axiom-spritekit

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)

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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.