# `Cauldron2D.Projection.Volume.Native`
[🔗](https://github.com/jaman/cauldron/blob/v0.2.2/cauldron_2d/lib/cauldron_2d/projection/volume/native.ex#L1)

The per-pixel half of `Cauldron2D.Projection.Volume`, in C.

`tint/6` takes a rectangle of pixels, the rays that look through it and one volume,
and gives the rectangle back with the volume's colour blended in. It understands the
shapes of `Cauldron2D.Projection.Volume.Shapes` and nothing else; a volume with a
shape module of its own is drawn in Elixir.

`available?/0` says whether the library built and loaded. Where it did not, `Volume`
draws every volume in Elixir and answers the same picture some fifteen times slower.

# `available?`

```elixir
@spec available?() :: boolean()
```

Whether the library is loaded and volumes are drawn in C.

# `tint`

```elixir
@spec tint(binary(), pos_integer(), pos_integer(), tuple(), binary(), tuple()) ::
  binary()
```

`pixels`, a `width` by `height` rectangle of RGBA, with `volume` blended in.

`plan` is `{origin, origin_x, origin_y, direction, direction_x, direction_y}`, each a
triple, giving the ray through the rectangle's pixel `{column, row}` as
`origin + column * origin_x + row * origin_y` looking along
`direction + column * direction_x + row * direction_y`.

`limits` is one native float per pixel, how far that pixel can see before something
opaque stops it, or an empty binary for no limit.

`volume` is `{kind, falloff, {x, y}, {red, green, blue}, {strength, density,
thickness}, params, cells}`, where `params` is the shape's numbers as native doubles
and `cells` is `nil` or `{x, y, width, height, bits}`, one byte per tile.

---

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