How to get Screen size in elixir?

Elixir Framework Forums Elixir Desktop Forum
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1

Background

I am working on an Elixir desktop application, and I need it to adapt to the monitor/screen size of the user.
Using Elixir Desktop (GitHub - elixir-desktop/desktop: Elixir library to write Windows, macOS, Linux, Android apps with OTP24 & Phoenix.LiveView), I would normally do something like this:

      {Desktop.Window,
       [
         # simplified for the sake of brevity
         title: "Market Manager",
         size: {940, 980},
         icon: "static/images/resized_logo_5_32x32.png"
       ]}

Where size will be the size (in pixels) of the window of the application.
This is all fine if all my users have monitors of the same size. However, this is not the case.

Problem

So I need to know the dimensions of the screen size of the user in order to create a Window that is, lets say, 60% width and 70% height.

Since the underlying library (Desktop) does not support relative sizes for the window afaik, I need to calculate them myself.

To this effect I found no library that gives me this.

Question

How can I find the screen dimensions ?

2

Take a look at wxdisplay, it should be exactly what you are looking for.

3

From the docs (Erlang -- wxDisplay) I understand I need to:

_wx = :wx.new()
display = :wxDisplay.new()
{x, y, w, h} = :wxDisplay.getClientArea(display)

Being the first time I am using this library, do I really need the first line _wx = :wx.new()?
Am I missing something?

1 Like
4

No idea, read some documentation on how this is done in wx, as this is just a erlang wrapper for wx library.

5

My guess is that it starts a process responsible for getting messages from requests, as in, a central point where everything has to go through. This is based on the docs:

https://www.erlang.org/doc/man/wx.html#new-0

However, I could not find any confirmation if my interpretation is correct, thus I asked.

6

Yes, you’re right. you can typically also get the same effect by using :wx.set_env(env) using an existing wx_env for this there is a helper in Desktop.Env: Desktop.Env — Desktop v1.5.1

:wx.set_env(Desktop.Env.wx_env())
display = :wxDisplay.new()
{x, y, w, h} = :wxDisplay.getClientArea(display)
3 Likes
7

In my specific use case, I cannot use :wx.set_env(Desktop.Env.wx_env()) as the Desktop application has not yet started:

See my application.ex:

 def start(_type, _args) do
    children = [
      Telemetry,
      {Phoenix.PubSub, name: PubSub},
      Endpoint,
      Manager,
      %{
        id: Desktop.Window,
        start: {Desktop.Window, :start_link, [[
          app: :web_interface,
          id: WebInterface,
          title: "Market Manager",
          size: calculate_window_size(0.4, 0.8),
          menubar: MenuBar,
          icon: "static/images/resized_logo_5_32x32.png",
          url: fn -> "#{WebInterface.Endpoint.url()}/#{@landing_page}" end
        ]]},
        restart: :transient,
        shutdown: 5_000
      }
    ]

    opts = [strategy: :one_for_one, name: WebInterface.Supervisor]
    Supervisor.start_link(children, opts)
  end

  @doc """
  Calculates the width and height for the window. Fetches the display
  information using :wx. Because we create a :wx server every time we call this
  function this is a heavy operation and should be used cautiously.

  Both percentages given must be > 0 and <= 1.
  """
  @spec calculate_window_size(float, float) :: {pos_integer, pos_integer}
  def calculate_window_size(width_percentage, height_percentage)
      when is_float(width_percentage) and width_percentage > 0 and width_percentage <= 1 and
             is_float(height_percentage) and height_percentage > 0 and height_percentage <= 1 do
    # Since Desktop has not yet started its wx server, we need to create one
    # to get the screen size first
    _wx_object = :wx.new()

    display = :wxDisplay.new()
    {_x, _y, total_width, total_height} = :wxDisplay.getClientArea(display)

    width_pixels = ceil(width_percentage * total_width)
    height_pixels = ceil(height_percentage * total_height)

    # we destroy the previously created wx server to save resources and avoid
    # a conflict with Desktop library
    :wx.destroy()

    {width_pixels, height_pixels}
  end

If I replace _wx_object = :wx.new() with :wx.set_env(Desktop.Env.wx_env()) then the application crashes on startup:

07:24:00.603 [notice] Application wx exited: :stopped
07:24:00.606 [notice] Application runtime_tools exited: :stopped
** (Mix) Could not start application web_interface: WebInterface.Application.start(:normal, []) returned an error: shutdown: failed to start child: Desktop.Window
    ** (EXIT) an exception was raised:
        ** (MatchError) no match of right hand side value: {:error, {:noproc, {:gen_server, :call, [#PID<0.717.0>, :register_me, :infinity]}}}
            (desktop 1.5.1) lib/desktop/window.ex:109: Desktop.Window.start_link/1
            (stdlib 4.1.1) supervisor.erl:414: :supervisor.do_start_child_i/3
            (stdlib 4.1.1) supervisor.erl:400: :supervisor.do_start_child/2
            (stdlib 4.1.1) supervisor.erl:384: anonymous fn/3 in :supervisor.start_children/2
            (stdlib 4.1.1) supervisor.erl:1250: :supervisor.children_map/4
            (stdlib 4.1.1) supervisor.erl:350: :supervisor.init_children/2
            (stdlib 4.1.1) gen_server.erl:851: :gen_server.init_it/2
            (stdlib 4.1.1) gen_server.erl:814: :gen_server.init_it/6

Therefore, the solution I found (and works for me) is to create a temporary wx_object and then kill it, to avoid conflicts with Desktop, just like in the code snippet I shared above.

This also reminds me of one question:

  • @dominicletz what do you think aboud adding a function that takes in percentages for the windows size instead of absolute pixel values, like the function I created?
1 Like