Launcher: laser drags scroll like a touchscreen; allow VR on every site

gamescope turns the laser into mouse clicks for apps Steam launches, so
dragging selected text. When Steam starts it, the launcher now runs Chromium
as a systemd user service outside Steam's process tree: its windows get their
own gamescope panel and real touches. Steam still tracks it and Stop closes it.
CHROMIUM_XR_STEAM_PANEL=1 keeps the old behaviour. --touch-events=enabled
because Xwayland labels its touch device as a pointer.

Before each start (when Chromium isn't running) the launcher also makes Allow
the default VR permission and drops per-site Blocks, so there's no
"Allow VR?" prompt.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -41,6 +41,7 @@ SteamVR 2.17.10) with Chromium **156.0.8071.0**, built for arm64:
 | three.js [stereo 360 video](https://threejs.org/examples/webxr_vr_video.html) | plays in 3D |
 | Launch from the Steam library | opens as its own panel, like any app; WebXR renders in the headset |
 | Controllers inside WebXR pages | tracked pose every frame; squeeze events and button state reach the page (trigger, thumbstick and left controller not tested) |
+| Laser pointer on the browser panel | reaches Chromium as a touchscreen, so trigger-and-drag scrolls the page (set up and checked on the Frame; the drag itself not yet tried in the headset) |
 | Frame rate | 72 fps, every frame 13.9–14 ms over 16 s (simple scene); SteamVR dropped frames only at startup |
 
 This is an unofficial, experimental build. See [Limitations](#limitations)
@@ -112,15 +113,18 @@ Library**, and pick Chromium XR.
    the headset.
 2. Go to a WebXR site, for example the
    [WebXR Samples](https://immersive-web.github.io/webxr-samples/).
-3. Press the site's **Enter VR** button.
-4. Chromium asks **Allow VR?** in the browser panel. Choose *Allow this time*
-   or *Allow while visiting the site*.
-5. To leave VR, use the site's exit button or the Steam button.
+3. Press the site's **Enter VR** button. It opens in the headset straight
+   away: the launcher sets Chromium's VR permission to Allow for every site,
+   so there's no **Allow VR?** prompt.
+4. To leave VR, use the site's exit button or the Steam button.
 
 The first time you launch it, Steam may show an **External Controller
 Translation** notice. It's only information about controller button icons;
 choose OK.
 
+Point at the panel and pull the trigger to click. Hold the trigger and drag
+to scroll, as on a touchscreen.
+
 From a terminal on the Frame, `chromium-xr https://example.com` opens a
 page directly.
 
@@ -140,6 +144,21 @@ page directly.
 - **No controller vibration.** SteamVR reports no haptic actuators to the page.
 - **No DRM video.** There's no Widevine, so paid streaming services that
   need it won't play.
+- **Its panel isn't Steam's app panel.** gamescope sends the laser to apps
+  Steam launches as mouse clicks, so dragging would select text. The
+  launcher therefore runs Chromium outside Steam's process tree, where each
+  window gets a plain gamescope panel and the laser acts as a touchscreen.
+  Steam still shows Chromium XR as running, and stopping it there closes
+  Chromium. Chromium's output goes to the journal
+  (`journalctl --user -u 'chromium-xr-*'`). Start it with
+  `CHROMIUM_XR_STEAM_PANEL=1` in the shortcut's launch options (as
+  `CHROMIUM_XR_STEAM_PANEL=1 %command%`) to keep it in Steam's panel, with
+  mouse clicks.
+- **Every site can start VR.** Each launch sets the VR permission's default
+  to Allow and removes any per-site Block, so any page can take over the
+  headset when you press its button (or, on some sites, without one). You
+  can still block a site in `chrome://settings/content/vr`, but only until
+  the next launch.
 - **One window at a time per profile.** If Chromium XR is already open,
   launching it again opens the page in the existing window.
 - **Not a default browser.** It works as one (the desktop entry registers

docs/technical-notes.md

@@ -57,7 +57,9 @@ isn't needed.
 ## What a working session looks like
 
 - The page's `isSessionSupported("immersive-vr")` resolves `true`.
-- After the **Allow VR?** prompt, `requestSession("immersive-vr")` succeeds.
+- `requestSession("immersive-vr")` succeeds. (Chromium asks **Allow VR?**
+  first unless the site's VR permission is Allow; the launcher makes Allow
+  the default, see below.)
   The first frame has a viewer pose with 2 views and a 2880 × 1440 framebuffer
   (1440 × 1440 per eye).
 - SteamVR's log (`~/.local/share/Steam/logs/vrserver.txt`) shows the app move
@@ -91,6 +93,82 @@ Measured with a session that clears to red, with `hand-tracking` and
 - Requesting `hand-tracking` makes Chromium ask **Allow hand tracking?** in
   the browser panel before the session starts.
 
+## The laser pointer on the browser panel (2026-09-28)
+
+gamescope (3.16.28 on the Frame) turns SteamVR's laser events for a panel
+into input for the app. A trigger press is `VREvent_MouseButtonDown` with the
+left button, which gamescope sends as a Wayland touch, then Xwayland passes
+it on as an XInput 2 touch. What happens next depends on gamescope's *touch
+click mode* for that panel (`GetTouchClickMode` in
+`src/Backends/OpenVRBackend.cpp`):
+
+- **Windows of an app Steam launched** (app id taken from the `STEAM_GAME`
+  property, the `app-steam-app<id>-<pid>.scope` cgroup, or a
+  `reaper SteamLaunch AppId=<id>` ancestor): forced to *left click*, in a
+  code path commented as a workaround for Steam not setting
+  `STEAM_TOUCH_CLICK_MODE` on the Frame. The touch becomes a left mouse
+  button, so holding the trigger and dragging selects text.
+- **Windows with no app id**: *passthrough*. Each gets its own panel
+  (`gamescope.gamescope-0.window.<n>`) and receives real touches. The
+  Desktop Mode panel is one of these, which is why a browser there scrolls
+  when you drag.
+
+The thumbstick sends `VREvent_ScrollSmooth`, which gamescope turns into mouse
+wheel events in either mode.
+
+Chromium registers itself in a systemd scope of its own
+(`app-org.chromium.Chromium-<pid>.scope`), so gamescope finds the app id by
+walking up to Steam's `reaper`. Forking can't escape that, because `reaper`
+is a subreaper. When `SteamAppId` is set, the `chromium-xr` launcher starts
+Chromium with `systemd-run --user` instead, and waits for it to exit.
+Chromium's parent is then the user's systemd, and its windows get no app id.
+Chromium's menus and bubbles are override-redirect windows, which gamescope
+shows only over a focused window with the same app id. They come from the
+same process, so they get app id 0 as well.
+
+Verified on the Frame (SteamOS build 20260922.6101926), without wearing the
+headset:
+
+- Launched from Steam, the old launcher's window had app id 2349681812 and
+  panel `valve.steam.desktopgame.2349681812`. Setting `STEAM_GAME` to 0 on
+  it destroyed that panel and created `gamescope.gamescope-0.window.70`.
+- With the new launcher, Chromium's parent is `systemd`, not `reaper`. Its
+  panel is `gamescope.gamescope-0.window.88`, `GAMESCOPE_FOCUSABLE_APPS` is
+  empty, and `SIGTERM` to the launcher, which is what Steam's Stop does,
+  closes Chromium and removes the service.
+- Xwayland 24.1.9 gives every device the XI1 type `xwayland-pointer`,
+  including `xwayland-touch`. Chromium's X11 hotplug code only counts
+  `TOUCHSCREEN` or `xwayland-touch` as a touchscreen, so it reports
+  `navigator.maxTouchPoints` 0 and leaves out the touch API. Its XI2 touch
+  handling (`TouchFactory`) still accepts the device's touches. The launcher
+  passes `--touch-events=enabled`, and pages then see `ontouchstart`.
+- Chromium's `--touch-devices=<id>` switch isn't a way around this. It
+  would make every button of the shared `xwayland-pointer` a touch,
+  including wheel and right-click.
+
+Not yet checked in the headset: dragging a page, fling, and menus and
+permission prompts showing on the new panel.
+
+## The VR permission (2026-09-28)
+
+Chromium's VR permission is the `vr` content setting, default Ask, with
+Allow, Ask and Block all valid defaults
+(`components/content_settings/core/browser/content_settings_registry.cc`).
+No policy or command-line switch sets it, and managed policies would have to
+go in `/etc/chromium`, which is on the Frame's read-only root. So before each
+start, if Chromium isn't already running (its `SingletonLock` link names a
+live process), the launcher sets `profile.default_content_setting_values.vr`
+to 1 (Allow) in `Default/Preferences` and deletes `vr` exceptions whose
+setting is 2 (Block). **Verified on the Frame:** aframe.io, which had no
+saved exception, started an immersive session from `requestSession` with no
+prompt, and the value was still 1 after Chromium quit and rewrote the file.
+It doesn't cover **Allow hand tracking?** (the `hand_tracking` setting).
+
+The same test showed WebXR still works with Chromium outside Steam's
+process tree. The launcher keeps Steam's environment, including
+`SteamAppId`, and SteamVR still bound the session to
+`steam.app.2349681812`.
+
 ## Graphics
 
 Chromium's GPU process uses ANGLE on OpenGL, which runs on zink over the

frame/chromium-xr

@@ -35,10 +35,107 @@ fi
 # --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.
-exec "$CHROME" \
-  --user-data-dir="$HOME/.config/chromium-xr" \
-  --enable-features=OpenXR \
-  --ozone-platform=x11 \
-  --no-first-run --no-default-browser-check --password-store=basic \
-  --disable-seccomp-filter-sandbox \
-  "$@"
+# --touch-events=enabled: Xwayland labels its touch device as a pointer, so
+#   Chromium doesn't offer pages the touch API on its own.
+profile=$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