图像局部放大功能。包括主要的三个消息处理函数，由鼠标拖动画出需放大区域，松开即将图像局部放大到整个客户区，能够实现层层放大。-enlarge images partial function. Including the three main message processing function, the mouse scrolling painted by the need to enlarge the regional, Loosen the forthcoming local enlarge images of the entire client area, can be achieved at every level to enlarge.