fractional scaling in X11

modules/gnome-fractional-scaling.home.nix

@@ -4,12 +4,57 @@
   # https://wiki.archlinux.org/title/HiDPI#Wayland
   # Results in blurry font in non-Wayland applications :/
 
+  # https://wiki.archlinux.org/title/HiDPI#Xorg
+
   programs.dconf.enable = true;
 
+  # Overlays.
+  # https://nixos.wiki/wiki/Overlays#In_NixOS
+  nixpkgs.overlays = [
+    (
+      # Patched version of mutter.
+      # Outdated example: https://nixos.wiki/wiki/Overlays#Overriding_a_package_inside_a_scope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
+      #
+      #=> building '/nix/store/yh0jnwyq5351l1rjspjlkimas3wvpf6g-mutter-44.2.drv'...
+
+      # 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: {
+            patches = (oldAttrs.patches or []) ++ [
+              (prev.fetchpatch {
+                url = "https://salsa.debian.org/gnome-team/mutter/-/raw/ubuntu/44.2-3ubuntu1/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-GCtz87C1NgxenYE5nbxcIIxqNhutmdngscnlK10fRyQ=";
+              })
+            ];
+          });
+        });
+      }
+    )
+  ];
+
   home-manager.users.yoda = { osConfig, config, pkgs, ... }: {
     dconf.settings = {
       "org/gnome/mutter" = {
-        experimental-features = [ "scale-monitor-framebuffer" ];
+        experimental-features = [
+          # Wayland fractional scaling
+          "scale-monitor-framebuffer"
+          # X11 fractional scaling
+          "x11-randr-fractional-scaling"
+        ];
       };
     };
   };