Tri's Verts and UV's

Mrguy

Hi everyone. At one point I was under the impression that tri's mattered so it was best to watch your tri count. Now we've been working in a game for Unity for a few momnths now and it's come to our attention that Verts are the counter you really want to look out for. NOW, just recently we did some number crunching to find out how expensive our verts are with memory and found that the actual number you should look at is UV's. Mathematically it seems correct to propose limits via the UV's but this is the first time I've heard and even considered using them as a limiter.

Are verts more common place because they are easier to control during the modeling process? Are tri's used as terminology because most games aren't working in such extreme (mobile) constants? Are lower vert counts imposed by engineers with the thought that the actual UV number is going to increase?

Thank you!

Farfarer

The vertex count you see in your 3D app doesn't reflect the true count of vertices as the game engine sees them. It doesn't count all the vertex splits due to UV, normal or colour differences (or any other per-vertex attribute that can have different values for each polygon the vertex belongs to).

So generally triangle count in that respect is a decent yard stick for the "cost" of the mesh in the game. It's also the thing that won't change between your 3D app and your engine. So it's the best constant you'll find to measure things by. And generally you should find that, by and large, the true cost of the mesh will (on average) scale as a multiple of the triangle count assuming things are generally UVed and shaded to the same standard.

You can think of the vertex count (the real one, with all the splits) as the storage (and data transfer) and transform cost of the mesh. It's mesh complexity cost.

Triangles are a good measure of the rendering cost of the mesh (although there are a lot more factors that can affect that, like distance to camera/on screen triangle size, clipping, fragment quad overlap, etc). That's before you factor in shader costs, too.

So yeah, it's a rough guide that generally works.

Mrguy

Hum. Thanks for the answer. I think I just never considered anything but tri's because I was coming more from an artistic background. Now that I'm deeper into the technical processes I'm starting to uncover (what you said) data costs and rendering costs. Thanks again for the insight.

Eric Chadwick

The info on this page might help too
http://wiki.polycount.com/wiki/Polygon_Count

Mrguy

Thanks Eric for that extra bit of info!