nix-git/modules/gnome-fractional-scaling.nix

{ config, pkgs, lib, ... }:
let
  version = "45.4";
in
{
  # https://wiki.archlinux.org/title/HiDPI#Wayland
  # Results in blurry font in non-Wayland applications :/

  # https://wiki.archlinux.org/title/HiDPI#Xorg

  # https://devicetests.com/set-different-scaling-multi-monitors-gnome
  #   "scale-monitor-framebuffer": This allows GNOME to scale each monitor’s framebuffer independently, which is necessary for per-monitor scaling.
  #   "x11-randr-fractional-scaling": This allows fractional scaling, which gives you finer control over the scaling factor.

  # TODO open issue: Fractional scaling can't be enabled with multiple monitors.
  #   https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/2076
  #   https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/2365
  #   -> https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/2008355

  programs.dconf.enable = true;

  # Overlays.
  # https://nixos.wiki/wiki/Overlays#In_NixOS
  # https://discourse.nixos.org/t/use-specific-pkg-version-in-overlay/32741/3

  # If on X11, then use patched version of mutter.
  nixpkgs.overlays = lib.mkIf (! config.services.xserver.displayManager.gdm.wayland) [
    (
      # Patched version of mutter 44.2.
      # Outdated example: https://nixos.wiki/wiki/Overlays#Overriding_a_package_inside_a_scope
      #
      # On the AUR, they apply only one patch, not three.
      # And they pick the patch that corresponds to the mutter version.
      # https://aur.archlinux.org/packages/mutter-x11-scaling
      #
      # New patch URL:
      # -> https://salsa.debian.org/gnome-team/mutter/-/blob/ubuntu/master/debian/patches/ubuntu/x11-Add-support-for-fractional-scaling-using-Randr.patch
      # For release 44.2:
      # -> https://salsa.debian.org/gnome-team/mutter/-/tags?sort=updated_desc&search=ubuntu%2F
      # -> https://salsa.debian.org/gnome-team/mutter/-/tags/ubuntu%2F44.2-3ubuntu1
      # -> https://salsa.debian.org/gnome-team/mutter/-/raw/ubuntu/44.2-3ubuntu1/debian/patches/ubuntu/x11-Add-support-for-fractional-scaling-using-Randr.patch
      # For release 45.3:
      # -> https://salsa.debian.org/gnome-team/mutter/-/tags?sort=updated_desc&search=ubuntu%2F
      # -> https://salsa.debian.org/gnome-team/mutter/-/tags/ubuntu%2F45.3-1ubuntu1
      # -> https://salsa.debian.org/gnome-team/mutter/-/raw/ubuntu/45.3-1ubuntu1/debian/patches/ubuntu/x11-Add-support-for-fractional-scaling-using-Randr.patch

      # Elements of nixpkgs must be taken from final and prev.
      final: prev: {
        # Elements of pkgs.gnome must be taken from gfinal and gprev.
        gnome = prev.gnome.overrideScope' (gfinal: gprev: {
          mutter = gprev.mutter.overrideAttrs (oldAttrs:
            if oldAttrs.version == version then
              {
                patches = (oldAttrs.patches or []) ++ [
                  (prev.fetchpatch {
                    url = "https://salsa.debian.org/gnome-team/mutter/-/raw/ubuntu/${version}-1ubuntu1/debian/patches/ubuntu/x11-Add-support-for-fractional-scaling-using-Randr.patch";
                    # Determining the hash: https://github.com/NixOS/nixpkgs/issues/191128#issuecomment-1246030431
                    hash = "sha256-snEgCuTsTEo0wQ5XsjEM53K2j7l4ZQ3t9FT3+Yfoti0=";
                  })
                ];
              }
            else throw "Mutter version mismatch. Please update patch to ${oldAttrs.version}"
          );
        });
      }
    )
  ];

  home-manager.users.yoda = { osConfig, config, pkgs, ... }: {
    dconf.settings = {
      "org/gnome/mutter" = {
        experimental-features = (
          if (osConfig.services.xserver.displayManager.gdm.wayland)
          # Wayland
          then ["scale-monitor-framebuffer"]
          # X11
          else ["scale-monitor-framebuffer" "x11-randr-fractional-scaling"]
        );
      };
    };
  };
}