show object (scene) in widget in class class mainwindow

[viulskiez]

If you only need one scene, you can set your OgreWidget directly as the central widget in your QMainWindow instance by calling QMainWindow::setCentralWidget.
And if you need more than one scene, you can use QMdiArea, QMdiSubWindow and use QMdiArea::addSubWindow.
More example can be found on the Qt Reference Documentation.