沿着圆角矩形swift的恒定长度的线条动画

Question

请，如何在不停止的情况下沿路径（圆角矩形）进行无限线动画，每次都必须有恒定/相同的长度 - 请参阅附件picture 我发现只有这个解决方案，但这不是我想要的。

---路径：

path = UIBezierPath(roundedRect: CGRect.init(x: 0, y: 0, width: 100, height: 100), byRoundingCorners:.allCorners, cornerRadii: CGSize(width:16, height:16))

---动画：

let strokeEndAnimation: CAAnimation = {
        let animation = CABasicAnimation(keyPath: "strokeEnd")
        animation.fromValue = 0
        animation.toValue = 1
        animation.duration = 10
        animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)

        let group = CAAnimationGroup()
        group.duration = 12
        group.repeatCount = MAXFLOAT
        group.animations = [animation]
        return group
    }()

    let strokeStartAnimation: CAAnimation = {
        let animation = CABasicAnimation(keyPath: "strokeStart")
        animation.beginTime = 2
        animation.fromValue = 0
        animation.toValue = 1
        animation.duration = 10
        animation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)

        let group = CAAnimationGroup()
        group.duration = 12
        group.repeatCount = MAXFLOAT
        group.animations = [animation]
        return group
    }()

谢谢