[Development] LXQt desktop project needs some help from Qt developers

[PCMan]

Hello,
I'm pcman, a developer of LXQt project (http:/lxqt.org/).
This is a new open-source Qt-based desktop environment, just like KDE.
We already ported the whole desktop to Qt5 and is preparing for a new
release, but now we're blocked by some XCB related problems of Qt 5.

https://bugreports.qt-project.org/browse/QTBUG-40681
https://bugreports.qt-project.org/browse/QTBUG-40744
https://bugreports.qt-project.org/browse/QTBUG-40768

The main problem is, Qt might change the native WinId of the QWidget
at runtime under some conditions. However, the winId stored in the
QWidget is not updated sometimes. So for programs which use the
winId() to interact with X11, this breaks them. Even worse, this
breaks QBackingStore and cause paint error and the windows disappered
sometimes.

Another issue is, there is no way to know if the underlying native
window of a QWidget is going to be destroyed and created again
(re-create the native window handle). We have QEvent::WinIdChange, but
when we get the event, the old window is already destroyed. So it's
not possible to undo some changes previously done on the old window
before its destruction. For example, if you embed a native window from
anothe process in your QWidget, and for some reason QWidget decide to
change its native WinId, then the internal window is destroyed and
created again. Your embedded window from the other process will be
destroyed together. You don't have a chance to unparent it before the
WinIdChange. This can breaks some XEMBED based programs.

I understand that there are tons of bug reports of Qt, but we really
need help since there's no way to workaround these issues.
LXQt is the merged product of LXDE and Razor-qt projects. LXDE used to
be a GTK+ desktop but now we've proven that migration to Qt is
possible. This also encouraged other developers to try Qt. So helping
LXQt can also promote Qt.
If we can migrate the whole desktop environment from GTK+ to Qt
smoothly, this can prove how good Qt is.
Please give us some help if possible.

Thank you very much!
Have a nice day.