View Full Version : Participating volume in mental ray.
11 November 2006, 08:42 PM
I almost added this in the Mental Ray Shader thread but since it's half shader / half light related I wasn't too sure so, here it is, orphan and all alone :)
I went to a friend of mine who uses Maya and he demonstrated me something he learnt to do in a Digital Tutors DVD
Basically, it will allow you to simulate dust or smoke in a room.
Here is how you proceed : you create a volume (let's say a box) that will encompass the volume of your room. On this volume you apply a shader composed of a Transmat shader in the surface slot and a Parti Volume shader in the Volume slot.
Then you create a light (apparently this light needs to be in the volume) and you apply a Physical Light shader to it.
You play with the various settings of the Transmat and Physical Light shaders and you end with a nice volumetric effect for your light.
In fact the result was quiet nice so I decided to give it a try in max but despite my numerous try never managed to reproduce it.
Does someone amongst you dear readers managed to get this to work, and if so, how ? :)
Thank you in advance for any help :)
11 November 2006, 02:59 AM
I've been using it for some projects my company is working on. Its actually pretty cool. In fact, for a train station shot I just wanted it for the shafts of light from the moonlight, but it also added a glow around all the gaslights I have in the scene. It really gave the shot a beautiful look.
You're doing everything correct, but one thing you need to do is set extinction to a very small number. It defaults to .001 and I use it at .0001
I also set the scatter color to a very low color value, again it defaults to .5 and I set it to .05 or even .005, adjusting for the color I want it to be. These work to give me a very subtle shafts and glows. Look in the MR docs for the values you need in r,g1,g2. In fact the docs tell you everything you need to know about participating media.
Hope this helps
11 November 2006, 07:52 AM
Thank you slebed :)
With your help I partially got it to work (I think I still have some problem with the physical light itself in fact, I need to chain two "output map" in the color slot to get it to produce enough light, I still probably do something wrong - tried with all kind of lights, standard max, mr, ies).
Otherwise I do start to get some "dust" provided the camera see the light. I guess now it will only be a matter of experimentation :)
11 November 2006, 05:59 PM
The scatter color controls not only the color, but also the strength of the rays. Just coming upping the intensity of the color and the rays will become more prominent.
11 November 2006, 08:07 AM
Thank you slebed, I guess now I just need to find a way to get the physical_light shader to produce more light without piling up two output maps on it. Seems it needs to be "overdriven" with a value higher than the white swatch allow :)
Thank you for your help, much appreciated :)
05 May 2007, 03:28 AM
I also set the scatter color to a very low color value, again it defaults to .5 and I set it to .05 or even .005, adjusting for the color I want it to be...
...The scatter color controls not only the color, but also the strength of the rays. Just coming upping the intensity of the color and the rays will become more prominent.
Thanks, that saved me a lot of headaches!
05 May 2007, 08:48 AM
for partivolumen it is important 1unit=1meter, then can you use the default value.
here some links:
how to use partivolumen: http://forum.german-mentalray-wiki.info/viewtopic.php?t=39&highlight=parti
partivolumen indoor: http://forum.german-mentalray-wiki.info/viewtopic.php?t=296&highlight=volumen
ice with partivolumen: http://forum.german-mentalray-wiki.info/viewtopic.php?t=41&highlight=volumen
Only when you are registered on the GMRF can you download the sample szene.
some threads are in english of www.mymentalray.com (http://www.mymentalray.com/)
05 May 2007, 08:48 AM
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