Ray casts platform support

Understand the AR Foundation capabilities implemented by the OpenXR Spatial Entities ray cast provider.

This package implements the following optional features of AR Foundation's XRRaycastSubsystem:

Feature	Descriptor Property	Supported
World based ray cast	supportsWorldBasedRaycast	Yes
Viewport based ray cast	supportsViewportBasedRaycast
Tracked ray casts	supportsTrackedRaycasts
Trackable types	supportedTrackableTypes	Determined at runtime

Supported runtimes

This provider requires three OpenXR extensions: XR_ANDROID_spatial_discovery_raycast, XR_EXT_spatial_entity, and XR_EXT_future. If a runtime doesn't enable all three, the provider fails to initialize and reports no trackable types.

Refer to the following table to understand the expected behavior of the Spatial Entities Ray Casts feature on supported runtimes:

Runtime	Supported	Trackable types
Android XR	Yes	PlaneWithinPolygon, Depth
Meta Horizon OS		None

As of this package's release date, Meta Horizon OS doesn't implement XR_ANDROID_spatial_discovery_raycast. To cast rays against Meta Horizon OS depth data, use the ray cast feature in the Unity OpenXR: Meta package instead.

Supported trackable types

The trackable types this provider reports depend on your project configuration, not only on the OpenXR runtime. supportedTrackableTypes is empty until a session starts, so check it only after that. If you enable the Spatial Entities Ray Casts feature and change nothing else, it remains empty.

Trackable type	Requires
PlaneWithinPolygon	The Spatial Entities Planes feature and a runtime that reports ray cast results for plane tracking.
Depth	Depth ray casts, which are disabled by default.