# `Cauldron3D.Bsp.Draw`
[🔗](https://github.com/jaman/cauldron/blob/v0.2.2/cauldron_3d/lib/cauldron_3d/bsp/draw.ex#L1)

The faces of a BSP world a view can see, as polygons for `Cauldron3D.Render`.

    polygons = Cauldron3D.Bsp.Draw.polygons(bsp, view, surfaces: cache, light: light)

The world's faces come from the leaves the camera's leaf can see, its brush models'
faces from where each model stands; faces turned away from the camera are left out.
Solid faces are painted with their lit surfaces (`Cauldron3D.Bsp.Surfaces`) at a mip
level chosen by distance, liquid faces ripple (`{:warp, ...}`), sky faces show the
texture's `:layers` (`{:sky, ...}`), and hidden faces are not drawn.

## Options

  * `:surfaces` — the surface cache (required where there are solid faces)
  * `:light` — the light map `Cauldron3D.Bsp.Surfaces` takes (required likewise)
  * `:models` — brush models to draw besides the world, each `{model, origin}`,
    `{model, origin, {pitch, yaw, roll}}` (degrees, turned as `Cauldron3D.Camera`
    turns, yaw about `z` first) or a map (see below)
  * `:time` — seconds, for liquid and sky movement, default 0.0
  * `:liquid` — options added to every `{:warp, ...}` paint, or a function of the
    liquid's texture giving them
  * `:sky` — options added to every `{:sky, ...}` paint
  * `:skybox` — six faces for `{:skybox, ...}` (see `Cauldron3D.Paint.Rgba`), drawn on
    sky faces instead of the texture's layers
  * `:mip_bias` — multiplies the distance a mip level is chosen at, default 1.0
  * `:world?` — whether to draw the world's own faces, default true
  * `:rtlights` — lights added over the solid and masked faces of the world and of
    unblended brush models (see `Cauldron3D.Paint.Rgba`'s `{:lit, ...}`), each face
    lit by those whose sphere reaches its plane and its box

A brush model given as a map has `:model` and `:origin`, and may have:

  * `:axes` — `{forward, left, up}`, where the model's own x, y and z axes point;
    default the world's
  * `:scale` — how many times its own size it is drawn, default 1.0
  * `:tint` — `{r, g, b, a}` its faces' colours and alpha are multiplied by
  * `:blend`, `:depth` — as `Cauldron3D.Polygon`'s, for every face
  * `:alpha_test` — given to its faces of kind `:masked`
  * `:light` — the light map its surfaces are made with instead of `:light`

# `model_faces`

```elixir
@spec model_faces(Cauldron3D.Bsp.t(), non_neg_integer()) :: [non_neg_integer()]
```

The face indices of brush model `model`.

# `polygons`

```elixir
@spec polygons(Cauldron3D.Bsp.t(), Cauldron3D.View.t(), keyword()) :: [
  Cauldron3D.Polygon.t()
]
```

The polygons of the world and its brush models that `view` can see.

# `world_faces`

```elixir
@spec world_faces(Cauldron3D.Bsp.t(), Cauldron3D.Vec.t()) :: [non_neg_integer()]
```

The world faces seen from `point`: those of every leaf its leaf can see, each once.

---

*Consult [api-reference.md](api-reference.md) for complete listing*