By taking a quick look at prefilter.c , it has a function to convert the normal vector to angular map space (and vice versa), I don’t think that it’s hard to get it to work in cube map space instead. I might actually give it a try converting it to python to get the process to running in real-time and with cube maps.
ucupumar, I guess lack of research, prefilter was not made by me, I just used it for testing the shader.
Jackii, if you manage to make it work with default cubemaps, please I would like to know.
It would be interesting to know how hypersomniac is doing it for his viewport shader and if he is using 3rd order spherical harmonics (9 coeffs)