gdk_window_add_filter not working as expected

[Tom McCallum <termcc googlemail com>]

Hello all,

Using gtk-2.2 on Fedora 14 and X11.

I have been trying to find out how to keep track of the mouse pointer  
location anywhere on the screen, so that whenever and whereever the mouse  
moves, my function will be called.  All the other posts I have found  
through google tell me how I can get the mouse position at a single time  
point, but not how to have a event driven function into the GTK event loop  
to successfully capture the mouse co-ordinates (those that do, do not work  
as far as I can tell).

This is what I have so far:

// Event Handler for GDK events
extern "C" GdkFilterReturn
desktopMouseMotionHandler( GdkXEvent* xevent, GdkEvent *event, gpointer  
data ) {
        // event->type is always GDK_NOTHING (-1)
	// xevent->type is mostly 28 which is only ever actived moving in and out  
of windows, a POINTER_MOTION_MASK is never passed through, nor for that  
matter any button or keyboard calls when using GTK_ALL_EVENTS_MASK
        XEvent* xe = (XEvent*) xevent;
        cout << "desktop event handler (Event: " << xe->type << " gtk:" <<  
event->type << ")" << endl;
}

...later on in the code...

GdkWindow *root_window;
root_window = gdk_get_default_root_window ();   // desktop window
gdk_window_set_events( root_window, (GdkEventMask)  
(GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK ) );  // tried  
GTK_ALL_EVENTS_MASK as well but still did not get any pointer motion or  
keyboard or button events through
gdk_window_add_filter( root_window, desktopMouseMotionHandler, NULL ); //  
supposedly will pass all pointer motion events through to my function above

Using this method I can only capture GDK_PROPERTY_CHANGE_MASK events, not  
the ones I actually want.  Everything else does not appear to be passed  
through to the filter function.  When using this mask GTK_ALL_EVENTS_MASK  
with GdkEvent *event the type is always GTK_NOTHING (-1), which is useless.

There is a really old post  
http://www.digipedia.pl/usenet/thread/12440/768/ with a similar problem  
but no solution.  There is a bug report as well on this for pygtk but  
again, this does not really deal with the fact that not all events are  
passed through to the filter.

I have tried looking at Xlib calls, but I would have to have a separate  
thread polling XQueryPointer and XNextEvent which seems inefficient when  
this polling and filtering already happens in the main GTK loop.

If there is a bug which has never got fixed, does anyone know what the  
workaround was?

I do not believe I can be the only person who has ever required to do  
this, so it must be possible -- can anyone suggest how to do this?

Many thanks for your help.

Tom