Skill v1.0.2

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dpearson2699/swift-ios-skills/realitykit

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PublishedApril 26, 2026 at 06:39 PM

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version: "1.0.2" name: realitykit description: "Build augmented reality experiences with RealityKit and ARKit on iOS. Use when adding 3D content with RealityView, loading entities and models, placing objects via raycasting, configuring AR camera sessions, handling world tracking, scene understanding, or implementing entity interactions and gestures."

RealityKit

Build AR experiences on iOS using RealityKit for rendering and ARKit for world tracking. Covers RealityView, entity management, raycasting, scene understanding, and gesture-based interactions. Targets Swift 6.3 / iOS 26+.

Setup
RealityView Basics
Loading and Creating Entities
Anchoring and Placement
Raycasting
Gestures and Interaction
Scene Understanding
Common Mistakes
Review Checklist
References

Setup

Project Configuration

Add NSCameraUsageDescription to Info.plist
For iOS, RealityKit uses the device camera by default via RealityViewCameraContent (iOS 18+, macOS 15+)
No additional capabilities required for basic AR on iOS

Device Requirements

AR features require devices with an A9 chip or later. Always verify support before presenting AR UI.

swift

import ARKit
 
guard ARWorldTrackingConfiguration.isSupported else {
    showUnsupportedDeviceMessage()
    return
}

Key Types

Type	Platform	Role
`RealityView`	iOS 18+, visionOS 1+	SwiftUI view that hosts RealityKit content
`RealityViewCameraContent`	iOS 18+, macOS 15+	Content displayed through the device camera
`Entity`	All	Base class for all scene objects
`ModelEntity`	All	Entity with a visible 3D model
`AnchorEntity`	All	Tethers entities to a real-world anchor

RealityView Basics

RealityView is the SwiftUI entry point for RealityKit. On iOS, it provides RealityViewCameraContent which renders through the device camera for AR.

swift

import SwiftUI
import RealityKit
 
struct ARExperienceView: View {
    var body: some View {
        RealityView { content in
            // content is RealityViewCameraContent on iOS
            let sphere = ModelEntity(
                mesh: .generateSphere(radius: 0.05),
                materials: [SimpleMaterial(
                    color: .blue,
                    isMetallic: true
                )]
            )
            sphere.position = [0, 0, -0.5]  // 50cm in front of camera
            content.add(sphere)
        }
    }
}

Make and Update Pattern

Use the update closure to respond to SwiftUI state changes:

swift

struct PlacementView: View {
    @State private var modelColor: UIColor = .red
 
    var body: some View {
        RealityView { content in
            let box = ModelEntity(
                mesh: .generateBox(size: 0.1),
                materials: [SimpleMaterial(
                    color: .red,
                    isMetallic: false
                )]
            )
            box.name = "colorBox"
            box.position = [0, 0, -0.5]
            content.add(box)
        } update: { content in
            if let box = content.entities.first(
                where: { $0.name == "colorBox" }
            ) as? ModelEntity {
                box.model?.materials = [SimpleMaterial(
                    color: modelColor,
                    isMetallic: false
                )]
            }
        }
 
        Button("Change Color") {
            modelColor = modelColor == .red ? .green : .red
        }
    }
}

Loading and Creating Entities

Loading from USDZ Files

Load 3D models asynchronously to avoid blocking the main thread:

swift

RealityView { content in
    if let robot = try? await ModelEntity(named: "robot") {
        robot.position = [0, -0.2, -0.8]
        robot.scale = [0.01, 0.01, 0.01]
        content.add(robot)
    }
}

Programmatic Mesh Generation

swift

// Box
let box = ModelEntity(
    mesh: .generateBox(size: [0.1, 0.2, 0.1], cornerRadius: 0.005),
    materials: [SimpleMaterial(color: .gray, isMetallic: true)]
)
 
// Sphere
let sphere = ModelEntity(
    mesh: .generateSphere(radius: 0.05),
    materials: [SimpleMaterial(color: .blue, roughness: 0.2, isMetallic: true)]
)
 
// Plane
let plane = ModelEntity(
    mesh: .generatePlane(width: 0.3, depth: 0.3),
    materials: [SimpleMaterial(color: .green, isMetallic: false)]
)

Adding Components

Entities use an ECS (Entity Component System) architecture. Add components to give entities behavior:

swift

let box = ModelEntity(
    mesh: .generateBox(size: 0.1),
    materials: [SimpleMaterial(color: .red, isMetallic: false)]
)
 
// Make it respond to physics
box.components.set(PhysicsBodyComponent(
    massProperties: .default,
    material: .default,
    mode: .dynamic
))
 
// Add collision shape for interaction
box.components.set(CollisionComponent(
    shapes: [.generateBox(size: [0.1, 0.1, 0.1])]
))
 
// Enable input targeting for gestures
box.components.set(InputTargetComponent())

Anchoring and Placement

AnchorEntity

Use AnchorEntity to anchor content to detected surfaces or world positions:

swift

RealityView { content in
    // Anchor to a horizontal surface
    let floorAnchor = AnchorEntity(.plane(
        .horizontal,
        classification: .floor,
        minimumBounds: [0.2, 0.2]
    ))
 
    let model = ModelEntity(
        mesh: .generateBox(size: 0.1),
        materials: [SimpleMaterial(color: .orange, isMetallic: false)]
    )
    floorAnchor.addChild(model)
    content.add(floorAnchor)
}

Anchor Targets

Target	Description
`.plane(.horizontal, ...)`	Horizontal surfaces (floors, tables)
`.plane(.vertical, ...)`	Vertical surfaces (walls)
`.plane(.any, ...)`	Any detected plane
`.world(transform:)`	Fixed world-space position

Raycasting

Use RealityViewCameraContent to convert between SwiftUI view coordinates and RealityKit world space. Pair with SpatialTapGesture to place objects where the user taps on a detected surface.

Gestures and Interaction

Drag Gesture on Entities

swift

struct DraggableARView: View {
    var body: some View {
        RealityView { content in
            let box = ModelEntity(
                mesh: .generateBox(size: 0.1),
                materials: [SimpleMaterial(color: .blue, isMetallic: true)]
            )
            box.position = [0, 0, -0.5]
            box.components.set(CollisionComponent(
                shapes: [.generateBox(size: [0.1, 0.1, 0.1])]
            ))
            box.components.set(InputTargetComponent())
            box.name = "draggable"
            content.add(box)
        }
        .gesture(
            DragGesture()
                .targetedToAnyEntity()
                .onChanged { value in
                    let entity = value.entity
                    guard let parent = entity.parent else { return }
                    entity.position = value.convert(
                        value.location3D,
                        from: .local,
                        to: parent
                    )
                }
        )
    }
}

Tap to Select

swift

.gesture(
    SpatialTapGesture()
        .targetedToAnyEntity()
        .onEnded { value in
            let tappedEntity = value.entity
            highlightEntity(tappedEntity)
        }
)

Scene Understanding

Per-Frame Updates

Subscribe to scene update events for continuous processing:

swift

RealityView { content in
    let entity = ModelEntity(
        mesh: .generateSphere(radius: 0.05),
        materials: [SimpleMaterial(color: .yellow, isMetallic: false)]
    )
    entity.position = [0, 0, -0.5]
    content.add(entity)
 
    _ = content.subscribe(to: SceneEvents.Update.self) { event in
        let time = Float(event.deltaTime)
        entity.position.y += sin(Float(Date().timeIntervalSince1970)) * time * 0.1
    }
}

visionOS Note

On visionOS, ARKit provides a different API surface with ARKitSession, WorldTrackingProvider, and PlaneDetectionProvider. These visionOS-specific types are not available on iOS. On iOS, RealityKit handles world tracking automatically through RealityViewCameraContent.

Common Mistakes

DON'T: Skip AR capability checks

Not all devices support AR. Showing a black camera view with no feedback confuses users.

swift

// WRONG -- no device check
struct MyARView: View {
    var body: some View {
        RealityView { content in
            // Fails silently on unsupported devices
        }
    }
}
 
// CORRECT -- check support and show fallback
struct MyARView: View {
    var body: some View {
        if ARWorldTrackingConfiguration.isSupported {
            RealityView { content in
                // AR content
            }
        } else {
            ContentUnavailableView(
                "AR Not Supported",
                systemImage: "arkit",
                description: Text("This device does not support AR.")
            )
        }
    }
}

DON'T: Load heavy models synchronously

Loading large USDZ files on the main thread causes frame drops and hangs. The make closure of RealityView is async -- use it.

swift

// WRONG -- synchronous load blocks the main thread
RealityView { content in
    let model = try! Entity.load(named: "large-scene")
    content.add(model)
}
 
// CORRECT -- async load
RealityView { content in
    if let model = try? await ModelEntity(named: "large-scene") {
        content.add(model)
    }
}

DON'T: Forget collision and input target components for interactive entities

Gestures only work on entities that have both CollisionComponent and InputTargetComponent. Without them, taps and drags pass through.

swift

// WRONG -- entity ignores gestures
let box = ModelEntity(mesh: .generateBox(size: 0.1))
content.add(box)
 
// CORRECT -- add collision and input components
let box = ModelEntity(
    mesh: .generateBox(size: 0.1),
    materials: [SimpleMaterial(color: .red, isMetallic: false)]
)
box.components.set(CollisionComponent(
    shapes: [.generateBox(size: [0.1, 0.1, 0.1])]
))
box.components.set(InputTargetComponent())
content.add(box)

DON'T: Create new entities in the update closure

The update closure runs on every SwiftUI state change. Creating entities there duplicates content on each render pass.

swift

// WRONG -- duplicates entities on every state change
RealityView { content in
    // empty
} update: { content in
    let sphere = ModelEntity(mesh: .generateSphere(radius: 0.05))
    content.add(sphere)  // Added again on every update
}
 
// CORRECT -- create in make, modify in update
RealityView { content in
    let sphere = ModelEntity(mesh: .generateSphere(radius: 0.05))
    sphere.name = "mySphere"
    content.add(sphere)
} update: { content in
    if let sphere = content.entities.first(
        where: { $0.name == "mySphere" }
    ) as? ModelEntity {
        // Modify existing entity
        sphere.position.y = newYPosition
    }
}

DON'T: Ignore camera permission

RealityKit on iOS needs camera access. If the user denies permission, the view shows a black screen with no explanation.

swift

// WRONG -- no permission handling
RealityView { content in
    // Black screen if camera denied
}
 
// CORRECT -- check and request permission
struct ARContainerView: View {
    @State private var cameraAuthorized = false
 
    var body: some View {
        Group {
            if cameraAuthorized {
                RealityView { content in
                    // AR content
                }
            } else {
                ContentUnavailableView(
                    "Camera Access Required",
                    systemImage: "camera.fill",
                    description: Text("Enable camera in Settings to use AR.")
                )
            }
        }
        .task {
            let status = AVCaptureDevice.authorizationStatus(for: .video)
            if status == .authorized {
                cameraAuthorized = true
            } else if status == .notDetermined {
                cameraAuthorized = await AVCaptureDevice
                    .requestAccess(for: .video)
            }
        }
    }
}

Review Checklist

[ ] NSCameraUsageDescription set in Info.plist
[ ] AR device capability checked before presenting AR views
[ ] Camera permission requested and denial handled with a fallback UI
[ ] 3D models loaded asynchronously in the make closure
[ ] Entities created in make, modified in update (not created in update)
[ ] Interactive entities have both CollisionComponent and InputTargetComponent
[ ] Collision shapes match the visual size of the entity
[ ] SceneEvents.Update subscriptions used for per-frame logic (not SwiftUI timers)
[ ] Large scenes use ModelEntity(named:) async loading, not Entity.load(named:)
[ ] Anchor entities target appropriate surface types for the use case
[ ] Entity names set for lookup in the update closure

References

Extended patterns (physics, animations, lighting, ECS): references/realitykit-patterns.md
RealityKit framework
RealityView
RealityViewCameraContent
Entity
ModelEntity
AnchorEntity
ARKit framework
ARKit in iOS
ARWorldTrackingConfiguration
Loading entities from a file

← v1.0.0 All versions v1.0.3 →

Skill v1.0.2

RealityKit

Contents

Setup

Project Configuration

Device Requirements

Key Types

RealityView Basics

Make and Update Pattern

Loading and Creating Entities

Loading from USDZ Files

Programmatic Mesh Generation

Adding Components

Anchoring and Placement

AnchorEntity

Anchor Targets

Raycasting

Gestures and Interaction

Drag Gesture on Entities

Tap to Select

Scene Understanding

Per-Frame Updates

visionOS Note

Common Mistakes

DON'T: Skip AR capability checks

DON'T: Load heavy models synchronously

DON'T: Forget collision and input target components for interactive entities

DON'T: Create new entities in the update closure

DON'T: Ignore camera permission

Review Checklist

References