By looking through a face on the target mesh, as if it where a window, you should be able to see every polygon on your source mesh pointing more or less in your direction.
Existing polygon clipping algorithms are all offered for a rectangular window or a convex polygonal window.
已有的多边形裁剪算法都是针对矩形窗口或凸多边形窗口进行的。
3
The cutting object is complicacy geometry entity, which is complicacy polygon with arc, arc boundary and hole, the cutting window can be cave or convex polygon.