单独一个或几个角收缩

//核心动画
   CGRect rect = CGRectMake(50, 100, 100, 100);
    CAShapeLayer * shapeLayer = [CAShapeLayer layer];
    shapeLayer.frame = rect;
    shapeLayer.strokeColor = [[UIColor redColor] CGColor];
    //圆形
    //UIBezierPath * Bpath = [UIBezierPath bezierPathWithOvalInRect:rect];
    //长方形
    //UIBezierPath * Bpath = [UIBezierPath bezierPathWithRect:rect];
    //圆角矩形
    UIBezierPath * Bpath = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:60];
    //单独一个或几个角
    //UIBezierPath * Bpath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:(UIRectCornerTopLeft) cornerRadii:(CGSize){ 50,50 }];
    
    shapeLayer.path = Bpath.CGPath;
    
    [self.view.layer addSublayer:shapeLayer];