8 bits per mask, more than one mask, packed into a 32-bit value. 1st one is typically a brush-in one - basically just Alpha brushed in from various alpha-brush

8 bits per mask, more than one mask, packed into a 32-bit value. 1st one is typically a brush-in one - basically just Alpha brushed in from various alpha-brushes over the map 2nd can be a noise function, where the 1st alpha mask is multiplied by the second to get a brushed noise, and the noise might be useful for randomly-shaped patches of different-colored grass in a scene 3rd might be a shadow mask, where any objects "stamped" on top apply a default shadow at a given angle, and that default shadow is written into this channel. Then the map-maker can alter those if (for example) a shadow hits a wall. Then there's the shader mask - so you can select a given shader for a given area of the map. These'll all be batched up later, but if you want flowing water, brush in where you want the water shader to be applied. Same for smoke, lava, etc. etc.