Channels

FGroundClass per cell: batter row, physical material, cost; kHoleClass = hole.

Legacy paint (save versions 1-4): material layers per cell, two 4-bit indices, layer A in the low nibble, layer B in the high nibble (16 layers).

A value 0..15 is layer A alone (B = 0, weight 0), which is what the paint brush writes. Pairs with PaintWeight; the renderer packs both into the layer texture. Superseded by the slot planes below (ids 16-30); from save version 5 only the v4 loader reads ids 1 and 2 (PaintFromV4).

Legacy paint: weight of PaintLayer's layer B over layer A per cell, 0..255; 0 shows A alone.

Paint as slot planes (save version 5): a post holds up to kMaxPaintSlots (layer, weight) pairs, one u8 plane per field.

Layer planes are ids 16-23 (slot 0-7), weight planes ids 24-30 (slot 1-7); slot 0's weight is 255 minus the others and has no plane. Id 31 stays reserved. Ids 3-15 and 32-127 stay the terrain's, 128-255 the buyer's. Layer plane of slot 0; slot s is PaintSlotLayerFirst + s.

Weight plane of slot 1; slot s is PaintSlotWeightFirst + s - 1.

Last id of the paint planes (weight of slot 7).