Draws the backgrounds for the different chart types.
        
        :param      painter | <QPainter>
                    rect    | <QRect>

def drawBackground( self, painter, rect ):
        """
        Draws the backgrounds for the different chart types.
        
        :param      painter | <QPainter>
                    rect    | <QRect>
        """
        if ( self._dirty ):
            self.rebuild()
        
        if ( self.showGrid() ):
            self.drawGrid(painter)