# `Storehouse.Renderer`
[🔗](https://github.com/hattoriai/storehouse/blob/v0.2.0/lib/storehouse/renderer.ex#L1)

What makes a file's variants (`Storehouse.Variants`), or the URLs of
the service that makes them. A renderer does one or both:

  * `c:render/4` - renders a variant in the app, from the original on
    the disk, to a file: `Storehouse.Variants` downloads the original,
    stores the result under the original's key, once however many ask
    for it, and `Storehouse.Variants.Plug` serves it.
    `Storehouse.Renderer.Vix` (libvips) is one.
  * `c:url/3` - the URL of a variant another service renders (imgproxy,
    thumbor, Cloudflare Images), behind a CDN: the app renders nothing.
    `Storehouse.Renderer.Imgproxy` is one.

A renderer with `c:url/3` gives every variant's URL; one with only
`c:render/4` has `Storehouse.Variants.Plug`'s. Either way, only the
presets' sizes are ever asked for.

Configured as a module, or `{module, options}`; the options are given to
each callback:

    config :storehouse, Storehouse.Variants,
      renderer: {Storehouse.Renderer.Imgproxy, url: "https://images.example.com", ...}

A renderer of the app's own (another service's URLs, URLs of its own
shape) implements either callback.

# `render`
*optional* 

```elixir
@callback render(
  source :: Path.t(),
  destination :: Path.t(),
  Storehouse.Variant.t(),
  opts :: keyword()
) ::
  :ok | {:error, term()}
```

Renders `variant` from the original at `source` to `destination`, a path
with the format's extension. Never larger than the original.

# `url`
*optional* 

```elixir
@callback url(Storehouse.Variant.t(), Storehouse.File.t(), opts :: keyword()) ::
  String.t()
```

The URL of `variant`. Its `:format` is a list when the format is to be
chosen from the browser's `Accept`, by the service.

---

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