Yes there are shortcuts even in unbiased renderers.

A true physics simulation would have the volution of each photo carried out through it's entire path, not just where it intersects a polygon. This would be true volumetric rendering. It is as much out of range right now as unbiased rendering was out of range, computationally, just 15 years ago. Nobody was doing it.

This is most obvious in SSS of any sort.

But still, unbiased renderers are a lot closer to flinging photons around than your typical scan line renderer. That's why they take so long - they don't do statistical shortcuts.

In my gold shader, the reflection of the sun (infinite light) was not done with rays. It was done with a statistical model (Blinn node). That's biased. It's a simplification based on probability, that given I'm looking from the camera to here, and from here the light is here, then this function (Blinn) can predict how much light would pass back to the camera from that light. That is one evaluation of a statistical model. It breaks down in a lot of cases. I did not set up any of those cases, though, so it didn't matter.

On the other hand, the LuxRender engine doesn't even have that statistical model. It sent over a thousand rays from every pixel in that image, looking for light. It made no statistical assumptions that would reduce that work.

 

 

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)