屏幕中间出现一个矩形，用鼠标点击移动，鼠标相对矩形的位置不变，当鼠标移动出客户区只要不up左键，还可继续移动。-Middle of the screen appears a rectangle with a mouse click to move, Mouse the same position relative to the rectangle when the mouse moves out of the client area as long as the button is not up