Lightgrid

A three-dimensional data structure used to store static lighting on models. Lightgrid are created during LIGHT phase each time map is compiled.

How it works
Each cell of lightgrid stores this information:
 * Ambient RGB
 * Average light vector (used for diffuse lighting)
 * Diffuse RGB

When rendered, entity sample it's position at lightgrid and get average ambient and diffuse components to be applied during shading. Any entity that doesnt use lightmaps and not fullbright, is, by default, lit with lightgrid.

Resolution
Lightgrid resolution on a particular map comes from it's bounds and cell size.

Default lightgrid cell size in game units is '64 64 128'. It can be customized with "gridsize" worldspawn key. Most of Blood Omnicide maps using lightgrid size '32 32 32' or '32 32 64'.

Often map bounds is much bigger than the space players and NPC can walk in. To not waste memory and reduce map compile time, level designer should place a brush covered by common/lightgrid material. That brush will set the area where lightgrid will be calculated and applied.

Corrections
Sometimes lightgrid is lighter or darker that the rest of environments which makes entities to look out of the place.

In order to make lightgrid match environments, a corrections should be made in a map build script. There is two coefficients to mess with:
 * diffuse scale: scales intensity of diffise lightgrid component
 * ambient scale: scales ambient RGB component