EyeTrackVR Calibration Overlay

Cross-platform OpenXR + Vulkan eye-tracking calibration overlay for EyeTrackVR. Renders a follow-the-dot target (plus instruction text) in the headset and streams capture signals to the EyeTrackVR Python app over localhost UDP.

Runs on any PC OpenXR runtime (SteamVR, WMR, Oculus, Monado) on Windows and Linux, and uses a native OpenVR overlay on SteamVR so it never closes the running game.

Two backends (auto-selected)

On SteamVR a focused OpenXR session becomes the scene application, and SteamVR allows only one — so launching an OpenXR calibration would terminate whatever game is running (e.g. VRChat). To avoid that, the tool has two rendering backends and picks the right one at startup:

• OpenVR overlay (src/ovr_app.cpp) — used whenever SteamVR is already running. The dot, instruction text and an opaque grey backdrop are drawn as IVROverlay overlays composited on top of the running game. The game keeps running underneath; quitting the calibration returns straight to it, with no relaunch. Attaches with VRApplication_Background, so it never launches SteamVR itself.
• OpenXR + Vulkan (src/xr_app.cpp) — used otherwise (native Virtual Desktop, standalone runtimes, Monado, etc.), where a focused session evicts nothing. The dot/text are head-locked XrCompositionLayerQuad layers over an opaque grey projection background.

Force a backend with --backend=openvr or --backend=openxr (the latter restores the game-evicting focused-session behaviour on SteamVR).

Both backends place targets using the runtime's authoritative per-eye field of view (XrFovf, or SteamVR's GetProjectionRaw): each eye's frustum is intersected with the overlay plane and the two are overlapped to get the binocular region, centred on the true optical axis. This guarantees every target is inside both eyes' visible field and centred correctly.

Modes

EyeTrackVR-Overlay [mode] [--coverage=0.85] [--max-deg=40] [--backend=openvr|openxr]

mode	behaviour
(default)	classic 9-point grid; signals point index 0–8, then 9
center	single centre point; signals 9
ellipse	orbit + inward spiral for dense ellipse-fit sampling
datacollect	9-point normal pass + 9-point squint pass
interactive	driven by the EyeTrackVR Python app over UDP

• --coverage= (0–1): fraction of the binocular FOV the outermost targets reach.
• --max-deg= (0–90): hard cap on target eccentricity in degrees.

UDP protocol

Unchanged from the OpenVR build — the Python side needs no changes. Big-endian int32 signals are sent to 127.0.0.1:2112; interactive mode receives commands on 2113. See the comments in src/modes.cpp for the full command/signal table.

Building

Requires CMake ≥ 3.21, a C++20 compiler, and vcpkg. Dependencies (openxr-loader, vulkan-headers, vulkan-loader, stb) are declared in vcpkg.json and installed automatically at configure time. The OpenVR SDK used by the overlay backend is vendored as a git submodule (external/OpenVR) — clone with --recurse-submodules (or run git submodule update --init). On Windows the build links it and copies openvr_api.dll next to the executable; on other platforms only the OpenXR backend is built.

cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=<vcpkg>/scripts/buildsystems/vcpkg.cmake
cmake --build build --config Release

The build copies assets/ (the dot image and bundled Open Sans font) and the required runtime DLLs next to the executable. Launch with your OpenXR runtime (e.g. SteamVR) active and the headset on.