ZBrushCentral

UV mapping changes and normal mapping (Games related)

ZBrush Usage Questions
#1

Hi guys

I hope you can give me a hint or two as to what is going wrong in my pipeline.
I am using MAX and Zbrush to create normal maps for ingame models at the moment.

What I do is:

  1. Create the lo-poly mesh in MAX.
  2. Unwrap in max.
  3. Import lo-poly into ZBrush
  4. Subdivide, and create detail.
  5. Import lo-poly mesh into lowest subdivission level again to get the correct normal calculation.
  6. Create normal map in ZBrush.

Now I went back to MAX to get rid of some overlapping UVs that I had forgotten all about, and moved them to a corner, they still have coordinates within 1.
That done I exported as OBJ, and imported the new lo-poly mesh with the tweaked UV set into the lowest subdivision level of the Tool in ZBrush. But my normal map is going crazy now, when I generate it.
The poly and vertex count have not been, and all UVs are the same as well, apart from the few that had overlapping coordinates and are now moved away.

So my question is why is ZBrush not generating a correct normal map now?

Also, I have noticed that I can not make any changes to the low poly mesh once you have imported it into ZBrush and started the subdivision and sculpting process. For example if I decide to optimize and get rid of say 20 polygons, then I can not import the tweaked low poly mesh into the lowest subdivissions because the vertex and face count has been altered

Is it only me missing something obvious, or is it simply not possible to do so?

#2

Regarding the first part of your question, could you show an example of what you mean by “crazy”? This might help us figure out what’s wrong. The culprit is most likely a setting in the OBJ exporter, however, since the workflow that you describe is correct.

Regarding the second question, the high resolution model must be a derivative of the low res model in order for you to be able to import the low res model for difference map calculations. If you modify the low res model, you will not be able to import it back into subdivision level 1.

#3

Certainly.

I have used the exact same settings in the OBJ exporter as I did for the model I exported before.

My hunch is, that ZBrush simply wil not allow any changes what to the UV lay out once you have started your subdivision and modification. Ie. you can not load a new low poly target object into subdivions level 1, with an altered UV set.

#4

Actually, you CAN load a version of your model with different UV mapping into subdivision level 1. I still think that there is something being overlooked in the import/export features with Max. For example, the point order might be getting changed, somehow.

#5

Well that is good news indeed :slight_smile:

I just had a thought, one I have posted in the other UV problem thread:
http://www.zbrushcentral.com/zbc/showthread.php?p=179950&posted=1#post179950

I made the old model in Max6.0 and the UV tweaks were done in Max7.0 maybe there is a connection…

#6

Alas it does not seem to be Max 7.0

However, on the low poly model, I deleted the right half, copied the left and mirrored it, then attached.
Would this cause the problems?

I can still import the low poly model into ZBrush without getting any error messages, but the normal map still looks like the picture above.

Here are the OBJ export settings I use:

Cheers,
Max

#7

yes, see that would cause the vertex numbers and order to change. I think what you would have to do is start over with that new mirrored model. but todn’t panic yet. Now, have you tried applying the normal map, or displacement map in Zbrush freshly, so that you can edit? I remember this being explained in the telephone tutorial at the end, they talk about loading the displacement map back in on the lowres in ZB. My first attempt at this failed miserably, it’s on my list to test again. I have lots to test for my pipeline of going Maya, ZB, back into Maya, export into my game engine. my biggest concern is dealing with iterations. Inevitably, in game development, there will be changes to the model. So, I want to know that even my older displacement map based on the older model, will be able to be loaded onto the slightly modified model by imbedding it into the new high-subdivided ZB model, and then continue editing and working on it again, creating the new normal or disp map. Has anyone tested this and had success?

#8

just to be clear: I intend to use tangent normal maps on my maya model and in the game engine, but I think to re-apply the details made, you have to save off and load on displacement maps in ZB, not normal maps.

#9

Ah yes that could be a way around it too.

I am slowly adjusting my workflow and my techniques to suit ZBrush, every day I learn something new now, and that is great! :smiley:

#10

I have just completed a test–a simple but crucial one for us game art makers: the ability to edit. No, you cannot reimport a model that has changed vert count into an existing tool, but you can start over. This is also described in the telephone tutorial at the end.

-Delete all the higher res-es. Keep your displacement map handy in the alpha palette.
-Now import your modified model obj and subdivide the same amount again.
-In displacement rollout, change the “intensity slider” to say the same # as your alpha depth factor,
-click on “mode”,
-now hit “apply disp map”

Your new model should appear displaced. Now you can edit this highres again within ZB and export new disp and normal maps.

Hope that helps!

#11

I’ve experienced problems with making normalmaps in Zbrush.

I typically work after this order:

  1. low res mesh built in max, UVWs laid out, unwrapped, then exported to OBJ with the obj exporter.

  2. Import OBJ to zbrush.

  3. add geometry in zbrush, then hi-res detail.

  4. use zbrush to create normalmap.

This is where things sometimes get messed up. I’m not sure why, but on some models (not all, can’t figure out what triggers it) the normalmap doesn’t project properly onto the mesh’s surface.

You can actually SEE in within zbrush, even before exporting the normal map. Once zbrush puts your normalmap onto the mesh, you can ROTATE the mesh and actually see, visible to the eye, that the normal map has sections that seem to flow and twist as you rotate it.

And of course, if you save the normalmap and apply it to your model, it looks awful.

The appearance is as if it had been made with TRIAGLES (it wasn’t - I always keep my meshes quad and export them as such - all accounts say that zbrush hates tris). And that the UVWs coords for the triangles had been FLIPPED in some areas, twisting and undulating the way the normalmap projects onto the mesh.

I’ve heard a lot of back and forth on the forums about similar issues, but they seem to be about DISPLACEMENT maps, not normalmaps.

Has anyone figured out why this is happening, or know how to fix it?

Slyrr