Composite and MapNotifies

[Soeren Sandmann]

When a compositing manager is running, there is currently a bug where
metacity stops paying attention to the GNOME panel. What's going on
is:

- RedirectSubwindows causes all windows to get unmapped, then mapped
  again. Composite makes sure the MapWindow requests don't get turned
  into MapRequests by temporarily turning on overrideRedirect for the
  window.

- So the window manager gets an UnmapNotify for all its windows, then
  a sequence of MapNotifies.

To a window manager UnmapNotify means "stop paying attention to this
window until I try and map it again". The problem is then that
metacity does not interprete MapNotifies as "you should start paying
attention again", because metacity expects to get MapRequests, not
MapNotifies. So as far as it knows, the windows are still
withdrawn. For windows with a frame, metacity does manage to cope,
because the windows in questions are frame windows. But for frameless,
but managed, windows such as the GNOME panel and nautilus, metacity
still thinks they are withdrawn.

Now, metacity can certainly be changed to work around this, but I'd
expect many other window managers to have similar problems. And the
assumption:

        If I have SubstructureRedirect selected on the root window,
        then non-override-redirect toplevels do not get mapped without
        me being involved

is pretty fundamental to being a window manager.

So I propose the attached patch which turn off generation of the
Map/UnmapNotifies for the windows during the redirection process. The
window manager will then not even know that anything happened.


Soren


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