what data do lightmass store exectly?

[nichaohao]

I’m reading the source file of lightmass, but not deep enough to make things clear.
I wanna know what data do lightmass store exactly, irradance ? HL2(half-life 2 basis)? Spherical Harmonics? Spherical Gaussian?
Thanks !

[Manoel.Neto]

You can get an idea by looking at the shader that reads the lightmap: https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Shaders/Private/LightmapCommon.ush

It looks like it uses two textures: one stores combined RGB color (in log-space) and the other stores a four (three?) coefficient SH for directionality (also in log space, it seems). A scale and bias value is applied to the entire lightmap (for each mesh?) to bring it back into HDR. Alpha channel stores log luminance.

[nichaohao]

@Manoel.Neto

You can get an idea by looking at the shader that reads the lightmap: https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Shaders/Private/LightmapCommon.ush

It looks like it uses two textures: one stores combined RGB color (in log-space) and the other stores a four (three?) coefficient SH for directionality (also in log space, it seems). A scale and bias value is applied to the entire lightmap (for each mesh?) to bring it back into HDR. Alpha channel stores log luminance.

Thanks buddy, very helpful.