GR_WINDOW_ID GrNewInputWindow ( GR_WINDOW_ID parent, GR_COORD x, GR_COORD y, GR_SIZE width, GR_SIZE height );
The GrNewInputWindow function creates a window with special focus rules to help with user input. An input-only window is invisible and cannot be drawn into. You can select events for an input-only window and set the window's cursor. Like input-output windows, input-only windows start out unmapped, and you must map the window to make it effective. The new window inherits the cursor of the parent window, and initially is set to select no events.
Note: Wiget sets, such as FLTK, have largely removed the need for input windows.