MFC，多线程画矩形和定时器实现画矩形，多线程实现时还可以操作其他菜单而不受影响，定时器实现主界面在画图时就无法响应-MFC, multi-threaded timer, draw a rectangle and draw a rectangle, multithreading can have affected the operation of other menus, timer, the main interface will not respond when drawing