Add live-reload to new_example

[axelson]

The heavy lifting is done by exsync which supports both Mac and Linux
https://github.com/falood/exsync

Architecture

When exsync detects a file system change it recompiles the changed filed into
the BEAM. After this recompilation sequence finishes, it calls the configured
callback function which is handled in the Nav component. The Nav component
then restarts scenic by killing it's root process.

If there was an easy/non-invasive way to get the current scene then we could
restart just that instead of the entire process tree.

Note: currently relies on an unreleased version of exsync.

[codecov]

Codecov Report

Merging #19 into master will not change coverage.
The diff coverage is n/a.

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  Coverage    96.5%   96.5%           
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  Files           4       4           
  Lines         143     143           
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  Hits          138     138           
  Misses          5       5

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[boydm]

This is going to take me a while to think through. Not sure I want to take a dependency on exsync. There are Erlang apis to do similar tasks and may go that direction instead.

No matter how it goes, love the research on this!

[boydm]

Currently thinking Live Reload type functionality should exist in an optional package. Still thinking about the overall approach.

[axelson]

Yeah, that's the direction I was leaning towards as well, although we may need some API changes in scenic itself to support it cleanly. I've been playing with a more general approach (although still dependent on exsync) that is suitable to an external library and I think that it would be helpful if Scenic supported a way to get the pids of the active top-level scenes.

Here is a code snippet that has been working well for me so far (but obviously depends on Scenic internals):

  def reload_scenes() do
    scene_pids()
    |> Enum.each(fn
      {:ok, pid} ->
        Process.exit(pid, :kill)

      _ ->
        nil
    end)
  end

  # WARNING: This uses a private Scenic API
  defp scene_pids() do
    scenes_table = Scenic.ViewPort.Tables.scenes_table()

    :ets.match_object(scenes_table, :"$1")
    |> Enum.map(fn {_ref, registration} -> scene_pid(registration) end)
  end

  defp scene_pid({scene_pid, _child_pid, _supervisor_pid}) do
    {:ok, scene_pid}
  end

  defp scene_pid(other), do: {:error, :not_found}

[boydm]

I'm willing to expose/change the necessary api for this. Hope to get a large enough block of time to work on it - prob tomorrow.

[axelson]

Sounds great! If you want to play with my scene reloading code above you can find it at axelson/scenic_asteroids@3481230

I'll clean it up before I merge it to master, but it has been working in the use-cases that I've tried so far. I investigated using set_root to get the root of the graph but it didn't end up fruitful.

[axelson]

@boydm I've cleaned up my generic scene reloader: axelson/scenic_asteroids#8

The main files of interest are:

• https://github.com/axelson/scenic_asteroids/blob/87d9beb2d577dc2b9193a9636daecc9fcb8891c3/scenic_live_reload/lib/scenic_live_reload.ex
• https://github.com/axelson/scenic_asteroids/blob/87d9beb2d577dc2b9193a9636daecc9fcb8891c3/scenic_live_reload/lib/scenic_live_reload/private/get_scene_pids.ex

Would be nice to have a public API to get the scene pids.

[axelson]

@boydm I've further cleaned up my generic scene reloader into a re-usable library: https://github.com/axelson/scenic_live_reload/

Are you still willing to expose an api to get the pid of the root scene? Or provide a different way to reload the root scene?