add support for hand tracking and configurable reference spaces

crates/bevy_xr_utils/src/hand_gizmos.rs

@@ -0,0 +1,34 @@
+use bevy::{prelude::*, transform::TransformSystem};
+use bevy_xr::hands::{HandBone, HandBoneRadius};
+pub struct HandGizmosPlugin;
+impl Plugin for HandGizmosPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(
+            PostUpdate,
+            draw_hand_gizmos.after(TransformSystem::TransformPropagate),
+        );
+    }
+}
+fn draw_hand_gizmos(
+    mut gizmos: Gizmos,
+    query: Query<(&GlobalTransform, &HandBone, &HandBoneRadius)>,
+) {
+    for (transform, bone, radius) in &query {
+        let pose = transform.compute_transform();
+        gizmos.sphere(pose.translation, pose.rotation, **radius, gizmo_color(bone));
+    }
+}
+
+fn gizmo_color(bone: &HandBone) -> Color {
+    match bone {
+        HandBone::Palm => Color::WHITE,
+        HandBone::Wrist => Color::GRAY,
+        b if b.is_thumb() => Color::RED,
+        b if b.is_index() => Color::ORANGE,
+        b if b.is_middle() => Color::YELLOW,
+        b if b.is_ring() => Color::GREEN,
+        b if b.is_little() => Color::BLUE,
+        // should be impossible to hit
+        _ => Color::rgb(1.0, 0.0, 1.0),
+    }
+}

crates/bevy_xr_utils/src/lib.rs

@@ -0,0 +1,3 @@
+// use bevy::prelude::*;
+pub mod hand_gizmos;
+