Update README.md with NixOS intructions

[andre-brandao]

Instructions to use themes on NixOS

[VuiMuich]

Just in case this helps the review of this PR, I can confirm the example given is working as expected.

[0x006E]

I can also confirm this works great with my nix. But how can I also add distrologo to the theme?

[andre-brandao]

I can also confirm this works great with my nix. But how can I also add distrologo to the theme?

you probably need to override the theme script and copy the logo file in the install phase, I did something like that to change the background of my sddm-theme

it might be different but if you wanna take a look of how I solved a similar issue with sddm i will link my config

https://github.com/andre-brandao/nixos/blob/main/packages/sddm-theme.nix

[RAVENz46]

@0x006E
Hi, I could add distro logo to it.
Here is the example. I hope it helps.
I want to remove selected_theme line from overlays.nix but IDK it's possible.

# configuration.nix
boot = {
  plymouth = {
    enable = true;
    theme = "CHANGEME";
    themePackages = with pkgs; [
      (adi1090x-plymouth-themes.override {
        selected_themes = [ config.boot.plymouth.theme ];
      })
      (runCommand "add-logos" { inherit (config.boot.plymouth) logo theme; } ''
        mkdir -p $out/share/plymouth/themes/$theme
        ln -s $logo $out/share/plymouth/themes/$theme/header-image.png
      '')
    ];
  };
};

# overlays.nix
final: prev: {
  adi1090x-plymouth-themes = prev.adi1090x-plymouth-themes.overrideAttrs (oldAttrs: rec {
    selected_themes = [ "CHANGEME" ];
    installPhase = oldAttrs.installPhase + ''
      for theme in ${toString selected_themes}; do
        echo 'nixos_image = Image("header-image.png");' >> $out/share/plymouth/themes/$theme/$theme.script
        echo 'nixos_sprite = Sprite();' >> $out/share/plymouth/themes/$theme/$theme.script
        echo 'nixos_sprite.SetImage(nixos_image);' >> $out/share/plymouth/themes/$theme/$theme.script
        echo 'nixos_sprite.SetX(Window.GetX() + (Window.GetWidth() / 2 - nixos_image.GetWidth() / 2));' >> $out/share/plymouth/themes/$theme/$theme.script
        echo 'nixos_sprite.SetY(Window.GetHeight() - nixos_image.GetHeight() - 50);' >> $out/share/plymouth/themes/$theme/$theme.script
      done
    '';
  });
}