alien: add gamescope

system/hosts/alien/default.nix

@@ -47,6 +47,14 @@
     };
     defaultSession = "niri";
   };
+
+  environment = {
+    systemPackages = [ pkgs.mangohud ];
+    loginShellInit = ''
+      [[ "$(tty)" = "/dev/tty1" ]] && ./gs.sh
+    '';
+  };
+
   security.sudo.wheelNeedsPassword = true;
 
   hardware.nvidia = {

system/hosts/alien/gs.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+set -xeuo pipefail
+
+gamescopeArgs=(
+    --adaptive-sync # VRR support
+    --hdr-enabled
+    --mangoapp # performance overlay
+    --rt
+    --steam
+)
+steamArgs=(
+    -pipewire-dmabuf
+    -tenfoot
+)
+mangoConfig=(
+    cpu_temp
+    gpu_temp
+    ram
+    vram
+)
+mangoVars=(
+    MANGOHUD=1
+    MANGOHUD_CONFIG="$(IFS=,; echo "${mangoConfig[*]}")"
+)
+
+export "${mangoVars[@]}"
+exec gamescope "${gamescopeArgs[@]}" -- steam "${steamArgs[@]}"