Hard surface uv unwrap question

electricsauce

I know that you have to create a uv seam on sharp edges so that the normal maps can be applied properly. I was wondering at what angle do these edges start to become a problem?

Also, I sometimes use an automated unwrap (in Blender) based on an edge angle. This can result in uv maps with maybe a hundred small islands depending on the model. Besides the texturing having to be done in 3d space, what are some of the downsides to this method?

Mark Dygert

In general its good to place UV seams and smoothing breaks in the same place, but you shouldn't have to do that to get things to bake right. The normal map overrides whatever the low poly normals actually are.

So something is broken in the process if you have to break smoothing at UV seams to get the normal map to bake right.

cryrid

electricsauce wrote: »

This can result in uv maps with maybe a hundred small islands depending on the model. Besides the texturing having to be done in 3d space, what are some of the downsides to this method?

A potentially increased vertex count might be one.

EarthQuake

Mark Dygert wrote: »

In general its good to place UV seams and smoothing breaks in the same place, but you shouldn't have to do that to get things to bake right. The normal map overrides whatever the low poly normals actually are.

So something is broken in the process if you have to break smoothing at UV seams to get the normal map to bake right.

Just to clarify, you do not need to have hard edges everywhere you have uv splits, but you *do* need to have uv splits everywhere you have hard edges, otherwise you will get seams/errors in the bake.

Though in general, if your uv layout has hundreds of little islands, this would seem to indicate that you have way, way too many hard edges, and perhaps some issues in your baking pipeline(ie, broken tangent space).

electricsauce

This is the model I'm working on at the moment:


It has lots of sharp edges that I'm assuming require a uv split so that the normal render correctly in game. At the moment Blender doesn't export binormals or tangents (it should be fixed shortly I think). Do they make a big difference with hard edges?