I recall there was one gimmick where a camera processes the position of the pupils of an observer and changes a display based on the position of the pupils rela

I recall there was one gimmick where a camera processes the position of the pupils of an observer and changes a display based on the position of the pupils relative to the display. It is not strictly stereoscopic, but there's an uncanny 3D effect where foreground and background move relative to each other when the observer shifts position. Sort of like paper-cutouts.