Bresenham算法绘制线段并利用“橡皮筋”功能绘制折线。将绘制的折线连接成多边形，并选择种子填充法或扫描线填充法进行填充



鼠标交互生成矩形裁剪框，实现对绘制的折线的裁剪

-Bresenham algorithm for drawing lines and using the " rubber band"　feature to draw a line. The line will connect into a polygon drawing, and select the scan line seed fill method or method of filling a rectangle filled with mouse interaction to generate the crop box, to achieve the cut line drawn