Making UVs for complex objects - general rules/advice on the size of UV islands

dzibarik · May 2014

I'm almost done with making low poly of my car and now I'm thinking about unwrapping the whole thing. Even though it's the most complex model I've done unwrapping it has been quite easy so far. But I'm worried about packing UVs and saving precious space.

So how would you approach this? Are there any tricks to save space? Should I make parts which I want to have more details bigger than others? I've heard about making symmetrical UVS and laying islands on top of each other (if I understood this right) but will it work with baking normal maps?

LMP · May 2014

Generally it's a good idea to keep texel density fairly even.

WarrenM · May 2014

One thing that helps is to know how the asset will be used. If it's, say, a vending machine that will always be used up against a wall you can devote less uv space to the polygons on the back since they won't be seen by people playing the game.

stevston89 · May 2014

Basically things that are smaller, not seen often, or lack detail get less space. Things that need more detail, are always seen, and are larger get more space. It really depends on the model, it's usage, and the type of game. Also watch out using symmetry across large clean areas you can get seam issues doing that.

dzibarik · May 2014

Ok, here it is. It's not a final UV unwrap, I made it just to test if it is suitable for texturing at 2048 res (it's not).

I made it as a model for a non-existing vehicle-focused open world next-gen game (like Mad Max), so 50K tris is ok (I guess, but intend to bring it down to 40 anyway) but the main issue is that there is too much objects to cram into one UV space. And since the model is symmetrical most of them repeat themselves.

So what could be done? Can I place repeating UV islands on top of each other? Can I break a model into separate meshes and then join them into one prefab in an engine? How people usually deal with this stuff?

ZacD · May 2014

Woah, lot of UV islands.

1. Delete any faces that cannot or will not be seen, but be careful, it might cause some lighting issues depending on your target engine.

2. Mirror and stack UV's. If the geometry is exactly the same, it's safe to have them use the same uv space. But you will want to offset them by 1 when baking.

3. Separate some things out to separate textures, if parts of the model are going to be used elsewhere it can be good to have those parts on a separate texture.

4. Scale down uv islands that are barely going to be seen in game, but need to be there. Wheel wells, under the car, inside roof, etc.

Eric Chadwick · May 2014

Definitely reuse/overlap pieces. You can re-use a ton with this model. How much reuse depends on how dirty/marked-up the texture will be. Dirt or rust patterns can make repeats much more obvious.

Each pontoon could re-use the same texture space. Left and right sides of the car body could use the same texture.

If there's a logo or text on the sides, then either don't mirror those UVs, or do the text as decals.

We have some resources here about UVs.
http://wiki.polycount.com/TextureCoordinates

Making UVs for complex objects - general rules/advice on the size of UV islands

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