How are dual/double role films shot in which the actor is shown on the screen at the same time in the same or different z-index planes and are in a fight scene in which one actor is punching the other, especially on the face?
I've heard of split filming and stitching the scene, green screen, and lastly computer processed overlays of the actor's face on another actor's body with the same build. The last one I've seen in The Social Network but I'm referring to films that were shot pre 2005.
And it looks very real.