How to overly a transparent QWidget on a QWindow?

[lygstate]

In the following code, scadeWindow is a instance of customized class ScadeWindow which is a subclass of QWindow. Now I want to put a transparent QLabel on scadeWindow, but failed.
request for a solution for this problem.

@
ScadeWidget::ScadeWidget(QWidget *parent):QWidget(parent)
{
QSurfaceFormat format;
format.setSamples(16);
scadeWindow = new ScadeWindow(format);

// Combining Qt Widgets and QML with QWidget::createWindowContainer()
//  http://www.ics.com/blog/combining-qt-widgets-and-qml-qwidgetcreatewindowcontainer#.UlzdRlAge-U
// OpenGL in Qt 5.1 – Part 5
//  http://www.kdab.com/opengl-in-qt-5-1-part-5/
// OpenGL Window Example
//  http://qt-project.org/doc/qt-5.1/qtgui/openglwindow.html
container = QWidget::createWindowContainer(scadeWindow, this);
container->setAttribute(Qt::WA_TranslucentBackground);
container->setMinimumSize(scadeWindow->width(), scadeWindow->height());
auto label = new QLabel("Hello, the world!", this);
label->setAttribute(Qt::WA_TranslucentBackground);
label->setAlignment(Qt::AlignHCenter | Qt::AlignVCenter);

}
@
I use this

[NicuPopescu]

what if add:

@label->setStyleSheet("background:transparent");@

?