vanadium: set ext display "default" software brightness

nix/configurations/vanadium/nixos/display.nix

@@ -50,13 +50,22 @@
       */
       genAttrs' = xs: func: builtins.listToAttrs (map func xs);
 
-      mkExtSwitch = {dpi}: {
+      mkDpiSwitch = {dpi}: {
         "10_xrdb-dpi" = "xrdb -merge ${pkgs.writeText "xrdb-dpi-config" ''
           Xcursor.size: 64
           Xft.dpi:   ${toString dpi}
         ''}";
       };
 
+      mkBrightnessSwitch = {
+        device,
+        brightness,
+      }: {
+        "10_xrandr_brightness" = ''
+          xrandr --output ${device} --brightness ${toString brightness}
+        '';
+      };
+
       # Note: the "position" field corresponds to the "pos" field outputted by autorandr
       # To get the current config, run `xrandr --auto` and then `autorandr --config`
       configs = {
@@ -89,7 +98,7 @@
         fingerprint.eDP-1 = built-in;
         config = with configs;
           allOff // enableBuiltin;
-        hooks.postswitch = mkExtSwitch {dpi = 150;};
+        hooks.postswitch = mkDpiSwitch {dpi = 150;};
       };
 
       mkAsusProfile = name: {
@@ -99,7 +108,12 @@
         };
         config = with configs;
           allOff // enableDevice name;
-        hooks.postswitch = mkExtSwitch {dpi = 110;};
+        hooks.postswitch =
+          mkDpiSwitch {dpi = 110;}
+          // mkBrightnessSwitch {
+            device = name;
+            brightness = 0.7; # just a random sensible choice
+          };
       };
     in
       {default = frameworkBuiltin;}