Call this method when point (X,Y) is to be drawn in the
        canvas. This methods expands the bounding box to include
        this point.

def setbb(self, x, y):
        """Call this method when point (X,Y) is to be drawn in the
        canvas. This methods expands the bounding box to include
        this point."""
        self.__xmin = min(self.__xmin, max(x, self.__clip_box[0]))
        self.__xmax = max(self.__xmax, min(x, self.__clip_box[2]))
        self.__ymin = min(self.__ymin, max(y, self.__clip_box[1]))
        self.__ymax = max(self.__ymax, min(y, self.__clip_box[3]))