Recycling emitter nodes with particle pools

We do not need to create a new emitter node for every single crate in our game. Instead, we will create a small pool of emitter nodes when the game starts and reposition them when the player smashes a crate. This is a performance best practice as emitter nodes can use system resources quickly. Follow these steps to create a particle emitter node pooling system:

1. In Xcode, create a new .swift file named ParticlePool.swift, and add the following code to your new file:

           import SpriteKit 
    
           class ParticlePool { 
               var cratePool: [SKEmitterNode] = [] 
               var heartPool: [SKEmitterNode] = [] 
               var crateIndex = 0 
               var heartIndex = 0 
               // A property to store a reference to the GameScene: 
               var gameScene = SKScene() 
        
               init() { 
                   // Create 5 crate explosion emitter nodes: 
                   for i in 1...5 { 
                       // Create a crate emitter...