Access coordinates from the parent of a widget - c++

Question

I have a QGraphicsView inside the MainWindow that has implemented a QGraphicScene. I need to pop up a widget when I right click the mouse on a certain portion of the QGraphicScene. The parent of the widget needs to be MainWindow.
My problem is that I need to verify the validity of the portion on witch I clicked inside a mousePressEvent in QGraphicScene and to pop up the widget at the exact same location but the coordinates of the QGraphicScene and MainWindow are obvious not the same. For that I use a custom signal that trigger a slot inside MainWindow and get the coordinates from the mousePressEvent of the MainWindow. The problem is that the mouseEvent from the QGraphicsScene is triggered before the mouseEvent from MainWindow. This makes perfect sense and works if I right click twice but I need it to work from the first right click.
I can not implement a filter or change the focus because I have tons of events in the application.
QGraphicScene:
void CGraphicScene :: mousePressEvent(QGraphicsSceneMouseEvent *event)
{
if(event -> button() == Qt::RightButton)
{
//test stuff
emit signalChangeContextualMenuPosition();
m_contextualMenu -> show();
}
}
MainWindow:
CGraphicScene *scene;
CContextualMenu *m_contextualMenu;
m_contextualMenu = new CContextualMenu(this);
m_contextualMenu ->close();
scene = new CGraphicScene(m_contextualMenu);
ui->gvInterface -> setScene(scene);
connect(scene, SIGNAL(signalChangeContextualMenuPosition()), this, SLOT(openPopUp()));
void MainWindow :: openPopUp()
{
m_contextualMenu ->move(m_xCoordPopMenu, m_yCoordPopMenu);
}
void MainWindow :: mousePressEvent(QMouseEvent *event)
{
if(event -> button() == Qt::RightButton)
{
m_xCoordPopMenu = event -> x();
m_yCoordPopMenu = event -> y();
}
}

Answer 1

Use the QGraphicsView::mapFromScene() to map scene coordinates to the view widget coordinates and then QWidget::mapToParent() to map the coordinates to it's parent widget, which is probably your main window. You can also find useful the method QWidget::mapTo().