Smoothing Groups and Normal Map Seams

Erock · Aug 2012

I am still trying to learn the ropes of creating good assets that will work properly with game engines and noticed that a lot of artist use smoothing groups when modeling low polygon models to save polygons when making rounded surfaces. I was wondering if I should start using smoothing groups when modeling my low polygon in-game models for some of the surfaces and if smoothing groups will effect any normal map baking. With the power of current hardware, are smoothing groups really that relevant anymore? Could someone possibly provide some real-world examples of when I might want to use a smoothing group over just adding more polygons to create a curved surface? I am basically just having a hard time understanding, from an artist stand point, when and where I should use smoothing groups when I create my in-game models.

Also I had one quick question in regards to UV mapping a low polygon model that I am baking normals to. From my understanding, after I unwrap my model, I should not rotate or flip the UV maps, only scale and move them, to help minimize the seams. Is this correct?

Thanks,

Eric

Kurt Russell Fan Club · Aug 2012

Yes, smoothing groups will affect your normal map baking. Smoothing (or hard/soft edges) is just a way of controlling vertex normals and normal maps are defined as deviation from the vertex normal. So you change the vertex normal and the normal map has to change to accommodate.

A real-world example where you want a smoothing group or hard edge is a 90 degree corner.

You can rotate and flip UV maps. Some engines don't like it, but they're rare as hens teeth. You want to be able to flip UVs to mirror half your model where appropriate. Talk to your programmers if you're worried.

Erock · Aug 2012

Thanks for the insight, I think once I finish the model I am working on I will do some tests and see how everything turns out just to get the feel for it. I think I have a pretty good understanding of everything involved with the process at this point so hopefully my first in-game model will turn out well

I am use to doing just CG stuff, so moving from that to real-time graphics has been a bit of a process to say the least, but I think I finally have a pretty good grasp on things now, though I am sure I will run into some little quirks along the way.

Smoothing Groups and Normal Map Seams

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