ZBrushCentral

Multi Tile Multi Subtool Workflow

ZBrush Usage Questions
#1

Hi there,

for my first shotfilm I´m going to try and push the limits a bit and therefore UI was looking into ways of getting more detail out of Zbrush, since its the only 3D App apart from 3ds Max I´ll be using.

I found a tutorial about the multi subtool multi Uv tiles workflow here:

http://www.cgstudentawards.com/magazine/entry/making-of-the-beast-by-javier-blanco

It also uses Mari and Maya instead of 3ds Max but for now this is the best description I found, to get the amount of detail I´m after.

I already know, that I will only be needing that amount of detail in some shots and on some objects, for the Rest single tile uvs without subtools wll be enough.

But for thos instances, I will need the amount of detail I´m after, I´m not sure if I got all of the workflow right, so I´m hoping someone with a little experience in that field could help me out:

  1. Basic sculpt in Zbrush or create Basemesh in 3ds Max.
  2. Start sculpting up to maximum level of detail I get out of Zbrush in one subtool (around 10 mill polys).
  3. Export new lvl 1 Mesh to 3ds max and unwrap (preferably try and keep the edges straight, as laid out in this tutorial:
    http://polygonspixelsandpaint.tumblr.com/post/19733351349)
  4. Place UV shells in diffferent UV islands.
  5. Reimport unwrapped basemesh to zbrush sculpt (alternatively import as separate subtool and just copy and paste UVs via UV-Master. Sometimes that seems to work faster).
  6. Create polygroups from UVs.
  7. Duplicate subtool to keep original subtool.
  8. Split duplicated subtool by polygroups.
  9. Subdivide new subtools to new highest level and finish detailing on each.

The next parts are a bit unclear…
9. Create bridge meshes from original unsplit model.
10. reproject highest details from all split subtools onto that bridgemesh.
11. Fix seams on bridgemesh.
12. reproject bridgemesh on all subtools.

After that it should be pretty straight forward:
13. Export displacement/polypaint map for each subtool.
14. In 3ds Max use the original Basemesh from step 4.
15. Load all maps from the split subtools, offset the U and V values and create a compositemap with all maps.
16. Use that compositemap as final displacement map.

Alternatively, but only for static meshes:

-Don´t use the LVL 1 mesh, but rather a Level 3 or even 4 Mesh.
-Use Vector Displacement.

Can you please check that workflow and see if you can spot any problems?

Or are there other, better workflows, without the use of other commercial software?

I wish they would just change Geometry HD, so you don´t need to delete the lower subdivisions, that would be the perfect solution to achieve this level of detail without such a complicated workaround…

#2

Ok, just to give an update:

I got it to work at last!

I hit a couple of bumps in the road though:

  1. Splitting my mesh into subtools messed up my UVs on my first try. When I started again from scratch it worked, so I´m not sure, where I went wrong.
  2. Spltting my mesh into subtools when it was more then about a million polys crashed zbrush.

There are 2 possible workarounds for this:

A) Don´t use “group split”, instead hide by polygroup and then “split hidden” until all polygroups are a single subtool.
Problem with that workflow is, that the subtools get artefacts, which means you´d have to reproject the details from the original mesh.
B) Only subdivide your mesh up to the save number of polys and then use “group split”. Experiment to find up up to which level you can subdivide BEFORE you start sculpting.

With method A you can do the sculpting up to a medium high level, but you´ll have to do a lot of reprojecting, and only after that you could do the highest level of detail on the split subtools.

With mehod B you could only sculpt up to a medium level of detail (less than a million polys), and you would have to do both the medium high level and the very high levels of detail on the split subtools.
Which means you would have to consider the seams while sculpting. That is ok for stuff like rocks or other objects with a rather irregular surface, for objects with more pattern like surfaces like scales or stuff like that, I guess that would be a bit tedious (in the linked tutorial from above the first pass of detail came from a displacement map painted in Mari, that already took care of most of those issues with the seams).

Do NOT forget to turn off “SMT” (smoothing) in the geometry rollout after you split the subtools, before you further subdivide them, or they just won´t match up anymore at the splitting seams.

To correctly create and use the bridge meshes:

  1. Create the bridge mesh from the original mesh BEFORE you split it into subtools, by hiding all other polygons and then delete hidden or split hidden, OR after you splt the model by taking parts from adjacent subtools, splitting them and then merging them and welding them into a single subtool.
  2. After sculpting the last levels of detail into the split subtools, you have to reproject that detail from all subtools onto the bridge mesh/ meshes.
  3. Then you sculpt away the seams on the bridge mesh.
  4. Last but not least you now have top reproject the bridge mesh onto all split subtools.
  5. Voila: If you export via Multimap Exporter all visible subtools (including of course only your split subtools), you now have perfect seamless maps for you final render mesh…

The next issue came when I actually started testrendering.
I used a grey override material and one light to simplify things and it seemed like not all of the detail had transferred over, there was a clearly visible difference between the Zbrush Viewport and what I got in the 3ds Max render.
After experimenting with different settings (lowering edge length in the vraydisplacement modifier, increasing DBSubpix in Zbrush and increasing map size of the multi tiles up to 8 k each), I started fresh with just some displaced text on my mesh in different strengths, and as it turned out: The displacement carried over identically, so really the problem was with the testrendering.
Zbrush makes all the fine details pop way more than a standard material and light setup while rendering can.
I found the chalk matcap to be closest do the testrender, so it might help to get used to that while sculpting the fine details or wait til diffuse and specmaps are painted aswell to really judge the quality of the displacement…

This has been quite lengthy already, but I kind of use these posts also as a tutorial for my future forgetful self…

I might do a full tutorial with a couple of example pics, so if you have something to add, that could simplify that workflow or make it otherwise better, please do, I´ll add it to that tutorial.