    parent.addChild(entity)
}

RealityKit automatically batches entities with identical mesh and material resources.

Component Churn

Anti-pattern: Creating and replacing components every frame.

swift

// BAD — component allocation every frame
func update(context: SceneUpdateContext) {
    for entity in context.entities(matching: query, updatingSystemWhen: .rendering) {
        entity.components[ModelComponent.self] = ModelComponent(
            mesh: .generateBox(size: 0.1),
            materials: [newMaterial]  // New allocation every frame
        )
    }
}

// GOOD — modify existing component
func update(context: SceneUpdateContext) {
    for entity in context.entities(matching: query, updatingSystemWhen: .rendering) {
        // Only update when actually needed
        if needsUpdate {
            var model = entity.components[ModelComponent.self]!
            model.materials = [cachedMaterial]
            entity.components[ModelComponent.self] = model
        }
    }
}

Collision Shape Optimization

Use simple shapes (box, sphere, capsule) instead of mesh-based collision

generateCollisionShapes(recursive: true)

is convenient but expensive

For static geometry, generate shapes once during setup

Profiling

Use Xcode's RealityKit debugger:

Entity Inspector: View entity hierarchy and components
Statistics Overlay: Entity count, draw calls, triangle count
Physics Visualization: Show collision shapes

13. Multiplayer

Synchronization Basics

swift

// Components sync automatically if they conform to Codable
struct ScoreComponent: Component, Codable {
    var points: Int
}

// SynchronizationComponent controls what syncs
entity.components[SynchronizationComponent.self] = SynchronizationComponent()

MultipeerConnectivityService

swift

let service = try MultipeerConnectivityService(session: mcSession)
// Entities with SynchronizationComponent auto-sync across peers

Ownership

Only the owner of an entity can modify it
Request ownership before modifying shared entities
Non-Codable component data does not sync

14. Anti-Patterns

Anti-Pattern 1: UIKit-Style Thinking in ECS

Time cost: Hours of frustration from fighting the architecture

swift

// BAD — subclassing Entity for behavior
class PlayerEntity: Entity {
    func takeDamage(_ amount: Int) { /* logic in entity */ }
}

// GOOD — component holds data, system has logic
struct HealthComponent: Component { var hp: Int }
struct DamageSystem: System {
    static let query = EntityQuery(where: .has(HealthComponent.self))
    func update(context: SceneUpdateContext) {
        // Process damage here
    }
}

Anti-Pattern 2: Monolithic Entities

Time cost: Untestable, inflexible architecture

Don't put all game logic in one entity type. Split into components that can be mixed and matched.

Anti-Pattern 3: Frame-Based Updates Without Systems

Time cost: Missed frame updates, inconsistent behavior

swift

// BAD — timer-based updates
Timer.scheduledTimer(withTimeInterval: 1/60, repeats: true) { _ in
    entity.position.x += 0.01
}

// GOOD — System update
struct MovementSystem: System {
    static let query = EntityQuery(where: .has(VelocityComponent.self))
    func update(context: SceneUpdateContext) {
        for entity in context.entities(matching: Self.query,
                                        updatingSystemWhen: .rendering) {
            let velocity = entity.components[VelocityComponent.self]!
            entity.position += velocity.value * Float(context.deltaTime)
        }
    }
}

Anti-Pattern 4: Not Generating Collision Shapes for Interactive Entities

Time cost: 15-30 min debugging "why taps don't work"

Gestures require

CollisionComponent

. If an entity has

InputTargetComponent

(visionOS) or

ManipulationComponent

but no

CollisionComponent

, gestures will never fire.

Anti-Pattern 5: Storing Entity References in Systems

Time cost: Crashes from stale references

swift

// BAD — entity might be removed between frames
struct BadSystem: System {
    var playerEntity: Entity?  // Stale reference risk

    func update(context: SceneUpdateContext) {
        playerEntity?.position.x += 0.1  // May crash
    }
}

// GOOD — query each frame
struct GoodSystem: System {
    static let query = EntityQuery(where: .has(PlayerComponent.self))

    func update(context: SceneUpdateContext) {
        for entity in context.entities(matching: Self.query,
                                        updatingSystemWhen: .rendering) {
            entity.position.x += Float(context.deltaTime)
        }
    }
}

15. Code Review Checklist

Custom components registered via
```
registerComponent()
```
before use
Systems registered via
```
registerSystem()
```
before scene loads
Components are value types (structs), not classes
Read-modify-write pattern used for component updates
Interactive entities have
```
CollisionComponent
```
visionOS interactive entities have
```
InputTargetComponent
```
Collision shapes are simple (box/sphere/capsule) where possible
No entity references stored across frames in Systems
Mesh and material resources shared across identical entities
Component updates only occur when values actually change
USD/USDZ format used for 3D assets (not .scn)
Async loading used for all model/scene loading
```
[weak self]
```
in closure-based subscriptions if retaining view/controller

16. Pressure Scenarios

Scenario 1: "ECS Is Overkill for Our Simple App"

Pressure: Team wants to avoid learning ECS, just needs one 3D model displayed

Wrong approach: Skip ECS, jam all logic into RealityView closures.

Correct approach: Even simple apps benefit from ECS. A single

ModelEntity

in a

RealityView

is already using ECS — you're just not adding custom components yet. Start simple, add components as complexity grows.

Push-back template: "We're already using ECS — Entity and ModelComponent. The pattern scales. Adding a custom component when we need behavior is one struct definition, not an architecture change."

Scenario 2: "Just Use SceneKit, We Know It"

Pressure: Team has SceneKit experience, RealityKit is unfamiliar

Wrong approach: Build new features in SceneKit.

Correct approach: SceneKit is soft-deprecated. New features won't be added. Invest in RealityKit now — the ECS concepts transfer to other game engines (Unity, Unreal, Bevy) if needed.

Push-back template: "SceneKit is in maintenance mode — no new features, only security patches. Every line of SceneKit we write is migration debt. RealityKit's concepts (Entity, Component, System) are industry-standard ECS."

Scenario 3: "Make It Work Without Collision Shapes"

Pressure: Deadline, collision shape setup seems complex

Wrong approach: Skip collision shapes, use position-based proximity detection.

Correct approach:

entity.generateCollisionShapes(recursive: true)

takes one line. Without it, gestures won't work and physics won't collide. The "shortcut" creates more debugging time than it saves.

Push-back template: "Collision shapes are required for gestures and physics. It's one line:

entity.generateCollisionShapes(recursive: true)

. Skipping it means gestures silently fail — a harder bug to diagnose."

Resources

WWDC: 2019-603, 2019-605, 2021-10074, 2022-10074, 2023-10080, 2023-10081, 2024-10103, 2024-10153

Docs: /realitykit, /realitykit/entity, /realitykit/realityview, /realitykit/modelentity, /realitykit/anchorentity, /realitykit/component

Skills: axiom-realitykit-ref, axiom-realitykit-diag, axiom-scenekit, axiom-scenekit-ref

axiom-realitykit

NPX Install

Tags

SKILL.md Content

RealityKit Development Guide

When to Use This Skill

1. Mental Model: ECS vs Scene Graph

Scene Graph (SceneKit)

Entity-Component-System (RealityKit)

The ECS Mental Shift

2. Entity Hierarchy

Creating Entities

Hierarchy Management

Transform

3. Components

Built-in Components

Custom Components

Component Lifecycle

4. Systems

System Protocol

System Best Practices

Event Handling

5. SwiftUI Integration

RealityView (iOS 18+, visionOS 1.0+)

RealityView with Camera (iOS)

Loading Content Asynchronously

Model3D (Simple Display)

SwiftUI Attachments (visionOS)

State Binding Pattern

6. AR on iOS

AnchorEntity

SpatialTrackingSession (iOS 18+)

AR Best Practices

7. Interaction

ManipulationComponent (iOS, visionOS)

InputTargetComponent (visionOS)

Gesture Integration with SwiftUI

Hit Testing

8. Materials and Rendering

Material Types

PhysicallyBasedMaterial

OcclusionMaterial (AR)

Environment Lighting

9. Physics and Collision

Collision Shapes

Physics Body

Collision Groups and Filters

Collision Events

Applying Forces

10. Animation

Transform Animation

Playing USD Animations

Animation Playback Control

11. Audio

Spatial Audio

Ambient Audio

12. Performance

Entity Count

Instancing

Component Churn

Collision Shape Optimization

Profiling

13. Multiplayer

Synchronization Basics

MultipeerConnectivityService

Ownership

14. Anti-Patterns

Anti-Pattern 1: UIKit-Style Thinking in ECS

Anti-Pattern 2: Monolithic Entities

Anti-Pattern 3: Frame-Based Updates Without Systems

Anti-Pattern 4: Not Generating Collision Shapes for Interactive Entities

Anti-Pattern 5: Storing Entity References in Systems

15. Code Review Checklist

16. Pressure Scenarios

Scenario 1: "ECS Is Overkill for Our Simple App"

Scenario 2: "Just Use SceneKit, We Know It"

Scenario 3: "Make It Work Without Collision Shapes"

Resources