# `Cauldron2D.Net.Channel`
[🔗](https://github.com/jaman/cauldron/blob/v0.1.3/cauldron_2d_net/lib/cauldron_2d/net/channel.ex#L1)

The Phoenix channel a game's browser players join, one per player, driven by
`Cauldron2D.Net.Session`.

    defmodule MyGame.Web.WorldChannel do
      use Cauldron2D.Net.Channel, game: MyGame.Client, topic: "world", audio: %{rate: 22_050, channels: 2}
    end

`:game` implements `Cauldron2D.Client.Game`. The topic is `"world:<id>"` (`:topic`
names another prefix); `id` is the arena, as its id writes, among the game's
`arenas/1` given the socket's assigns. The socket's assigns must carry `:username`; `:settings` (a map with `:sfx`
and `:music`) and `:sheet_url` are read when present. The join params reach the game's
`join_props/1` as `:params`, and whatever it returns joins the world as props; a
join param `"audio"` of `%{"rate" => hertz, "channels" => 1 | 2}` (8 000 to 48 000
Hz) is the PCM format the browser wants, as `cauldron.js`'s `audio` option sends it;
without one the format is the `:audio` option of `use` (default 44 100 Hz stereo), and
`false` asks for no sound; what the session gets is `Cauldron2D.Net.Audio`'s to say.
A refusal is shown as the game's `refusal_text/1` gives it, `inspect/1` without one.

Frames from the world are pushed as `"map"` and `"frame"`, a changed atlas as a new
`"sheet"` and the `"map"` again, the audio as binary
`"pcm"` pushes (the session's own stage and the world's shared music mixed, as
`Cauldron2D.Net.Audio`'s policy has it); `"input"` (`held`, `aim` and an optional `strength`), `"levels"`,
`"music"` (`on`, the music switched off or back on at its level) and
`"pause"` (for a world of the player's own) from the browser reach the session. Leaving the channel leaves the world. Input
messages arrive many times a second and are not logged.

# `audio`

```elixir
@spec audio(map()) :: [{:audio, %{rate: pos_integer(), channels: 1 | 2} | :off}]
```

The `:audio` option for `Cauldron2D.Net.Session.join/5` from the join params: the format asked, `:off` for `"audio": false`, `[]` without a valid `"audio"`.

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