#include <QApplication>
#include <QWidget>
#include <QWindow>
#include "qdebug.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;

    QWindow *window = new QWindow();
    window->setGeometry(0, 0, 500, 600);

    QWidget *container = QWidget::createWindowContainer(window); // No parent
    QWindow *containerWindow = container->windowHandle();
    containerWindow->setPosition(QPoint());
    qDebug() << "before setParent" << containerWindow->geometry();
    container->setParent(&w);
    qDebug() << "after setParent" << containerWindow->geometry();

    return a.exec();
}