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View Full Version : Mental Ray going down

chris.scherer
02-25-2005, 01:05 PM
Hello,

I am deeply troubled by a scene of mine that utilizes an imported polygon object (170 MB, default-blinn-material), a Maya-ramped sphere for reflections and final gathering-emission as well as a few (3) area lights.

Somehow, without (knowingly) altering anything on the setup (apart of referencing in some additional meshes) the rendering-performance keeps declining. Whereas once the whole scene rendered for about 10 minutes at default-settings (for a 2x1k image with depth 2 raytracing and accuracy 1000 FG) on a single dual xeon it now takes approx. 5 hours just to collect the FG-points ( I usually cancelled after 2 hours), even if distributing to other, more powerful machines...

It is obviously the raytracing that kills the mocking user here. If I deactivate it, it renders within the blink of an eye.
I even tried going back to just a single raytracing-ray and a single shadow-ray, but rendering times stay exessively out of proportions.

Anybody experienced anything similar. Or even came up with a solution ?
twistedpoly
02-26-2005, 10:52 AM
same here.

calculating of fg points takes forever
floze
02-26-2005, 03:00 PM
Do you have mirrored (scale -1) geometry in your scene? Or do you get the 'angle between normal and geometry normal more than 90 degree' warning?
twistedpoly
02-26-2005, 04:23 PM
yes it happens a lot of times that i get "angle between normal and geometry normal more than 90 degree" message. Hot to fix that? and i guess i have some mirrored objects too in my scene, can that really be the problem??
floze
02-26-2005, 04:39 PM
That's definitely causing slowdown, maybe at least partially in your case. It is told that one might just ignore that error, but imho it indicates something's wrong (or maybe not right enough) with your scene. Try to avoid mirroring. Export possible problem causing objects as dxf/obj or anything else, then maybe resave it another program, and reimport it into maya. Of course, 170MB would be heavy to export/reimport... :hmm:
I get that error very often when importing external formats (3ds/wrl stuff etc.). Maybe try to avoid this too.
Also, try to make sure all normals point in the wanted direction.
anevsky
02-26-2005, 09:07 PM
ok and how would you avoid duplicating something with -1 value when exactly this action is needed? or in other words - what to do to make it less troublesome for mentalray?
twistedpoly
02-26-2005, 09:28 PM
i was thinking...wouldn't simple freeze trensformation help on that?
floze
02-28-2005, 03:19 PM
Today I was able to test around with a scene where I could isolate the >90 degree problem. The cause of it seemed to be 'overbent' normals, for instance very sharp/tight triangle ridges. I could get rid of the error by making all normals hard, or, and that's also a fast way to test, by turning off the 'Smooth Shading' rendering flag. Any response regarding this problem is highly appreciated since I'm suffering from it as well as everyone else here.
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