Merge branch 'oc-forced-trackers' into 'main'

fossvr/opencomposite: Add non-tracker-device-as-tracker section

See merge request lvra/lvra.gitlab.io!88

content/docs/fossvr/opencomposite/_index.md

@@ -17,7 +17,21 @@ OpenComposite is required for Steam Play games to work in VR regardless of API.
 
 Contributions to improve the OpenVR to OpenXR mapping are welcome.
 
-## Rebinding Controls
+## Forcing additional devices as trackers
+
+OpenComposite has the environment variable `OPENCOMPOSITE_TRACKER_SERIALS` to allow using non-tracker devices as trackers in SteamVR games. The expected format is as follows: `serial1;serial2` where each 'serial' is a device serial like `LHR-00000000` or `WiVRn HMD`. You can set this on games by setting this launch option in Steam: `env OPENCOMPOSITE_TRACKER_SERIALS="LHR-00000001;LHR-00000002" %command%`.
+
+To obtain info for lighthouse devices, you may look at the top of the Monado stdout when using steamvr_lh. For other types of devices there are multiple ways of obtaining device serials:
+
+- OpenComposite log file
+
+  The OpenComposite log file at `~/.local/state/OpenComposite/logs/opencomposite.log` will log all seen devices when checking for trackers, so you can search for `Checking for generic trackers...` in the log file and look below for `Found usable xdev`.
+
+- motoc
+
+  motoc has the `show` subcommand for viewing all device names, serials, and positions relative to the space origin.
+
+## Rebinding controls
 
 > Changing OpenVR bindings is currently a very manual process. This will change in the future.