CAEmitterLayer *snowEmitter = [CAEmitterLayer layer];

  //例子发射位置

  snowEmitter.emitterPosition = CGPointMake(120,20);

  //发射源的尺寸大小

  snowEmitter.emitterSize = CGSizeMake(self.view.bounds.size.width * 20, 20);

  //发射模式

  snowEmitter.emitterMode = kCAEmitterLayerSurface;

  //发射源的形状

  snowEmitter.emitterShape = kCAEmitterLayerLine;

  //创建雪花类型的粒子

  CAEmitterCell *snowflake = [CAEmitterCell emitterCell];

  //粒子的名字

  snowflake.name = @"snow";

  //粒子参数的速度乘数因子

  snowflake.birthRate = 1.0;

  snowflake.lifetime = 120.0;

  //粒子速度

  snowflake.velocity =10.0;

  //粒子的速度范围

  snowflake.velocityRange = 10;

  //粒子y方向的加速度分量

  snowflake.yAcceleration = 2;

  //周围发射角度

  snowflake.emissionRange = 0.5 * M_PI;

  //子旋转角度范围

  snowflake.spinRange = 0.25 * M_PI;

  snowflake.contents = (id)[[UIImage imageNamed:@"DazFlake"] CGImage];

  //设置雪花形状的粒子的颜色

  snowflake.color = [[UIColor colorWithRed:0.200 green:0.258 blue:0.543 alpha:1.000] CGColor];

  //创建星星形状的粒子

  CAEmitterCell *snowflake1 = [CAEmitterCell emitterCell];

  //粒子的名字

  snowflake1.name = @"snow";

  //粒子参数的速度乘数因子

  snowflake1.birthRate = 1.0;

  snowflake1.lifetime = 120.0;

  //粒子速度

  snowflake1.velocity =10.0;

  //粒子的速度范围

  snowflake1.velocityRange = 10;

  //粒子y方向的加速度分量

  snowflake1.yAcceleration = 2;

  //周围发射角度

  snowflake1.emissionRange = 0.5 * M_PI;

  //子旋转角度范围

  snowflake1.spinRange = 0.25 * M_PI;

  //粒子的内容和内容的颜色

  snowflake1.contents = (id)[[UIImage imageNamed:@"DazStarOutline"] CGImage];

  snowflake1.color = [[UIColor colorWithRed:0.600 green:0.658 blue:0.743 alpha:1.000] CGColor];

  snowEmitter.shadowOpacity = 1.0;

  snowEmitter.shadowRadius = 0.0;

  snowEmitter.shadowOffset = CGSizeMake(0.0, 1.0);

  //粒子边缘的颜色

  snowEmitter.shadowColor = [[UIColor redColor] CGColor];

  snowEmitter.emitterCells = [NSArray arrayWithObjects:snowflake,snowflake1,nil];

  [self.view.layer insertSublayer:snowEmitter atIndex:0];

  // Do any additional setup after loading the view