核心动画 - 粒子效果

新建一个 xcode 项目，然后在 ViewController.m 编写代码实现效果。
ViewController.m
#import "ViewController.h"

@interface ViewController ()

@property(nonatomic,strong)CAEmitterLayer * emitterLayer;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor blackColor];
    
    // 1. 设置CAEmitterLayer
    self.emitterLayer = [CAEmitterLayer layer];
    [self.view.layer addSublayer:self.emitterLayer];
    
    //发射源的尺寸大小
    self.emitterLayer.emitterSize = self.view.frame.size;
    //发射源的形状
    self.emitterLayer.emitterShape = kCAEmitterLayerPoint;
    //发射模式
    self.emitterLayer.emitterMode = kCAEmitterLayerPoints;
    //粒子发射形状的中心点
    self.emitterLayer.emitterPosition = CGPointMake(self.view.frame.size.width, 0);
    
    // 2. 配置CAEmitterCell
    CAEmitterCell * emitterCell = [CAEmitterCell emitterCell];
    //粒子名称
    emitterCell.name = @"emitterCell";
    //粒子产生率,默认为0
    emitterCell.birthRate = 20.0f;
    //粒子生命周期
    emitterCell.lifetime = 10.0f;
    //粒子速度,默认为0
    emitterCell.velocity = 40.0f;
    //粒子速度平均量
    emitterCell.velocityRange = 100.0f;
    //x,y,z方向上的加速度分量,三者默认都是0
    emitterCell.yAcceleration = 15.0f;
    //指定纬度,纬度角代表了在x-z轴平面坐标系中与x轴之间的夹角，默认0:
    emitterCell.emissionLongitude = M_PI; //向左
    //发射角度范围,默认0，以锥形分布开的发射角度。角度用弧度制。粒子均匀分布在这个锥形范围内;
    emitterCell.emissionRange = M_PI_4; //围绕X轴向左90度
    //缩放比例, 默认是1
    emitterCell.scale = 0.2f;
    //缩放比例范围,默认是0
    emitterCell.scaleRange = 0.1f;
    //在生命周期内的缩放速度,默认是0
    emitterCell.scaleSpeed = 0.02f;
    //粒子的内容，为CGImageRef的对象
    emitterCell.contents = (id)[UIImage imageNamed:@"circle_white"].CGImage;
    //颜色
    emitterCell.color = [UIColor colorWithRed:0.5f green:0.0f blue:0.5f alpha:1.0f].CGColor;
    //粒子颜色red,green,blue,alpha能改变的范围,默认0
    emitterCell.redRange = 1.0f;
    emitterCell.greenRange = 1.0f;
    emitterCell.alphaRange = 0.8f;
    //粒子颜色red,green,blue,alpha在生命周期内的改变速度,默认都是0
    emitterCell.blueSpeed = 1.0f;
    emitterCell.alphaSpeed = -0.1f;
    
    //添加
    self.emitterLayer.emitterCells = @[emitterCell];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    UITouch * touch = [[event allTouches] anyObject];
    CGPoint  point = [touch locationInView:self.view];
    [self setBallInPosition:point];
}

-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    UITouch * touch = [[event allTouches] anyObject];
    CGPoint  point = [touch locationInView:self.view];
    [self setBallInPosition:point];
}

#pragma mark - 移动发射源到某个点上
-(void)setBallInPosition:(CGPoint)point
{
    //创建基础动画
    CABasicAnimation * basicAnimation = [CABasicAnimation animationWithKeyPath:@"emitterCells.emitterCell.scale"];
    //fromValue
    basicAnimation.fromValue = @0.2f;
    //toValue
    basicAnimation.toValue = @0.5f;
    //duration
    basicAnimation.duration = 1.0f;
    //线性起搏，使动画在其持续时间内均匀地发生
    basicAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    
    //用事务包装隐式动画
    [CATransaction begin];
    //设置是否禁止由于该事务组内的属性更改而触发的操作
    [CATransaction setDisableActions:YES];
    //为 emitterLayer 添加动画
    [self.emitterLayer addAnimation:basicAnimation forKey:nil];
    //为 emitterLayer 指定位置添加动画效果
    [self.emitterLayer setValue:[NSValue valueWithCGPoint:point] forKey:@"emitterPosition"];
    //提交动画
    [CATransaction commit];
}

@end
运行效果如下：
粒子.png