dpearson2699/swift-ios-skills

Agent skills for iOS, iPadOS, Swift, SwiftUI, and modern Apple framework development.

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name:: scenekit
description:: Build 3D scenes and visualizations using SceneKit. Use when creating 3D views with SCNView and SCNScene, building node hierarchies with SCNNode, applying materials and lighting, animating with SCNAction, simulating physics with SCNPhysicsBody, loading 3D models (.usdz, .scn), adding particle effects, or embedding SceneKit in SwiftUI with SceneView. Note: SceneKit was deprecated at WWDC 2025 and is in maintenance mode; RealityKit is recommended for new projects.

SceneKit

Name: dpearson2699/swift-ios-skills
Rating: 71.89999999999999 (1 reviews)
Author: dpearson2699

Apple's high-level 3D rendering framework for building scenes and visualizations on iOS using Swift 6.3. Provides a node-based scene graph, built-in geometry primitives, physically based materials, lighting, animation, and physics.

Deprecation notice (WWDC 2025): SceneKit is officially deprecated across all Apple platforms and is now in maintenance mode (critical bug fixes only). Existing apps continue to work. For new projects or major updates, Apple recommends RealityKit. See WWDC 2025 session 288 for migration guidance.

Scene Setup
Nodes and Geometry
Materials
Lighting
Cameras
Animation
Physics
Particle Systems
Loading Models
SwiftUI Integration
Common Mistakes
Review Checklist
References

Scene Setup

SCNView in UIKit

import SceneKit

let sceneView = SCNView(frame: view.bounds)
sceneView.scene = SCNScene()
sceneView.allowsCameraControl = true
sceneView.autoenablesDefaultLighting = true
sceneView.backgroundColor = .black
view.addSubview(sceneView)

allowsCameraControl adds built-in orbit, pan, and zoom gestures. Typically disabled in production where custom camera control is needed.

Creating an SCNScene

let scene = SCNScene()                                          // Empty
guard let scene = SCNScene(named: "art.scnassets/ship.scn")     // .scn asset catalog
    else { fatalError("Missing scene asset") }
let scene = try SCNScene(url: Bundle.main.url(                  // .usdz from bundle
    forResource: "spaceship", withExtension: "usdz")!)

Nodes and Geometry

Every scene has a rootNode. All content exists as descendant nodes. Nodes define position, orientation, and scale in their parent's coordinate system. SceneKit uses a right-handed coordinate system: +X right, +Y up, +Z toward the camera.

let parentNode = SCNNode()
scene.rootNode.addChildNode(parentNode)

let childNode = SCNNode()
childNode.position = SCNVector3(0, 1, 0)  // 1 unit above parent
parentNode.addChildNode(childNode)

Transforms

node.position = SCNVector3(x: 0, y: 2, z: -5)
node.eulerAngles = SCNVector3(x: 0, y: .pi / 4, z: 0)  // 45-degree Y rotation
node.scale = SCNVector3(2, 2, 2)
node.simdPosition = SIMD3<Float>(0, 2, -5)  // Prefer simd for performance

Built-in Primitives

SCNBox, SCNSphere, SCNCylinder, SCNCone, SCNTorus, SCNCapsule, SCNTube, SCNPlane, SCNFloor, SCNText, SCNShape (extruded Bezier path).

let node = SCNNode(geometry: SCNSphere(radius: 0.5))

Finding Nodes

let maxNode = scene.rootNode.childNode(withName: "Max", recursively: true)
let enemies = scene.rootNode.childNodes { node, _ in
    node.name?.hasPrefix("enemy") == true
}

Materials

SCNMaterial defines surface appearance. Use firstMaterial for single-material geometries or the materials array for multi-material.

Color and Texture

let material = SCNMaterial()
material.diffuse.contents = UIColor.systemBlue     // Solid color
material.diffuse.contents = UIImage(named: "brick") // Texture
material.normal.contents = UIImage(named: "brick_normal")
sphere.firstMaterial = material

Physically Based Rendering (PBR)

let pbr = SCNMaterial()
pbr.lightingModel = .physicallyBased
pbr.diffuse.contents = UIImage(named: "albedo")
pbr.metalness.contents = 0.8       // Scalar or texture
pbr.roughness.contents = 0.2       // Scalar or texture
pbr.normal.contents = UIImage(named: "normal")
pbr.ambientOcclusion.contents = UIImage(named: "ao")

Lighting Models

.physicallyBased (metalness/roughness), .blinn (default), .phong, .lambert (diffuse-only), .constant (unlit), .shadowOnly.

Each material property is an SCNMaterialProperty accepting UIColor, UIImage, CGFloat scalar, SKTexture, CALayer, or AVPlayer.

Transparency

material.transparency = 0.5
material.transparencyMode = .dualLayer
material.isDoubleSided = true

Lighting

Attach an SCNLight to a node. The light's direction follows the node's negative Z-axis.

Light Types

// Ambient: uniform, no direction
let ambient = SCNLight()
ambient.type = .ambient
ambient.color = UIColor(white: 0.3, alpha: 1)

// Directional: parallel rays (sunlight)
let directional = SCNLight()
directional.type = .directional
directional.castsShadow = true

// Omni: point light, all directions
let omni = SCNLight()
omni.type = .omni
omni.attenuationEndDistance = 20

// Spot: cone-shaped
let spot = SCNLight()
spot.type = .spot
spot.spotInnerAngle = 20
spot.spotOuterAngle = 60

Attach to a node:

let lightNode = SCNNode()
lightNode.light = directional
lightNode.eulerAngles = SCNVector3(-Float.pi / 3, 0, 0)
lightNode.position = SCNVector3(0, 10, 10)
scene.rootNode.addChildNode(lightNode)

Shadows

light.castsShadow = true
light.shadowMapSize = CGSize(width: 2048, height: 2048)
light.shadowSampleCount = 8
light.shadowRadius = 3.0
light.shadowColor = UIColor(white: 0, alpha: 0.5)

Category Bit Masks

light.categoryBitMask = 1 << 1     // Category 2
node.categoryBitMask = 1 << 1      // Only lit by category-2 lights

SceneKit renders a maximum of 8 lights per node. Use attenuationEndDistance on point/spot lights so SceneKit skips them for distant nodes.

Cameras

Attach an SCNCamera to a node to define a viewpoint.

let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
cameraNode.position = SCNVector3(0, 5, 15)
cameraNode.look(at: SCNVector3Zero)
scene.rootNode.addChildNode(cameraNode)
sceneView.pointOfView = cameraNode

Configuration

camera.fieldOfView = 60                        // Degrees
camera.zNear = 0.1
camera.zFar = 500
camera.automaticallyAdjustsZRange = true

// Orthographic
camera.usesOrthographicProjection = true
camera.orthographicScale = 10

Depth-of-field (wantsDepthOfField, focusDistance, fStop) and HDR effects (wantsHDR, bloomIntensity, bloomThreshold, screenSpaceAmbientOcclusionIntensity) are configured directly on SCNCamera.

Animation

SceneKit provides three animation approaches.

SCNAction (Declarative, Game-Oriented)

Reusable, composable animation objects attached to nodes.

let move = SCNAction.move(by: SCNVector3(0, 2, 0), duration: 1)
let rotate = SCNAction.rotateBy(x: 0, y: .pi, z: 0, duration: 1)
node.runAction(.group([move, rotate]))

// Sequential
node.runAction(.sequence([.fadeOut(duration: 0.3), .removeFromParentNode()]))

// Infinite loop
let pulse = SCNAction.sequence([
    .scale(to: 1.2, duration: 0.5),
    .scale(to: 1.0, duration: 0.5)
])
node.runAction(.repeatForever(pulse))

SCNTransaction (Implicit Animation)

SCNTransaction.begin()
SCNTransaction.animationDuration = 1.0
node.position = SCNVector3(5, 0, 0)
node.opacity = 0.5
SCNTransaction.completionBlock = { print("Done") }
SCNTransaction.commit()

Explicit Animations (Core Animation)

let animation = CABasicAnimation(keyPath: "rotation")
animation.toValue = NSValue(scnVector4: SCNVector4(0, 1, 0, Float.pi * 2))
animation.duration = 2
animation.repeatCount = .infinity
node.addAnimation(animation, forKey: "spin")

Physics

Physics Bodies

node.physicsBody = SCNPhysicsBody(type: .dynamic, shape: nil)   // Forces + collisions
floor.physicsBody = SCNPhysicsBody(type: .static, shape: nil)    // Immovable
platform.physicsBody = SCNPhysicsBody(type: .kinematic, shape: nil) // Code-driven

When shape is nil, SceneKit derives it from geometry. For performance, use simplified shapes:

let shape = SCNPhysicsShape(
    geometry: SCNBox(width: 1, height: 2, length: 1, chamferRadius: 0),
    options: nil
)
node.physicsBody = SCNPhysicsBody(type: .dynamic, shape: shape)
node.physicsBody?.mass = 2.0
node.physicsBody?.restitution = 0.3

Applying Forces

node.physicsBody?.applyForce(SCNVector3(0, 10, 0), asImpulse: false) // Continuous
node.physicsBody?.applyForce(SCNVector3(0, 5, 0), asImpulse: true)   // Instant
node.physicsBody?.applyTorque(SCNVector4(0, 1, 0, 2), asImpulse: true)

Collision Detection

struct PhysicsCategory {
    static let player:     Int = 1 << 0
    static let enemy:      Int = 1 << 1
    static let ground:     Int = 1 << 2
}

playerNode.physicsBody?.categoryBitMask = PhysicsCategory.player
playerNode.physicsBody?.collisionBitMask = PhysicsCategory.ground | PhysicsCategory.enemy
playerNode.physicsBody?.contactTestBitMask = PhysicsCategory.enemy

scene.physicsWorld.contactDelegate = self

func physicsWorld(_ world: SCNPhysicsWorld, didBegin contact: SCNPhysicsContact) {
    handleCollision(between: contact.nodeA, and: contact.nodeB)
}

Gravity

scene.physicsWorld.gravity = SCNVector3(0, -9.8, 0)
node.physicsBody?.isAffectedByGravity = false

Particle Systems

SCNParticleSystem creates effects like fire, smoke, rain, and sparks.

let particles = SCNParticleSystem()
particles.birthRate = 100
particles.particleLifeSpan = 2
particles.particleSize = 0.1
particles.particleColor = .orange
particles.emitterShape = SCNSphere(radius: 0.5)
particles.particleVelocity = 2
particles.isAffectedByGravity = true
particles.blendMode = .additive

let emitterNode = SCNNode()
emitterNode.addParticleSystem(particles)
scene.rootNode.addChildNode(emitterNode)

Load from Xcode particle editor with SCNParticleSystem(named: "fire.scnp", inDirectory: nil). Particles can collide with geometry via colliderNodes.

Loading Models

SceneKit loads .usdz, .scn, .dae, .obj, and .abc. Prefer .usdz.

guard let scene = SCNScene(named: "art.scnassets/ship.scn") else { return }
let scene = try SCNScene(url: Bundle.main.url(
    forResource: "model", withExtension: "usdz")!)
guard let modelNode = scene.rootNode.childNode(withName: "mesh", recursively: true) else { return }

Use SCNReferenceNode with .onDemand loading policy for large models. Use SCNSceneSource to inspect or selectively load entries from a file.

SwiftUI Integration

SceneView embeds SceneKit in SwiftUI:

import SwiftUI
import SceneKit

struct SceneKitView: View {
    let scene: SCNScene = {
        let scene = SCNScene()
        let sphere = SCNNode(geometry: SCNSphere(radius: 1))
        sphere.geometry?.firstMaterial?.lightingModel = .physicallyBased
        sphere.geometry?.firstMaterial?.diffuse.contents = UIColor.systemBlue
        sphere.geometry?.firstMaterial?.metalness.contents = 0.8
        scene.rootNode.addChildNode(sphere)
        return scene
    }()

    var body: some View {
        SceneView(scene: scene,
                  options: [.allowsCameraControl, .autoenablesDefaultLighting])
    }
}

Options: .allowsCameraControl, .autoenablesDefaultLighting, .jitteringEnabled, .temporalAntialiasingEnabled.

For render loop control, wrap SCNView in UIViewRepresentable with an SCNSceneRendererDelegate coordinator. See references/scenekit-patterns.md.

Common Mistakes

Not adding a camera or lights

// DON'T: Scene renders blank or black -- no camera, no lights
sceneView.scene = scene

// DO: Add camera + lights, or use convenience flags
let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
cameraNode.position = SCNVector3(0, 5, 15)
scene.rootNode.addChildNode(cameraNode)
sceneView.pointOfView = cameraNode
sceneView.autoenablesDefaultLighting = true

Using exact geometry for physics shapes

// DON'T
node.physicsBody = SCNPhysicsBody(type: .dynamic,
    shape: SCNPhysicsShape(geometry: complexMesh))

// DO: Simplified primitive
node.physicsBody = SCNPhysicsBody(type: .dynamic,
    shape: SCNPhysicsShape(
        geometry: SCNBox(width: 1, height: 2, length: 1, chamferRadius: 0),
        options: nil))

Modifying transforms on dynamic bodies

// DON'T: Resets physics simulation
dynamicNode.position = SCNVector3(5, 0, 0)

// DO: Use forces/impulses
dynamicNode.physicsBody?.applyForce(SCNVector3(10, 0, 0), asImpulse: true)

Exceeding 8 lights per node

// DON'T: 20 lights with no attenuation
for _ in 0..<20 {
    let light = SCNNode()
    light.light = SCNLight()
    light.light?.type = .omni
    scene.rootNode.addChildNode(light)
}

// DO: Set attenuationEndDistance so SceneKit skips distant lights
light.light?.attenuationEndDistance = 10

Review Checklist

References

See references/scenekit-patterns.md for custom geometry, shader modifiers, node constraints, morph targets, hit testing, scene serialization, render loop delegates, performance optimization, SpriteKit overlay, LOD, and Metal shaders.
SceneKit documentation
SCNScene
SCNNode
SCNView
SceneView (SwiftUI)
SCNGeometry
SCNMaterial
SCNLight
SCNCamera
SCNAction
SCNPhysicsBody
SCNParticleSystem
WWDC 2025 session 288: Bring your SceneKit project to RealityKit

skills

accessorysetupkit

activitykit

adattributionkit

alarmkit

app-clips

app-intents

app-store-optimization

app-store-review

apple-on-device-ai

appmigrationkit

audioaccessorykit

authentication

avkit

background-processing

browserenginekit

callkit

carplay

cloudkit

contacts-framework

core-bluetooth

core-data

core-motion

core-nfc

coreml

cryptokit

cryptotokenkit

debugging-instruments

device-integrity

dockkit

energykit

eventkit

financekit

focus-engine

gamekit

healthkit

homekit

ios-accessibility

ios-localization

ios-networking

ios-simulator

mapkit

metrickit

musickit

natural-language

paperkit

passkit

pdfkit

pencilkit

permissionkit

photokit

push-notifications

realitykit

relevancekit

scenekit

references

SKILL.md

sensorkit

shareplay-activities

speech-recognition

spritekit

storekit

swift-api-design-guidelines

swift-architecture

swift-charts

swift-codable

swift-concurrency

swift-formatstyle

swift-language

swift-security

swift-testing

swiftdata

swiftlint

swiftui-animation

swiftui-gestures

swiftui-layout-components

swiftui-liquid-glass

swiftui-patterns

swiftui-performance

swiftui-uikit-interop

swiftui-webkit

tabletopkit

tipkit

vision-framework

weatherkit

widgetkit

CHANGELOG.md

README.md

tile.json