View Full Version : rendering fur with mental ray

12 December 2006, 06:20 PM
hi guys,

I have a nice meadow with the fur grass shader on it. I assigned maps for length, baldness and so.
In the Fur Render Settings I set the Fur Shader to Volume so it renders fast. The problem is, if I render a sequence, I get strange artifacts that are different from standard flickering (see the picture). When I set the Fur Shader to Hair Primitive or user Maya Software, the artifacts are gone.

I swear that there are no shadow-casting lights in the scene, cause the artifacts look like shadows a little! Raytracing is turned off...

I want to get rid of these artifacts and use the Volume method!!!
Help is highly appreciated, I'm working on a project with deadline...

the ground plane is NURBS and I'm using Maya8

12 December 2006, 07:47 PM
Hi joit
Looking at your render it looks like an animated noise map being applied to the grass. Grass is staionary, only the noise moves.
I don't know about this Volume method of rendering fur, is it new to Maya 8?, if not how does one set it up?

sorry I can't be of more help

12 December 2006, 08:04 PM
hi thomas,

thanks for the tip. No, I don't have any animated noise map.
The volume method is very easy to set up. Open the mental ray attribute in your Fur Render Settings / Fur Globals and switch from Hair Primitive to Volume. It is really fast!

12 December 2006, 04:24 AM
Have by any chance baked (or cached, rather) the fur ? I never used fur but I've read that caching would totally avoid any flickering to occure when shooting an animation... :shrug:

Just in case try to render the ground plane with the textures u used for fur in some shading channels, to check if they are really still.

12 December 2006, 08:55 AM
nice idea with the caching!
I checked it in the FurFeedbackShape but it didn't help.
Do you think I have to activate it somerwhere else?

12 December 2006, 08:01 AM
I really can't answer you, sorry ! At least I'm sure hair has caching ability, may be not fur...

12 December 2006, 10:02 AM
I actually think that volume rendering method is buggy.
Simple test: create new fur, give it a bear preset 100%, and try rendering with hair primitive; now keep the file in render view, then rerender it with volume.
They don't look the same.

12 December 2006, 11:48 AM
i'm not sure, but i think volume fur is not a supported feature in 8. i might be wrong. check the docs if you find anything about it.

cheers, ronny

12 December 2006, 03:22 PM
They don't look the same.

Yep, but that's what the doc says. There must be a downside of the quicker render times ;) But you can tweak the volume...

12 December 2006, 04:42 PM

I contacted Autodesk and they told me that the problems come from the Noise Amtplitude/Frequency values. So I turned all of them down and the flickering was gone. Then I put them all up again and turned them down individually. No chance to get rid of the flkickering this way. So I tried it the other way around and turned all noises down and raised them individually. I found out that the flickering comes from base color AND tip color noise.

Simple workaround:
Create a noise map in Photoshop and asign it to base color.
Don't even think about asigning a map to tip color. This will lead to even crazier artifacts...

Feel free to reproduce ;)

12 December 2006, 03:37 AM
Nice done research.
Thx for sharing results :thumbsup:

12 December 2006, 11:35 AM
Hey guys. How 'bout rendering hair (no fur) in volume mode? Is it possible?

I succeeded rendering hair with MR shaders using ctrl_fur geo shader. But it seems volume shaders do not work, shadows are rendered though.

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12 December 2006, 11:35 AM
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