Choose a baseline marker format

[AdaRoseCannon]

The marker-tracking API should probably have at least one kind of marker format that works reasonably well across a wide range of AR platforms.

We should check to see what seems to track well between existing native implementations to find a lowest common denominator

[AdaRoseCannon]

/agenda

[toji]

Android XR supports several extensions related to marker tracking, including XR_ANDROID_trackables_qr_code, which (as you might guess) enables QR code support.

It's my understanding that the functionality in the Android extension is also covered by XR_EXT_spatial_marker_tracking for other OpenXR devices. That extension also includes tracking capabilities for Micro QR codes, ArUco Markers, and April Tags.

There are several other OpenXR extensions from vendors like Magic Leap and Microsoft that also include marker tracking in various capacities. QR code tracking appears to be common between all of them.