Native descendants of a virtual children are not automatically destroyed
with the parent as if it was a native window, so we need to handle
the native recursion tracking manually in _gdk_window_destroy_hierarchy()
It turns out that XCopyArea handling of obscured source regions is
buggy. It clears the destination area even outside the GC clip
region. We work around this for the pixmap->window case as that
can happen in gtk+ and is easy to work around.
X Bug report at:
http://lists.freedesktop.org/archives/xorg/2009-February/043318.html
Some apps really need to set custom event masks on native child windows,
for example emacs sets the event masks with gdk, but then reads out
the raw X events via a filter, so gdk event emulation doesn't work for that.
When we get motion or button events we map back from the event position and
window to the toplevel before doing anything, because a toplevel native window
could e.g. overlap a child window or whatever.
These are generated when we get an implicit grab on a native
child window, and we can't filter them with _has_grab() because
they are sent before the button press event where we detect
the implicit grab.
This makes clicks work in the flash plugin again
It turns out we really have to ignore grab/ungrab events or we'll
report double crossing events when we grab or ungrab.
However, we also can't ignore crossing events from grabs from other clients
as that leads to missed enter/leave events on e.g. alt-tab in metacity.
Fortunately we now track grabs very precisely, so we know with certainty
whether we have a grab at the time (serial) of the native crossing events,
and only if we do we ignore them.
If we get crossing events with subwindow unexpectedly being NULL
that means there is a native subwindow that gdk doesn't know about.
We track these and forward them, with the correct virtual window
events inbetween.
This is important to get right, as metacity uses gdk for the frame
windows, but gdk doesn't know about the client windows reparented
into the frame.
For instance if we grab the pointer and then check if its grabbed
so that we know to ungrab we don't care that the grab is not
yet active, so report the steady state (i.e. the last grab)
