I wanted to have a portable lightmapper that is part of the map editor that will be shared with the community. Thus I chose to build CPU powered lightmapper. And to my amazement, it is really fast as OpenImageDenoise works like magic and the noisy path tracer result gets smoothed out. The lightmapper is based on design described by the creator of Bakery-addon for Unity (Link here). The only downside is that the OpenImageDenoise is huge. The .dll takes around 45 megabytes. Anyway, I think it is worth having as the visuals of the game rely heavily on the lightmapper quality. Here is a image of preliminary result. I will upload some video later on when the editor gets more polished.