//创建Layer
CAEmitterLayer *emitterLayer = [CAEmitterLayer layer];
//边框
emitterLayer.borderWidth = 1.0f;
//尺寸
emitterLayer.frame = CGRectMake(100, 100, 100, 100);
emitterLayer.masksToBounds = YES;
//发射点
emitterLayer.emitterPosition = CGPointMake(0, 0);
//发射模式
emitterLayer.emitterMode = kCAEmitterLayerOutline;
//发射形状
emitterLayer.emitterShape = kCAEmitterLayerCircle;
[self.view.layer addSublayer:emitterLayer];
//创建粒子
CAEmitterCell *cell = [CAEmitterCell emitterCell];
//粒子产生率
cell.birthRate = 2.f;
//粒子生命周期
cell.lifetime = 10.f;//秒
//粒子速度值
cell.velocity = 10;
//速度变化值
cell.velocityRange = 3.f;//7--13
//y轴加速度
cell.yAcceleration = 2.f;
//发射角度
cell.emissionRange = 4.0*M_1_PI;
//粒子颜色
cell.color = [UIColor blueColor].CGColor;
//设置图片
cell.contents = (__bridge id)[UIImage imageNamed:@"snow.png"].CGImage;
emitterLayer.emitterCells = @[cell];