saphid--chromium-webxr-steam-frame/frame/chromium-xr

#!/bin/bash
# Start the WebXR Chromium build. frame/install.sh copies this to
# ~/.local/bin/chromium-xr; the Steam library shortcut and the desktop entry
# both run it. Arguments go to Chromium, so `chromium-xr URL` opens a page.
set -euo pipefail

CHROME="${CHROMIUM_XR_HOME:-$HOME/chromium-xr}/chrome"
[[ -x "$CHROME" ]] || { echo "chromium-xr: no build at $CHROME (run frame/install.sh)" >&2; exit 1; }

# Steam preloads its in-game overlay (gameoverlayrenderer.so) into anything it
# launches. It segfaults in Chromium's zygote, the GPU process then can't
# start, and Chromium quits with "GPU process isn't usable". Drop it and keep
# anything else that was preloaded.
if [[ -n "${LD_PRELOAD:-}" ]]; then
  keep=()
  # Split on spaces and colons only, like ld.so, with no glob expansion.
  # read -d '' takes the whole value, newlines included (it returns 1 at EOF).
  IFS=' :' read -r -d '' -a libs < <(printf '%s' "$LD_PRELOAD") || true
  for lib in ${libs[@]+"${libs[@]}"}; do
    [[ -z "$lib" || "$lib" == *gameoverlayrenderer.so ]] || keep+=("$lib")
  done
  if (( ${#keep[@]} )); then
    LD_PRELOAD=${keep[0]}
    for lib in "${keep[@]:1}"; do LD_PRELOAD+=":$lib"; done
    export LD_PRELOAD
  else
    unset LD_PRELOAD
  fi
fi

# --enable-features=OpenXR: the Linux OpenXR device is off by default.
# --ozone-platform=x11: gamescope's X display, where each app is a panel.
# --no-first-run and --password-store=basic: otherwise startup can stop at a
#   first-run or keyring prompt you can't see.
# --disable-seccomp-filter-sandbox: with the XR process's seccomp policy on,
#   SteamVR sees the wrong process ID and refuses the session (see
#   docs/technical-notes.md). The namespace sandbox stays on.
# --touch-events=enabled: Xwayland labels its touch device as a pointer, so
#   Chromium doesn't offer pages the touch API on its own.
profile=$HOME/.config/chromium-xr

# Let every site enter VR without the "Allow VR?" prompt: make Allow the
# default for the VR permission, and drop per-site Block exceptions. There's
# no policy or switch for this, and Chromium only reads Preferences at start,
# so skip it while Chromium is running. flock stops two launches editing the
# file at once; the running check is inside it, so it's fresh for each edit.
mkdir -p "$profile"
flock "$profile/.chromium-xr-prefs.lock" python3 - "$profile" <<'EOF' ||
import json, os, sys, tempfile
profile = sys.argv[1]
try:
    # SingletonLock is a symlink to "<host>-<pid>" while Chromium runs.
    os.kill(int(os.readlink(os.path.join(profile, 'SingletonLock')).rsplit('-', 1)[1]), 0)
    sys.exit(0)  # Chromium is running
except (OSError, ValueError, IndexError):
    pass  # no lock, or a stale one: not running
path = os.path.join(profile, 'Default', 'Preferences')
try:
    with open(path) as f:
        prefs = json.load(f)
except FileNotFoundError:
    prefs = {}
settings = prefs.setdefault('profile', {})
settings.setdefault('default_content_setting_values', {})['vr'] = 1  # Allow
vr = settings.get('content_settings', {}).get('exceptions', {}).get('vr', {})
for pattern in [p for p, v in vr.items() if isinstance(v, dict) and v.get('setting') == 2]:
    del vr[pattern]  # Block
os.makedirs(os.path.dirname(path), exist_ok=True)
# Private (0600) and unique, so the file never widens its permissions and two
# launches can't write into each other's copy.
fd, tmp = tempfile.mkstemp(dir=os.path.dirname(path), prefix='.Preferences.')
try:
    with os.fdopen(fd, 'w') as f:
        json.dump(prefs, f)
    os.replace(tmp, path)
except BaseException:
    os.unlink(tmp)
    raise
EOF
  echo "chromium-xr: couldn't set the VR permission to Allow" >&2

cmd=("$CHROME"
  --user-data-dir="$profile"
  --enable-features=OpenXR
  --ozone-platform=x11
  --no-first-run --no-default-browser-check --password-store=basic
  --disable-seccomp-filter-sandbox
  --touch-events=enabled
  "$@")

# gamescope turns the controller's laser into mouse clicks for apps that Steam
# launched, so dragging selects text instead of scrolling. Windows outside
# Steam's process tree still get their own panel, but the laser reaches them
# as a touchscreen, as in Desktop Mode. So when Steam starts us, run Chromium
# as its own systemd user service and wait for it, which keeps it "running"
# in Steam. CHROMIUM_XR_STEAM_PANEL=1 keeps the old behaviour.
if [[ -z "${SteamAppId:-}" || "${CHROMIUM_XR_STEAM_PANEL:-}" == 1 ]] ||
    ! command -v systemd-run >/dev/null; then
  exec "${cmd[@]}"
fi

# Pass our environment through by name (-E NAME copies its value), minus
# systemd's per-service bookkeeping.
env_args=()
for name in $(compgen -e); do
  case $name in
    INVOCATION_ID|JOURNAL_STREAM|MANAGERPID|SYSTEMD_EXEC_PID|NOTIFY_SOCKET|MEMORY_PRESSURE_*|LISTEN_*) ;;
    *) env_args+=(-E "$name") ;;
  esac
done
unit=chromium-xr-$$
# Steam's Stop, or the reaper ending us, closes Chromium too. Set before
# starting it, so a Stop during startup isn't lost (bash runs the trap once
# systemd-run returns).
stopping=
trap 'stopping=1; systemctl --user stop --no-block "$unit" 2>/dev/null' TERM INT HUP
if ! systemd-run --user --quiet --collect --same-dir --unit="$unit" \
    --service-type=exec --expand-environment=no "${env_args[@]}" "${cmd[@]}"; then
  # A Stop can make systemd-run fail too; don't start Chromium again then.
  [[ -z "$stopping" ]] || exit 0
  echo "chromium-xr: systemd-run failed; starting in Steam's panel instead" >&2
  exec "${cmd[@]}"
fi
# MainPID is 0 once the service has ended (and been collected), e.g. when
# Chromium passed the URL to a window that was already open. A failed query
# is retried rather than taken to mean Chromium has gone.
pid=
for _ in 1 2 3 4 5; do
  pid=$(systemctl --user show -p MainPID --value "$unit") && break
  pid=
  sleep 1
done
if [[ -z "$pid" ]]; then
  echo "chromium-xr: can't query $unit; Chromium keeps running, but Steam won't track it" >&2
  exit 1
fi
[[ "$pid" != 0 ]] || exit 0
while kill -0 "$pid" 2>/dev/null; do
  tail --pid="$pid" -f /dev/null &
  wait $! || true
done