LightMaskFillLightOptions
The light a light mask’s texture lays on the land it lights, from its green, blue and alpha as linear RGB, 0 to 1 each. It lights as the sky’s fill does, from every side, so a character, a trunk and the ground in the pool all take it with their own colours. Pools join by adding, so write them with an additive blend, where red joins by its larger value.