程序运行后生成500×500的窗口，可在窗口中实现橡皮筋功能的直线绘制，并实现矩形选框剪裁功能。左键键拖动绘制直线，按下右键可实现橡皮筋的拖拽，中键可以拖动绘制矩形选框，配合键盘上C键可以实现对直线的剪裁。-Generated after the program runs 500 × 500 window, can be achieved in the window rubber band drawing a straight line features, and to achieve tail