(1)仅调用系统的画点函数，绘制直线、圆、椭圆、圆角矩形、正三角形等；（2）可改变线型、线宽、线色，可对图形进行平移，拉伸，放大，缩小，镜像等；（3）可保存，打开绘图-(1) only point of calling the system function of painting, drawing lines, circles, ellipses, rounded rectangles, triangles and so on (2) can change the line type, li