Action to be taken when an event is triggered.

        Event is scroll of the mouse's wheel. This leads to changing the temporal frame displayed.

        :param event: Scroll of mouse wheel

def onscroll(self, event):
        """Action to be taken when an event is triggered.

        Event is scroll of the mouse's wheel. This leads to changing the temporal frame displayed.

        :param event: Scroll of mouse wheel
        """
        if event.button == 'up':
            self.ind = (self.ind + 1) % self.slices
        else:
            self.ind = (self.ind - 1) % self.slices
        self.update()