[Radiance-dev] Errors in ambient calculation in 3R7P1?

[Greg Ward]

Hi Mark,

> I am sorry if I am responsible for ruining your weekend.

Well, it was a difficult weekend on many counts, and I'd rather hear  
sooner when a new release is broken than later.

> Does the benchmark scene look OK to you (exercise the proper  
> calculations, include enough interesting stuff to be general, etc.)?

I really like the fact that you incorporated many of Radiance's  
features in a single test.  It is really impossible to be  
comprehensive, but I appreciate your effort and I think you did an  
admirable job.  This is certainly a lot more challenging than any of  
the test scenes I usually run, which I think is why this problem  
showed up here rather than in my own prerelease checks.

I may have some tweaks to suggest once I get this bug fixed.  I think  
I've found the problem, and it wasn't the gradient calculation after  
all but a ramification of some changes I made to accommodate Russian  
roulette ray termination.  There were really quite a few changes to  
the core renderer in this release, and that's the danger of altering  
something as complicated as Radiance, even for the original author....

> Would it help your work if I ran more cases with older Radiance  
> versions?

No, that's not necessary, thanks.  I resurrected 3.6 and verified  
that it works properly with this scene, unlike 3.7.1.

> It's a bummer I missed you all at the conference. Hopefully when I  
> get my degree (and a job), I'll be more able to attend.

Yes, we definitely missed having you there.  Christoph showed off  
some of your artistic Radiance renderings to an appreciative  
audience, and I related how they were even more impressive in a full- 
sized print, like the one I saw at SIGGRAPH last year.

Thanks again for your help in discovering this bug.  I am running a  
test now with my hopeful fix, and if that's working, I'll put  
together a 3.7.2 patch release tomorrow and make an announcement to  
radiance-general.

-Greg