Displacement render

[Guest]

Hi peeps,

Is there an outline of how to get displacements to work?
I am unsure how to link the displacement image to the geo in Modo Vray? So far I've got the geo properties assigned to my mesh and loaded an exr displacement image into the shader stack, and set it to disp function.
I'm familiar with Vray for Maya, so trying to follow the same logic, normally assign disp property to mesh and link my image to that.

Note: Using these assets (geo and map) in maya and modo works. So I'm clearly not doing something right with modo Vray.

Also I'd been keen to see a user manual or guide. Does that exist?

any advise appreciated

Cheers

[vladimir.nedev]

Setting up displacement should work the same way you do it with the MODO renderer. With V-Ray you can additionally add the V-Ray geometry properties
to the mesh to specify stuff like water level, amount of triangles generated, etc. Note that the displacement amount specified in the material
properties will multiply the "displacement amount", "displacement shift" and "water level" from the geometry properties. This way you can reuse the same
material and modify the displacement amount from the geometry properties per mesh item.
For the V-Ray materials, the displacement and bump properties are in the "Texture Layers" tab.

If you still have problems please post a scene so I can see what's going wrong.

Greetings,
Vladimir Nedev

[riggles]

Ahh, thank you. I was wondering about this as well, and didn't even think to look in the Texture Layers tab. This location is a bit confusing for MODO users since we're used to material properties being on material tabs and textures having texture layer tabs. Would you consider migrating basic things like bump and displacement into either the V-Ray Material Basic or Advanced tabs?

[vladimir.nedev]

The naming is confusing, yes, my logic for putting them there was because there is a lot of free space in that tab.
And the V-Ray Material Basic or Advanced tabs already take a lot of space. Also these properties are
not specific to the V-Ray Material. V-Ray Fast SSS2, Skin, Car Paint, all V-Ray materials have them.
This way the bump/displacement properties are in the same tab for all V-Ray materials.

I don't feel like moving them, but if more people get confused I may have to do it.

Greetings,
Vladimir Nedev

[Guest]

This is my setup, simple nothing fancy.
As you can see from the render image, the area with the marque is receiving the displacement, but it is also shrinking the mesh.
I've attached images of my settings, would be great to know what I am doing wrong?

Note: The displacement map was generated with zbrush, it is a 32bit exr. The mid value was set to 0, in other words black not mid grey. And it works fine in Modo and Vray for Maya.
Which is why I am not using any off set in the displacement shift.

Cheers

[vladimir.nedev]

The V-Ray material also has "displacement amount", under the "Texture layers" tab. It is multiplied by the amount in the
V-Ray geometry properties. It defaults to 20mm, maybe change that to 1m as well ?

Can you try the same setup for both modo and V-Ray ? So, a modo material with no V-Ray geometry properties. The renders
should be basically the same.

Greetings,
Vladimir Nedev

[Guest]

Thanks for clarifying the material settings. I have it working now.

I noticed a difference in the setup between vray modo and native modo renders. What looked like a "shrinking" in my previous renders was actually the reverse.
The meshes were all being "pushed" out. In my modo native tests, only geometry with a specific displacement map would actually be displaced, the rest would just subdivide.
It seems like in vray modo everything is being displaced? or perhaps there was a modo native setting that was multiplying the un-mapped geo and pushing it out?

Using vray geometry properties to control the displacement (and setting it to ignore modo subdivision) on individual meshes has resolved the issue.
Thanks for the help, much appreciated

[vladimir.nedev]

One thing to note is that when using modo's own subdivision with V-Ray, the "keep continuity" option will not work correctly in most cases.
It will actually break up the mesh even more after displacement. This is because the modo API for getting the subdivided mesh will give it
to V-Ray split up in separate parts, and the "keep continuity" option does a normal smoothing operation on the mesh, which relies
on the mesh being connected.

If you have scenes where the behavior with the modo renderer and V-Ray is strangely different, please attach them so I can take a look.

Greetings,
Vladimir Nedev

[Headcrash3001]

On a related topic, I'm having trouble getting negative displacements to render properly. Looking through the documentation I see mention of an option to "Allow negative shader colors" in the Maya version of VRay but I can't find that option available in Modo. Should VRay just "do the right thing" when using an EXR vector displacement map or do I need to manually tell it to pay attention to the negative pixel values in the texture?

[vladimir.nedev]

In V-Ray for MODO "Allow negative shader colors" is always set to true. So it must be some other problem.

Greetings,
Vladimir Nedev

[Steffen Dünner]

One thing to note is that when using modo's own subdivision with V-Ray, the "keep continuity" option will not work correctly in most cases.
It will actually break up the mesh even more after displacement. This is because the modo API for getting the subdivided mesh will give it
to V-Ray split up in separate parts, and the "keep continuity" option does a normal smoothing operation on the mesh, which relies
on the mesh being connected.

If you have scenes where the behavior with the modo renderer and V-Ray is strangely different, please attach them so I can take a look.

Greetings,
Vladimir Nedev

Is there anything (in the future) that can be done about this? Do the MODO developers know about this issue?

Cheers
Steffen

[vlado]

Is there anything (in the future) that can be done about this? Do the MODO developers know about this issue?

Well, we can try to automatically weld the vertices internally, and we will do it if worse comes to worse. Vladimir did mention this to the Foundry, but I don't know if there is any hope for that to change.

Best regards,
Vlado

[Steffen Dünner]

Do you guys @Chaosgroup have access to the latest SP3 betas of MODO?

I'm not an expert in this area, but maybe the upcoming "Rendercache API" will help a lot?!

[vlado]

Do you guys @Chaosgroup have access to the latest SP3 betas of MODO?

Yes.

I'm not an expert in this area, but maybe the upcoming "Rendercache API" will help a lot?!

No :/ At least not as far as this particular problem is concerned.

Best regards,
Vlado