wayland: fix window position restore (support xdg_session_manager_v1 when it comes of age)

[KJ7LNW]

See also: #81

Under Wayland the compositor owns placement outright since there is no separate window manager to delegate to. A session-restore protocol exists but only in an experimental, opt-in form that no compositor exposes by default at the time of this writing.

Since the protocol for allowing window position restores has not yet stabilized and it is unavailable for general use, there aren't any distributions that really have this built out yet. However, if you want to try the bleeding-edge feature, continue reading through this thread.

If you notice that your window manager does not remember where the windows were placed when you close the program, first verify that your distribution supports xdg_session_manager_v1, by:

1. Run a program that supports window placement (firefox?)
2. Move the window.
3. Close the program.
4. Reopen the program and see if it opens where you left it.

If you're running Wayland and you're not able to reproduce the procedure above, for any program that does not come with your window manager, then it is unlikely that support is available.

On the other hand, if you do see a supporters available, please let me know so we can get this implemented. I will need to know your distribution details so I have a good test platform to work from.

See below for the procedure to test it in an experimental environment.

[KJ7LNW]

@Peter3579 ,

This isn't cleaned up yet, but here's a bleeding edge implementation that allows it to save window positions using the draft xx-session-management-v1.xml spec.

• https://github.com/KJ7LNW/xnec2c/tree/wayland

Notice that KWin gates the xx_ global behind an opt-in: it advertises
xx_session_manager_v1 only when KWIN_WAYLAND_SUPPORT_XX_SESSION_MANAGER=1
is exported into the compositor environment before KWin starts (placed
in ~/.config/plasma-workspace/env, outside this tree). Without it the
registry never offers the global and restore is unavailable.

[KJ7LNW]

One other thing you will have to build with this, because GTK does not have the feature available yet until the (as of now unreleased) v3.24.53 comes out.

It completely builds Gtk and many dependencies, so it takes a while. However, once it is built under that tree, you can use it outside of the development build environment:

This is the PR that has been merged but not released:

• https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/9852

The following nix script pulls it in:

{ pkgs ? import <nixpkgs> {
    overlays = [
      (final: prev: {
        mesa = (prev.mesa.override { libdisplay-info = null; }).overrideAttrs (old: {
          mesonFlags = (old.mesonFlags or []) ++ [ (prev.lib.mesonEnable "display-info" false) ];
        });
        gtk3 = prev.gtk3.overrideAttrs (old: {
          patches = (old.patches or [ ]) ++ [
            (final.fetchpatch {
              # MR !9852: gdk_wayland_window_get_xdg_toplevel + xdg-toplevel-realized signal.
              # Unreleased on gtk-3-24; remove once nixpkgs gtk3 >= 3.24.53.
              url = "https://gitlab.gnome.org/GNOME/gtk/-/commit/edc9d508c3227d96de1e34aa3d5808a255f0e10b.patch";
              hash = "sha256-KYx8/2Oh4HpefPz98rWsX1lxU7lSaZlU0BbarnF5KEQ=";
            })
          ];
        });
      })
    ];
  }
}:
pkgs.mkShell {
  buildInputs = with pkgs; [
    gnumake
    autoconf
    automake
    libtool
    pkg-config
    gtk3
    gsl
    libepoxy
    mesa
    gettext
    desktop-file-utils
    adwaita-icon-theme
    autoconf-archive
    wayland
    wayland-scanner
    wayland-protocols
  ];
}