axiom-spritekit

name	axiom-spritekit
description	Use when building SpriteKit games, implementing physics, actions, scene management, or debugging game performance. Covers scene graph, physics engine, actions system, game loop, rendering optimization.
license	MIT
metadata	{"version":"1.0.0"}

SpriteKit Game Development Guide

Purpose: Build reliable SpriteKit games by mastering the scene graph, physics engine, action system, and rendering pipeline iOS Version: iOS 13+ (SwiftUI integration), iOS 11+ (SKRenderer) Xcode: Xcode 15+

When to Use This Skill

Use this skill when:

• Building a new SpriteKit game or interactive simulation
• Implementing physics (collisions, contacts, forces, joints)
• Setting up game architecture (scenes, layers, cameras)
• Optimizing frame rate or reducing draw calls
• Implementing touch/input handling in a game
• Managing scene transitions and data passing
• Integrating SpriteKit with SwiftUI or Metal
• Debugging physics contacts that don't fire
• Fixing coordinate system confusion

Do NOT use this skill for:

• SceneKit 3D rendering (axiom-scenekit)
• GameplayKit entity-component systems
• Metal shader programming (axiom-metal-migration-ref)
• General SwiftUI layout (axiom-swiftui-layout)

---

1. Mental Model

Coordinate System

SpriteKit uses a bottom-left origin with Y pointing up. This differs from UIKit (top-left, Y down).

SpriteKit:          UIKit:
┌─────────┐         ┌─────────┐
│    +Y    │         │  (0,0)  │
│    ↑     │         │    ↓    │
│    │     │         │    +Y   │
│(0,0)──→+X│        │    │    │
└─────────┘         └─────────┘

Anchor Points define which point on a sprite maps to its position. Default is (0.5, 0.5) (center).

// Common anchor point trap:
// Anchor (0, 0) = bottom-left of sprite is at position
// Anchor (0.5, 0.5) = center of sprite is at position (DEFAULT)
// Anchor (0.5, 0) = bottom-center (useful for characters standing on ground)
sprite.anchorPoint = CGPoint(x: 0.5, y: 0)

Scene anchor point maps the view's frame to scene coordinates:

• (0, 0) — scene origin at bottom-left of view (default)
• (0.5, 0.5) — scene origin at center of view

Node Tree

Everything in SpriteKit is an SKNode in a tree hierarchy. Parent transforms propagate to children.

SKScene
├── SKCameraNode (viewport control)
├── SKNode "world" (game content layer)
│   ├── SKSpriteNode "player"
│   ├── SKSpriteNode "enemy"
│   └── SKNode "platforms"
│       ├── SKSpriteNode "platform1"
│       └── SKSpriteNode "platform2"
└── SKNode "hud" (UI layer, attached to camera)
    ├── SKLabelNode "score"
    └── SKSpriteNode "healthBar"

Z-Ordering

zPosition controls draw order. Higher values render on top. Nodes at the same zPosition render in child array order (unless ignoresSiblingOrder is true).

// Establish clear z-order layers
enum ZLayer {
    static let background: CGFloat = -100
    static let platforms: CGFloat = 0
    static let items: CGFloat = 10
    static let player: CGFloat = 20
    static let effects: CGFloat = 30
    static let hud: CGFloat = 100
}

---

2. Scene Architecture

Scale Mode Decision

Mode	Behavior	Use When
.aspectFill	Fills view, crops edges	Full-bleed games (most games)
.aspectFit	Fits in view, letterboxes	Puzzle games needing exact layout
.resizeFill	Stretches to fill	Almost never — distorts
.fill	Matches view size exactly	Scene adapts to any ratio

class GameScene: SKScene {
    override func sceneDidLoad() {
        scaleMode = .aspectFill
        // Design for a reference size, let aspectFill crop edges
    }
}

Camera Node Pattern

Always use SKCameraNode for viewport control. Attach HUD elements to the camera so they don't scroll.

let camera = SKCameraNode()
camera.name = "mainCamera"
addChild(camera)
self.camera = camera

// HUD follows camera automatically
let scoreLabel = SKLabelNode(text: "Score: 0")
scoreLabel.position = CGPoint(x: 0, y: size.height / 2 - 50)
camera.addChild(scoreLabel)

// Move camera to follow player
let follow = SKConstraint.distance(SKRange(constantValue: 0), to: playerNode)
camera.constraints = [follow]

Layer Organization

// Create layer nodes for organization
let worldNode = SKNode()
worldNode.name = "world"
addChild(worldNode)

let hudNode = SKNode()
hudNode.name = "hud"
camera?.addChild(hudNode)

// All gameplay objects go in worldNode
worldNode.addChild(playerSprite)
worldNode.addChild(enemySprite)

// All UI goes in hudNode (moves with camera)
hudNode.addChild(scoreLabel)

Scene Transitions

// Preload next scene for smooth transitions
guard let nextScene = LevelScene(fileNamed: "Level2") else { return }
nextScene.scaleMode = .aspectFill

let transition = SKTransition.fade(withDuration: 0.5)
view?.presentScene(nextScene, transition: transition)

Data passing between scenes: Use a shared game state object, not node properties.

class GameState {
    static let shared = GameState()
    var score = 0
    var currentLevel = 1
    var playerHealth = 100
}

// In scene transition:
let nextScene = LevelScene(size: size)
// GameState.shared is already accessible
view?.presentScene(nextScene, transition: .fade(withDuration: 0.5))

Note: A singleton works for simple games. For larger projects with testing needs, consider passing a GameState instance through scene initializers to avoid hidden global state.

Cleanup in willMove(from:):

override func willMove(from view: SKView) {
    removeAllActions()
    removeAllChildren()
    physicsWorld.contactDelegate = nil
}

---

3. Physics Engine

Bitmask Discipline

This is the #1 source of SpriteKit bugs. Physics bitmasks use a 32-bit system where each bit represents a category.

struct PhysicsCategory {
    static let none:       UInt32 = 0
    static let player:     UInt32 = 0b0001  // 1
    static let enemy:      UInt32 = 0b0010  // 2
    static let ground:     UInt32 = 0b0100  // 4
    static let projectile: UInt32 = 0b1000  // 8
    static let powerUp:    UInt32 = 0b10000 // 16
}

Three bitmask properties (all default to 0xFFFFFFFF — everything):

Property	Purpose	Default
categoryBitMask	What this body IS	0xFFFFFFFF
collisionBitMask	What it BOUNCES off	0xFFFFFFFF
contactTestBitMask	What TRIGGERS delegate	0x00000000

The default collisionBitMask of 0xFFFFFFFF means everything collides with everything. This is the most common source of unexpected physics behavior.

// CORRECT: Explicit bitmask setup
player.physicsBody?.categoryBitMask = PhysicsCategory.player
player.physicsBody?.collisionBitMask = PhysicsCategory.ground | PhysicsCategory.enemy
player.physicsBody?.contactTestBitMask = PhysicsCategory.enemy | PhysicsCategory.powerUp

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

Bitmask Checklist

For every physics body, verify:

1. categoryBitMask set to exactly one category
2. collisionBitMask set to only categories it should bounce off (NOT 0xFFFFFFFF)
3. contactTestBitMask set to categories that should trigger delegate callbacks
4. Delegate is assigned: physicsWorld.contactDelegate = self

Contact Detection

class GameScene: SKScene, SKPhysicsContactDelegate {
    override func didMove(to view: SKView) {
        physicsWorld.contactDelegate = self
    }

    func didBegin(_ contact: SKPhysicsContact) {
        // Sort bodies so bodyA has the lower category
        let (first, second): (SKPhysicsBody, SKPhysicsBody)
        if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
            (first, second) = (contact.bodyA, contact.bodyB)
        } else {
            (first, second) = (contact.bodyB, contact.bodyA)
        }

        // Now dispatch based on categories
        if first.categoryBitMask == PhysicsCategory.player &&
           second.categoryBitMask == PhysicsCategory.enemy {
            guard let playerNode = first.node, let enemyNode = second.node else { return }
            playerHitEnemy(player: playerNode, enemy: enemyNode)
        }
    }
}

Modification rule: You cannot modify the physics world inside didBegin/didEnd. Set flags and apply changes in update(_:).

var enemiesToRemove: [SKNode] = []

func didBegin(_ contact: SKPhysicsContact) {
    // Flag for removal — don't remove here
    if let enemy = contact.bodyB.node {
        enemiesToRemove.append(enemy)
    }
}

override func update(_ currentTime: TimeInterval) {
    for enemy in enemiesToRemove {
        enemy.removeFromParent()
    }
    enemiesToRemove.removeAll()
}

Body Types

Type	Created With	Responds to Forces	Use For
Dynamic volume	init(circleOfRadius:), init(rectangleOf:), init(texture:size:)	Yes	Players, enemies, projectiles
Static volume	Dynamic body + isDynamic = false	No (but collides)	Platforms, walls
Edge	init(edgeLoopFrom:), init(edgeFrom:to:)	No (boundary only)	Screen boundaries, terrain

// Screen boundary using edge loop
physicsBody = SKPhysicsBody(edgeLoopFrom: frame)

// Texture-based body for irregular shapes
guard let texture = enemy.texture else { return }
enemy.physicsBody = SKPhysicsBody(texture: texture, size: enemy.size)

// Circle for performance (cheapest collision detection)
bullet.physicsBody = SKPhysicsBody(circleOfRadius: 5)

Tunneling Prevention

Fast-moving objects can pass through thin walls. Fix:

// Enable precise collision detection for fast objects
bullet.physicsBody?.usesPreciseCollisionDetection = true

// Make walls thick enough (at least as wide as fastest object moves per frame)
// At 60fps, an object at velocity 600pt/s moves 10pt/frame

Forces vs Impulses

// Force: continuous (applied per frame, accumulates)
body.applyForce(CGVector(dx: 0, dy: 100))

// Impulse: instant velocity change (one-time, like a jump)
body.applyImpulse(CGVector(dx: 0, dy: 50))

// Torque: continuous rotation
body.applyTorque(0.5)

// Angular impulse: instant rotation change
body.applyAngularImpulse(1.0)

---

4. Actions System

Core Patterns

// Movement
let move = SKAction.move(to: CGPoint(x: 200, y: 300), duration: 1.0)
let moveBy = SKAction.moveBy(x: 100, y: 0, duration: 0.5)

// Rotation
let rotate = SKAction.rotate(byAngle: .pi * 2, duration: 1.0)

// Scale
let scale = SKAction.scale(to: 2.0, duration: 0.3)

// Fade
let fadeOut = SKAction.fadeOut(withDuration: 0.5)
let fadeIn = SKAction.fadeIn(withDuration: 0.5)

Sequencing and Grouping

// Sequence: one after another
let moveAndFade = SKAction.sequence([
    SKAction.move(to: target, duration: 1.0),
    SKAction.fadeOut(withDuration: 0.3),
    SKAction.removeFromParent()
])

// Group: all at once
let spinAndGrow = SKAction.group([
    SKAction.rotate(byAngle: .pi * 2, duration: 1.0),
    SKAction.scale(to: 2.0, duration: 1.0)
])

// Repeat
let pulse = SKAction.repeatForever(SKAction.sequence([
    SKAction.scale(to: 1.2, duration: 0.3),
    SKAction.scale(to: 1.0, duration: 0.3)
]))

Named Actions (Critical for Management)

// Use named actions so you can cancel/replace them
node.run(pulse, withKey: "pulse")

// Later, stop the pulse:
node.removeAction(forKey: "pulse")

// Check if running:
if node.action(forKey: "pulse") != nil {
    // Still pulsing
}

Custom Actions with Weak Self

// WRONG: Retain cycle risk
node.run(SKAction.run {
    self.score += 1  // Strong capture of self
})

// CORRECT: Weak capture
node.run(SKAction.run { [weak self] in
    self?.score += 1
})

// For repeating actions, always use weak self
let spawn = SKAction.repeatForever(SKAction.sequence([
    SKAction.run { [weak self] in self?.spawnEnemy() },
    SKAction.wait(forDuration: 2.0)
]))
scene.run(spawn, withKey: "enemySpawner")

Timing Modes

action.timingMode = .linear     // Constant speed (default)
action.timingMode = .easeIn     // Accelerate from rest
action.timingMode = .easeOut    // Decelerate to rest
action.timingMode = .easeInEaseOut  // Smooth start and end

Actions vs Physics

Never use actions to move physics-controlled nodes. Actions override the physics simulation, causing jittering and missed collisions.

// WRONG: Action fights physics
playerNode.run(SKAction.moveTo(x: 200, duration: 0.5))

// CORRECT: Use forces/impulses for physics bodies
playerNode.physicsBody?.applyImpulse(CGVector(dx: 50, dy: 0))

// CORRECT: Use actions for non-physics nodes (UI, effects, decorations)
hudLabel.run(SKAction.scale(to: 1.5, duration: 0.2))

---

5. Input Handling

Touch Handling

// CRITICAL: isUserInteractionEnabled must be true on the responding node
// SKScene has it true by default; other nodes default to false

class Player: SKSpriteNode {
    init() {
        super.init(texture: SKTexture(imageNamed: "player"), color: .clear, size: CGSize(width: 50, height: 50))
        isUserInteractionEnabled = true  // Required!
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        // Handle touch on this specific node
    }
}

Coordinate Space Conversion

// Touch location in SCENE coordinates (most common)
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    guard let touch = touches.first else { return }
    let locationInScene = touch.location(in: self)

    // Touch location in a SPECIFIC NODE's coordinates
    let locationInWorld = touch.location(in: worldNode)

    // Hit test: what node was touched?
    let touchedNodes = nodes(at: locationInScene)
}

Common mistake: Using touch.location(in: self.view) returns UIKit coordinates (Y-flipped). Always use touch.location(in: self) for scene coordinates.

Game Controller Support

import GameController

func setupControllers() {
    NotificationCenter.default.addObserver(
        self, selector: #selector(controllerConnected),
        name: .GCControllerDidConnect, object: nil
    )

    // Check already-connected controllers
    for controller in GCController.controllers() {
        configureController(controller)
    }
}

---

6. Performance

Performance Priorities

For detailed performance diagnosis, see axiom-spritekit-diag Symptom 3. Key priorities:

1. Node count — Remove offscreen nodes, use object pooling
2. Draw calls — Use texture atlases, replace SKShapeNode with pre-rendered textures
3. Physics cost — Prefer simple body shapes, limit usesPreciseCollisionDetection
4. Particles — Limit birth rate, set finite emission counts

Debug Overlays (Always Enable During Development)

if let view = self.view as? SKView {
    view.showsFPS = true
    view.showsNodeCount = true
    view.showsDrawCount = true
    view.showsPhysics = true  // Shows physics body outlines

    // Performance: render order optimization
    view.ignoresSiblingOrder = true
}

Texture Atlas Batching

Sprites using textures from the same atlas render in a single draw call.

// Create atlas in Xcode: Assets → New Sprite Atlas
// Or use .atlas folder in project

let atlas = SKTextureAtlas(named: "Characters")
let texture = atlas.textureNamed("player_idle")
let sprite = SKSpriteNode(texture: texture)

// Preload atlas to avoid frame drops
SKTextureAtlas.preloadTextureAtlases([atlas]) {
    // Atlas ready — present scene
}

SKShapeNode Trap

SKShapeNode generates one draw call per instance. It cannot be batched. Use it for prototyping and debug visualization only.

// WRONG: 100 SKShapeNodes = 100 draw calls
for _ in 0..<100 {
    let dot = SKShapeNode(circleOfRadius: 5)
    addChild(dot)
}

// CORRECT: Pre-render to texture, use SKSpriteNode
let shape = SKShapeNode(circleOfRadius: 5)
shape.fillColor = .red
guard let texture = view?.texture(from: shape) else { return }
for _ in 0..<100 {
    let dot = SKSpriteNode(texture: texture)
    addChild(dot)
}

Object Pooling

For frequently spawned/destroyed objects (bullets, particles, enemies):

class BulletPool {
    private var available: [SKSpriteNode] = []
    private let texture: SKTexture

    init(texture: SKTexture, initialSize: Int = 20) {
        self.texture = texture
        for _ in 0..<initialSize {
            available.append(createBullet())
        }
    }

    private func createBullet() -> SKSpriteNode {
        let bullet = SKSpriteNode(texture: texture)
        bullet.physicsBody = SKPhysicsBody(circleOfRadius: 3)
        bullet.physicsBody?.categoryBitMask = PhysicsCategory.projectile
        bullet.physicsBody?.collisionBitMask = PhysicsCategory.none
        bullet.physicsBody?.contactTestBitMask = PhysicsCategory.enemy
        return bullet
    }

    func spawn() -> SKSpriteNode {
        if available.isEmpty {
            available.append(createBullet())
        }
        let bullet = available.removeLast()
        bullet.isHidden  
        bullet.physicsBody.isDynamic  
         bullet
    }

     ( : ) {
        bullet.removeAllActions()
        bullet.removeFromParent()
        bullet.physicsBody.isDynamic  
        bullet.physicsBody.velocity  .zero
        bullet.isHidden  
        available.append(bullet)
    }
}

Offscreen Node Removal

// Manual removal is faster than shouldCullNonVisibleNodes
override func update(_ currentTime: TimeInterval) {
    enumerateChildNodes(withName: "bullet") { node, _ in
        if !self.frame.intersects(node.frame) {
            self.bulletPool.recycle(node as! SKSpriteNode)
        }
    }
}

---

7. Game Loop

Frame Cycle (8 Phases)

1. update(_:)              ← Your game logic here
2. didEvaluateActions()    ← Actions completed
3. [Physics simulation]    ← SpriteKit runs physics
4. didSimulatePhysics()    ← Physics done, adjust results
5. [Constraint evaluation] ← SKConstraints applied
6. didApplyConstraints()   ← Constraints done
7. didFinishUpdate()       ← Last chance before render
8. [Rendering]             ← Frame drawn

Delta Time

private var lastUpdateTime: TimeInterval = 0

override func update(_ currentTime: TimeInterval) {
    let dt: TimeInterval
    if lastUpdateTime == 0 {
        dt = 0
    } else {
        dt = currentTime - lastUpdateTime
    }
    lastUpdateTime = currentTime

    // Clamp delta time to prevent spiral of death
    // (when app returns from background, dt can be huge)
    let clampedDt = min(dt, 1.0 / 30.0)

    updatePlayer(deltaTime: clampedDt)
    updateEnemies(deltaTime: clampedDt)
}

Pause Handling

// Pause the scene (stops actions, physics, update loop)
scene.isPaused = true

// Pause specific subtree only
worldNode.isPaused = true  // Game paused but HUD still animates

// Handle app backgrounding
NotificationCenter.default.addObserver(
    self, selector: #selector(pauseGame),
    name: UIApplication.willResignActiveNotification, object: nil
)

---

8. Particle Effects

Emitter Best Practices

// Load from .sks file (designed in Xcode Particle Editor)
guard let emitter = SKEmitterNode(fileNamed: "Explosion") else { return }
emitter.position = explosionPoint
addChild(emitter)

// CRITICAL: Auto-remove after emission completes
let duration = TimeInterval(emitter.numParticlesToEmit) / TimeInterval(emitter.particleBirthRate)
    + TimeInterval(emitter.particleLifetime + emitter.particleLifetimeRange / 2)
emitter.run(SKAction.sequence([
    SKAction.wait(forDuration: duration),
    SKAction.removeFromParent()
]))

Target Node for Trails

Without targetNode, particles move with the emitter. For trails (like rocket exhaust), set targetNode to the scene:

let trail = SKEmitterNode(fileNamed: "RocketTrail")!
trail.targetNode = scene  // Particles stay where emitted
rocketNode.addChild(trail)

Infinite Emitter Cleanup

// WRONG: Infinite emitter never cleaned up
let fire = SKEmitterNode(fileNamed: "Fire")!
fire.numParticlesToEmit = 0  // 0 = infinite
addChild(fire)
// Memory leak — particles accumulate forever

// CORRECT: Set emission limit or remove when done
fire.numParticlesToEmit = 200  // Stops after 200 particles

// Or manually stop and remove:
fire.particleBirthRate = 0  // Stop new particles
fire.run(SKAction.sequence([
    SKAction.wait(forDuration: TimeInterval(fire.particleLifetime)),
    SKAction.removeFromParent()
]))

---

9. SwiftUI Integration

SpriteView (Recommended, iOS 14+)

The simplest way to embed SpriteKit in SwiftUI. Use this unless you need custom SKView configuration.

import SpriteKit
import SwiftUI

struct GameView: View {
    var body: some View {
        SpriteView(scene: {
            let scene = GameScene(size: CGSize(width: 390, height: 844))
            scene.scaleMode = .aspectFill
            return scene
        }(), debugOptions: [.showsFPS, .showsNodeCount])
        .ignoresSafeArea()
    }
}

UIViewRepresentable (Advanced)

Use when you need full control over SKView configuration (custom frame rate, transparency, or multiple scenes).

import SwiftUI
import SpriteKit

struct SpriteKitView: UIViewRepresentable {
    let scene: SKScene

    func makeUIView(context: Context) -> SKView {
        let view = SKView()
        view.showsFPS = true
        view.showsNodeCount = true
        view.ignoresSiblingOrder = true
        return view
    }

    func updateUIView(_ view: SKView, context: Context) {
        if view.scene == nil {
            view.presentScene(scene)
        }
    }
}

SKRenderer for Metal Hybrid

Use SKRenderer when SpriteKit is one layer in a Metal pipeline:

let renderer = SKRenderer(device: metalDevice)
renderer.scene = gameScene

// In your Metal render loop:
renderer.update(atTime: currentTime)
renderer.render(
    withViewport: viewport,
    commandBuffer: commandBuffer,
    renderPassDescriptor: renderPassDescriptor
)

---

10. Anti-Patterns

Anti-Pattern 1: Default Bitmasks

Time cost: 30-120 minutes debugging phantom collisions

// WRONG: Default collisionBitMask is 0xFFFFFFFF
let body = SKPhysicsBody(circleOfRadius: 10)
node.physicsBody = body
// Collides with EVERYTHING — even things it shouldn't

// CORRECT: Always set all three masks explicitly
body.categoryBitMask = PhysicsCategory.player
body.collisionBitMask = PhysicsCategory.ground
body.contactTestBitMask = PhysicsCategory.enemy

Anti-Pattern 2: Missing contactTestBitMask

Time cost: 30-60 minutes wondering why didBegin never fires

// WRONG: contactTestBitMask defaults to 0 — no contacts ever fire
player.physicsBody?.categoryBitMask = PhysicsCategory.player
// Forgot contactTestBitMask!

// CORRECT: Both bodies need compatible masks
player.physicsBody?.contactTestBitMask = PhysicsCategory.enemy
enemy.physicsBody?.categoryBitMask = PhysicsCategory.enemy

Anti-Pattern 3: Actions on Physics Bodies

Time cost: 1-3 hours of jittering and missed collisions

// WRONG: SKAction.move overrides physics position each frame
playerNode.run(SKAction.moveTo(x: 200, duration: 1.0))
// Physics body position is set by action, ignoring forces/collisions

// CORRECT: Use physics for physics-controlled nodes
playerNode.physicsBody?.applyForce(CGVector(dx: 100, dy: 0))

Anti-Pattern 4: SKShapeNode for Gameplay

Time cost: Hours diagnosing frame drops

Each SKShapeNode is a separate draw call that cannot be batched. 50 shape nodes = 50 draw calls. See the pre-render-to-texture pattern in Section 6 (SKShapeNode Trap) for the fix.

Anti-Pattern 5: Strong Self in Action Closures

Time cost: Memory leaks, eventual crash

// WRONG: Strong capture in repeating action
node.run(SKAction.repeatForever(SKAction.sequence([
    SKAction.run { self.spawnEnemy() },
    SKAction.wait(forDuration: 2.0)
])))

// CORRECT: Weak capture
node.run(SKAction.repeatForever(SKAction.sequence([
    SKAction.run { [weak self] in self?.spawnEnemy() },
    SKAction.wait(forDuration: 2.0)
])))

---

11. Code Review Checklist

Physics

• Every physics body has explicit categoryBitMask (not default)
• Every physics body has explicit collisionBitMask (not 0xFFFFFFFF)
• Bodies needing contact detection have contactTestBitMask set
• physicsWorld.contactDelegate is assigned
• No world modifications inside didBegin/didEnd callbacks
• Fast objects use usesPreciseCollisionDetection

Actions

• No SKAction.move/rotate on physics-controlled nodes
• Repeating actions use withKey: for cancellation
• SKAction.run closures use [weak self]
• One-shot emitters are removed after emission

Performance

• Debug overlays enabled during development
• ignoresSiblingOrder = true on SKView
• No SKShapeNode in gameplay sprites (use pre-rendered textures)
• Texture atlases used for related sprites
• Offscreen nodes removed manually

Scene Management

• willMove(from:) cleans up actions, children, delegates
• Scene data passed via shared state, not node properties
• Camera used for viewport control

---

12. Pressure Scenarios

Scenario 1: "Physics Contacts Don't Work — Ship Tonight"

Pressure: Deadline pressure to skip systematic debugging

Wrong approach: Randomly changing bitmask values, adding 0xFFFFFFFF everywhere, or disabling physics

Correct approach (2-5 minutes):

1. Enable showsPhysics — verify bodies exist and overlap
2. Print all three bitmasks for both bodies
3. Verify contactTestBitMask on body A includes category of body B (or vice versa)
4. Verify physicsWorld.contactDelegate is set
5. Verify you're not modifying the world inside the callback

Push-back template: "Let me run the 5-step bitmask checklist. It takes 2 minutes and catches 90% of contact issues. Random changes will make it worse."

Scenario 2: "Frame Rate Is Fine on My Device"

Pressure: Authority says "it runs at 60fps for me, ship it"

Wrong approach: Shipping without profiling on minimum-spec device

Correct approach:

1. Enable showsFPS, showsNodeCount, showsDrawCount
2. Test on oldest supported device
3. If >200 nodes or >30 draw calls, investigate
4. Check for SKShapeNode in gameplay
5. Verify offscreen nodes are being removed

Push-back template: "Performance varies by device. Let me check node count and draw calls — takes 30 seconds with debug overlays. If counts are low, we're safe to ship."

Scenario 3: "Just Use SKShapeNode, It's Faster to Code"

Pressure: Sunk cost — already built with SKShapeNode, don't want to redo

Wrong approach: Shipping with 100+ SKShapeNodes causing frame drops

Correct approach:

1. Check showsDrawCount — each SKShapeNode adds a draw call
2. If >20 shape nodes in gameplay, pre-render to textures
3. Use view.texture(from:) to convert once, reuse as SKSpriteNode
4. Keep SKShapeNode only for debug visualization

Push-back template: "Each SKShapeNode is a separate draw call. Converting to pre-rendered textures is a 15-minute refactor that can double frame rate. SKSpriteNode from atlas = 1 draw call for all of them."

Resources

WWDC: 2014-608, 2016-610, 2017-609, 2013-502

Docs: /spritekit, /spritekit/skscene, /spritekit/skphysicsbody, /spritekit/maximizing-node-drawing-performance

Skills: axiom-spritekit-ref, axiom-spritekit-diag