KartFrame

Mario Kart Wii in VR, running natively on the Valve Steam Frame.

KartFrame is a fork of heurazy's Wiicompiled VR PLUS, the Mario Kart Wii VR port. The game in it is heurazy's static translation of the Wii game to C++, drawn by the aurora renderer on Dawn (WebGPU) and shown through OpenXR. KartFrame builds it as a Linux Arm64 program that runs in the Frame's own SteamVR. You do not need Lepton, an APK, adb or a PC.

You need your own Mario Kart Wii disc. No game data is in this repository or its releases.

What it does:

• Plays Mario Kart Wii in VR on the Steam Frame, in the Frame's SteamVR.
• Renders both eyes on every refresh of the 120 Hz display, from your head position at that refresh, at 1728 pixels per eye.
• Uses the Steam Frame controllers through SteamVR's own controller profile.
• Builds the game on your Frame from your own disc, once, in about 6 minutes.

All of that has been played on a Frame. One problem is still being worked on, the double image in races; this pre-release carries the mitigation that removes it. See The double image.

What this adds to Wiicompiled VR PLUS

Upstream runs on Windows and on the Meta Quest. On the Frame that would mean Lepton and an Android layer between the game and SteamVR. KartFrame changes the platform side and leaves the game as it is:

• A native Linux Arm64 build.
• Dawn's Vulkan backend bound to SteamVR's own Vulkan device, through upstream's own Dawn patch.
• Eye images handed to SteamVR only after the GPU has finished them.
• Both eyes rendered on every refresh from that refresh's head pose, with the game's own VR frame interpolation filling the display rate from the game's 60 frames a second.
• Pipelined frame pacing, with the older single stage mode kept as a switch.
• The Frame controller layout in code, with no SteamVR binding file.
• Simplified models of the Frame's controllers, converted at install from the Frame's own SteamVR files.
• The game's 2D screen shown as a flat quad layer in front of you.
• A first run that extracts your disc, translates the game and compiles it on the Frame with a bundled compiler, using a kit of prebuilt runtime parts.
• A launch wrapper that sets SteamVR's per-app settings (120 Hz, no throttling, no extra prediction, motion smoothing off, 1728 resolution) at every launch and writes a session log folder.

Status

Version 0.9.0-alpha.1 is a pre-release. It plays, at 120 Hz and 1728 pixels per eye, through twenty headset sessions so far. Version numbers stay below 1.0.0 until the double image (next section) is fixed at its cause rather than worked around.

Confirmed in the headset: the native build in SteamVR; 119 to 120 sets of eyes a second in races with under 1 % late; the game at its full 60 frames a second; the menus as a steady flat screen; the race HUD on the virtual screen with correct clipping; the Frame controls, hand steering and the controller models; the first run from a disc; the installer, the library entry, the launch wrapper and the session logs.

Known issues: the Time Trial ghost is flat; full-view 2D effects such as Blooper ink do not cover the whole view; the laser pointer's dot is not visible on the 2D menu screen (the ray is); two and four player races are heavier and not yet measured in the headset. The short list of what is built but not yet confirmed is in frame/UNTESTED.md.

The double image (known issue)

In races, turning your head could show the world twice, one copy about two refreshes of head motion ahead of the other, alternating every refresh, worse in one eye. Menus were always clean, and so was GalaxyFrame on the same SteamVR.

Twenty sessions of measurement, each one eliminating something by a direct test, ended with this: SteamVR's compositor on the Frame takes each eye's most recently handed-over image at its own point inside the refresh, the right eye after the left. The game was handing frames over right where those points sit, so from one refresh to the next the two eyes did not always get the same set. A probe that showed SteamVR the game's own recorded race images was clean in every variation, and logging every compositor frame beside the game's own timeline showed the clean launches keeping one side of the pick-up every frame and the doubled ones flipping.

What this build does about it: the launch wrapper runs a small helper that reads SteamVR's compositor timing and publishes its grid, and the game hands every frame over at a fixed point against that grid, just after the compositor's update (KARTFRAME_END_PHASE=after, the default). The doubling is gone with that. What remains, and why this is a mitigation rather than a fix: the right eye runs one set ahead of the left, which reads as the right eye being a touch more sensitive to head movement, and the compositor shows a frame twice now and then. The probe hands its frames over at the same point as the old default and is clean, so the point itself is not the cause; the remaining difference is the 4 to 7 ms of GPU work the game submits right after each hand-over on the GPU the compositor also composes on. That is the next experiment. The records of every session are in frame/perf/, and the mechanism is written up in the technical notes.

If you want the old behaviour to compare, put KARTFRAME_END_PHASE=off in session.env for one launch.

What has been done so far

The work since the first headset session, in the order it mattered:

• The game ran at 38 frames a second under gamescope: a window-sync call slept 10 ms every game frame. Fixed; the game runs at its full 60.
• The 2D menus moved from projected panels to a quad layer, as upstream does on PC, which ended the flicker and the 5 to 7 ms of GPU the menus cost.
• An sRGB sink and a cut of the native render pass: copying the eyes to the swapchain went from 2.3 ms to 0.47 ms, which is what lets races hold 120 Hz at 1728.
• Pipelined pacing with the sets of eyes rendered two refreshes ahead, every frame handed over at the same point of the refresh, each set released only after a GPU fence, a retained repeat when a set is late, half rate never by default.
• Turnip's sysmem mode by default: 7 to 8 % faster for this draw-bound game.
• Thread priority through RealtimeKit and a utilisation clamp, so the game thread and the frame worker stay on the big cores.
• The race HUD clipped to its frame on the virtual screen, the thin line beside the map removed, full-view fades only for untextured colour fades.
• Input kept through SteamVR's short focus losses; the refresh rate requested only when SteamVR offers it.
• The double-image work above, with the tools it needed: a mock OpenXR runtime with exact checks, a probe that replays recorded eye images, per-frame compositor timing, panel recordings and their analysis.

Requirements

• A Steam Frame with SteamVR, and about 1 GB free for the toolchain and kit, plus the extracted disc.
• Your own clean PAL Mario Kart Wii disc image (RMCP01).
• A terminal on the Frame for the one time setup: SSH, or Konsole from desktop mode.
• Steam running on the Frame while you install, so the installer can add the library entry.

Install

1. Get the repository:

   git clone https://github.com/simplysanatori/KartFrame.git
   cd KartFrame
   

2. Download kartframe-0.9.0-alpha.1-linux-arm64.tar.gz and its .sha256 file from the Releases page. Check the download and install it:

   sha256sum -c kartframe-0.9.0-alpha.1-linux-arm64.tar.gz.sha256
   frame/install.sh ~/Downloads/kartframe-0.9.0-alpha.1-linux-arm64.tar.gz
   

   The installer unpacks the program into ~/Games/KartFrame/app. It adds KartFrame to your Steam library as a non-Steam shortcut, or updates the entry if it is there. It converts the Frame's controller models from SteamVR's own files. The script talks to Steam through its local debugging port, which SteamOS has on by default.

3. Build the game from your disc, once:

   ~/Games/KartFrame/app/setup.sh /path/to/MarioKartWii.iso
   

   Setup checks that the disc is RMCP01, extracts it to ~/.local/share/KartFrame/game, translates the game, compiles it with the bundled compiler and installs the finished program. It took about 6 minutes on my Frame. It can be run again after an interruption and picks up where it stopped.

4. Put the headset on and launch KartFrame from your Steam library.

To update, download the new tarball and run frame/install.sh again, then setup.sh again if it tells you the kit changed. Your game files, saves and settings stay where they are.

The installer changes nothing outside the folders listed under Files, the Steam shortcut and the controller models. To remove KartFrame, run ~/Games/KartFrame/app/tools/uninstall.sh. It keeps your data folder unless you pass --purge.

First run

The launch wrapper checks that the installed program was built for the installed kit. If it was not, it stops and writes the reason to the session log; run setup.sh again.

On the very first start the game creates its own settings file and a fresh Wii save area. The game makes the Wii licence in-game on first boot.

If the game cannot find the disc files, the setup did not finish. Run setup.sh status to see which step is missing.

Controls

The game sees a Wii wheel and pad. The Frame controllers are mapped like this.

Steam Frame	In the game
Right trigger, A	Accelerate
Left trigger	Reverse
B	Brake, and back in menus
X, left bumper	Use item
Y	Look back
Both grips, right bumper	Drift
Left D-pad	D-pad
Right Menu	Start
Left View	Back. Held for half a second, it opens the VR settings panel. Pressed while the panel is open, it closes it

Hand steering: in the first-person cockpit the grips hold the wheel, and the right bumper drifts there. Elsewhere the grips drift.

Settings

Hold left View for half a second. The VR settings panel opens. Everything on it is also in ~/.local/share/KartFrame/UserData/Config.toml, which is seeded from Config.frame.toml on the first run. The keys that matter:

Key	Default	What it does
[vr] render_scale	1.0	Eye size relative to the size SteamVR's resolution setting gives the game (1728 per eye at SteamVR's 100 %)
[vr] frame_interpolation_fps	1	1 renders at the headset's refresh rate, interpolated from the game's 60 frames a second
[vr] frame_pacing	"auto"	auto, inline or pipelined. Auto picks pipelined
[vr] refresh_rate	120	The refresh rate the game asks for
[vr] menu_shader_quality	0	0 is a plain dark background behind the menus
[vr] hand_steering	true	Grips hold the wheel in the first-person cockpit
[vr] hud_virtual_screen	true	Menus and the race HUD on a virtual screen
[vr] hud_distance_meters	2.0	How far away that screen is
[vr] hud_width_meters	2.4	How wide it is
[video] resolution_multiplier	1.0	Resolution of the flat desktop mirror

I do not ship a default below 1728 per eye. Lower values of render_scale work, but the picture gets soft.

Switches for testing go in ~/.local/share/KartFrame/session.env, one NAME=value per line, read at the next launch only:

Name	What it does
KARTFRAME_PACING	auto, inline or pipelined, overriding the config
KARTFRAME_REFRESH_HZ	90 or 120, the rate asked of SteamVR
KARTFRAME_SYSMEM	0 turns off the GPU's direct memory rendering mode (TU_DEBUG=sysmem); it is on by default
KARTFRAME_FDM_LAYER	0 disables Valve's foveation layer in the Vulkan chain, to compare
KARTFRAME_END_PHASE	after (default), before, or off: when in the refresh each frame is handed to SteamVR, against the compositor grid the wrapper's helper publishes. off hands over at the wake-up, which doubles the image
KARTFRAME_END_DELAY_US	A fixed delay after the wake-up instead of the grid, in microseconds; also the fallback when the grid is missing (4000)
KARTFRAME_VRTIMING_FRAMES	1 logs every compositor frame to vrframes.log in the session folder
KARTFRAME_HOME	The data folder, if it is not ~/.local/share/KartFrame

Performance

Measured on my Frame, from the session logs:

Display	120 Hz, 1728 x 1728 per eye
Races	119 to 120 sets of eyes a second, 0.2 to 1 % late, 2 to 3 % retained repeats
Menus	110 to 113 sets a second (the quad layer and the intro screens)
GPU per set	about 5 ms in races (about 7 with the hand-over timing of this build, since the next set starts before the hand-over), 1.5 to 2.5 ms in menus
Game thread	60 frames a second; about 8 % of race frames take 20 to 33 ms (the game's own course loading and item logic); a 144 ms hitch at race start
First run	about 6 minutes from the disc: extract 1 minute, translate 50 seconds, compile 5 minutes

What the build does, so you know what the numbers mean:

• At 120 Hz there are about 8.3 ms per refresh, and about 7 ms of that is the GPU's for both eyes beside SteamVR's compositor.
• Each refresh locates the head once and renders both eyes from that pose, two refreshes ahead of the refresh that shows them.
• A set of eyes is handed to SteamVR only after the GPU has finished it, at a fixed point of the refresh against the compositor's own clock. If a set is not finished in time, the previous set is shown again and the miss is counted.
• Every second, the game logs one vr pacing: line with the refresh rate, the sets rendered, interpolated, late and missed, and GPU and encode times; every 10 seconds an end phase: line with the achieved hand-over phase. report.txt in each session folder sums them up, and tools/session-report.py lays several sessions side by side.

Files

What	Where
Program, wrapper, kit, toolchain, translator	~/Games/KartFrame/app
Game files, built game, saves, settings	~/.local/share/KartFrame (game/, build/, bin/, UserData/)
Controller models	~/.local/share/KartFrame/UserData/controller_models/frame
Session logs	~/.local/share/KartFrame/sessions/<date-time>/ (launch.log, stdout.log, game.log, vrtiming.log, report.txt); sessions/latest points at the newest
Downloaded tools	~/.cache/kartframe (nodtool, fetched by setup.sh)
One launch's test settings	~/.local/share/KartFrame/session.env

The game does not write to ~/.local/share/WiiCompiled.

Troubleshooting

• install.sh says Steam's debugging port is not reachable. Start Steam and run it again.
• The game does not start and launch.log says it refuses. Read the reason in ~/.local/share/KartFrame/sessions/latest/launch.log. If it names a kit mismatch, run setup.sh again.
• setup.sh says the disc is not Mario Kart Wii RMCP01. Only the clean PAL disc is supported.
• SteamVR's per-app settings were not applied. launch.log lists each one and what SteamVR holds after the write. They are only set when the game is started from the Steam library.
• The world doubles when you turn your head in a race. That is the known issue above. Check launch.log says KARTFRAME_END_PHASE=after and game.log has end phase: locked to the compositor grid; if it says it fell back to the fixed delay, the helper did not get SteamVR's timing (it needs SteamVR's libopenvr_api.so, which the wrapper finds under /opt/steamvr).
• The right eye feels more sensitive to head movement than the left. The known issue's remainder: the right eye runs one set ahead. Not fixed yet.
• Motion is uneven. report.txt shows late and repeated sets per second. A few percent is normal; more usually means something else is using the GPU (a recording, a stream).

Reporting a problem

Open an issue with what you did, what you expected and what happened, and the output of:

~/Games/KartFrame/app/tools/collect-logs.sh

It gathers the newest session's logs into one archive and masks IP and MAC addresses, host names, network names, serial numbers, Steam ids, email addresses and user names in paths. The masking is a best effort. Read the files before you attach them.

Build from source

See the technical notes. The patched Dawn is built once on the Frame, then the game and the release kit. frame/tools/privacy-check.sh checks the tree, the history and a release tarball for personal data before publishing, and frame/boundary-check.sh checks that nothing from the disc is in a release.

Support

KartFrame exists because of heurazy's Wiicompiled VR PLUS. If you want to support someone, support them first: star and follow it, report what you find there, and send improvements to the game upstream.

If you would like more Steam Frame ports, you can also buy me a coffee. It pays for the Claude API credits these ports are built with, spent as carefully as I can.

Credits

• Built by simplysanatori.
• Wiicompiled VR PLUS by heurazy, which this is built on, and heurazy's Mario Kart Wii VR port before it.
• Wiicompiled VR by iChris4, the OpenXR port of WiiCompiled that Wiicompiled VR PLUS started from, and the WiiCompiled translator that turns the Wii game into C++.
• aurora, the renderer, and Dawn, the WebGPU implementation under it.
• SDL3 and the OpenXR SDK.
• nod and nodtool by encounter, which extracts the disc.
• LLVM, the compiler bundled for the first run, and the .NET runtime, which the translator carries.
• Valve, for the Frame controller models. They are converted on your Frame from your own SteamVR files and never redistributed.
• framecorder, my headset recorder, which recorded the panels the double-image work was measured on.
• bigmak94's GalaxyQuest and the GalaxyFrame work, for what I learned about pacing for SteamVR and for the test tools (xrmock, and xrprobe, GPLv3).

THIRD-PARTY-NOTICES.md has the full list with licences.

Mario Kart Wii, Nintendo and their logos are trademarks of Nintendo. This is an unofficial fan project. It is not affiliated with or endorsed by Nintendo, Valve or the upstream author.

Licence

GPLv3, as upstream: see LICENSE. Third-party parts keep their own licences: see THIRD-PARTY-NOTICES.md and the licenses/ folder. The test probe in frame/tools/xrprobe is GPLv3 and is not part of the game. No Nintendo game data is included.

Upstream's own README is kept as README.upstream.md.

How this was made

I wanted Mario Kart Wii on my Frame without Lepton, so I started from Wiicompiled VR PLUS and had it built natively for SteamVR: a Linux Arm64 build, Dawn's Vulkan backend on SteamVR's own device, pacing written for the Frame's compositor, the Frame controllers in code, and a first run that builds the game from your own disc on the Frame itself.

This is vibe coded, with manual review throughout. I wrote it with Claude Code, using Anthropic's Fable 5.1, Opus 5.5 and Sonnet 5.5 models running on the Frame itself, in parallel lanes with a mock OpenXR runtime so that almost everything could be proven without putting the headset on. The double image took twenty headset sessions of about a minute each, every one of them a test of one thing, and the records of those are in frame/perf/.

Developer notes and what was learned about SteamVR on the Frame are in the technical notes.