Normal smoothing
From Blood Wiki
Normal smoothing is the form of automatic smoothing. It averages normals of coincident vertexes between brush faces (or model triangles) whose angle is greater than 'break' angle.
Normal smoothing can be set explicitly on entity with "_np" "degrees" key or on all entities by -np degrees compiler key (BSP phase only). A valid break angle is from 1 to 179 degrees.
Since normal smoothing affects vertex data, it works both for LIGHT phase and realtime lighting.
Important: Normal smoothing only works with metasurface pipeline. So BSP -meta key is required.
Bug: Normal smoothing may break parallax mapping since it uses vertex normals for displacement.