glutShowWindow (3) - Linux Manuals
glutShowWindow: Request that the <i>current window</i> be visible
NAME
glutShowWindow - Request that the <i>current window</i> be visibleLIBRARY
OpenGLUT - windowSYNOPSIS
In openglut.h Ft void Fn glutShowWindow voidDESCRIPTION
glutShowWindow() requests that the window system make the Bf LiThis is generally not necessary. When you create a window, it will normally become visible. Unless you specifically hide it, it will remain visible. Though visible, of course, it may be covered by other windows; that would be an issue for window stacking order not visibility.
When, and if, your window's visibility status changes, you may find out via a glutWindowStatusFunc() callback.