Using multiple uvw's...

Jimmy

Long time reader, first time poster... So here is my question:
Does multiple uvw's (for diffuse, normal, etc) have any noticeable impact on performance? I guess it depends on the engine, but I would like to hear your experience about this and if there even is a common opinion that you should avoid it for some reasons?
In my case I think I could get away with a pretty small tiled diffuse texture, by using a different uvw for a normal map, which probably also will be smaller than if they were using the same uvw's.

MoP

Depends on what game engine you're using, I guess.
Extra UV sets mean extra data for every single vertex of your model - that can really add up in the end, and is probably something you want to avoid unless absolutely necessary.

The Doom3 engine has a material system which allows the user to specify the tiling amount (on the same UVWs) of different map types - so you could have a single unique local normal map, then tell the material to tile the diffuse and specular maps, say, 4 times. Requires a little more forethought with the UVs if you want to hide seams on both the regular and tiled versions, but maybe it's something worth considering if at all possible.

Eric Chadwick

Like MoP says, increases your vertex count. But it only matters if you're transform-bound, and only way to know that is by profiling your assets in-game.

NVIDIA's PerfHUD is one example of a profiler. Most game engines incorporate their own though.

Jimmy

This time my model is only for my portfolio, so I doesn't really matter what I do, but I went with the same uv for diffuse and normal anyway... But it was interesting to hear this and I would say that article on your web page Eric, was really interesting. That is just the kind of things I would like to read to get a better understanding how the "whole thing" works, and what I could do with my models for better in game performance.