Phaser Gamedev

# Arcade Physics Deep Dive

Comprehensive reference for Phaser 3 Arcade Physics system.

## World Configuration

```javascript
// In game config
physics: {
  default: 'arcade',
  arcade: {
    gravity: { x: 0, y: 300 },
    debug: true,                    // Show collision bodies
    debugShowBody: true,
    debugShowStaticBody: true,
    debugShowVelocity: true,
    debugBodyColor: 0xff00ff,
    debugStaticBodyColor: 0x0000ff,
    debugVelocityColor: 0x00ff00,
    fps: 60,                        // Physics update rate
    timeScale: 1,                   // 0.5 = half speed, 2 = double
    checkCollision: {
      up: true,
      down: true,
      left: true,
      right: true
    },
    overlapBias: 4,                 // Overlap tolerance
    tileBias: 16,                   // Tile collision bias
    forceX: false,                  // Prioritize X-axis separation
    maxEntries: 16,                 // Quadtree max per node
    useTree: true                   // Spatial hash (false for >5000 bodies)
  }
}
```

## Body Types

### Dynamic Bodies

Move, respond to velocity, gravity, and collisions.

```javascript
// Create with physics enabled
const player = this.physics.add.sprite(100, 100, 'player');

// Or add to existing sprite
const sprite = this.add.sprite(100, 100, 'player');
this.physics.add.existing(sprite);

// Body properties
player.body.setVelocity(100, -200);
player.body.setVelocityX(100);
player.body.setVelocityY(-200);
player.body.setBounce(0.5, 0.5);
player.body.setDrag(100, 100);
player.body.setFriction(0.5, 0.5);
player.body.setMaxVelocity(300, 400);
player.body.setGravityY(500);           // Additional gravity
player.body.setAcceleration(100, 0);
player.body.setCollideWorldBounds(true);
player.body.onWorldBounds = true;       // Enable worldbounds event
```

### Static Bodies

Immovable, no velocity or gravity response. Efficient for platforms.

```javascript
// Create static group
const platforms = this.physics.add.staticGroup();
platforms.create(400, 568, 'ground');

// Or make existing body static
sprite.body.setImmovable(true);
sprite.body.moves = false;

// After scaling/moving static bodies
sprite.refreshBody();
```

## Body Sizing and Shape

```javascript
// Custom body size
sprite.body.setSize(width, height, center);
sprite.body.setSize(32, 48, true);      // Centered

// Offset body from sprite
sprite.body.setOffset(x, y);

// Circular body (for rolling objects)
sprite.body.setCircle(radius, offsetX, offsetY);
sprite.body.setCircle(16, 0, 0);
```

## Collision Detection

### Collider vs Overlap

```javascript
// Collider: Physical collision, objects separate
this.physics.add.collider(player, platforms);
this.physics.add.collider(player, enemies, hitEnemy, null, this);

// Overlap: Detect overlap without physical response
this.physics.add.overlap(player, coins, collectCoin, null, this);

function collectCoin(player, coin) {
  coin.disableBody(true, true);  // (disableGameObject, hideGameObject)
}
```

### Collision Callbacks

```javascript
// Process callback (return false to skip collision)
function shouldCollide(player, enemy) {
  return !player.isInvincible;
}

this.physics.add.collider(player, enemies, hitEnemy, shouldCollide, this);
```

### Collision Events

```javascript
// World bounds event
this.physics.world.on('worldbounds', (body, up, down, left, right) => {
  if (down) {
    // Hit bottom of world
  }
});

// Enable on body first
player.body.onWorldBounds = true;
player.body.setCollideWorldBounds(true);
```

## Groups

### Static Groups

```javascript
const platforms = this.physics.add.staticGroup();

// Add children
platforms.create(400, 568, 'ground');
platforms.createMultiple({
  key: 'brick',
  repeat: 10,
  setXY: { x: 50, y: 300, stepX: 70 }
});

// After modifying
platforms.refresh();
```

### Dynamic Groups

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

// Group defaults
const bullets = this.physics.add.