A window can be in front of or behind other windows, as determined by the z-order from front to back. Top-level OpenGLUT windows can be placed at the front or back of the z-order by means of the glutPopWindow() and glutPushWindow() API functions.
A z-order also applies to the subwindows of a top-level window. While the z-order of top-level windows can usually be adjusted by the user, subwindow z-order is controlled entirely by the application.
There may not be an immediate effect to this function. Wait for the glutWindowStatusFunc() callback to tell you about whatever obscured/visible status your window achieves.
Not applicable to offscreen windows.