spritekit

SpriteKit

Build 2D games and interactive animations for iOS 26+ using SpriteKit and Swift 6.3. Covers scene lifecycle, node hierarchy, actions, physics, particles, camera, touch handling, and SwiftUI integration.

Contents

• Scene Setup
• Nodes and Sprites
• Actions and Animation
• Physics
• Touch Handling
• Camera
• Particle Effects
• SwiftUI Integration
• Common Mistakes
• Review Checklist
• References

Scene Setup

SpriteKit renders content through SKView, which presents an SKScene -- the root node of a tree that the framework animates and renders each frame.

Creating a Scene

Subclass SKScene and override lifecycle methods. The coordinate system origin is at the bottom-left by default.

import SpriteKit

final class GameScene: SKScene {
    override func didMove(to view: SKView) {
        backgroundColor = .darkGray
        physicsWorld.contactDelegate = self
        physicsBody = SKPhysicsBody(edgeLoopFrom: frame)
        setupNodes()
    }

    override func update(_ currentTime: TimeInterval) {
        // Called once per frame before actions are evaluated.
    }
}

Presenting a Scene (UIKit)

guard let skView = view as? SKView else { return }
skView.ignoresSiblingOrder = true

let scene = GameScene(size: skView.bounds.size)
scene.scaleMode = .resizeFill
skView.presentScene(scene)

Scale Modes

Use .resizeFill when the scene should adapt to view size changes (rotation, multitasking). Use .aspectFill for fixed-design game scenes. .aspectFit letterboxes; .fill stretches and may distort.

Frame Cycle

Each frame follows this order:

1. update(_:) -- game logic
2. Evaluate actions
3. didEvaluateActions() -- post-action logic
4. Simulate physics
5. didSimulatePhysics() -- post-physics adjustments
6. Apply constraints
7. didApplyConstraints()
8. didFinishUpdate() -- final adjustments before rendering

Override only the callbacks where work is needed.

Nodes and Sprites

Use SKNode (without a visual) as an invisible container or layout group. Child nodes inherit parent position, scale, rotation, alpha, and speed. SKSpriteNode is the primary visual node.

Common Node Types

Class	Purpose
SKSpriteNode	Textured image or solid color
SKLabelNode	Text rendering
SKShapeNode	Vector paths (expensive per draw call)
SKEmitterNode	Particle effects
SKCameraNode	Viewport control
SKTileMapNode	Grid-based tiles
SKAudioNode	Positional audio
SKCropNode / SKEffectNode	Masking / CIFilter
SK3DNode	Embedded SceneKit content

Creating Sprites

let player = SKSpriteNode(imageNamed: "hero")
player.position = CGPoint(x: frame.midX, y: frame.midY)
player.name = "player"
addChild(player)

Drawing Order

Set ignoresSiblingOrder = true on SKView for better performance; SpriteKit then uses zPosition to determine order. Without it, nodes draw in tree order.

background.zPosition = -1
player.zPosition = 0
foregroundUI.zPosition = 10

Naming and Searching

Assign name to find nodes without instance variables. Use childNode(withName:), enumerateChildNodes(withName:using:), or subscript. Patterns: // searches the entire tree, * matches any characters, .. refers to the parent.

player.name = "player"
if let found = childNode(withName: "player") as? SKSpriteNode { /* ... */ }

Actions and Animation

SKAction objects define changes applied to nodes over time. Actions are immutable and reusable. Run with node.run(_:).

Basic Actions

let moveUp = SKAction.moveBy(x: 0, y: 100, duration: 0.5)
let grow = SKAction.scale(to: 1.5, duration: 0.3)
let spin = SKAction.rotate(byAngle: .pi * 2, duration: 1.0)
let fadeOut = SKAction.fadeOut(withDuration: 0.3)
let remove = SKAction.removeFromParent()

Combining Actions

// Sequential: run one after another
let dropAndRemove = SKAction.sequence([
    SKAction.moveBy(x: 0, y: -500, duration: 1.0),
    SKAction.removeFromParent()
])

// Parallel: run simultaneously
let scaleAndFade = SKAction.group([
    SKAction.scale(to: 0.0, duration: 0.3),
    SKAction.fadeOut(withDuration: 0.3)
])

// Repeat
let pulse = SKAction.repeatForever(
    SKAction.sequence([
        SKAction.scale(to: 1.2, duration: 0.5),
        SKAction.scale(to: 1.0, duration: 0.5)
    ])
)

Texture Animation

let walkFrames = (1...8).map { SKTexture(imageNamed: "walk_\($0)") }
let walkAction = SKAction.animate(with: walkFrames, timePerFrame: 0.1)
player.run(SKAction.repeatForever(walkAction))

Control the speed curve with timingMode (.linear, .easeIn, .easeOut, .easeInEaseOut). Assign keys to actions for later access:

let easeIn = SKAction.moveTo(x: 300, duration: 1.0)
easeIn.timingMode = .easeInEaseOut

player.run(pulse, withKey: "pulse")
player.removeAction(forKey: "pulse") // stop later

Physics

SpriteKit provides a built-in 2D physics engine. The scene's physicsWorld manages gravity and collision detection.

Adding Physics Bodies

// Circle body
player.physicsBody = SKPhysicsBody(circleOfRadius: player.size.width / 2)
player.physicsBody?.restitution = 0.3

// Static rectangle
ground.physicsBody = SKPhysicsBody(rectangleOf: ground.size)
ground.physicsBody?.isDynamic = false

// Texture-based body for irregular shapes
player.physicsBody = SKPhysicsBody(texture: player.texture!, size: player.size)

Category and Contact Masks

Use bit masks to control collisions and contact callbacks:

struct PhysicsCategory {
    static let player:  UInt32 = 0b0001
    static let enemy:   UInt32 = 0b0010
    static let ground:  UInt32 = 0b0100
}

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

categoryBitMask identifies the body. collisionBitMask controls physics response (bouncing). contactTestBitMask triggers didBegin/didEnd.

Contact Detection

Implement SKPhysicsContactDelegate and set physicsWorld.contactDelegate = self in didMove(to:):

extension GameScene: SKPhysicsContactDelegate {
    func didBegin(_ contact: SKPhysicsContact) {
        let mask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
        if mask == PhysicsCategory.player | PhysicsCategory.enemy {
            queuePlayerHit()
        }
    }
}

Contact callbacks run during physics simulation. Make queuePlayerHit() set a flag or append an event, then apply node/body/world mutations in update(_:).

Forces and Impulses

player.physicsBody?.applyForce(CGVector(dx: 0, dy: 50))      // continuous
player.physicsBody?.applyImpulse(CGVector(dx: 0, dy: 200))   // instant
player.physicsBody?.applyAngularImpulse(0.5)                  // spin

Use .applyImpulse for jumps and projectile launches. Configure gravity with physicsWorld.gravity = CGVector(dx: 0, dy: -9.8) and per-body with affectedByGravity.

Touch Handling

SKScene inherits from UIResponder. Override touchesBegan, touchesMoved, touchesEnded on the scene. Use nodes(at:) to hit-test.

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touch = touches.first else { return }
    let location = touch.location(in: self)
    let tappedNodes = nodes(at: location)

    if tappedNodes.contains(where: { $0.name == "playButton" }) {
        startGame()
    }
}

For node-level touch handling, subclass the node and set isUserInteractionEnabled = true. That node then receives touches directly instead of the scene.

Camera

SKCameraNode controls the visible portion of the scene. Add it as a child and assign to scene.camera.

let cameraNode = SKCameraNode()
addChild(cameraNode)
camera = cameraNode
cameraNode.position = CGPoint(x: frame.midX, y: frame.midY)

Following a Character

Update the camera position in didSimulatePhysics() or use constraints:

override func didSimulatePhysics() {
    cameraNode.position = player.position
}

// Constrain camera to world bounds
let xRange = SKRange(lowerLimit: frame.midX, upperLimit: worldWidth - frame.midX)
let yRange = SKRange(lowerLimit: frame.midY, upperLimit: worldHeight - frame.midY)
cameraNode.constraints = [SKConstraint.positionX(xRange, y: yRange)]

Camera Zoom and HUD

Scale the camera node inversely: setScale(0.5) zooms in 2x, setScale(2.0) zooms out 2x. Nodes added as children of the camera stay fixed on screen (HUD elements):

let scoreLabel = SKLabelNode(text: "Score: 0")
scoreLabel.position = CGPoint(x: 0, y: frame.height / 2 - 40)
scoreLabel.fontName = "AvenirNext-Bold"
scoreLabel.fontSize = 24
cameraNode.addChild(scoreLabel)

Particle Effects

SKEmitterNode generates particle effects. Design emitters in Xcode's SpriteKit Particle File editor (.sks) or configure in code.

// Load from file
guard let emitter = SKEmitterNode(fileNamed: "Fire") else { return }
emitter.position = CGPoint(x: frame.midX, y: 100)
addChild(emitter)

One-Shot Emitters

Set numParticlesToEmit for finite effects and remove after completion:

func spawnExplosion(at position: CGPoint) {
    guard let explosion = SKEmitterNode(fileNamed: "Explosion") else { return }
    explosion.position = position
    explosion.numParticlesToEmit = 100
    addChild(explosion)

    let wait = SKAction.wait(forDuration: TimeInterval(explosion.particleLifetime))
    explosion.run(SKAction.sequence([wait, .removeFromParent()]))
}

Set targetNode to the scene so particles stay in world space when the emitter moves: emitter.targetNode = self.

SwiftUI Integration

SpriteView embeds a SpriteKit scene in SwiftUI.

import SwiftUI
import SpriteKit

struct GameView: View {
    @State private var scene: GameScene = {
        let s = GameScene()
        s.size = CGSize(width: 390, height: 844)
        s.scaleMode = .resizeFill
        return s
    }()

    var body: some View {
        SpriteView(scene: scene)
            .ignoresSafeArea()
    }
}

SpriteView Options

Pass options: [.allowsTransparency] for transparent backgrounds, .shouldCullNonVisibleNodes for offscreen culling, or .ignoresSiblingOrder for zPosition-based draw order. Use debugOptions: [.showsFPS, .showsNodeCount] during development.

Communicating Between SwiftUI and the Scene

Pass data through a shared @Observable object. Store the scene in @State to avoid re-creation on view re-renders:

@Observable final class GameState {
    var score = 0
    var isPaused = false
}

struct GameContainerView: View {
    @State private var gameState = GameState()
    @State private var scene = GameScene()

    var body: some View {
        SpriteView(scene: scene, isPaused: gameState.isPaused)
            .onAppear { scene.gameState = gameState }
    }
}

Common Mistakes

Creating a new scene on every SwiftUI re-render

// DON'T: Scene is recreated on every body evaluation
var body: some View {
    SpriteView(scene: GameScene(size: CGSize(width: 390, height: 844)))
}

// DO: Create once and reuse
@State private var scene = GameScene(size: CGSize(width: 390, height: 844))
var body: some View {
    SpriteView(scene: scene)
}

Adding a child node that already has a parent

A node can only have one parent. Remove from the current parent first or create a separate instance. Adding a node that already has a parent crashes.

Forgetting to set contactTestBitMask

// DON'T: Bodies collide but didBegin is never called
player.physicsBody?.categoryBitMask = PhysicsCategory.player
enemy.physicsBody?.categoryBitMask = PhysicsCategory.enemy

// DO: Set contactTestBitMask to receive contact callbacks
player.physicsBody?.contactTestBitMask = PhysicsCategory.enemy

Using SKShapeNode for performance-critical rendering

SKShapeNode uses a separate draw call per instance. Prefer SKSpriteNode with a texture for repeated elements to enable batched rendering.

Not removing nodes that leave the screen

// DON'T
enemy.run(SKAction.moveBy(x: -800, y: 0, duration: 3.0))
addChild(enemy)

// DO: Remove after leaving the visible area
enemy.run(SKAction.sequence([
    SKAction.moveBy(x: -800, y: 0, duration: 3.0),
    SKAction.removeFromParent()
]))
addChild(enemy)

Setting physicsWorld.contactDelegate too late

Set physicsWorld.contactDelegate = self in didMove(to:), not in update(_:) or after a delay.

Review Checklist

• Scene subclass overrides didMove(to:) for setup, not init
• scaleMode chosen appropriately for the game's design
• ignoresSiblingOrder set to true on SKView for performance
• zPosition used consistently when ignoresSiblingOrder is enabled
• Physics contactDelegate set in didMove(to:)
• Category, collision, and contact bit masks configured correctly
• contactTestBitMask set for any pair needing didBegin/didEnd callbacks
• Contact callbacks queue changes instead of mutating the physics world directly
• Static bodies use isDynamic = false
• SKShapeNode avoided in performance-critical paths; SKSpriteNode preferred
• Actions that move nodes offscreen include .removeFromParent() in sequence
• One-shot emitters remove themselves after particle lifetime expires
• Emitter targetNode set when particles should stay in world space
• Scene stored in @State when used with SpriteView in SwiftUI
• Texture atlases used for related sprites to reduce draw calls
• update(_:) uses delta time for frame-rate-independent movement
• Nodes removed from parent before being re-added elsewhere

References

• See references/spritekit-patterns.md for tile maps, texture atlases, shaders, scene transitions, game loop patterns, audio, and SceneKit embedding.
• SpriteKit documentation
• SKScene
• SKSpriteNode
• SKAction
• SKPhysicsBody
• SKEmitterNode
• SKCameraNode
• SpriteView
• SKTileMapNode