realitykit

RealityKit

Create augmented reality and 3D experiences on iOS using RealityKit for rendering and ARKit for world tracking and scene understanding. Targets Swift 6.3 / iOS 26+.

Contents

• Capabilities and Permissions
• RealityView and Architecture
• Raycasting vs Entity Hit Testing
• Entity-Component-System (ECS)
• Route by Task
• Common Mistakes
• Review Checklist
• References

Capabilities and Permissions

Add NSCameraUsageDescription to Info.plist. Add arkit to UIRequiredDeviceCapabilities only if AR is an absolute requirement for the app; otherwise, check ARWorldTrackingConfiguration.isSupported at runtime and provide a 3D fallback (content.camera = .virtual).

RealityView and Architecture

RealityView is the modern SwiftUI container for RealityKit content:

• Make closure: Asynchronously loads entities, materials, and sets up initial scene hierarchies.
• Update closure: Observes SwiftUI state changes and mutates entity properties or animations.
• Attachments: SwiftUI views anchored to 3D entities in space via RealityViewContent.attachments.

Raycasting vs Entity Hit Testing

[!IMPORTANT] Distinguish between real-world raycasting and virtual entity hit testing:

• ARKit Raycast (raycast(from:allowing:alignment:)): Intersects real-world physical surfaces (floors, tables, walls) discovered by camera feature points.
• RealityKit Hit Test (scene.hitTest(_:) / entity.hitTest(_:)): Intersects virtual 3D mesh geometry that has a CollisionComponent.

Entity-Component-System (ECS)

RealityKit uses ECS architecture:

1. Entity: Identity container in the 3D scene hierarchy.
2. Component: Pure data structs attached to entities (ModelComponent, CollisionComponent, InputTargetComponent, custom components).
3. System: Per-frame update logic conforming to System protocol that processes entities matching specific component sets.

Route by Task

• For loading USDZ models, custom materials, and programmatic geometries, read Entity Creation and Materials.
• For anchoring entities to planes, faces, images, or world coordinates, read Anchoring and World Tracking.
• For gesture-driven manipulation (rotate, scale, drag) and hit testing, read Gestures and Interaction.
• For physics simulations, collision detection, and raycast placement, read Physics and Raycasting.

Common Mistakes

• Missing NSCameraUsageDescription in Info.plist, causing instant crash when RealityView initializes.
• Attempting to interact with entities that lack CollisionComponent and InputTargetComponent.
• Loading heavy USDZ models synchronously on the main actor, dropping UI frame rates.
• Confusing virtual hit testing with ARKit real-world surface raycasting.
• Forgetting to provide a non-AR fallback (content.camera = .virtual) for devices without world tracking.

Review Checklist

• NSCameraUsageDescription declared in Info.plist
• Runtime support verified with ARWorldTrackingConfiguration.isSupported
• USDZ models and textures loaded asynchronously (Entity(named:) async)
• Interactive entities have both CollisionComponent and InputTargetComponent
• Real-world placement uses ARKit raycast; virtual manipulation uses entity hit test
• Per-frame system updates avoid allocating memory or performing blocking I/O
• Non-AR devices supported with virtual camera fallback

References

• RealityKit extended patterns and gesture handling
• RealityKit documentation
• RealityView
• Entity
• ARKit documentation