The first spline is drawn from the first point to the fourth point by using the second and third points as control points. Each subsequent spline in the sequence needs exactly three more points: the end point of the previous spline is used as the starting point, the next two points in the sequence are control points, and the third is the end point.
其实你是没看懂它的说明。
大意是:第一个样条是使用第2 和第3 个点作为控制点从第一个点拉到第4 个点而成。在其后的每条顺序样条都是需要增加3 个点:而前一条样条的终点被用作这条样条的起始点,接下来的两个点是控制点,并且在下一个点(第三点)是终点。
从以上来看,生成的是三次样条,所以一条样条需要4个点。而且只通过起始点,中间两点是控制点。
解决方法是:插入控制点。这个你可以看看相关的资料。