Lighting irregularities, per-frame and per-computer

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  01 January 2013
Lighting irregularities, per-frame and per-computer

Hey everyone.
I made two posts somewhat recently. The first one was about a strange issue in which my renders looked okay in one frame, but the lighting would change dramatically in the next frame. The next issue was that I was getting really strange 'blocks' with DBR where the blocks handled by my slave PC would be brighter for some frames/angles, but otherwise worked fine in others.

However, I have just realized that the two problems are related: If I render the same thing on both computers separately, they each have some 'flickering' where some frames become way too bright (first issue), but when rendering together on the same scene, the flickering is on a per-bucket basis rather than per-frame.

While I don't have many theories as to why this is happening, the only one that I think has any merit is this one (and I'm not even sure of it): My scene has a few visible light sources that actually emit direct light. The way I'm handling this is to make the geometry where the light is supposed to be emitting from self-illuminating but without indirect lighting. I then add a photometric light right at the center of each light and align it accordingly. My guess is that while this works somewhat, there will be fighting for places on the z-buffer, ensuring that the lights are visible and working properly on one frame, but are blocked by the geometry on the other.

Is the way I'm doing it okay, or does anyone have any better ways of dealing with it? Thanks a lot. =)
 
  02 February 2013
Sorry to bump this relatively old thread, but I'm still having the issue, and I realized it's worse than I thought: I'm now having lighting irregularities on a per-bucket basis, even when rendering on a single computer.

See this picture [I've circled and pointed to the problem areas; notice how there's a drastic change in lighting. Note that the 'noise' on the nose isn't the issue - this is a somewhat test-quality render]:
 
  02 February 2013
Well, I appear to have found a solution.

I think that MentalRay didn't like me using photometric lights without a MR shader on them. Using one I haven't had any issues so far (apart from the speed penalty).
 
  02 February 2013
Originally Posted by Aikku: Well, I appear to have found a solution.

I think that MentalRay didn't like me using photometric lights without a MR shader on them. Using one I haven't had any issues so far (apart from the speed penalty).

Thanks for updating with your progress.

Gotta say, I'd have never guessed it was that. It appears not to make a great deal of sense. I can only assume that, for some mad reason, it does some bias'ing or otherwise some sort of non-deterministic calculation on a per-bucket basis, but why you'd ever want that is beyond me.
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  02 February 2013
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