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VRCSDK Patching Notes

How VRCSDK is meant to work

The Unity EditorPref key VRC_installedClientPath is meant to hold a string of a absolute path that points to VRChat.exe.

This is always set after VRCSDK initializes; if it was not already set, it pulls the value from some key in the registry, which was probably set beforehand by VRChat.exe or launch.exe.

In the settings page, the user has an option to change VRC_installedClientPath. I have no idea what the practical use-case is for doing this. Clicking "Revert to Default" resets it by reading from the registry again.

The VRCSDK.World "Build and test" button will execute VRChat.exe directly, giving it many arguments that launch the game in offline mode with a file:/// URI to the built world AssetBundle ending in .vrcw. It only falls back to "executing" the equivalent vrchat:// link directly if VRChat.exe hasn't been found -- that is, VRC_installedClientPath is unset because the registry key was missing, or VRChat was recently moved to a different Steam library.

The VRCSDK fetches avatars in the Content Manager window, by searching directly inside Environment.SpecialFolder.LocalApplicationData. This is AppData/LocalLow on Windows and ~/.local/share/VRChat on Linux, but there's no practical reason for the latter to exist. This dir has even been known to interfere with VRCFaceTracking. The AssetBundle can technically work no matter where you save it, but it's best if it's saved to the LocalLow inside VRChat's Proton prefix.

Alternatives

Prior to this doc, we've been manually launching Proton, and the user must select the Proton version by way of searching for the proton Python script file to use as an entrypoint. It also did not locate the VRChat game directory, so moving it to a non-default Steam library would break it.

Now, we use SteamLocator, VrcLocator, and ProtonLocator to find everything, reconciling it with Unity preferences.

There is still the option to ask Steam to launch it, with steam -applaunch 438100 or something, but I don't know if it would work. We want it to use offline mode, allow multiple instances, and not interfere with any instance running in online mode. The URI handler below has the same effect as launching it from Steam. The vrchat:// URIs can work on Linux, but they need a .desktop file.

How we patch VRCSDK

This is an exhaustive list.

  • Fixes the VRCSDK initialization so it can correctly find VRChat.exe.
    • We replace the LoadRegistryVRCInstallPath method to call our VrcLocator instead.
  • Prevents the pointless creation (lol) and use of ~/.local/share/VRChat, instead saving test worlds and avatars to the Proton prefix.
    • We replace the method that looks for LocalLow to do Not that.
  • Fixes the Content Manager tab so it can show your test avatars.
  • Fixes the Build and Test button.
    • We replace the entire VRCWorldAssetExporter.RunWorldTestDesktop method to:
      • Translate the path of the saved AssetBundle to a winepath relative to Z:/.
      • Call Proton instead, with all STEAM_COMPAT_ env vars set.
      • We do not launch it in Steam Linux Runtime, and I hope it doesn't come to that. But it is possible, we'd just read toolmanifest.vdf and wrap the command further.
  • Adds some UI in VRCSDK Settings tab to select a different Proton to use instead of what's set in Steam.

Ideas/Roadmap

  • Warn if ~/.local/share/VRChat exists, because the latest VRCFaceTracking.Avalonia release (currently v1.1.1.0) will break if it sees this.
  • Run xdg-mime query and offer to set up the URI handler.
  • Patch UdonSharp exception watcher.
  • MIT license button in Tools menu.

Snippets

VRChat Offline Mode

Example command I use to run VRChat in offline mode, supporting multiple clients all loaded into an instance of a world AssetBundle stored locally:

STEAM_COMPAT_DATA_PATH=/mnt/steam/steamapps/compatdata/438100/ STEAM_COMPAT_CLIENT_INSTALL_PATH=$HOME/.local/share/Steam/ STEAM_COMPAT_INSTALL_PATH=/mnt/steam/steamapps/common/VRChat/ ~/.local/share/Steam/compatibilitytools.d/GE-Proton10-33-rtsp24-1/proton run /mnt/steam/steamapps/common/VRChat/VRChat.exe '--url=create?roomId=8094722763&hidden=true&name=BuildAndRun&url=file:///Z:/mnt/steam/steamapps/common/VRChat/VRChat_Data/StreamingAssets/Worlds/errorworld.vrcw' --enable-debug-gui --enable-sdk-log-levels --enable-udon-debug-logging --no-vr

VRChat URI Handler

Save to ~/.local/share/applications/vrchat-uri-handler.desktop, and Firefox will let you click "Launch World" buttons on the website. It'll let you xdg-open vrchat:// too.

[Desktop Entry]
Name=URI-vrchat
Comment=URI handler for vrchat://
Exec=/usr/bin/env steam -applaunch 438100 %U
Terminal=false
Type=Application
Categories=Game;
MimeType=x-scheme-handler/vrchat;
NoDisplay=true