中文说明：鼠标按下并拖动释放，完成直线的绘制；可以参考此程序编写各类鼠标响应程序，如鼠标按下、拖动、以及释放时应进行如何设置，希望对大家有用
English Description：
Mouse down and drag release, complete the line drawing; can refer to this program to write all kinds of mouse response procedures, such as mouse down, drag, and release should be how to set, hope to be useful to you