Finds and reads the evdev input devices a panel comes with, and finds them again when they go away.

A keyboard on a Nerves device is /dev/input/eventN for some N that changes with what else is plugged in, may not exist at boot, and goes away when unplugged; a touch panel is another such device. This module owns both: which device to read, starting an input_event reader on it with the device grabbed (so keystrokes do not also reach the kernel console), translating what it delivers into ExRatatui.Event structs (RasterExRatatui.Input.Evdev for keys, RasterExRatatui.Input.Touch for fingers), and looking again, every retry_ms:, whenever there is nothing to read. It has no process of its own: the caller keeps the struct, hands it every message it receives, and gets events back, from a surface's RasterExRatatui.Surface.handle_info/2 or from any process that traps exits.

defmodule Kiosk.Surface do
  use RasterExRatatui.Surface, app: Kiosk.Dashboard, format: RasterExRatatui.PixelFormat.RGB565

  alias RasterExRatatui.Input.Devices

  @impl true
  def init(_opts) do
    {:ok, devices} = Devices.start(Devices.new(keyboard: true))
    {:ok, [size: {480, 320}], devices}
  end

  @impl true
  def push(patches, devices), do: write(patches) && devices

  @impl true
  def handle_info(msg, devices) do
    case Devices.handle_info(msg, devices) do
      {:events, keys, devices} -> {:events, keys, devices}
      {:noreply, devices} -> {:noreply, devices}
      :unknown -> {:noreply, devices}
    end
  end

  @impl true
  def terminate(_reason, devices), do: Devices.stop(devices)
end

input_event is the consumer's dependency

The reader is input_event, a C port that only builds on Linux, so this library does not depend on it: the consumer adds {:input_event, "~> 1.4"} to its own deps. start/1 checks that the module is there and returns {:error, :input_event_missing} otherwise, so a host build without it still runs, without input. input: swaps the module for a stub in tests.

Options

new/1 takes:

• :keyboard — true (default) to read the first device that reports letter keys, a "/dev/input/eventN" path to read that one, or false
• :touch — true to read the first touch panel found (touch_path/1), a path, or false (default). Its taps and drags come back as ExRatatui.Event.Mouse events on the cell under the finger, which takes the two options below
• :size — the physical panel in pixels, for the touch axes (required with :touch)

• :cell_at — ({px, py} -> {col, row} | :outside), normally RasterExRatatui.Raster.cell_at/2 of the raster the panel shows (required with :touch)

• :swap_xy, :invert_x, :invert_y — for a touch controller that does not follow the panel's orientation, see RasterExRatatui.Input.Touch
• :retry_ms — how long to wait before looking for a missing device again (default 2_000)
• :input — the module standing in for InputEvent (default InputEvent)
• :layout, :emit_release — passed to RasterExRatatui.Input.Evdev.new/1

Messages

start/1 sends the calling process a first {RasterExRatatui.Input.Devices, :scan}; handle_info/2 handles it and every later one, the {:input_event, path, events} and {:input_event, path, :disconnect} messages of the readers it started, and their {:EXIT, pid, reason} (a reader stops when its device goes away, and the search starts over). Everything else is :unknown, including the :normal exits of the short-lived readers that InputEvent.enumerate/0 starts from the caller while scanning.