Radiosity, HemiCube, radiative energy transfer.

[AcidFaucent]

@ed022

Have you considered the technique involving two parabolic surfaces? I’m not sure what it’s name is

Dual-parabaloid. http://cdn.imgtec.com/sdk-documentation/Dual+Paraboloid+Environment+Mapping.Whitepaper.pdf

It works, just have to watch out with poorly tessellated geometry.