Simplified lightmap UVs reduce the number of lightmap pixels required. Near mesh parts are merged into a single chart and share the same area of the lightmap. Enlighten can further reduce the number of lightmap pixels required by enabling different meshes to share the same lightmap, using mesh projection.

This technique can be used with any two meshes in close proximity. One of the meshes is designated as the target; for this mesh, simplified lightmap UVs are generated in the usual way. The lightmap UVs for the other mesh are determined by projecting its vertices onto the surface of the target mesh.

The target mesh is always included in the radiosity computation, while the projected mesh is excluded and has no effect on the indirect lighting result.

Mesh LOD

For a renderer that supports mesh LOD, each mesh may have one or more LODs, each containing fewer triangles than the last. Ideally, all LODs of the mesh should have the same indirect lighting.

When such a mesh is lit using lightmaps, there is no need to generate separate lightmaps for each LOD. Instead, all LODs can share the same lightmap space. One LOD is chosen to be the target mesh, and Enlighten generates lightmap UVs for the remaining LODs using mesh projection.

Nearby meshes

Using mesh projection, nearby meshes can share the lightmap of a larger lightmapped target mesh such as a wall or floor. For example:

debris or other small objects on a floor or a table

decals used to apply variation to surfaces
objects attached to walls or ceilings
grass and roads on terrain

This gives good lighting results for meshes within the distance of one lightmap pixel from the target mesh surface.

Simplified proxy meshes

For meshes with a complex topology, it's sometimes difficult to produce simplified lightmap UVs automatically or manually. For these meshes, the artist may find it easier to generate lightmap UVs using a simplified target mesh proxy.