实现中空窗口

MoveWindow(0,0,600,400);
 HRGN hBigRgn = CreateRectRgn(0,0,600,400);
 HRGN hSmallRgn = CreateRectRgn(100,50,500,350);
 HRGN hNewRgn = CreateRectRgn(0,0,1,1);
 CombineRgn(hNewRgn,hBigRgn,hSmallRgn,RGN_DIFF);
 HRGN hOldRgn = (HRGN)SetWindowRgn(hNewRgn,TRUE);
 DeleteObject(hBigRgn);
 DeleteObject(hSmallRgn);