Did a rough version of the lightmapper in Lua, only collision is handled in C by ODE. Api of unity and luxinia shouldnt be too different, so in theory you should be able to follow this. The "interpolator" code is a bit rough, as I made it generic (any vectors of any length can be passed). So if you need help about it, ask,…
keen, I might be able to help you on the texel to worldpos thing. And write a little uv rasterizer that you can make use of. edit: working on a luxinia tutorial for this task. lua and javascript are similar, so you shall be able to adjust the important bits for your tool.