On Freitag, 17. Oktober 2014 14:56:16 CEST, Paulo Lieuthier wrote:
I'm now trying to check if there is an active window manager,
for lxqt-session. That's what I'm doing:
NETRootInfo rootInfo(QX11Info::connection(), NET::Supported);
qDebug() << "SupportingWMCheck: " <<
rootInfo.isSupported(NET::SupportingWMCheck);
That appears to be the correct way to check it
NETWM spec:
-------------------------------------------
NET_SUPPORTING_WM_CHECK, WINDOW/32
The Window Manager MUST set this property on the root window to be the ID of a
child window created by himself, to indicate that a compliant window manager is
active. The child window MUST also have the _NET_SUPPORTING_WM_CHECK property
set to the ID of the child window. The child window MUST also have the
_NET_WM_NAME property set to the name of the Window Manager.
Rationale: The child window is used to distinguish an active Window Manager
from a stale _NET_SUPPORTING_WM_CHECK property that happens to point to another
window. If the _NET_SUPPORTING_WM_CHECK window on the client window is missing
or not properly set, clients SHOULD assume that no conforming Window Manager is
present.
-------------------------------------------
tl;dr:
-------
you must fetch the support window WId from the root property and check the
property again on that window.
KWin does apparently not withdraw the root property (not even the support
list), but isn't oblieged to do so either.
You MUST check the hinted support window anyway, because if the WM was killed -9 or -11
it will unlikely (in case of -9 "no way") have withdrawn any root property and
your findings based upon this data alone would be wrong.
There's no convenience function for that in KWindowSystem, is there?
(I don't see it)
Cheers,
Thomas
