feat(steam): configure SteamVR support

configs/nixos/hosts/zeus/default.nix

@@ -46,7 +46,10 @@
   modules.desktop.apps.r2modman.enable = true;
   modules.desktop.emulation.enable = true;
   modules.desktop.apps.signal.enable = true;
-  modules.desktop.apps.steam.enable = true;
+  modules.desktop.apps.steam = {
+    enable = true;
+    vr.enable = true;
+  };
   modules.desktop.apps.vencord.enable = true;
 
   home-manager.users.${config.user.name}.wayland.windowManager.hyprland.settings.monitor = [

configs/nixos/modules/desktop/apps/steam.nix

@@ -6,28 +6,62 @@
   ...
 }:
 # Steam game launcher and runtime integration.
+let
+  cfg = config.modules.desktop.apps.steam;
+  steamVrLauncher = "/home/${config.user.name}/.local/share/Steam/steamapps/common/SteamVR/bin/linux64/vrcompositor-launcher";
+in
 {
-  options.modules.desktop.apps.steam.enable = lib.mkEnableOption "Steam game launcher";
+  options.modules.desktop.apps.steam = {
+    enable = lib.mkEnableOption "Steam game launcher";
 
-  config = lib.mkIf config.modules.desktop.apps.steam.enable {
+    vr.enable = lib.mkEnableOption "SteamVR with VRLink";
-    programs.gamemode.enable = true;
-
-    programs.steam = {
-      enable = true;
-      package = pkgs.steam.override {
-        extraEnv.STEAM_FORCE_DESKTOPUI_SCALING = "1.5";
-      };
-    };
-
-    hardware.steam-hardware.enable = true;
-
-    environment.systemPackages = [
-      pkgs.gamescope
-    ];
-
-    registry.window-icon.${config.networking.hostName}.steam = {
-      class = "[Ss]team";
-      icon = util.glyph "f1b6";
-    };
   };
+
+  config = lib.mkIf cfg.enable (
+    lib.mkMerge [
+      {
+        programs.gamemode.enable = true;
+
+        programs.steam = {
+          enable = true;
+          package = pkgs.steam.override {
+            extraEnv.STEAM_FORCE_DESKTOPUI_SCALING = "1.5";
+          };
+        };
+
+        hardware.steam-hardware.enable = true;
+
+        programs.gamescope.enable = true;
+
+        registry.window-icon.${config.networking.hostName}.steam = {
+          class = "[Ss]team";
+          icon = util.glyph "f1b6";
+        };
+      }
+      (lib.mkIf cfg.vr.enable {
+        networking.firewall.allowedUDPPorts = [ 10400 ];
+
+        programs.gamescope.capSysNice = true;
+
+        systemd.paths.steamvr-capabilities = {
+          wantedBy = [ "multi-user.target" ];
+          pathConfig = {
+            PathChanged = steamVrLauncher;
+            Unit = "steamvr-capabilities.service";
+          };
+        };
+
+        systemd.services.steamvr-capabilities = {
+          wantedBy = [ "multi-user.target" ];
+          path = [ pkgs.libcap ];
+          script = ''
+            if [ -e ${lib.escapeShellArg steamVrLauncher} ]; then
+              setcap cap_sys_nice=eip ${lib.escapeShellArg steamVrLauncher}
+            fi
+          '';
+          serviceConfig.Type = "oneshot";
+        };
+      })
+    ]
+  );
 }