例2-5 在屏幕客户区内绘制内切椭圆，椭圆的形状依据客户区形状而改变。椭圆边界为1像素宽的蓝线，内部填充为绿色(Example 2-5 draws an inscribed ellipse in the screen client area, and the shape of the ellipse varies according to the shape of the client area. The ellipse boundary is 1 pixels wide blue line, and the inner is filled with green)