Prepare UVs For Mari?

[Guest tar]

FYI this is what a Ptex atlas looks like:

http://3dcoat.com/forum/index.php?/topic/4834-ptex-format-for-3dcoat/&page=2

 

[Atom]

Thanks for the PTex reference image. I can see the similarities but it looks like Ptex areas are all rectangular.

 

Here is the result of 3 channels exported from Mari and supplied to Mantra for rendering. These channels are diffuse, specular and bump. I ended up with 18 maps on output because you get a single image for each UDIM square.

[Guest tar]

Great work! 

Ptex is created so you can paint without doing any UV laying out, the caveat being you can't edit the tile effectively - the major downside to Ptex is that pipelines of software may not fully support it.  There was some commotion about memory usage a few years ago, but upon closer inspection it was Arnold propaganda against Renderman renderers. 

[Jero3d]

In my experience I found it was usually better to go for more uv islands and less stretching, rather than having very big areas unwrapped together that would end up with some stretching. Also since I painted in Mari, the placement is almost irrelevant, very rarely do I go into the UVs to project. Here is a turntable of a helicopter I painted in Mari, and I will explain my workflow of how I organized my UV layout and what I spent time manually unwrapping and what I did automatically.

 

The UVs are spread over around 6 tiles if I remember correctly (don't have access to the file right now), and the way I approached unwrapping was the following: Any big important pieces, I would manually unwrap. So the body of the helicopter is carefully unwrapped with the seams placed in places where they wouldn't be so visible. The reason why you need to have a balance between hundreds of UV patches vs 1 UV patch is because there's a lot of procedural work in Mari. The helicopter has a tiled diffuse texture for example (the procedural textures in Mari are applied on the UV space, not object space, so you would have a very clear difference between every patch), and if it the UVs had seams all over the place, I would have to manually paint over them, which really kills the procedural nature of the process. I only had very few seams in this case, and it would only take 5 minutes to just project my texture over the seam and make it look seamless.

Now for all the small objects, I just did automatic projections in Maya (which would be the same as you are doing in Houdini), not even caring about where the seams were. The reason for this is that it's very hard to spot the seams on those objects, and if any extra work is required you can again paint it out manually.

Finally for laying out the UVs, I organize my UV tiles based on material. I plan ahead roughly how many materials I will use, and I organize my layout that way. For example, I put all the objects that would have green paint in the same tiles. I also have a tile for glass, one for rubber, another one for chrome and so on. In Mari it's then very easy to select that UV tile and give it a procedural texture. I also use automatic layout for each of these objects, so they are spread across the UV tile in a way that wouldn't make sense if you had to paint in Photoshop.

I think you can barely see any seams in this way, despite all being arranged in a random way. Every rivet and bolt that make every panel was manually painted using projections, and they are spread out along different UV patches and also different tiles, but you can't tell the difference. They aren't arranged in any logical way, but it doesn't matter since you paint in the viewport in Mari. It took about 2-3 weeks to texture the helicopter. This is my workflow though, doesn't mean it's the right way, I'm sure there's a huge room for improvement, but I thought it would be useful to share how you can work in Mari.

 

Edit: I will try to upload a picture of the UV's tonight

Edited June 8, 2016 by Jero3d