post: add vr + nixos + nvidia

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+---
+title: VR + NixOS + Nvidia
+---
+
+For the longest time, getting VR working nicely with Linux (and especially NixOS) was a monumental task.
+Nowadays however, it is easier than ever: only requiring a handful of lines of Nix!
+
+## Prerequisites
+
+In this blog post, I will be focusing on getting VR working with Steam games, using an Oculus Quest 2 headset.
+Ensure you have the proprietary Nvidia drivers installed, as this will most likely not work without them.
+You will also need Home Manager setup, as we will be utilising that to get Steam games working.
+
+```nix
+# Generic drivers, good to have
+hardware.graphics = {
+  enable = true;
+  enable32Bit = true;
+};
+
+# Nvidia specific
+hardware.nvidia = {
+  modesetting.enable = true;
+  open = true;
+};
+
+services.xserver.videoDrivers = ["nvidia"];
+```
+
+## Installing WiVRn
+
+As I am using a Quest 2, I am going to use an application called WiVRn, which will allow me to stream both wired _or_ wirelessly.
+If you are using a tethered headset such as a HTC Vive or Valve Index, I can recommend you look into [Monado](https://gitlab.freedesktop.org/monado/monado).
+WiVRn is actually based on Monado, so gertting it up and running should be fairly similar.
+All we need to get WiVRn installed is put the following in our configuration!
+
+```nix
+/* configuration.nix */
+services.wivrn = {
+  enable = true;
+  openFirewall = true; # Required for wireless streaming
+  defaultRuntime = true;
+};
+```
+
+Although we don't _necessarily_ need anything else now, installing some quality-of-life tools will definitely benefit us.
+
+```nix
+/* configuration.nix */
+environment.systemPackages = with pkgs; [
+  wlx-overlay-s # In-VR overlay
+  android-tools # Allows for wired WiVRn
+];
+```
+
+## Getting Steam games working
+
+If all we want to do is play OpenXR games, we're set!
+Most, if not all, steam games use OpenVR though, so we will need a compatibility layer: OpenComposite.
+We can tell Steam to use OpenComposite and WiVRn for games by writing a few configuration files.
+Because these files live in our home directory, we need to use Home Manager.
+In home.nix, or wherever you have your home configuration:
+
+```nix
+/* home.nix */
+xdg.configFile."openxr/1/active_runtime.json".source =
+  "${osConfig.services.wivrn.package}/share/openxr/1/openxr_wivrn.json";
+
+xdg.configFile."openvr/openvrpaths.vrpath".text = ''
+   {
+    "config" :
+    [
+      "${config.xdg.dataHome}/Steam/config"
+    ],
+    "external_drivers" : null,
+    "jsonid" : "vrpathreg",
+    "log" :
+    [
+      "${config.xdg.dataHome}/Steam/logs"
+    ],
+    "runtime" :
+    [
+      "${pkgs.opencomposite}/lib/opencomposite"
+    ],
+    "version" : 1
+  }
+'';
+```
+
+We are using `osConfig` in this case, as to use the same package we use when enabling WiVRn, meaning that if we changed `services.wivrn.package` in the future, it will use that package instead of the generic one from nixpkgs.
+
+Going back to our main configuration, we now need to tell the game to actually use these settings.
+
+We can do this by setting our game launch options to `PRESSURE_VESSEL_FILESYSTEMS_RW=$XDG_RUNTIME_DIR/wivrn/comp_ipc %command%`, however that isn't very "Nix", is it?
+To do this for _every_ game, we can override our steam package to include this environment variable.
+
+```nix
+/* configuration.nix */
+programs.steam.package = lib.mkDefault (
+  pkgs.steam.override (prev: {
+    extraEnv =
+    {
+      PRESSURE_VESSEL_FILESYSTEMS_RW = "$XDG_RUNTIME_DIR/wivrn/comp_ipc";
+    }
+    // (prev.extraEnv or {});
+  })
+);
+```
+
+Don't worry about your flatscreen games: they should just ignore this setting!
+
+## Done!
+
+We should now just be able to open the "WiVRn server" GUI application, and start gaming!
+You can read the [official WiVRn documentation](https://github.com/WiVRn/WiVRn?tab=readme-ov-file#running-1) for platform independent help on getting it up and running now, as the Nix specific stuff has now been sorted.