Thursday, July 2, 2015

Shadow rays and I are getting a divorce

Like most batch rendering people I have a love-hate relationship with shadow rays.   They are wonderfully simple and can easily get you effects like accurate shadows of an eclipse.   And yet without getting fancy you start having car interiors turn black because the shadow rays hit the windows.    And brute force methods give better pictures given huge amounts of rays.   But I think I am finally believing my own BS and thinking computers are fast enough.  In my new rendering project I am abandoning shadow rays so the floor under the glass is automatically illuminated.   Note the quasi-TV is the only light source in the room.   No importance sampling here yet-- just getting the functionality in.   (I think there is still a bug in the glass but getting close).


Pseudonym said...

Of course there's no importance sampling there. Shadow rays ARE importance sampling.

So you're not optimising direct illumination at all, then?

Peter Shirley said...

Correct-- no importance sampling at all yet. Your point about shadow rays being importance sampling is a good one, but in my "internal vocabulary" I don't call it that-- I think of it as breaking up the integral (my internal vocabulary is wrong, but useful-- I just need to keep it internal :P). That is why shadow rays introduce complexity to the software.

Making directions where direct illumination comes from more likely to be sampled is the next step after I fix my refraction bug. I have confirmed there is one...