该功能主要实现通过鼠标选中客户区中的图片，然后按住鼠标左键拖动，就可以看到此时图片会随着你的鼠标的移动而在客户区中移动。主要用到CRgn类来实现。-The function is mainly implemented through the mouse over the client area of the image, and then hold the left mouse button drag, you can see the picture with your mouse move a