managed to find the answer my self.
apparently, some display have an *LCD* stereo grating barrier.
i.e. the barrier it self is a second black-and-white transparent LCD stacked above the main colour screen.
thus the barrier can be turned on or off
some autostereo displays even feature alternatives grating. by switching fast enough between odd and even columns, grating can change whitch eye sees which half of the display.
thus these fast-switching display can increase their visible resolution by horizontal interlacing.