Viture on Raspberry Pi 5: SBS desktop (sway) + stereo shim for GLES apps

[GlassOnTin]

The Pi 5 has no USB-C DP-alt mode, so the glasses' single USB-C can't deliver video and IMU together on this board — you get one or the other, which rules out the usual XRLinuxDriver setup. Wrote up what does work instead.

Display: Pi HDMI → glasses works fine; holding the power button toggles SBS mode, which switches the EDID between 1920×1080 and 3840×1080@60.

Two tools (MIT):

• glasses-desktop — sway session that shows the full desktop in both eyes (desktop on a headless output, per-eye mirrors on the physical one). Follows the 2D/SBS toggle live.
• gles-stereo-shim — LD_PRELOAD shim for unmodified GLES apps: flat SBS, or depth-reprojected 3D synthesized from the app's depth buffer. Verified against a true two-camera renderer (0.93 disparity correlation, ~3 px median error). aarch64 only for now.

Head tracking: planning an external IMU (XIAO nRF52840 Sense → 3DOF) since the native one is unreachable on this board. If anyone has a Pi-friendly route to the built-in IMU alongside HDMI video, I'd like to hear it.

[GlassOnTin]

Update: glasses-desktop now renders per-window stereo depth (windows ranked by focus order, focused pops toward you) at 60 fps on the Pi 5. Getting there needed one lesson worth sharing: on split render/display boards, Mesa's Wayland EGL goes linear-only and v3d shadow-copies linear textures through uncached memory (~190 ms/frame) — rendering via the GBM platform on the render node directly and presenting dmabufs manually fixed it. Tagged v1.0.0.