Using Nuaj and Cirrus to create test projects is alright, but came a time where I needed to start what I was put on this Earth to do : deferred HDR rendering. So naturally I started writing a deferred rendering pipeline which is quite advanced already. At some point, I needed a sky model so, naturally again, I turned to HDR rendering to visualize the result.
When you start talking HDR, you immediately imply tone mapping. I implemented a version of the "filmic curve" tone mapping discussed by John Hable from Naughty Dog (a more extensive and really interesting talk can be found here [1]) (warning, it's about 50Mb !).
But to properly test your tone mapping, you need a well balanced lighting for your test scene, that means no hyper dark patches in the middle of a hyper bright scene, as is usually the case when you implement directional lighting by the Sun and... no ambient !
That's when I decided to re-use my old "ambient SH" trick I did a few years ago. The idea was to pre-compute some SH for the environment at different places in the game map, and to evaluate the irradiance for each object depending on its position in the map.