基于CAEmitterLayer的下雨、下雪、火焰、烟花粒子动画

基于CAEmitterLayer的下雨、下雪、火焰、烟花粒子动画效果demo
demo源码地址：https://github.com/zhaoqianJoyce/ZQCAEmitterLayer

• CAEmitterLayer是继承自CALayer的layer类,拥有很多属性，其中此demo用到的属性有：

   `emitterCells`：是用来与`CAEmitterLayer`关联显示粒子效果的，是`CAEmitterCell`的实例化对象，必须有值；
   `emitterPosition`：粒子排放位置，默认值是(0, 0)；
   `emitterShape`：粒子排放形状，默认值是`kCAEmitterLayerPoint`；
   `emitterSize`：粒子排放的大小，取决于`emitterShape`，可忽略；
   `emitterMode`：粒子排放模式，默认值是`kCAEmitterLayerVolume`；
   `renderMode`：粒子渲染模式，默认值是`kCAEmitterLayerUnordered`.
  

• CAEmitterCell继承自NSObject且遵循一定协议的类，拥有很多属性，其中此demo用到的属性有：

  `birthRate`：粒子每秒产生个数；
  `lifetime`：粒子的生命周期；
  `emissionRange`:粒子排放的范围；
  `velocity`：粒子的速度；
  `velocityRange`：粒子速度变化值；
  `alphaSpeed`：粒子生命周期内颜色变化速度；
  `contents`：，`CAEmitterCell`的内容，是`CGImageRef`类型。
  

• 核心代码

// 下雨、下雪
/**
 *  设置emitterLayer的属性
 */
- (void)initEmitterLayerProperties {
    
    self.emitterLayer.emitterSize     = self.frame.size;
    self.emitterLayer.emitterPosition = CGPointMake(self.frame.origin.x, self.frame.origin.y);
}

/**
 *  设置emitterCell的属性并与emitterLayer关联显示动画效果
 *
 *  @param weather 天气名称
 */
- (void)showWeather:(NSString *)weather {
    
    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.birthRate      = 20.f;
    emitterCell.lifetime       = 100.f;
    emitterCell.velocity       = 10.f;
    emitterCell.velocityRange  = 3.f;
    emitterCell.yAcceleration  = 5.f;
    emitterCell.emissionRange  = 6 * M_2_PI;
    emitterCell.contents       = (__bridge id _Nullable)([UIImage imageNamed:weather].CGImage);
    
    self.emitterLayer.emitterCells = @[emitterCell];
}
// 火焰
/**
 *  设置emitterLayer的属性
 */
- (void)initEmitterLayerProperties {
    
    self.emitterLayer.emitterSize     = self.frame.size;
    self.emitterLayer.emitterPosition = CGPointMake(self.frame.origin.x, self.frame.origin.y);
    self.emitterLayer.emitterMode     = kCAEmitterLayerPoints;
    self.emitterLayer.renderMode      = kCAEmitterLayerBackToFront;
}

/**
 *  设置emitterCell的属性并与emitterLayer关联显示动画效果
 */
- (void)show {
    
    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.birthRate      = 200.f;
    emitterCell.lifetime       = 10.f;
    emitterCell.velocity       = 10.f;
    emitterCell.velocityRange  = 15.f;
    emitterCell.emissionRange  = 2 * M_PI;
    emitterCell.alphaSpeed    -= 0.5f;
    emitterCell.contents       = (__bridge id _Nullable)([UIImage imageNamed:@"fire_selected"].CGImage);
    
    self.emitterLayer.emitterCells = @[emitterCell];
}
// 烟花
/**
 *  设置emitterLayer的属性
 */
- (void)initEmitterLayerProperties {
    
    self.emitterLayer.emitterSize     = self.frame.size;
    self.emitterLayer.emitterPosition = CGPointMake(self.frame.origin.x, self.frame.origin.y);
    self.emitterLayer.emitterMode     = kCAEmitterLayerPoints;
    self.emitterLayer.renderMode      = kCAEmitterLayerBackToFront;
}

/**
 *  设置emitterCell的属性并与emitterLayer关联显示动画效果
 */
- (void)show {
    
    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.birthRate      = 50.f;
    emitterCell.lifetime       = 6.f;
    emitterCell.velocity       = 50.f;
    emitterCell.velocityRange  = 100.f;
    emitterCell.emissionRange  = 2 * M_PI;
    emitterCell.alphaSpeed    -= 0.5f;
    emitterCell.contents       = (__bridge id _Nullable)([UIImage imageNamed:@"fireworks_selected"].CGImage);
    
    self.emitterLayer.emitterCells = @[emitterCell];
}