Vector Displacement Maps in Modo

[Dentzz]

Was playing around and trying to get a Vector Displacement out of zbrush rendered into modo vray. I see that vector displacement is mentioned in the changelog back in 2014 so I figure that it works. I am currently just plugging the vector displacement, into the modo vector displacement as I don't see a vray specific one is this correct? Also does anyone know what the correct export settings in Zbrush are for Vray currently have it working for modo's render but I think you have to flip a bunch of settings and don't know what needs to be changed for vray? Lots of settings so if someone has done this and knows what to do would be interested to hear.

[vladimir.nedev]

You should definitely add the "V-Ray Geometry Properties" to your mesh and turn on "V-Ray Subdivision". This will disable MODO's sub-division,
which breaks up the mesh into pieces before giving it to V-Ray. The "V-Ray Geometry Properties" also have an option to choose the vector
displacement type. I don't have Zbrush and I haven't checked what the correct options are.

Greetings,
Vladimir Nedev

[Dentzz]

Thanks this definitely helps solve some of the problems, as I was getting some mesh break up. Using V-Ray subdivsion dynamic, is classic catmull clark open sub d or is it something else as I see OpenSubd as static subdivsion not sure the difference or which should be used?

Anyone else who maybe has used zbrush and vray in another software before know the correct settings in zbrush so I can at least concentrate on trying to get it to look right in modo vray?

[vladimir.nedev]

Thanks this definitely helps solve some of the problems, as I was getting some mesh break up. Using V-Ray subdivsion dynamic, is classic catmull clark open sub d or is it something else as I see OpenSubd as static subdivsion not sure the difference or which should be used?

OpenSubdiv uses the library from Pixar, it will subdivide the mesh before rendering starts, and I don't think it currently supports view-dependent subdivision, meaning the mesh will be subdivided equally everywhere.
"classic catmull clark" is still our implementation, but using the "catmull clark" subdivision weights. It should support view-dependent sub-division.
I might be wrong on this one though.

Greetings,
Vladimir Nedev

[Dentzz]

That makes sense when I was just just subdividing a cube they both rendered the crease weights what appeared to be the same way which matched up with psubs which is modo's catmull clark implementation. The static vs dynamic must refer to the view dependent sub division. Though I thought either version 2 or 3 of open subD had view-dependent, render-time tessellation. However I just read the marketing brochure and don't actually do the coding so how things actually function I don't really know.

[vladimir.nedev]

That makes sense when I was just just subdividing a cube they both rendered the crease weights what appeared to be the same way which matched up with psubs which is modo's catmull clark implementation.

Only the OpenSubdiv sub-division in V-Ray supports creased vertices/edges. Note that the final normals are computed a little differently from what I've tested. V-Ray will smooth them out, so in order to get a completely sharp edge,
currently you need to increase the sub-division level.

The static vs dynamic must refer to the view dependent sub division.

Static in the "Static subidivision and displacement" check-box refers only to the V-Ray sub-division.
OpenSubdiv is always static (which is by the way faster during rendering).

Though I thought either version 2 or 3 of open subD had view-dependent, render-time tessellation. However I just read the marketing brochure and don't actually do the coding so how things actually function I don't really know.

I am not sure which version we are using, but in any case there is a lot of code that bridges V-Ray to OpenSubdiv. I don't think that this code currently supports view-dependent tessellation.

Greetings,
Vladimir Nedev

[Dentzz]

My mistake on the creasing on vraydynamic subdivsion. I thought the weight you were referring to on the dynamic subdivision (classic catmull-clark) was edge weight is the weight you are referring to how triangle sub divisions are handled?

Sorry to keep you busy with all these questions.

[vladimir.nedev]

is the weight you are referring to how triangle sub divisions are handled?

I was referring to the weights used during the sub-division algorithm (when there are no creases).
Actually I think the correct name is "masks", not "weights". They specify how the vertex positions from one level are combined in order to get the vertex positions for the next level.
Also note what the "Classic Catmull-Clark" tool-tip says - it will work only if the mesh contains only quadrangles.

The "Weight map" in MODO specifies the vertex/edge creases. It works only with Opensubdiv sub-division in V-Ray.

Greetings,
Vladimir Nedev

[Dentzz]

Okay so the weight is the weighted average on the masks. I think I understand or at least to some kind of extent. I read the OSD 3.0 docs and it says that they plan on adding dynamic feature adaptive isolation at some point in the near term but they haven't yet, meanwhile some other sites talking about OSD say it is already part maybe it is referring to something else?

After some fiddling I am able to get a vector displacement map created in modo to render correctly or what looks correct in a non moving test render in vray. Is there any reason that Object vector displacement is the default in the vray mesh property since Modo's I think is tangent and at least as far as I knew that or absolute was needed to hold up for deformation? Not sure at all the difference between tangent and absolute tangent for vector displacement.

Hopefully someone else reading this thread has done this using Zbrush or I'll just spend the weekend messing around trying to get something that isn't diced or an eldritch abomination assuming it is the same as Modo's settings.

[vladimir.nedev]

Is there any reason that Object vector displacement is the default in the vray mesh property since Modo's I think is tangent and at least as far as I knew that or absolute was needed to hold up for deformation?

No reason, I couldn't get it to work with the sea-horse example that MODO has, so I left it at the default value that it has in the V-Ray plug-in.
And I didn't have time to test ZBrush/Mudbox, as I don't have them installed.

Not sure at all the difference between tangent and absolute tangent for vector displacement.

Here is what the "Vector displacement type" tool-tip says :
"""When this is "tangent", the red, green and blue channels of the vector displacement map will be used to perform vector displacement with base 0.5.
If this is "Tangent (absolute)", then the map matches the Mudbox displacement maps."""
This is directly taken from the description of that parameter in the V-Ray plug-in that implements the vector displacement.

Greetings,
Vladimir Nedev

[Dentzz]

Didn't try with the sea horse, so maybe I don't know the default settings. I just created geometry in modo and when creating a vector displacement map from that geometry I just accepted the default settings which as the second part of your answer describe it defaults the image map base value in RGB as 0.5. Zbrush just visually looking at a vector displacement map looks mostly black with spots of color so maybe it is an absolute tangent or does some weird zbrush thing. Though either way modo in the texture layers allows remapping all the values so if it isn't working can very easily change to either have the values go from 0-1 or with 0 as the midpoint and -1, 1 or any variation to control the maps.