self.index = (-1 + delta) % len(self.sequence)

            elif delta < 0:

                self.index = delta % len(self.sequence)

        else:

            self.index = (self.index + delta) % len(self.sequence)

    def next(self):

        self.change_index(1)

        return self.sequence[self.index]

    def prev(self):

        self.change_index(-1)

        return self.sequence[self.index]

class AbstractSimpleController(SubClient):

    """Simple controller with minimal input and output:

    Input is 4 directions and 3 buttons.

    Output is an integer and a color and maybe more.

    Left + B1/right + B1: prev/next sub

    Y-axis + B2: set current level

    B3: toggle keep/solo mode

    Double-B3: clear kept levels"""

    def __init__(self, subnames):

        SubClient.__init__(self)

        self.subnames = subnames

        self.refresh()

    def refresh(self):

        # reload subs from disk

        self.submasters = Submasters()

        self.all_subs = circcycle(self.subnames)

        self.current_sub = self.submasters.get_sub_by_name(self.all_subs.next())

        self.current_level = 1.0

        self.kept_levels = {} # subname : level [0..1]

        self.keep_solo_mode = 'keep' # either 'keep' or 'solo'

    def clear_kept_levels(self):

        self.kept_levels.clear()

    def next(self):

        if self.keep_solo_mode == 'keep':

            self.kept_levels[self.current_sub] = self.current_level

        self.current_sub = self.submasters.get_sub_by_name(self.all_subs.next())

    def prev(self):

        if self.keep_solo_mode == 'keep':

            self.kept_levels[self.current_sub] = self.current_level

        self.current_sub = self.submasters.get_sub_by_name(self.all_subs.prev())

    def toggle_keep_mode(self):

        if self.keep_solo_mode == 'keep':

            self.keep_solo_mode = 'solo'

        else:

            self.keep_solo_mode = 'keep'

    def get_levels_as_sub(self):

        if self.keep_solo_mode == 'keep':

            # send all levels in self.kept_levels

            levelsub = combine_subdict(self.kept_levels)

        else:

            levelsub = self.current_sub * self.current_level

        return levelsub

class TkGyro(Tk.Canvas, AbstractSimpleController):

    def __init__(self, master, subnames):

        Tk.Canvas.__init__(self, master, bg='black', bd=0, highlightthickness=0,

            confine=None)

        AbstractSimpleController.__init__(self, subnames)

        height = int(self.winfo_screenheight())

        width = int(self.winfo_screenwidth())

        self.left = self.create_rectangle((0, 0, width / 2, height),

            tags='left', fill='black')

        self.right = self.create_rectangle((width / 2, 0, width, height),

            tags='right', fill='black')

        # the text is disabled so that it doesn't receive events

        self.modetext = self.create_text((width / 2, height / 2), 

            font='Courier 200', fill='white', text=self.keep_solo_mode,

            state='disabled')

        self.flashtextafter = '' # current after timer for displaying text

        def setfill(item, color):

            self.itemconfig(item, fill=color)

        def setlevel(evt):

            if evt.state & 512:

                y = (height - evt.y) / float(height)

                self.flash_text('<%d>' % (y * 100))

                self.current_level = y

                self.send_levels()

        data = ((self.left, 'left', '#000099', self.prev), 

                (self.right, 'right', '#990000', self.next))

        for item, tag, color, method in data:

            self.tag_bind(tag, '<Enter>', 

                lambda evt, item=item, color=color: setfill(item, color))

            self.tag_bind(tag, '<Leave>', 

                lambda evt, item=item, color=color: setfill(item, 'black'))

            self.tag_bind(tag, '<ButtonPress-1>',