如何在WPF中使用单点触摸旋转椭圆

Question

任何想法如何通过单指触摸旋转椭圆？

这是我的代码：

#1 : we found 5 at the begining output will be true. 0 will be eliminated.
#2 : string + int = int output will be true. 
     Priority of int is higher, 0 == 0 output will be true,
#3 : 2 is not found at the beginning of match value (ab2), output will be false.
#4 : 2 is found at the beginning of match value (2ab), output will be true.

如何在移动时计算触点角度？