    def process_event(self, event):
        """
        Handle input on the scroll bar.

        :param event: the event to be processed.

        :returns: True if the scroll bar handled the event.
        """
        # Convert into absolute coordinates if needed.
        new_event = event
        if self._absolute:
            new_event.y -= self._canvas.start_line

        # Process event if needed.
        if self.is_mouse_over(new_event) and event.buttons != 0:
            self._set_pos((new_event.y - self._y) / (self._height - 1))
            return True
        return False
Handle input on the scroll bar.

:param event: the event to be processed.

:returns: True if the scroll bar handled the event.
asciimatics/widgets/scrollbar.py