Vector Displacement issue

[runvray]

Hi,

This conversation initially started in

http://www.chaosgroup.com/forums/vbu...881#post545881

But since it turned out VDMs aren't support in VRay for Softimage yet, it morphed into a VRay for Maya question and I'm moving the it over here to a more appropriate
area of the forums.

If you experienced troubles such as random artefacts on your geometry when displaced or not displaced at all it would be nice to send us a scene to investigate.

I do have an example of a vector displacement that I've been having problems with in VRay, but I don't see any way to attach the file here in the forum.
It's relatively small, approx 4.25 MB, so it should be email-able if necessary.

Also, one thing that I've noticed that varies from the tutorials and forum threads that I've read, is that you really don't need the Maya displacement shader.
You can just plug the VDM straight into the shading group's displacement slot. It doesn't to seem hurt if you use the displacement shader but it doesn't
appear to have any benefits either.

Thanks,

Jeff

[Sammyjenkins]

So were you able to get the vector disp. map to render with v-ray?

[vlado]

You can send the scene to vraymaya@chaosgroup.com and we'll find a way to post it here.

Best regards,
Vlado

[runvray]

My focus has been elsewhere lately and I hadn't setup thread subscription properly,
so I didn't see these replies until now.

I never did get the VDM test to render correctly in Maya, it had problems with both vray & mental ray
though It does render perfectly fine in Softimage mental ray.

I did send the file to support back on March 23, and a support ticket on it was opened (271959)
so I assume it's in progess.

Something I ran into recently that might be of interest is this wiki entry about "mikktspace"
a tangent space code generation method developed by Morten S. Mikkelsen for his master's thesis.

http://wiki.blender.org/index.php/De...ce_Normal_Maps

The entry specifies normal maps but I believe it should be applicable to tangent space VDMs too.

Beyond the techincal problem solving and ease of use the method presents it's free for anyone
to use which makes it, to quote the article, "a perfect candidate for an implementation
standard. We hope the standard will be adopted by as many developers as possible."

Amen to that

-Jeff

[vlado]

Thanks for the link, but vector displacement is not quite the same as normal maps; things that worked fine with normal maps may not work well for vector displacement.

Best regards,
Vlado

[vlado]

The ticket didn't get to me yet but in the meantime, can you tell me which application generated the vector displacement map and what export options you set there?

Best regards,
Vlado

[runvray]

The VDM was generated in 3DCoat, using the "Big Mesh method".
This requires a low res & high res version of the object with matching UVs
And the following steps,

"File>Import>model for microvertex painting" for the lo res,
"File>Import>Big Mesh" for the hi res,
"Textures>Export>Vector Displacement Map" for the VDM

I used a very simple test sculpt done in ZBrush for the matching objects

For the texture export from 3DC I used the following settings

-What space should be used = Tangent space
-Map type = Zero level is black, not normalized

The ticket has a more detailed step by step, along with an image
that illustrates the render issue and the maya vray scene.

Thanks,

-Jeff

[vlado]

Ok, will get there. We haven't tested vector displacement out of 3DCoat, so there may be something specific to it. So far, I know that only Mudbox vector displacement works properly. (ZBrush also supports vector displacements, but what goes into that is still a total mystery for me).

Best regards,
Vlado