[raaaid]

that green screen apply the very same concept from your cave:

it renders the right perspective from the observer-camera point of view

if games did that which is posible with headtracking and you added it 3d you couldnt tell the difference from the game to looking at real life from a window

ive seen refered johny lee efect on tv as cheap 3d

and your rgiht moving sidways increases your depth perception is very tipical on movies