本例将实现图像的遮照效果，运行结果：一个椭圆在窗口中移动，椭圆中显示背景图像,椭圆以外为黑色，背景图像被遮住。当鼠标在窗格中移动时，显示背景图像的椭圆跟着鼠标移动-This case image masks the effect of operating results: an oval window mobile, oval display a background image, other than for the black oval, the background image to be