Fill Light-map UVs with geometry VS maintaining correct aspect ratios?

[scha (scha (inu games))]

@darthviper107

Yeah, that lightmap atlas will be the sized by the texture rather than the UV’s of the mesh that uses them.

@IronicParadox

Yes, they atlas into a larger texture, but as far as I know, it still takes the 0->1 UV spaces from individual meshes and just lays them out in a grid next to each other to form the atlas. The sizes of the “cells” are based on LM resolution. So a 256^2 tile would be the size of 4 128^2 tiles put into a square. I don’t think it actually arranges and optimizes a “master” uv atlas where it accounts for everything in the scene and optimizes it all at once. So if you had a mesh, where half the UV space was empty, it would still appear on the lightmap atlas; within it’s little cell of the atlas.

Is there a reason why UE doesn’t optimize lightmaps more? For example, I have a simple and very long piece of geometry and splitting it multiple parts to fill the uv space greatly increases poly count. Also, results in lightning artifacts on seams.

For example, if only the left half of the uv space is occupied, couldn’t lightmass treat it like 2 squares of 1/2 resolution? Or it wouldn’t work because mipmapping or something like that?