A world cut into convex leaves by a binary space partition, with its faces, textures, lightmaps, what each leaf can see, and its brush models.

A loader fills the struct from its own file format; the engine draws it (Cauldron3D.Bsp.Draw), lights its faces (Cauldron3D.Bsp.Surfaces) and moves things through it (Cauldron3D.Hull).

• planes — a tuple of {normal, distance}; a point p is in front when Vec.dot(p, normal) - distance >= 0
• nodes — a tuple of %{plane: index, front: child, back: child, mins: Vec, maxs: Vec}; a child at or above zero is a node, below zero the leaf -child - 1
• leaves — a tuple of %{contents: integer, faces: [face index], mins: Vec, maxs: Vec}
• faces — a tuple of Cauldron3D.Bsp.Face
• textures — a tuple of %{name: String.t(), kind: kind, mips: [Texture.t()]}, the mips halving in size, kind one of :solid, :masked (solid but see-through where it is colour 255), :sky, :liquid or :hidden
• lightmaps — the lightmap bytes faces point into
• light_channels — bytes per lightmap sample: 1 for a grey level, 3 for red, green and blue
• world_leaves — how many leaves after leaf 0 belong to the world itself (model 0); the leaves after them belong to the brush models. nil when every leaf is the world's
• game — the game the map was made for, :quake or :half_life
• visibility — a tuple holding for each leaf a bitset of the leaves it can see (bit i of byte div(i, 8), least significant first), or nil where it can see every world leaf; nil for a world that keeps none. A brush model's leaves are never among those seen
• models — a tuple of %{mins:, maxs:, origin:, heads: [node per hull], first_face:, face_count:}; model 0 is the world itself
• hulls — the collision hulls, as Cauldron3D.Hulls with the head of model 0

Contents follow one convention: -1 empty, -2 solid, -3 water, -4 slime, -5 lava, -6 sky.