OptionalheightsWorld rect the maps cover (min corner + span).
OptionalsplatSplat maps (A = layers 0-3, B = 4-7). Omit when not painting.
OptionalsplatOptionalholeHole mask. Omit when the terrain has none bound.
OptionalcolorPainted color/tint map. Omit when the terrain has none bound.
Optionallayer
Editable heights. Omit for a PAINT-ONLY session (region-streamed terrains sculpt through
TerrainRegionEditSessioninstead) — the height brushes then no-op.