[3DS Max] Unwrapping of ring piecies.

Immorthar

Hi, Polycount! I'm in confusion and need u'r help. Right now i'm making model of scope and it has many cylindrical parts, and as result many ring piecies when i unwrapping it, here is screenshot of fast uv packing and model itself:

I want to know what to do with ring piecies when i unwrapping such models. Should i divide this rings by two or more halfrings or anything else? Thanks for any response.

zachagreg

In my experience ring pieces like those should be unwrapped into straight islands. Under most cases this will give a better bake on the edges and won't result in artifacts that put bumps and waves on the surfaces of your mesh. Also it will drastically cut down on deadspace in your UV layout allowing you to get a higher texel density for the rest of the mesh.

Tim explains it eloquently in here.

https://www.youtube.com/watch?v=BbZ7ip-eCcI

poopipe

^^That's great until you Lod, at which point you're shafted.

Personally I'd be applying a planar map along the axis of the scope to the various ring faces - obviously overlaps need to be handled but they'll pack inside each other and when you're removing detail for lower LODs it's won't look shit and will be much cheaper

zachagreg

What happens when you Lod? I imagine mipping down destroys the bevel data in your normals, but why does that happen?

poopipe

Unwrapping straight will give you higher quality and survive mipping/filtering better as long as there is geometry to support it. If your concern is purely how good it looks up close and there's no LODs then that's the best way to go. 

If you need to Lod  then your priority should be making your lod transitions as close to imperceptible as possible and the best way to do that is to make sure that you can rip out geometry without smashing up uvs. 
If you do this right you can lod earlier and thus get more stuff on screen without screwing performance. 

In this case.. 
If you've unwrapped all the rings to independent straight shells you have to keep the edges that define the edges of the shells in your lod.

If you map the end of the scope as a planar projection and keep the shells together, you can remove any thing you like as long as it's withing the bounds of the outermost shell.

It's really hard to explain without pictures but basically if you  build the lowest lod and unwrap it  you'll get the basis for UVs that Lod well. 

zachagreg

Ahh okay so it's not so much that the mip messes it up rather that the actual removal of geo at those locations will cause strange distortions due to those straightened rings just being gone. Which would probably result in large seams going across the mesh due to the absence of geo at that spot.

Do I have that right?

I haven't dealt a whole lot with manual LODs recently so the info helps a ton. I assume this can also help OP because intent of the model does matter.

poopipe

That's pretty much it.  

It's not just something to consider for manual Lodding though. Simplygon etc will do a much better job if UVs are laid out in a lod sympathetic fashion as it still has to deal with the same limitations.