# `CauldronGPU.ColumnLayer`
[🔗](https://github.com/jaman/cauldron/blob/v0.3.3/cauldron_gpu/lib/cauldron_gpu/column_layer.ex#L1)

A texture redrawn column by column into a target, one layer of a `{:layers, [layer]}`
change: a warp given as a table.

  * `target` — `:frame` (the default) or a canvas handle
  * `clear` — `{r, g, b, a}` from 0 to 1 the target is filled with first, or `nil`
  * `port` — `{x, y, width, height}` in the target's pixels, the part redrawn; `nil`
    is the whole target
  * `source` — the handle of the texture or canvas read
  * `columns` — one `{u, v_scale, shade}` per column of the port, left to right

Each column of the port reads the source at the horizontal position `u` (0 its left
edge, 1 its right). A pixel `down` of the way from the port's top (0 to 1) reads the
vertical position `0.5 + (down − 0.5) × v_scale`. The source is sampled between its
four nearest pixels, edges repeated, and its colour multiplied by `shade`. A position
outside 0 to 1 draws opaque black. When the port has more pixels across than there are
columns, the columns are stretched to fill it.

# `t`

```elixir
@type t() :: %CauldronGPU.ColumnLayer{
  clear: {number(), number(), number(), number()} | nil,
  columns: [{number(), number(), number()}],
  port: {number(), number(), number(), number()} | nil,
  source: CauldronGPU.Handle.t(),
  target: :frame | CauldronGPU.Handle.t()
}
```

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