多边形裁剪程序：用到的是比较常见的裁剪算法：Sutherland-Hodgman算法。本程序中的裁剪顺序为左边、下边、右边、上边，那么裁剪是这样进行的：原待裁剪多边形作为输入多边形被裁剪矩形的左边裁剪，然后输出的裁剪结果作为下边裁剪的输入多边形，……，依次类推，直到最后一边矩形上边裁剪结束。,Polygon clipping process: it is more commonly used method of cutting: Sutherland-Hodgman algorithm. This procedure of cutting the order for the left, bottom, right, top, then the cutting is carried out: the original clipping polygon to be clipped polygon as input the left side of the rectangular cutting, then cutting output cut as the bottom of the input polygon, ... ... , and so on, until the last end side of the rectangular cut above.