# `Cauldron3D.Paint`
[🔗](https://github.com/jaman/cauldron/blob/v0.2.2/cauldron_3d/lib/cauldron_3d/paint.ex#L1)

How a polygon's pixels get their colours.

  * `{:flat, colour}` — one colour
  * `{:texture, texture, light}` — a `Cauldron3D.Texture` repeated across the polygon
    by its `uvs`, through the light table at `light` (0 to 255, 128 the texture's own
    colours), or as it is when `light` is `nil`
  * `{:shaded, texture}` — as `:texture`, the light carried across from the
    polygon's `lights`
  * `{:surface, texture}` — a texture already lit, its edge pixels repeated beyond it
  * `{:warp, texture, opts}` — a texture rippling as liquid does: each place on it
    moved by `:amplitude` pixels (default 8.0) along a sine of the other axis, of
    `:wavelength` pixels (default 128.0), moving with `:time` seconds at `:speed`
    (default 1.0) turns a second; `:light` as `:texture`'s, default `nil`
  * `{:sky, layers, opts}` — a sky at no distance: `layers` is a list of
    `{texture, speed}`, nearest first, each drawn where the one before is colour
    `:clear` (default 0) and moving `speed` pixels a second with `:time`; `:scale`
    (default 378.0) is how far across the sky a view straight ahead reaches, and
    `:flatten` (default 3.0) squashes it toward the horizon
  * `{:fun, fun}` — `fun.(first, stop, y, setup, context)` returns the `stop - first`
    colours of the run itself

The context is a map: `:light_table` (rows of 256 colours, brightest first),
`:light_rows` (how many rows it has), `:background` (the colour behind every polygon),
and `:view`, which `{:sky, ...}` reads. Light value `v` uses row
`(255 - v) * light_rows / 256`, held inside the table.

# `context`

```elixir
@type context() :: %{optional(atom()) => term()}
```

# `light_row`

```elixir
@spec light_row(number(), context()) :: non_neg_integer()
```

The light table row for light value `light` (0 to 255, brighter higher).

# `span`

```elixir
@spec span(term(), Cauldron3D.Setup.t(), integer(), integer(), integer(), context()) ::
  binary()
```

The colours of pixels `first` up to `stop` of row `y`, as a binary: a byte a pixel, or
in a full-colour picture (a context with `:rgba`) four, as `Cauldron3D.Paint.Rgba`
paints them.

---

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