@staticmethod
def draw_path(ctx, center_x, center_y, width, height=None):
    """Draws the path of the shape on the given Cairo context, without
        stroking or filling it.

        This method must be overridden in derived classes implementing custom shapes
        and declared as a static method using C{staticmethod(...)}.

        @param ctx: the context to draw on
        @param center_x: the X coordinate of the center of the object
        @param center_y: the Y coordinate of the center of the object
        @param width: the width of the object
        @param height: the height of the object. If C{None}, equals to the width.
        """
    raise NotImplementedError('abstract class')
