phaser-gamedev

SKILL.md

Phaser Game Development

Build fast, polished 2D browser games using Phaser 3's scene-based architecture and physics systems.

Philosophy: Games as Living Systems

Games are not static UIs—they are dynamic systems where entities interact, state evolves, and player input drives everything. Before writing code, think architecturally.

Before building, ask:

What scenes does this game need? (Boot, Menu, Game, Pause, GameOver)

What entities exist and how do they interact?

What state must persist across scenes?

What physics model fits? (Arcade for speed, Matter for realism)

What input methods will players use?

Core principles:

Scene-First Architecture: Structure games around scenes, not global state

Composition Over Inheritance: Build entities from game objects and components

Physics-Aware Design: Choose physics system before coding collisions

Asset Pipeline Discipline: Preload everything, reference by key

Frame-Rate Independence: Use delta time, not frame counting

Game Configuration

Every Phaser game starts with a configuration object.

Minimal Configuration

const config = {
  type: Phaser.AUTO,           // WebGL with Canvas fallback
  width: 800,
  height: 600,
  scene: [BootScene, GameScene]
};

const game = new Phaser.Game(config);

Full Configuration Pattern

const config = {
  type: Phaser.AUTO,
  width: 800,
  height: 600,
  parent: 'game-container',    // DOM element ID
  backgroundColor: '#2d2d2d',

  scale: {
    mode: Phaser.Scale.FIT,
    autoCenter: Phaser.Scale.CENTER_BOTH
  },

  physics: {
    default: 'arcade',
    arcade: {
      gravity: { y: 300 },
      debug: false              // Enable during development
    }
  },

  scene: [BootScene, MenuScene, GameScene, GameOverScene]
};

Physics System Choice

System
Use When

Arcade
Platformers, shooters, most 2D games. Fast, simple AABB collisions

Matter
Physics puzzles, ragdolls, realistic collisions. Slower, more accurate

None
Menu scenes, visual novels, card games

Scene Architecture

Scenes are the fundamental organizational unit. Each scene has a lifecycle.

Scene Lifecycle Methods

class GameScene extends Phaser.Scene {
  constructor() {
    super('GameScene');        // Scene key for reference
  }

  init(data) {
    // Called first. Receive data from previous scene
    this.level = data.level || 1;
  }

  preload() {
    // Load assets. Runs before create()
    this.load.image('player', 'assets/player.png');
    this.load.spritesheet('enemy', 'assets/enemy.png', {
      frameWidth: 32, frameHeight: 32
    });
  }

  create() {
    // Set up game objects, physics, input
    this.player = this.physics.add.sprite(100, 100, 'player');
    this.cursors = this.input.keyboard.createCursorKeys();
  }

  update(time, delta) {
    // Game loop. Called every frame
    // delta = milliseconds since last frame
    this.player.x += this.speed * (delta / 1000);
  }
}

Scene Transitions

// Start a new scene (stops current)
this.scene.start('GameOverScene', { score: this.score });

// Launch scene in parallel (both run)
this.scene.launch('UIScene');

// Pause/resume scenes
this.scene.pause('GameScene');
this.scene.resume('GameScene');

// Stop a scene
this.scene.stop('UIScene');

Recommended Scene Structure

scenes/
├── BootScene.js      # Asset loading, progress bar
├── MenuScene.js      # Title screen, options
├── GameScene.js      # Main gameplay
├── UIScene.js        # HUD overlay (launched parallel)
├── PauseScene.js     # Pause menu overlay
└── GameOverScene.js  # End screen, restart option

Game Objects

Everything visible in Phaser is a Game Object.

Common Game Objects

// Images (static)
this.add.image(400, 300, 'background');

// Sprites (can animate, physics-enabled)
const player = this.add.sprite(100, 100, 'player');

// Text
const score = this.add.text(16, 16, 'Score: 0', {
  fontSize: '32px',
  fill: '#fff'
});

// Graphics (draw shapes)
const graphics = this.add.graphics();
graphics.fillStyle(0xff0000);
graphics.fillRect(100, 100, 50, 50);

// Containers (group objects)
const container = this.add.container(400, 300, [sprite1, sprite2]);

// Tilemaps
const map = this.make.tilemap({ key: 'level1' });

Sprite Creation Patterns

// Basic sprite
const sprite = this.add.sprite(x, y, 'textureKey');

// Sprite with physics body
const sprite = this.physics.add.sprite(x, y, 'textureKey');

// From spritesheet frame
const sprite = this.add.sprite(x, y, 'sheet', frameIndex);

// From atlas
const sprite = this.add.sprite(x, y, 'atlas', 'frameName');

Physics Systems

Arcade Physics (Recommended Default)

Fast, simple physics for most 2D games.

// Enable physics on sprite
this.physics.add.sprite(x, y, 'player');

// Or add physics to existing sprite
this.physics.add.existing(sprite);

// Configure body
sprite.body.setVelocity(200, 0);
sprite.body.setBounce(0.5);
sprite.body.setCollideWorldBounds(true);
sprite.body.setGravityY(300);

// Collision detection
this.physics.add.collider(player, platforms);
this.physics.add.overlap(player, coins, collectCoin, null, this);

function collectCoin(player, coin) {
  coin.disableBody(true, true);  // Remove from physics and hide
  this.score += 10;
}

Physics Groups

// Static group (platforms, walls)
const platforms = this.physics.add.staticGroup();
platforms.create(400, 568, 'ground').setScale(2).refreshBody();

// Dynamic group (enemies, bullets)
const enemies = this.physics.add.group({
  key: 'enemy',
  repeat: 5,
  setXY: { x: 100, y: 0, stepX: 70 }
});

enemies.children.iterate(enemy => {
  enemy.setBounce(Phaser.Math.FloatBetween(0.4, 0.8));
});

Matter Physics

For realistic physics simulations.

// Config
physics: {
  default: 'matter',
  matter: {
    gravity: { y: 1 },
    debug: true
  }
}

// Create bodies
const ball = this.matter.add.circle(400, 100, 25);
const box = this.matter.add.rectangle(400, 400, 100, 50, { isStatic: true });

// Sprite with Matter body
const player = this.matter.add.sprite(100, 100, 'player');
player.setFriction(0.005);
player.setBounce(0.9);

Input Handling

Keyboard Input

// Cursor keys
this.cursors = this.input.keyboard.createCursorKeys();

// In update()
if (this.cursors.left.isDown) {
  player.setVelocityX(-160);
} else if (this.cursors.right.isDown) {
  player.setVelocityX(160);
}

if (this.cursors.up.isDown && player.body.touching.down) {
  player.setVelocityY(-330);  // Jump
}

// Custom keys
this.spaceKey = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.SPACE);

// Key events
this.input.keyboard.on('keydown-SPACE', () => {
  this.fire();
});

Pointer/Mouse Input

// Click/tap
this.input.on('pointerdown', (pointer) => {
  console.log(pointer.x, pointer.y);
});

// Make object interactive
sprite.setInteractive();
sprite.on('pointerdown', () => {
  sprite.setTint(0xff0000);
});
sprite.on('pointerup', () => {
  sprite.clearTint();
});

// Drag
this.input.setDraggable(sprite);
this.input.on('drag', (pointer, obj, dragX, dragY) => {
  obj.x = dragX;
  obj.y = dragY;
});

Animations

Creating Animations

// In create() - define once
this.anims.create({
  key: 'walk',
  frames: this.anims.generateFrameNumbers('player', { start: 0, end: 3 }),
  frameRate: 10,
  repeat: -1  // Loop forever
});

this.anims.create({
  key: 'jump',
  frames: [{ key: 'player', frame: 4 }],
  frameRate: 20
});

// From atlas
this.anims.create({
  key: 'explode',
  frames: this.anims.generateFrameNames('atlas', {
    prefix: 'explosion_',
    start: 1,
    end: 8,
    zeroPad: 2
  }),
  frameRate: 16,
  hideOnComplete: true
});

Playing Animations

// Play animation
sprite.anims.play('walk', true);  // true = ignore if already playing

// Play once
sprite.anims.play('jump');

// Stop
sprite.anims.stop();

// Animation events
sprite.on('animationcomplete', (anim, frame) => {
  if (anim.key === 'die') {
    sprite.destroy();
  }
});

Asset Loading

Preload Patterns

preload() {
  // Images
  this.load.image('sky', 'assets/sky.png');

  // Spritesheets
  this.load.spritesheet('player', 'assets/player.png', {
    frameWidth: 32,
    frameHeight: 48
  });

  // Atlases (TexturePacker)
  this.load.atlas('sprites', 'assets/sprites.png', 'assets/sprites.json');

  // Tilemaps
  this.load.tilemapTiledJSON('map', 'assets/level1.json');
  this.load.image('tiles', 'assets/tileset.png');

  // Audio
  this.load.audio('bgm', 'assets/music.mp3');
  this.load.audio('sfx', ['assets/sound.ogg', 'assets/sound.mp3']);

  // Progress tracking
  this.load.on('progress', (value) => {
    console.log(`Loading: ${Math.round(value * 100)}%`);
  });
}

Boot Scene Pattern

class BootScene extends Phaser.Scene {
  constructor() {
    super('BootScene');
  }

  preload() {
    // Loading bar
    const width = this.cameras.main.width;
    const height = this.cameras.main.height;

    const progressBar = this.add.graphics();
    const progressBox = this.add.graphics();
    progressBox.fillStyle(0x222222, 0.8);
    progressBox.fillRect(width/2 - 160, height/2 - 25, 320, 50);

    this.load.on('progress', (value) => {
      progressBar.clear();
      progressBar.fillStyle(0xffffff, 1);
      progressBar.fillRect(width/2 - 150, height/2 - 15, 300 * value, 30);
    });

    // Load all game assets here
    this.load.image('player', 'assets/player.png');
    // ... more assets
  }

  create() {
    this.scene.start('MenuScene');
  }
}

Tilemaps (Tiled Integration)

Loading and Creating

preload() {
  this.load.tilemapTiledJSON('map', 'assets/map.json');
  this.load.image('tiles', 'assets/tileset.png');
}

create() {
  const map = this.make.tilemap({ key: 'map' });
  const tileset = map.addTilesetImage('tileset-name-in-tiled', 'tiles');

  // Create layers (match names from Tiled)
  const backgroundLayer = map.createLayer('Background', tileset, 0, 0);
  const groundLayer = map.createLayer('Ground', tileset, 0, 0);

  // Enable collision on specific tiles
  groundLayer.setCollisionByProperty({ collides: true });
  // Or by tile index
  groundLayer.setCollisionBetween(1, 100);

  // Add collision with player
  this.physics.add.collider(this.player, groundLayer);
}

Object Layers

// Spawn points from Tiled object layer
const spawnPoint = map.findObject('Objects', obj => obj.name === 'spawn');
this.player = this.physics.add.sprite(spawnPoint.x, spawnPoint.y, 'player');

// Create objects from layer
const coins = map.createFromObjects('Objects', {
  name: 'coin',
  key: 'coin'
});
this.physics.world.enable(coins);

Project Structure

Recommended Organization

game/
├── src/
│   ├── scenes/
│   │   ├── BootScene.js
│   │   ├── MenuScene.js
│   │   ├── GameScene.js
│   │   └── UIScene.js
│   ├── gameObjects/
│   │   ├── Player.js
│   │   ├── Enemy.js
│   │   └── Collectible.js
│   ├── systems/
│   │   ├── InputManager.js
│   │   └── AudioManager.js
│   ├── config/
│   │   └── gameConfig.js
│   └── main.js
├── assets/
│   ├── images/
│   ├── audio/
│   ├── tilemaps/
│   └── fonts/
├── index.html
└── package.json

ES Module Setup

// main.js
import Phaser from 'phaser';
import BootScene from './scenes/BootScene';
import GameScene from './scenes/GameScene';
import { gameConfig } from './config/gameConfig';

const config = {
  ...gameConfig,
  scene: [BootScene, GameScene]
};

new Phaser.Game(config);

Anti-Patterns to Avoid

❌ Global State Soup: Storing game state on window or module globals
Why bad: Untrackable bugs, scene transitions break state
Better: Use scene data, registries, or dedicated state managers

❌ Loading in Create: Loading assets in create() instead of preload()
Why bad: Assets may not be ready when referenced
Better: Always load in preload(), use Boot scene for all assets

❌ Frame-Dependent Logic: Using frame count instead of delta time
Why bad: Game speed varies with frame rate
Better: this.speed * (delta / 1000) for consistent movement

❌ Physics Overkill: Using Matter for simple platformer collisions
Why bad: Performance hit, unnecessary complexity
Better: Arcade physics handles 90% of 2D game needs

❌ Monolithic Scenes: One giant scene with all game logic
Why bad: Unmaintainable, hard to add features
Better: Separate scenes for menus, gameplay, UI overlays

❌ Magic Numbers: Hardcoded values scattered in code
Why bad: Impossible to balance, inconsistent
Better: Config objects, constants files

❌ Ignoring Object Pooling: Creating/destroying objects every frame
Why bad: Memory churn, garbage collection stutters
Better: Use groups with setActive(false) / setVisible(false)

❌ Synchronous Asset Access: Assuming assets load instantly
Why bad: Race conditions, undefined textures
Better: Chain scene starts, use load events

❌ Assuming Spritesheet Frame Dimensions: Using guessed frame sizes without verifying
Why bad: Wrong dimensions cause silent frame corruption; off-by-pixels compounds into broken visuals
Better: Open asset file, measure frames, calculate with spacing/margin, verify math adds up

❌ Ignoring Spritesheet Spacing: Not specifying spacing for gapped spritesheets
Why bad: Frames shift progressively; later frames read wrong pixel regions
Better: Check source asset for gaps between frames; use spacing: N in loader config

❌ Hardcoding Nine-Slice Colors: Using single background color for all UI panel variants
Why bad: Transparent frame edges reveal wrong color for different asset color schemes
Better: Per-asset background color config; sample from center frame (frame 4)

❌ Nine-Slice with Padded Frames: Treating the full frame as the slice region when the art is centered/padded inside each tile
Why bad: Edge tiles contribute interior fill, showing up as opaque “side bars” inside the panel
Better: Trim tiles to their effective content bounds (alpha bbox) and composite/cache a texture; add ~1px overlap + disable smoothing to avoid seams

❌ Scaling Discontinuous UI Art: Stretching a cropped ribbon/banner row that contains internal transparent gaps
Why bad: The transparent gutters get stretched, so the UI looks segmented or the fill disappears behind the frame.
Better: Slice the asset into caps/center, stretch only the center, and stitch the pieces (with ~1px overlap + smoothing disabled) before rendering at pivot sizes.

Variation Guidance

IMPORTANT: Game implementations should vary based on:

Game Genre: Platformer physics differ from top-down shooter physics

Target Platform: Mobile needs touch input, desktop can use keyboard

Art Style: Pixel art uses nearest-neighbor scaling, HD art uses linear

Performance Needs: Many sprites → object pooling; few sprites → simple creation

Complexity: Simple games can inline; complex games need class hierarchies

Avoid converging on:

Always using 800x600 resolution

Always using Arcade physics

Always using the same scene structure

Copy-pasting boilerplate without adaptation

Quick Reference

Common Physics Properties

body.setVelocity(x, y)
body.setVelocityX(x)
body.setBounce(x, y)
body.setGravityY(y)
body.setCollideWorldBounds(true)
body.setImmovable(true)        // For static-like dynamic bodies
body.setDrag(x, y)
body.setMaxVelocity(x, y)

Useful Scene Properties

this.cameras.main              // Main camera
this.physics.world             // Physics world
this.input.keyboard            // Keyboard manager
this.sound                     // Audio manager
this.time                      // Time/clock manager
this.tweens                    // Tween manager
this.anims                     // Animation manager
this.registry                  // Cross-scene data store
this.data                      // Scene-specific data store

Essential Events

// Scene events
this.events.on('pause', callback)
this.events.on('resume', callback)
this.events.on('shutdown', callback)

// Physics events
this.physics.world.on('worldbounds', callback)

// Game object events
sprite.on('destroy', callback)
sprite.on('animationcomplete', callback)

See Also

references/arcade-physics.md - Deep dive into Arcade physics

references/tilemaps.md - Advanced tilemap techniques

references/performance.md - Optimization strategies

references/spritesheets-nineslice.md - Spritesheet loading (spacing/margin), nine-slice UI panels, asset inspection

Remember

Phaser gives you powerful primitives—scenes, sprites, physics, input—but architecture is your responsibility.

Think in systems: What scenes do you need? What entities exist? How do they interact? Answer these questions before writing code, and your game will be maintainable as it grows.

Claude is capable of building complete, polished Phaser games. These guidelines illuminate the path—they don't fence it.