Modify the XRHandModifier3D to scale appropriately with Skeleton3D.mo…

…tion_scale and XRServer.world_scale

doc/classes/XRHandModifier3D.xml

@@ -5,6 +5,8 @@
  </brief_description>
  <description>
  This node uses hand tracking data from a [XRHandTracker] to animate the skeleton of a hand mesh.
+ This node positions itself at the [constant XRHandTracker.HAND_JOINT_PALM] position and scales itself to [member XRServer.world_scale]. Adding the hand model as a child of this node will result in the model being positioned and scaled correctly for XR experiences.
+ The hand tracking position-data is scaled by [member Skeleton3D.motion_scale] when applied to the skeleton, which can be used to adjust the tracked hand to match the scale of the hand model.
  </description>
  <tutorials>
  <link title="XR documentation index">$DOCS_URL/tutorials/xr/index.html</link>

scene/3d/xr_hand_modifier_3d.cpp

@@ -213,21 +213,23 @@ void XRHandModifier3D::_update_skeleton() {
  return;
  }
 
+ // Get the world and skeleton scale.
+ const float ws = xr_server->get_world_scale();
+ const float ss = skeleton->get_motion_scale();
+
  // We cache our transforms so we can quickly calculate local transforms.
  bool has_valid_data[XRHandTracker::HAND_JOINT_MAX];
  Transform3D transforms[XRHandTracker::HAND_JOINT_MAX];
  Transform3D inv_transforms[XRHandTracker::HAND_JOINT_MAX];
 
- const float ws = xr_server->get_world_scale();
-
  if (tracker->get_has_tracking_data()) {
  for (int joint = 0; joint < XRHandTracker::HAND_JOINT_MAX; joint++) {
  BitField<XRHandTracker::HandJointFlags> flags = tracker->get_hand_joint_flags((XRHandTracker::HandJoint)joint);
  has_valid_data[joint] = flags.has_flag(XRHandTracker::HAND_JOINT_FLAG_ORIENTATION_VALID);
 
  if (has_valid_data[joint]) {
  transforms[joint] = tracker->get_hand_joint_transform((XRHandTracker::HandJoint)joint);
- transforms[joint].origin *= ws;
+ transforms[joint].origin *= ss;
  inv_transforms[joint] = transforms[joint].inverse();
  }
  }
@@ -253,8 +255,11 @@ void XRHandModifier3D::_update_skeleton() {
  skeleton->set_bone_pose_rotation(joints[joint].bone, Quaternion(relative_transform.basis));
  }
 
- // Transform to the skeleton pose.
- set_transform(transforms[XRHandTracker::HAND_JOINT_PALM]);
+ // Transform to the skeleton pose. This uses the HAND_JOINT_PALM position without skeleton-scaling, as it
+ // must be positioned to match the physical hand location. It is scaled with the world space to match
+ // the scaling done to the camera and eyes.
+ set_transform(
+ tracker->get_hand_joint_transform(XRHandTracker::HAND_JOINT_PALM) * ws);
 
  set_visible(true);
  } else {