A few notes on how to get Multi-UV displacements as good as you can get from Zbrush 3 to Maya. It seems that the alpha factor will only get calculated accurately for each map if they’re separated as subtools. Well, reliably at any rate. Sometimes it will do it correctly, sometimes it’ll calculate the same depth for each part if you do the old-school shift-control-click to hide each piece workflow.
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Before you start your export, save your ZTL. This is essential because you’ll need to get your watertight mesh back for tweaks after this point.
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If you’re using the UV Smooth option in displacement, go to the lowest subdivision level and calculate a 4k displacement over the entire model, never minding the overlapping UVs. We’re not going to save this one, we’re merely interested in smoothing the UVs on our watertight mesh before it is split.
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If you did the above action, export your new .OBJ file
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Under the subtool palette, use group->split. This will separate each of your UV sets into subtools.
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Hide all of the mesh and show each piece individually. When each piece is shown, create a displacement map at your desired settings. I used adaptive sampling, mode highlighted, 4k map, no UV smooth as I smoothed the UVs before exporting my geometry above, we don’t want them relaxing again.
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As each map is created, go to your alpha palette, and click on each map. Take a note of the alpha depth factor and write it down for each piece (if you don’t save it as part of the filename). This is crucial to create a seamless mesh.
The next part is optional, but I do this to sharpen my displacements that get a little muddy with 16-bit output.
- Go to two subdivision levels from your maximum (ie if your model is max at 5, go to 3), and generate a second set of maps with the mode button unchecked. There’s no need to note the alpha depth this time as we’re using this as a bump map (because normal map generation is broken right now).
Now we go to Photoshop
- Open all your maps, flip them vertically (image->rotate canvas->flip vertically), and save as uncompressed .TIF
Now to Maya
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Import your model, and reverse the normals. For some reason, Z3 likes to implode polymeshes. Your bump map will be reversed if you don’t do this step.
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Go to each of your shading groups and set up your displacement shaders. When you import each file node, go down to the color balance section.
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In the color balance section we’re setting the number we wrote down as our alpha gain, and negative half of that value as our alpha offset.
Example:
Alpha depth factor of 28.1217 from Zbrush
Alpha gain in Maya: 28.1217
Alpha offset in Maya: -14.06085
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Now you can attach your bump maps with a bump value of 1 as we didn’t use auto-levels or anything that would have shifted the midtone gray. As you do test renders, shift all of the bump values up or downward to taste, all with the same value. This will help to make the model sharper and more detailed.
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Click on your model, and in the attribute editor turn off feature displacement
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With the model highlighted, go to Window->Rendering->mental ray->Approximation Editor and create a new subdivision approximation for your model. The values in the Zpipeline guides are still valid on this point, so I’d follow their guidelines. One small note is that if you use Spatial mode, be mindful of the scale of your model. The pipeline guide may use a length of .010, but if your model is 9 meters tall, you’ll be subdividing needlessly. With my mesh at 9 meters tall, length of .5 was the best balance of detail, rendering speed and memory usage. The moral: start high (like with a value of 5), save at every step in case MR bombs, and do test renders each time cutting your length in half until you reach the sweet spot. (in my case, I went 5->2.5->1->.5->.250 (twice the rendering time, no visible difference in the render) -> .5.
The 16 bit maps are somewhat muddy and soft, but the addition of the bump maps make them a little crisper. Not ideal, but it appears this is the best we’re going to get until MD3 is released.
The same basic workflow seems to be working with multi-UV texturing. Basically save your model then do a UV smooth before you chop it up into subtools and you should be able to get your maps out individually.
Hope this helps someone who’s stuck in trial and error mode on deadline.
–T