I am a little curious if there any interplays between Global Illumination, rastering and shaders that they are exploiting on account of having complete engine control. Techniques that something special about their engine might be allowing.

I only wonder because I recall the reason they built an engine from scratch for The Witness was to achieve certain lighting goals, and that specific feel and style I have never encountered quite like that in any other game.

A lot of that is down to art and direction, but there's a raw quality of the lighting that just feels different to any game I have played. You can often feel a game's engine out if it's one of the big ones, through the feeling of its lighting. I suspect since all engines have certain default approaches and settings in their lighting setups and devs only move the knobs as far as they need to meet their artistic goals, leaving much alone.

> I recall the reason they built an engine from scratch for The Witness was to achieve certain lighting goals

I don’t buy that. Even back then, as an indie developer, the only reason you build your own engine is because you want to build your own engine.

You have to be doing something truly technically impressive to need a new engine and The Witness wasn’t pushing the envelope.