Overloads the base QGraphicsScene method to block the \
        selection signals, otherwise, each time an object is \
        bulk selected the selection changed signal will be \
        emitted.
                    
        :param      event   <QMousePressEvent>

def mousePressEvent( self, event ):
        """
        Overloads the base QGraphicsScene method to block the \
        selection signals, otherwise, each time an object is \
        bulk selected the selection changed signal will be \
        emitted.
                    
        :param      event   <QMousePressEvent>
        """
        if event.button() == Qt.MidButton:
            self.setViewMode(True)
            event.accept()
        elif event.button() == Qt.RightButton:
            event.accept()
        else:
            super(XNodeScene, self).mousePressEvent(event)
            self.blockSelectionSignals(True)