CGTalk - Mental Ray Rendering Problem....

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ArtbyBpc

07-18-2006, 04:55 AM

I am having problems rendering displacement maps via mental ray. I made the maps in zbrush exported them and have my settings set up correctly. When I render it renders great sometimes, but after maybe the first render (sometimes not even the first), when I re-render it only renders about half the image and decides to stop. I have a 2.4 AMD Athlon and 2g of ram. The geometry is pretty heavy at about 12,000 polys. Is it my machine's weakness that is causing the hault? I also have pretty big displacement maps at about 4096x4096. Can someone please help me out here? Thanks.

bgawboy

07-18-2006, 05:28 PM

It would help to find out more about your settings. Also, do you have translation>verbosity info (or progress) on to get more information before it stops?

Is your geometry subdivision surfaces?
If so, converted from poly, within Maya?

Are you using mental ray approximation nodes?

I don't think 12,000 polys is very much, but your displacement could be causing a lot of tessellation.

Large BSP?

Fine approx?

Memory limit = ?

Ash-Man

07-18-2006, 06:05 PM

you are running out of memory

there is a long thread that goes on that matter
but as a quick tip...convert the displacment map to mental ray map format
check zbrush centeral as well

ArtbyBpc

07-19-2006, 03:11 AM

Thanks to you both! I was using tiff as the displac. map file format. Changed it to 2048x2048 and into a targa and works great.

bgawboy

07-20-2006, 08:04 PM

To be clear, targa doesn't get treated any special way in mental ray. The reduced resolution is probably having an effect. As mentioned, it might be even better to use .map format. You can use the imf_copy command line to do that. It comes with Maya.

Hezza

07-23-2006, 04:45 PM

Also make sure you turn off Feature displacement on your objects. I forgot this once and had the same problem as you, would render one frame then give up on the second. Feature Displacement is maya's subdivision method, so essentially maya was dividing my model 5 or 6 times, then the mental ray subdiv approx was dividing it another 5-6 times and was ending up around 10mil polys. I was suprised it even knocked out one frame.

Hez

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