分析

每一个水波都是一个CAShapeLayer的实例，然后使用CADisplayLink来刷新界面，每次刷新的时候，CAShapeLayer的形状不一样，在每秒60帧的情况下，看起来就产生了动画效果。

代码

下面的示例只创建了一个水波

@interface JCWaterWave ()
@property(nonatomic, strong) CADisplayLink *displayLink;
@property(nonatomic, strong) CAShapeLayer *shapeLayer;
@property(nonatomic, assign) CGFloat offset;

@end

@implementation JCWaterWave

- (instancetype)initWithFrame:(CGRect)frame
{
    if (self = [super initWithFrame:frame]) {
        [self setup];
    }
    return self;
}

- (void)setup
{
    [self.layer addSublayer:self.shapeLayer];
    [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
}

- (void)startWave
{
    self.offset += 5;
    [self setFirstLayer];
}

- (void)setFirstLayer
{
    CGMutablePathRef path = CGPathCreateMutable();
    
    CGFloat width = self.frame.size.width;
    CGFloat height = self.frame.size.height;
    CGFloat rate = M_PI * 2 / width;//水平上只显示一个波周期
    
    for (CGFloat i = 0.0; i <= width; i++) {
        //5表示振幅
        CGFloat y = sin(rate * (i + self.offset)) * 5 + height / 2.0f;
        if (i > 0.0) {
            CGPathAddLineToPoint(path, nil, i, y);
        } else {
            CGPathMoveToPoint(path, nil, i, y);
        }
    }
    
    CGPathAddLineToPoint(path, nil, width, height);
    CGPathAddLineToPoint(path, nil, 0, height);
    CGPathCloseSubpath(path);
    
    self.shapeLayer.path = path;
    
    CGPathRelease(path);
}

- (CADisplayLink *)displayLink
{
    if (!_displayLink) {
        _displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(startWave)];
    }
    return _displayLink;
}

- (CAShapeLayer *)shapeLayer
{
    if (!_shapeLayer) {
        _shapeLayer = [CAShapeLayer layer];
        _shapeLayer.fillColor = [UIColor colorWithRed:0 green:0 blue:1 alpha:0.4].CGColor;
    }
    return _shapeLayer;
}