Add XR tracking state-change signals

doc/classes/XRNode3D.xml

@@ -51,4 +51,12 @@
 			Godot defines a number of standard trackers such as [code]left_hand[/code] and [code]right_hand[/code] but others may be configured within a given [XRInterface].
 		</member>
 	</members>
+	<signals>
+		<signal name="tracking_changed">
+			<param index="0" name="tracking" type="bool" />
+			<description>
+				Emitted when the [member tracker] starts or stops receiving updated tracking data for the [member pose] being tracked. The [param tracking] argument indicates whether the tracker is getting updated tracking data.
+			</description>
+		</signal>
+	</signals>
 </class>

doc/classes/XRPositionalTracker.xml

@@ -112,6 +112,12 @@
 				Emitted when the state of a pose tracked by this tracker changes.
 			</description>
 		</signal>
+		<signal name="pose_lost_tracking">
+			<param index="0" name="pose" type="XRPose" />
+			<description>
+				Emitted when a pose tracked by this tracker stops getting updated tracking data.
+			</description>
+		</signal>
 		<signal name="profile_changed">
 			<param index="0" name="role" type="String" />
 			<description>

scene/3d/xr_nodes.cpp

@@ -233,6 +233,8 @@ void XRNode3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_has_tracking_data"), &XRNode3D::get_has_tracking_data);
 	ClassDB::bind_method(D_METHOD("get_pose"), &XRNode3D::get_pose);
 	ClassDB::bind_method(D_METHOD("trigger_haptic_pulse", "action_name", "frequency", "amplitude", "duration_sec", "delay_sec"), &XRNode3D::trigger_haptic_pulse);
+
+	ADD_SIGNAL(MethodInfo("tracking_changed", PropertyInfo(Variant::BOOL, "tracking")));
 };
 
 void XRNode3D::_validate_property(PropertyInfo &p_property) const {
@@ -305,13 +307,7 @@ bool XRNode3D::get_is_active() const {
 }
 
 bool XRNode3D::get_has_tracking_data() const {
-	if (tracker.is_null()) {
-		return false;
-	} else if (!tracker->has_pose(pose_name)) {
-		return false;
-	} else {
-		return tracker->get_pose(pose_name)->get_has_tracking_data();
-	}
+	return has_tracking_data;
 }
 
 void XRNode3D::trigger_haptic_pulse(const String &p_action_name, double p_frequency, double p_amplitude, double p_duration_sec, double p_delay_sec) {
@@ -346,19 +342,24 @@ void XRNode3D::_bind_tracker() {
 		}
 
 		tracker->connect("pose_changed", callable_mp(this, &XRNode3D::_pose_changed));
+		tracker->connect("pose_lost_tracking", callable_mp(this, &XRNode3D::_pose_lost_tracking));
 
 		Ref<XRPose> pose = get_pose();
 		if (pose.is_valid()) {
 			set_transform(pose->get_adjusted_transform());
+			_set_has_tracking_data(pose->get_has_tracking_data());
 		}
 	}
 }
 
 void XRNode3D::_unbind_tracker() {
 	if (tracker.is_valid()) {
 		tracker->disconnect("pose_changed", callable_mp(this, &XRNode3D::_pose_changed));
+		tracker->disconnect("pose_lost_tracking", callable_mp(this, &XRNode3D::_pose_lost_tracking));
 
 		tracker.unref();
+
+		_set_has_tracking_data(false);
 	}
 }
 
@@ -382,9 +383,27 @@ void XRNode3D::_removed_tracker(const StringName p_tracker_name, int p_tracker_t
 void XRNode3D::_pose_changed(const Ref<XRPose> &p_pose) {
 	if (p_pose.is_valid() && p_pose->get_name() == pose_name) {
 		set_transform(p_pose->get_adjusted_transform());
+		_set_has_tracking_data(p_pose->get_has_tracking_data());
 	}
 }
 
+void XRNode3D::_pose_lost_tracking(const Ref<XRPose> &p_pose) {
+	if (p_pose.is_valid() && p_pose->get_name() == pose_name) {
+		_set_has_tracking_data(false);
+	}
+}
+
+void XRNode3D::_set_has_tracking_data(bool p_has_tracking_data) {
+	// Ignore if the has_tracking_data state isn't changing.
+	if (p_has_tracking_data == has_tracking_data) {
+		return;
+	}
+
+	// Handle change of has_tracking_data.
+	has_tracking_data = p_has_tracking_data;
+	emit_signal(SNAME("tracking_changed"), has_tracking_data);
+}
+
 XRNode3D::XRNode3D() {
 	XRServer *xr_server = XRServer::get_singleton();
 	ERR_FAIL_NULL(xr_server);

scene/3d/xr_nodes.h

@@ -78,7 +78,7 @@ class XRNode3D : public Node3D {
 private:
 	StringName tracker_name;
 	StringName pose_name = "default";
-	bool is_active = true;
+	bool has_tracking_data = false;
 
 protected:
 	Ref<XRPositionalTracker> tracker;
@@ -91,6 +91,8 @@ class XRNode3D : public Node3D {
 	void _removed_tracker(const StringName p_tracker_name, int p_tracker_type);
 
 	void _pose_changed(const Ref<XRPose> &p_pose);
+	void _pose_lost_tracking(const Ref<XRPose> &p_pose);
+	void _set_has_tracking_data(bool p_has_tracking_data);
 
 public:
 	void _validate_property(PropertyInfo &p_property) const;

servers/xr/xr_positional_tracker.cpp

@@ -62,6 +62,7 @@ void XRPositionalTracker::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("invalidate_pose", "name"), &XRPositionalTracker::invalidate_pose);
 	ClassDB::bind_method(D_METHOD("set_pose", "name", "transform", "linear_velocity", "angular_velocity", "tracking_confidence"), &XRPositionalTracker::set_pose);
 	ADD_SIGNAL(MethodInfo("pose_changed", PropertyInfo(Variant::OBJECT, "pose", PROPERTY_HINT_RESOURCE_TYPE, "XRPose")));
+	ADD_SIGNAL(MethodInfo("pose_lost_tracking", PropertyInfo(Variant::OBJECT, "pose", PROPERTY_HINT_RESOURCE_TYPE, "XRPose")));
 
 	ClassDB::bind_method(D_METHOD("get_input", "name"), &XRPositionalTracker::get_input);
 	ClassDB::bind_method(D_METHOD("set_input", "name", "value"), &XRPositionalTracker::set_input);
@@ -146,7 +147,10 @@ void XRPositionalTracker::invalidate_pose(const StringName &p_action_name) {
 	// only update this if we were tracking this pose
 	if (poses.has(p_action_name)) {
 		// We just set tracking data as invalid, we leave our current transform and velocity data as is so controllers don't suddenly jump to origin.
-		poses[p_action_name]->set_has_tracking_data(false);
+		Ref<XRPose> pose = poses[p_action_name];
+		pose->set_has_tracking_data(false);
+
+		emit_signal(SNAME("pose_lost_tracking"), pose);
 	}
 }