画勾：
CAShapLayer给定一个路径它就能跟着你的路径画出一个你想要的图形

CAAnimation——速度控制函数

速度控制函数(CAMediaTimingFunction) 

kCAMediaTimingFunctionLinear（线性）：匀速，给你一个相对静态的感觉

kCAMediaTimingFunctionEaseIn（渐进）：动画缓慢进入，然后加速离开

kCAMediaTimingFunctionEaseOut（渐出）：动画全速进入，然后减速的到达目的地

kCAMediaTimingFunctionEaseInEaseOut（渐进渐出）：动画缓慢的进入，中间加速，然后减速的到达目的地。这个是默认的动画行为。

 

设置动画的执行节奏

anim.timingFunction= [CAMediaTimingFunction
functionWithName:kCAMediaTimingFunctionLinear];
- (void)drawPic:(CGRect)rect context:(CGContextRef)context {
    
    
    
    _shap = [CAShapeLayer layer];
    CGPoint point[3] = {{150,200},{200,250},{300,150}};
    
    CGMutablePathRef mu = CGPathCreateMutable();
    
    CGPathAddLines(mu, nil, point, 3);
    
    _shap.path  = mu;

    _shap.strokeStart = 0;
    _shap.strokeEnd = 1;
    _shap.fillColor = [UIColor clearColor].CGColor;
    _shap.strokeColor = [UIColor redColor].CGColor;
    _shap.lineWidth = 13;
    [self.layer addSublayer:_shap];
    
    
    //动画
    CABasicAnimation *base = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    base.fromValue =  @(0);
    base.toValue = @(1);
    base.duration = 2;
    base.repeatCount = CGFLOAT_MAX;
    
//    base.fillMode = @"forwards";
//    base.removedOnCompletion = NO;
    
    [_shap addAnimation:base forKey:@"d"];
    
    CGPathRelease(mu);
    
}