CAEmitterLayer可以来制作粒子发射系统，主要包含两个部分CAEmitterLayer和CAEmitterCell。
CAEmitterLayer就是粒子发射器，决定粒子发射器的形状，位置，大小等；CAEmitterCell可以设置粒子的属性，包括形状，大小，速度，加速度，存活时间等。

CAEmitterLayer的常用属性：

emitterCells CAEmitterCell对象的数组
birthRate 粒子产生系数，默认为1.0；CAEmitterLayer也有birthRate属性，系统每秒实际产生的粒子数是这两个属性值的乘积
lifetime 粒子存活时间，默认1s
emitterPosition 发射器xy坐标轴上的位置
emitterZPosition 发射器在z坐标轴上的位置
preservesDepth 是否开启三维效果
velocity 粒子运动速度
scale 粒子缩放效果
spin 粒子自旋转速度
seed 随机数发生器
emitterSize 发射器尺寸
emitterDepth 发射器深度
emitterShape 发射器形状
    kCAEmitterLayerPoint 点状
    kCAEmitterLayerLine 线状
    kCAEmitterLayerRectangle 矩形
    kCAEmitterLayerCuboid 立方体
    kCAEmitterLayerCircle 圆形
    kCAEmitterLayerSphere 球形
emitterMode 发射模式
    kCAEmitterLayerPoints 从顶点发出
    kCAEmitterLayerOutline 从边缘发出
    kCAEmitterLayerSurface 从表面发出
    kCAEmitterLayerVolume 从立方体中发出
renderMode 渲染模式
    kCAEmitterLayerUnordered 粒子无序出现
    kCAEmitterLayerOldestFirst 先声明的粒子在上层
    kCAEmitterLayerOldestLast 后声明的粒子在上层
    kCAEmitterLayerBackToFront 在z轴上从后到前渲染
    kCAEmitterLayerAdditive 混合粒子

CAEmitterCell常用属性：

emitterCell 初始化方法
name 粒子名字
color 粒子颜色
enabled 粒子是否可渲染
contents 粒子内容
contentsRect 渲染范围
birthRate 粒子产生速度
lifetime 生命周期
lifetimeRange 生命周期浮动范围
velocity 粒子初始运动速度
velocityRange 粒子速度浮动范围
spin 粒子旋转角度
spinrange 粒子旋转角度范围
scale 粒子缩放比例
scaleRange 粒子缩放比例范围
scaleSpeed 粒子缩放速度
alphaRange 粒子透明度变化范围
alphaSpeed 粒子透明度变化速度
redRange 粒子颜色红色的变化范围
redSpeed 粒子颜色红色的变化速度
blueRange 粒子颜色蓝色的变化范围
blueSpeed 粒子颜色蓝色的变化速度
greenRange 粒子颜色绿色的变化范围
greenSpeed 粒子颜色绿色的变化速度
xAcceleration x轴方向的加速度分量
yAcceleration y轴方向的加速度分量
zAcceleration z轴方向的加速度分量
emissionRange 粒子发射角度范围
emissionLongitude 粒子在xy平面的发射角度
emissionLatitude 粒子在z轴方向的发射角度

使用CAEmitterLayer做一个从礼物盒里抛出来礼物的样式：

    //添加一个礼物盒
    UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(self.view.bounds.size.width/2-10, 600, 50, 50)];
    imgView.image = [UIImage imageNamed:@"礼物盒"];
    [self.view addSubview:imgView];
    //1.创建一个发射器
    CAEmitterLayer *emitterLayer = [CAEmitterLayer layer];
    emitterLayer.emitterPosition = CGPointMake(self.view.bounds.size.width/2, 600);
    emitterLayer.emitterShape = kCAEmitterLayerLine;
    emitterLayer.emitterMode = kCAEmitterLayerSurface;
    emitterLayer.emitterSize = CGSizeMake(20, 5);
    //2.创建发射的粒子
    NSMutableArray *cellsArray = [NSMutableArray array];
    for (int i = 1; i<5; i++) {
        CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
        emitterCell.birthRate = 0.5+0.1*i;
        emitterCell.speed = 1.5;
        emitterCell.velocity = 150;
        emitterCell.velocityRange = 30;
        emitterCell.lifetime = 3.5;
        emitterCell.lifetimeRange = 0.5;
        emitterCell.spin = 1;
        emitterCell.scale = 0.8;
        emitterCell.scaleRange = 0.5;
        emitterCell.emissionLongitude = 0;
        emitterCell.emissionRange = M_PI_4;
        emitterCell.yAcceleration = 120;
        emitterCell.contents = (id)[UIImage imageNamed:[NSString stringWithFormat:@"icon0%d", i]].CGImage;
        [cellsArray addObject:emitterCell];
    }
    emitterLayer.emitterCells = cellsArray;
    [self.view.layer addSublayer:emitterLayer];

emitter1.gif

创建一个点赞按钮的动画效果

    CAEmitterCell *emitterCell = [CAEmitterCell emitterCell];
    emitterCell.name = @"emitter";
    emitterCell.alphaRange = 0.10;
    emitterCell.alphaSpeed = -1.0;
    emitterCell.lifetime = 0.3;
    emitterCell.lifetimeRange = 0.1;
    emitterCell.birthRate = 0;
    emitterCell.velocity = 40.0;
    emitterCell.velocityRange = 0.00;
    emitterCell.scale = 0.3;
    emitterCell.scaleRange = 0.1;
    emitterCell.contents = (id)[UIImage imageNamed:@"点"].CGImage;
    
    self.emitterLayer = [CAEmitterLayer layer];
    self.emitterLayer.name = @"emitterLayer";
    self.emitterLayer.emitterShape = kCAEmitterLayerCircle;
    self.emitterLayer.emitterMode = kCAEmitterLayerOutline;
    self.emitterLayer.emitterSize = CGSizeMake(20, 0);
    self.emitterLayer.emitterCells = @[emitterCell];
    self.emitterLayer.renderMode = kCAEmitterLayerOldestFirst;
    self.emitterLayer.masksToBounds = NO;
    self.emitterLayer.position = likeBtn.center;
    self.emitterLayer.zPosition = -1;
    [self.view.layer addSublayer:self.emitterLayer];

//处理按钮点击
- (void)handleLikeOrNotLike:(UIButton *)button {
    button.selected = !button.selected;
    if (button.selected) {
        self.emitterLayer.beginTime = CACurrentMediaTime();
        //每秒喷射粒子的个数为80个
        [self.emitterLayer setValue:@1000 forKeyPath:@"emitterCells.emitter.birthRate"];
        [self performSelector:@selector(explode) withObject:nil afterDelay:0.1];
    }
    [button setImage:[UIImage imageNamed:@"点赞"] forState:UIControlStateNormal];
    [button setImage:[UIImage imageNamed:@"点赞-2"] forState:UIControlStateSelected];
}
//大量喷射
- (void)explode {
    //每秒喷射的个数为2500个
    [self.emitterLayer setValue:@2500 forKeyPath:@"emitterCells.emitter.birthRate"];
    [self performSelector:@selector(stop) withObject:nil afterDelay:0.1];
}
//停止喷射
- (void)stop {
    //每秒喷射粒子的个数为0个
    [self.emitterLayer setValue:@0 forKeyPath:@"emitterCells.emitter.birthRate"];
}

emitter2.gif