    def _update(self, frame_no):
        """
        This effect will be called every time the mainline animator
        creates a new frame to display on the screen.

        :param frame_no: The index of the frame being generated.
        """
This effect will be called every time the mainline animator
creates a new frame to display on the screen.

:param frame_no: The index of the frame being generated.
asciimatics/effects.py