Draws the background for the chart scene.
        
        :param      painter | <QPainter>
                    rect    | <QRect>

def drawBackground(self, painter, rect):
        """
        Draws the background for the chart scene.
        
        :param      painter | <QPainter>
                    rect    | <QRect>
        """
        chart = self.chart()
        chart._drawBackground(self, painter, rect)