说明：  VC实现图像平滑滚动效果,在有限的区域中显示了一幅大图，这时要浏览图像的各个部分，这就需要用到图像的滚动。但其中的关键点和难点，即拖动中的刷新和闪烁问题，下面我将详细分析实现方法。
(VC realize smooth image scrolling effects, in limited areas to display a large map, this time to visit all parts of the image, which requires use of the scroll image. However, the key points and difficult, that is, drag the refresh and flicker problem, I will be a detailed analysis of the following methods.)