swift 实现漂亮的粒子效果CAEmitterLayer

我们经常会在一些游戏或者应用中看到一些炫酷的粒子效果，我们在iOS中也能很轻松的搞一些粒子效果

我们本次做得是一个下雪的效果，看下效果图

源码地址：  https://github.com/smalldu/IOS-Animations 中的AnimationDemo10

iOS中的粒子效果是用CAEmitterLayer和CAEmitterCell 实现的 ， 对cell的粒子数 ，存活时间。。。各种东西进行配置就可以了

常用的产生粒子模式 三种kCAEmitterLayerPoint 点 kCAEmitterLayerLine线 kCAEmitterLayerRectangle 矩形，大家可以自己试试 。我就不一一展示了。

下面是所有代码 ,代码量很少 。而且都有注释

import UIKit  class ViewController: UIViewController {      override func viewDidLoad() {    super.viewDidLoad()    let rect = CGRect(x: 0.0, y: -70.0, width: view.bounds.width,        height: 50.0)    let emitter = CAEmitterLayer()    emitter.frame = rect    view.layer.addSublayer(emitter)    emitter.emitterShape = kCAEmitterLayerRectangle    //kCAEmitterLayerPoint    //kCAEmitterLayerLine    //kCAEmitterLayerRectangle    emitter.emitterPosition = CGPointMake(rect.width/2, rect.height/2)    emitter.emitterSize = rect.size    let emitterCell = CAEmitterCell()    emitterCell.contents = UIImage(named: "xh")!.scaleImageToWidth(30).CGImage    emitterCell.birthRate = 120  //每秒产生120个粒子    emitterCell.lifetime = 3    //存活1秒    emitterCell.lifetimeRange = 3.0    emitter.emitterCells = [emitterCell]  //这里可以设置多种粒子 我们以一种为粒子    emitterCell.yAcceleration = 70.0  //给Y方向一个加速度    emitterCell.xAcceleration = 20.0 //x方向一个加速度    emitterCell.velocity = 20.0 //初始速度    emitterCell.emissionLongitude = CGFloat(-M_PI) //向左    emitterCell.velocityRange = 200.0   //随机速度 -200+20 --- 200+20    emitterCell.emissionRange = CGFloat(M_PI_2) //随机方向 -pi/2 --- pi/2         //emitterCell.color = UIColor(red: 0.9, green: 1.0, blue: 1.0,     //   alpha: 1.0).CGColor //指定颜色    emitterCell.redRange = 0.3    emitterCell.greenRange = 0.3    emitterCell.blueRange = 0.3  //三个随机颜色    emitterCell.scale = 0.8    emitterCell.scaleRange = 0.8  //0 - 1.6     emitterCell.scaleSpeed = -0.15  //逐渐变小    emitterCell.alphaRange = 0.75   //随机透明度    emitterCell.alphaSpeed = -0.15  //逐渐消失    // Do any additional setup after loading the view, typically from a nib.      }      override func didReceiveMemoryWarning() {    super.didReceiveMemoryWarning()    // Dispose of any resources that can be recreated.      }  }