很简单的绘图程序，能绘直线，圆 ，矩形之类的简单图形-Very simple drawing program, can draw lines, circles, rectangles, like the simple graphics

当用户按下鼠标左键在如下图所示的面板上移动鼠标时，根据鼠标的移动轨迹在面板上画图。-When the user presses the left mouse button on the panel as shown in the following figure to move the mouse, according to the mouse movement trajectory in the panel drawing.