This Lightmap doubt doesn't let me sleep at night...

kapgowild

Hey guys, I'm kinda new to 3D, been studying for a couple of months, and I'm starting in UE4 now, and lately I heard about light maps, and that's totally new to me. The main points that I've captured about it after watching a few videos were: can't have UVs outside the 0-1 space, the UVs should be separed were there are hard edges, and also that it should have proper spacing between the UV shells, and that's the part were I'm having trouble to understand. Let's say I have an object with UVs that are already filling almost the entire 0-1 space, like this:

If I create a second UV channel for my light map, and cut the UVs in the hard edges, if becomes like this:

So when I cut the hard edges for my light map, there are not enough space between the shells, considering that light maps are really small compared to texture maps, is this kind of spacing gonna be a problem? If so, what can I do to work around this problem? Thanks in advance

monster

kapgowild said:

is this kind of spacing gonna be a problem?

Just do a light bake and see if it looks good.

You might be overthinking this though. If no UVs are overlapping or mirrored in your first UV channel just duplicate that. If you have UVs that are overlapping or mirrored, duplicate, then repack so they don't. Only cut the hard edges where it looks wrong.

sprunghunt

Don't just cut your UVs on the hard edges. For lightmaps this is not necessary. Create your lightmap UVs to have the least amount of cuts possible. Even if you have to distort your UVs. 

Have a look at this document from epic:
https://docs.unrealengine.com/en-US/Engine/Content/Types/StaticMeshes/LightmapUnwrapping/index.html

There's lots of examples in it that will help you understand

Kanni3d

Just check for overlaps/inverted faces, nothing out of 0-1 space, and try to keep faces as contiguous as possible (no need for split @ hard edges as sprunghunt mentioned). This will make it easier to unwrap, pack, and have much less seams in your light bakes as well on larger faces that are now welded together.