Lightmap affected by 3rd UV Channel.

As the title states.
I’ve got a mesh with 3 UV sets.

Set 1 is the material Set, Set 2 is a custom lightmap, and the 3rd for placing cards mapped to a normal map decal sheet.
The problem I’m having is when baking lighting, the lightmaps can be spot on, but as soon as i implement the 3rd UV set, it takes over.
For instance, if the 3rd UV set has overlapping uvs the lightbake will have overlapping light values, but if the 3rd uv is authored like a lightmap all is fine.

In the static mesh options, Generate lightmap UVs is turned off and the Source and destination indexes are set to 1,1.

Is there something i’m overlooking here, or is kind of by design / limitation?
I can work around this issue by swapping the purpose of my UV sets.


Probably you are overlooking lightmap coordinate index setting in static mesh options. If I am not mistaken, it is only visible when “show advanced” flag is enabled.

Thanks Deathrey, that was it!

Also, normals are only correct for the first UV channel, make sure you use that one for your normal maps.

Is this only for baked maps, or all normals in general? If I want to overlay some normals, I have to do that using 1st UV channel?

It’s for normals in general, they are only calculated for the first UV channel, if you try it with the others it will not look right.

Yeah we are using the DeriveTangentBasis function to fix that issue.