What is the trick to open a non-decorated fullscreen window on Ubuntu? I used to change the _NET_WM_STATE property to _NET_WM_STATE_FULLSCREEN to achieve this but while working fine on KDE it doesn't seem to work on Ubuntu (GNOME; tested with 12.04 LTS). The launcher on the left and the title bar are still there and appear above my non-decorated fullscreen window which is not what I want.
When switching to fullscreen mode in Firefox, however, Firefox's fullscreen window covers the complete screen including launcher panel and title bar so it must be possible somehow to open windows that cover the entire screen, including Ubuntu's launcher and title bar.
Could anybody explain how to achieve this behaviour using plain X11 without any middleware?
Thanks!