Adds the pixmap to the list for this slider.
        
        :param      pixmap | <QPixmap> || <str>

def addPixmap(self, pixmap):
        """
        Adds the pixmap to the list for this slider.
        
        :param      pixmap | <QPixmap> || <str>
        """
        scene = self.scene()
        scene.addItem(XImageItem(pixmap))
        self.recalculate()