Hi all

Is there anything similar to the Dirtmap shader available for Mental Ray that is available for Mantra or able to be built in Vops to be equivalent ?

(http://animus.brinkster.net/index.html) [animus.brinkster.net]

From what I hear the dirtmap shader is often used in industry.

J

Not sure about the Dirtmap, but you can use (and modify) the Rust and Mold VOPs to some pretty good effect.

JohnnyBGoode
Hi all

Is there anything similar to the Dirtmap shader available for Mental Ray that is available for Mantra or able to be built in Vops to be equivalent ?

(http://animus.brinkster.net/index.html) [animus.brinkster.net]

From what I hear the dirtmap shader is often used in industry.

J

In the houdini world it's referred to as “ambient occlusion”. Check the video tutorials on vislab, I'm pretty sure there is a global illumination example that shows the use of ambient occlusion.

-Drew

I was going to say that can't be right, but yes, in some circles it does appear that's what they use this thing for - fake GI. That's really strange, and a seriously misleading name. I'm pretty sure “dirtmap” just means what it sounds like, though - a dirt map shader as Jason alluded to, apart from any tricks that it's used for.

Cheers,

J.C.

JColdrick
I was going to say that can't be right, but yes, in some circles it does appear that's what they use this thing for - fake GI. That's really strange, and a seriously misleading name. I'm pretty sure “dirtmap” just means what it sounds like, though - a dirt map shader as Jason alluded to, apart from any tricks that it's used for.

Cheers,

J.C.

Misleading indeed, but the Dirtmap at http://animus.brinkster.net/index.html [animus.brinkster.net] is doing an occlusion calculation which you can see if you download the mental ray shader source. Its also referred to in this article http://www.evermotion.org/tutorials/rendering/xsi_dirtmap/. [evermotion.org] You can use the shader to get the look of things like polished objects where gunk gets stuck in crevices where in effect you have “cleaning occlusion”

-Drew

Sorry, I should have been a bit clearer about the ‘dirtmap’ use.I have used ambient occlusion quite a bit with houdini, what interests me about dirtmap is that as far as i know it is used as a fake-occlusion and also a fake-GI.

It can gather ambient colour from an environment map for one pass and occlusion for another.

As far as i know this is all fake, and is used by industry quite a bit. So i assume it produces much faster results as a shader than using actual ambient occlusion?

Is there anything similar for Houdini?

The dirtmap shader for Mental Ray is doing standard Ray Traced Ambient Occlusion. It isn't faking anything, although it might allow you to use an environment map or something, rather than just going Black and White.

-Craig

oh cool

thanks for clarifying that for me. So as far as i should be concerned the Ambient Occ done through using a GI light shader in houdini will be no slower and no different a technique? (doesnt houdini let you use an environment map anyway?)

I always thought dirtmap as a cheat way to avoid actually using ambient occ - the Evermotion link that Drew supplied suggests this too.

I just assumed it because I thought it odd to be using a shader to generate ambient occlusion rather than a lighting technique like in Houdini?

Cheers

J

You might want to look at this thread over at odforce

http://odforce.net/forum/index.php?showtopic=2876 [odforce.net]

It deals with the idea of fast ambient occlussion.