Improve XRInterface hooks into rendering

14 files changed, 163 insertions, 93 deletions

diff --git a/doc/classes/XRInterfaceExtension.xml b/doc/classes/XRInterfaceExtension.xml
index d2bb6aa59a..cd09f83335 100644
--- a/doc/classes/XRInterfaceExtension.xml
+++ b/doc/classes/XRInterfaceExtension.xml
@@ -9,46 +9,52 @@
 	<tutorials>
 	</tutorials>
 	<methods>
-		<method name="_commit_views" qualifiers="virtual">
+		<method name="_end_frame" qualifiers="virtual">
 			<return type="void" />
-			<argument index="0" name="render_target" type="RID" />
-			<argument index="1" name="screen_rect" type="Rect2" />
 			<description>
+				Called if interface is active and queues have been submitted.
 			</description>
 		</method>
 		<method name="_get_anchor_detection_is_enabled" qualifiers="virtual const">
 			<return type="bool" />
 			<description>
+				Return [code]true[/code] if anchor detection is enabled for this interface.
 			</description>
 		</method>
 		<method name="_get_camera_feed_id" qualifiers="virtual const">
 			<return type="int" />
 			<description>
+				Returns the camera feed id for the [CameraFeed] registered with the [CameraServer] that should be presented as the background on an AR capable device (if applicable).
 			</description>
 		</method>
 		<method name="_get_camera_transform" qualifiers="virtual">
 			<return type="Transform3D" />
 			<description>
+				Returns the [Transform3D] that positions the [XRCamera3D] in the world.
 			</description>
 		</method>
 		<method name="_get_capabilities" qualifiers="virtual const">
 			<return type="int" />
 			<description>
+				Returns the capabilities of this interface.
 			</description>
 		</method>
 		<method name="_get_name" qualifiers="virtual const">
 			<return type="StringName" />
 			<description>
+				Returns the name of this interface.
 			</description>
 		</method>
 		<method name="_get_play_area" qualifiers="virtual const">
 			<return type="PackedVector3Array" />
 			<description>
+				Returns an [PackedVector3Array] that denotes the play areas boundaries (if applicable).
 			</description>
 		</method>
 		<method name="_get_play_area_mode" qualifiers="virtual const">
 			<return type="int" />
 			<description>
+				Returns the [enum XRInterface.PlayAreaMode] that sets up our play area.
 			</description>
 		</method>
 		<method name="_get_projection_for_view" qualifiers="virtual">
@@ -58,27 +64,32 @@
 			<argument index="2" name="z_near" type="float" />
 			<argument index="3" name="z_far" type="float" />
 			<description>
+				Returns the projection matrix for the given view as a [PackedFloat64Array].
 			</description>
 		</method>
 		<method name="_get_render_target_size" qualifiers="virtual">
 			<return type="Vector2" />
 			<description>
+				Returns the size of our render target for this interface, this overrides the size of the [Viewport] marked as the xr viewport.
 			</description>
 		</method>
 		<method name="_get_suggested_pose_names" qualifiers="virtual const">
 			<return type="PackedStringArray" />
 			<argument index="0" name="tracker_name" type="StringName" />
 			<description>
+				Returns a [PackedStringArray] with pose names configured by this interface. Note that user configuration can override this list.
 			</description>
 		</method>
 		<method name="_get_suggested_tracker_names" qualifiers="virtual const">
 			<return type="PackedStringArray" />
 			<description>
+				Returns a [PackedStringArray] with tracker names configured by this interface. Note that user configuration can override this list.
 			</description>
 		</method>
 		<method name="_get_tracking_status" qualifiers="virtual const">
 			<return type="int" />
 			<description>
+				Returns a [enum XRInterface.TrackingStatus] specifying the current status of our tracking.
 			</description>
 		</method>
 		<method name="_get_transform_for_view" qualifiers="virtual">
@@ -86,50 +97,80 @@
 			<argument index="0" name="view" type="int" />
 			<argument index="1" name="cam_transform" type="Transform3D" />
 			<description>
+				Returns a [Transform3D] for a given view.
 			</description>
 		</method>
 		<method name="_get_view_count" qualifiers="virtual">
 			<return type="int" />
 			<description>
+				Returns the number of views this interface requires, 1 for mono, 2 for stereoscopic.
 			</description>
 		</method>
 		<method name="_initialize" qualifiers="virtual">
 			<return type="bool" />
 			<description>
+				Initializes the interface, returns [code]true[/code] on success.
 			</description>
 		</method>
 		<method name="_is_initialized" qualifiers="virtual const">
 			<return type="bool" />
 			<description>
+				Returns [code]true[/code] if this interface has been initialised.
 			</description>
 		</method>
 		<method name="_notification" qualifiers="virtual">
 			<return type="void" />
 			<argument index="0" name="what" type="int" />
 			<description>
+				Informs the interface of an applicable system notification.
+			</description>
+		</method>
+		<method name="_post_draw_viewport" qualifiers="virtual">
+			<return type="void" />
+			<argument index="0" name="render_target" type="RID" />
+			<argument index="1" name="screen_rect" type="Rect2" />
+			<description>
+				Called after the XR [Viewport] draw logic has completed.
+			</description>
+		</method>
+		<method name="_pre_draw_viewport" qualifiers="virtual">
+			<return type="bool" />
+			<argument index="0" name="render_target" type="RID" />
+			<description>
+				Called if this is our primary [XRInterfaceExtension] before we start processing a [Viewport] for every active XR [Viewport], returns [code]true[/code] if that viewport should be rendered. An XR interface may return [code]false[/code] if the user has taken off their headset and we can pause rendering.
+			</description>
+		</method>
+		<method name="_pre_render" qualifiers="virtual">
+			<return type="void" />
+			<description>
+				Called if this [XRInterfaceExtension] is active before rendering starts, most XR interfaces will sync tracking at this point in time.
 			</description>
 		</method>
 		<method name="_process" qualifiers="virtual">
 			<return type="void" />
 			<description>
+				Called if this [XRInterfaceExtension] is active before our physics and game process is called. most XR interfaces will update its [XRPositionalTracker]s at this point in time.
 			</description>
 		</method>
 		<method name="_set_anchor_detection_is_enabled" qualifiers="virtual">
 			<return type="void" />
 			<argument index="0" name="enabled" type="bool" />
 			<description>
+				Enables anchor detection on this interface if supported.
 			</description>
 		</method>
 		<method name="_set_play_area_mode" qualifiers="virtual const">
 			<return type="bool" />
 			<argument index="0" name="mode" type="int" />
 			<description>
+				Set the play area mode for this interface.
 			</description>
 		</method>
 		<method name="_supports_play_area_mode" qualifiers="virtual const">
 			<return type="bool" />
 			<argument index="0" name="mode" type="int" enum="XRInterface.PlayAreaMode" />
 			<description>
+				Returns [code]true[/code] if this interface supports this play area mode.
 			</description>
 		</method>
 		<method name="_trigger_haptic_pulse" qualifiers="virtual">
@@ -141,11 +182,13 @@
 			<argument index="4" name="duration_sec" type="float" />
 			<argument index="5" name="delay_sec" type="float" />
 			<description>
+				Triggers a haptic pulse to be emitted on the specified tracker.
 			</description>
 		</method>
 		<method name="_uninitialize" qualifiers="virtual">
 			<return type="void" />
 			<description>
+				Uninitialize the interface.
 			</description>
 		</method>
 		<method name="add_blit">
@@ -169,6 +212,7 @@
 			<return type="RID" />
 			<argument index="0" name="render_target" type="RID" />
 			<description>
+				Returns a valid [RID] for a texture to which we should render the current frame if supported by the interface.
 			</description>
 		</method>
 	</methods>
diff --git a/doc/classes/XRServer.xml b/doc/classes/XRServer.xml
index 3a7fdea8d0..335ca4c35f 100644
--- a/doc/classes/XRServer.xml
+++ b/doc/classes/XRServer.xml
@@ -69,24 +69,6 @@
 				Returns a list of available interfaces the ID and name of each interface.
 			</description>
 		</method>
-		<method name="get_last_commit_usec">
-			<return type="int" />
-			<description>
-				Returns the absolute timestamp (in μs) of the last [XRServer] commit of the AR/VR eyes to [RenderingServer]. The value comes from an internal call to [method Time.get_ticks_usec].
-			</description>
-		</method>
-		<method name="get_last_frame_usec">
-			<return type="int" />
-			<description>
-				Returns the duration (in μs) of the last frame. This is computed as the difference between [method get_last_commit_usec] and [method get_last_process_usec] when committing.
-			</description>
-		</method>
-		<method name="get_last_process_usec">
-			<return type="int" />
-			<description>
-				Returns the absolute timestamp (in μs) of the last [XRServer] process callback. The value comes from an internal call to [method Time.get_ticks_usec].
-			</description>
-		</method>
 		<method name="get_reference_frame" qualifiers="const">
 			<return type="Transform3D" />
 			<description>
diff --git a/modules/mobile_vr/mobile_vr_interface.cpp b/modules/mobile_vr/mobile_vr_interface.cpp
index 49044c4afe..8cd23ffb24 100644
--- a/modules/mobile_vr/mobile_vr_interface.cpp
+++ b/modules/mobile_vr/mobile_vr_interface.cpp
@@ -463,7 +463,7 @@ CameraMatrix MobileVRInterface::get_projection_for_view(uint32_t p_view, double
 	return eye;
 };
 
-Vector<BlitToScreen> MobileVRInterface::commit_views(RID p_render_target, const Rect2 &p_screen_rect) {
+Vector<BlitToScreen> MobileVRInterface::post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) {
 	_THREAD_SAFE_METHOD_
 
 	Vector<BlitToScreen> blit_to_screen;
diff --git a/modules/mobile_vr/mobile_vr_interface.h b/modules/mobile_vr/mobile_vr_interface.h
index 47dc33c0c7..8ecca3a2ae 100644
--- a/modules/mobile_vr/mobile_vr_interface.h
+++ b/modules/mobile_vr/mobile_vr_interface.h
@@ -151,7 +151,7 @@ public:
 	virtual Transform3D get_camera_transform() override;
 	virtual Transform3D get_transform_for_view(uint32_t p_view, const Transform3D &p_cam_transform) override;
 	virtual CameraMatrix get_projection_for_view(uint32_t p_view, double p_aspect, double p_z_near, double p_z_far) override;
-	virtual Vector<BlitToScreen> commit_views(RID p_render_target, const Rect2 &p_screen_rect) override;
+	virtual Vector<BlitToScreen> post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) override;
 
 	virtual void process() override;
 
diff --git a/modules/webxr/webxr_interface_js.cpp b/modules/webxr/webxr_interface_js.cpp
index 8eb0d8ff90..86b857f72c 100644
--- a/modules/webxr/webxr_interface_js.cpp
+++ b/modules/webxr/webxr_interface_js.cpp
@@ -385,7 +385,7 @@ CameraMatrix WebXRInterfaceJS::get_projection_for_view(uint32_t p_view, double p
 	return eye;
 }
 
-Vector<BlitToScreen> WebXRInterfaceJS::commit_views(RID p_render_target, const Rect2 &p_screen_rect) {
+Vector<BlitToScreen> WebXRInterfaceJS::post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) {
 	Vector<BlitToScreen> blit_to_screen;
 
 	if (!initialized) {
diff --git a/modules/webxr/webxr_interface_js.h b/modules/webxr/webxr_interface_js.h
index 8eddfbe484..31858194f6 100644
--- a/modules/webxr/webxr_interface_js.h
+++ b/modules/webxr/webxr_interface_js.h
@@ -88,7 +88,7 @@ public:
 	virtual Transform3D get_camera_transform() override;
 	virtual Transform3D get_transform_for_view(uint32_t p_view, const Transform3D &p_cam_transform) override;
 	virtual CameraMatrix get_projection_for_view(uint32_t p_view, double p_aspect, double p_z_near, double p_z_far) override;
-	virtual Vector<BlitToScreen> commit_views(RID p_render_target, const Rect2 &p_screen_rect) override;
+	virtual Vector<BlitToScreen> post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) override;
 
 	virtual void process() override;
 
diff --git a/servers/rendering/renderer_viewport.cpp b/servers/rendering/renderer_viewport.cpp
index 17a665922f..be96793ec4 100644
--- a/servers/rendering/renderer_viewport.cpp
+++ b/servers/rendering/renderer_viewport.cpp
@@ -549,8 +549,13 @@ void RendererViewport::draw_viewports() {
 	// get our xr interface in case we need it
 	Ref<XRInterface> xr_interface;
 
-	if (XRServer::get_singleton() != nullptr) {
-		xr_interface = XRServer::get_singleton()->get_primary_interface();
+	XRServer *xr_server = XRServer::get_singleton();
+	if (xr_server != nullptr) {
+		// let our XR server know we're about to render our frames so we can get our frame timing
+		xr_server->pre_render();
+
+		// retrieve the interface responsible for rendering
+		xr_interface = xr_server->get_primary_interface();
 	}
 
 	if (Engine::get_singleton()->is_editor_hint()) {
@@ -582,19 +587,26 @@ void RendererViewport::draw_viewports() {
 
 		bool visible = vp->viewport_to_screen_rect != Rect2();
 
-		if (vp->use_xr && xr_interface.is_valid()) {
-			visible = true; // XR viewport is always visible regardless of update mode, output is sent to HMD.
-
-			// Override our size, make sure it matches our required size and is created as a stereo target
-			Size2 xr_size = xr_interface->get_render_target_size();
-
-			// Would have been nice if we could call viewport_set_size here,
-			// but alas that takes our RID and we now have our pointer,
-			// also we only check if view_count changes in render_target_set_size so we need to call that for this to reliably change
-			vp->occlusion_buffer_dirty = vp->occlusion_buffer_dirty || (vp->size != xr_size);
-			vp->size = xr_size;
-			uint32_t view_count = xr_interface->get_view_count();
-			RSG::storage->render_target_set_size(vp->render_target, vp->size.x, vp->size.y, view_count);
+		if (vp->use_xr) {
+			if (xr_interface.is_valid()) {
+				// Override our size, make sure it matches our required size and is created as a stereo target
+				Size2 xr_size = xr_interface->get_render_target_size();
+
+				// Would have been nice if we could call viewport_set_size here,
+				// but alas that takes our RID and we now have our pointer,
+				// also we only check if view_count changes in render_target_set_size so we need to call that for this to reliably change
+				vp->occlusion_buffer_dirty = vp->occlusion_buffer_dirty || (vp->size != xr_size);
+				vp->size = xr_size;
+				uint32_t view_count = xr_interface->get_view_count();
+				RSG::storage->render_target_set_size(vp->render_target, vp->size.x, vp->size.y, view_count);
+
+				// Inform xr interface we're about to render its viewport, if this returns false we don't render
+				visible = xr_interface->pre_draw_viewport(vp->render_target);
+			} else {
+				// don't render anything
+				visible = false;
+				vp->size = Size2();
+			}
 		}
 
 		if (vp->update_mode == RS::VIEWPORT_UPDATE_ALWAYS || vp->update_mode == RS::VIEWPORT_UPDATE_ONCE) {
@@ -647,7 +659,7 @@ void RendererViewport::draw_viewports() {
 			// measure
 
 			// commit our eyes
-			Vector<BlitToScreen> blits = xr_interface->commit_views(vp->render_target, vp->viewport_to_screen_rect);
+			Vector<BlitToScreen> blits = xr_interface->post_draw_viewport(vp->render_target, vp->viewport_to_screen_rect);
 			if (vp->viewport_to_screen != DisplayServer::INVALID_WINDOW_ID && blits.size() > 0) {
 				if (!blit_to_screen_list.has(vp->viewport_to_screen)) {
 					blit_to_screen_list[vp->viewport_to_screen] = Vector<BlitToScreen>();
@@ -657,9 +669,6 @@ void RendererViewport::draw_viewports() {
 					blit_to_screen_list[vp->viewport_to_screen].push_back(blits[b]);
 				}
 			}
-
-			// and for our frame timing, mark when we've finished committing our eyes
-			XRServer::get_singleton()->_mark_commit();
 		} else {
 			RSG::storage->render_target_set_external_texture(vp->render_target, 0);
 
diff --git a/servers/rendering/rendering_server_default.cpp b/servers/rendering/rendering_server_default.cpp
index d7e9d210db..d93aad5d7b 100644
--- a/servers/rendering/rendering_server_default.cpp
+++ b/servers/rendering/rendering_server_default.cpp
@@ -93,6 +93,12 @@ void RenderingServerDefault::_draw(bool p_swap_buffers, double frame_step) {
 
 	RSG::rasterizer->end_frame(p_swap_buffers);
 
+	XRServer *xr_server = XRServer::get_singleton();
+	if (xr_server != nullptr) {
+		// let our XR server know we're done so we can get our frame timing
+		xr_server->end_frame();
+	}
+
 	RSG::canvas->update_visibility_notifiers();
 	RSG::scene->update_visibility_notifiers();
 
diff --git a/servers/xr/xr_interface.cpp b/servers/xr/xr_interface.cpp
index 758f2416ec..7ae111b5e7 100644
--- a/servers/xr/xr_interface.cpp
+++ b/servers/xr/xr_interface.cpp
@@ -168,8 +168,5 @@ XRInterface::TrackingStatus XRInterface::get_tracking_status() const {
 	return XR_UNKNOWN_TRACKING;
 }
 
-void XRInterface::notification(int p_what) {
-}
-
 void XRInterface::trigger_haptic_pulse(const String &p_action_name, const StringName &p_tracker_name, double p_frequency, double p_amplitude, double p_duration_sec, double p_delay_sec) {
 }
diff --git a/servers/xr/xr_interface.h b/servers/xr/xr_interface.h
index aee98f8fee..6e105ffc26 100644
--- a/servers/xr/xr_interface.h
+++ b/servers/xr/xr_interface.h
@@ -123,10 +123,13 @@ public:
 
 	// note, external color/depth/vrs texture support will be added here soon.
 
-	virtual Vector<BlitToScreen> commit_views(RID p_render_target, const Rect2 &p_screen_rect) = 0; /* commit rendered views to the XR interface */
-
 	virtual void process() = 0;
-	virtual void notification(int p_what);
+	virtual void pre_render(){};
+	virtual bool pre_draw_viewport(RID p_render_target) { return true; }; /* inform XR interface we are about to start our viewport draw process */
+	virtual Vector<BlitToScreen> post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) = 0; /* inform XR interface we finished our viewport draw process */
+	virtual void end_frame(){};
+
+	virtual void notification(int p_what){};
 
 	XRInterface();
 	~XRInterface();
diff --git a/servers/xr/xr_interface_extension.cpp b/servers/xr/xr_interface_extension.cpp
index 9dae3b162d..18131c1e89 100644
--- a/servers/xr/xr_interface_extension.cpp
+++ b/servers/xr/xr_interface_extension.cpp
@@ -52,9 +52,12 @@ void XRInterfaceExtension::_bind_methods() {
 	GDVIRTUAL_BIND(_get_transform_for_view, "view", "cam_transform");
 	GDVIRTUAL_BIND(_get_projection_for_view, "view", "aspect", "z_near", "z_far");
 
-	GDVIRTUAL_BIND(_commit_views, "render_target", "screen_rect");
-
 	GDVIRTUAL_BIND(_process);
+	GDVIRTUAL_BIND(_pre_render);
+	GDVIRTUAL_BIND(_pre_draw_viewport, "render_target");
+	GDVIRTUAL_BIND(_post_draw_viewport, "render_target", "screen_rect");
+	GDVIRTUAL_BIND(_end_frame);
+
 	GDVIRTUAL_BIND(_notification, "what");
 
 	/** input and output **/
@@ -274,7 +277,7 @@ CameraMatrix XRInterfaceExtension::get_projection_for_view(uint32_t p_view, doub
 void XRInterfaceExtension::add_blit(RID p_render_target, Rect2 p_src_rect, Rect2i p_dst_rect, bool p_use_layer, uint32_t p_layer, bool p_apply_lens_distortion, Vector2 p_eye_center, double p_k1, double p_k2, double p_upscale, double p_aspect_ratio) {
 	BlitToScreen blit;
 
-	ERR_FAIL_COND_MSG(!can_add_blits, "add_blit can only be called from an XR plugin from within _commit_views!");
+	ERR_FAIL_COND_MSG(!can_add_blits, "add_blit can only be called from an XR plugin from within _post_draw_viewport!");
 
 	blit.render_target = p_render_target;
 	blit.src_rect = p_src_rect;
@@ -293,12 +296,31 @@ void XRInterfaceExtension::add_blit(RID p_render_target, Rect2 p_src_rect, Rect2
 	blits.push_back(blit);
 }
 
-Vector<BlitToScreen> XRInterfaceExtension::commit_views(RID p_render_target, const Rect2 &p_screen_rect) {
+void XRInterfaceExtension::process() {
+	GDVIRTUAL_CALL(_process);
+}
+
+void XRInterfaceExtension::pre_render() {
+	GDVIRTUAL_CALL(_pre_render);
+}
+
+bool XRInterfaceExtension::pre_draw_viewport(RID p_render_target) {
+	bool do_render = true;
+
+	if (GDVIRTUAL_CALL(_pre_draw_viewport, p_render_target, do_render)) {
+		return do_render;
+	} else {
+		// if not implemented we're returning true
+		return true;
+	}
+}
+
+Vector<BlitToScreen> XRInterfaceExtension::post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) {
 	// This is just so our XR plugin can add blits...
 	blits.clear();
 	can_add_blits = true;
 
-	if (GDVIRTUAL_CALL(_commit_views, p_render_target, p_screen_rect)) {
+	if (GDVIRTUAL_CALL(_post_draw_viewport, p_render_target, p_screen_rect)) {
 		return blits;
 	}
 
@@ -306,8 +328,8 @@ Vector<BlitToScreen> XRInterfaceExtension::commit_views(RID p_render_target, con
 	return blits;
 }
 
-void XRInterfaceExtension::process() {
-	GDVIRTUAL_CALL(_process);
+void XRInterfaceExtension::end_frame() {
+	GDVIRTUAL_CALL(_end_frame);
 }
 
 void XRInterfaceExtension::notification(int p_what) {
diff --git a/servers/xr/xr_interface_extension.h b/servers/xr/xr_interface_extension.h
index e22ec2b872..5a436b9fd0 100644
--- a/servers/xr/xr_interface_extension.h
+++ b/servers/xr/xr_interface_extension.h
@@ -109,13 +109,20 @@ public:
 	GDVIRTUAL4R(PackedFloat64Array, _get_projection_for_view, uint32_t, double, double, double);
 
 	void add_blit(RID p_render_target, Rect2 p_src_rect, Rect2i p_dst_rect, bool p_use_layer = false, uint32_t p_layer = 0, bool p_apply_lens_distortion = false, Vector2 p_eye_center = Vector2(), double p_k1 = 0.0, double p_k2 = 0.0, double p_upscale = 1.0, double p_aspect_ratio = 1.0);
-	virtual Vector<BlitToScreen> commit_views(RID p_render_target, const Rect2 &p_screen_rect) override;
-	GDVIRTUAL2(_commit_views, RID, const Rect2 &);
 
 	virtual void process() override;
+	virtual void pre_render() override;
+	virtual bool pre_draw_viewport(RID p_render_target) override;
+	virtual Vector<BlitToScreen> post_draw_viewport(RID p_render_target, const Rect2 &p_screen_rect) override;
+	virtual void end_frame() override;
 	virtual void notification(int p_what) override;
 
 	GDVIRTUAL0(_process);
+	GDVIRTUAL0(_pre_render);
+	GDVIRTUAL1R(bool, _pre_draw_viewport, RID);
+	GDVIRTUAL2(_post_draw_viewport, RID, const Rect2 &);
+	GDVIRTUAL0(_end_frame);
+
 	GDVIRTUAL1(_notification, int);
 
 	/* access to some internals we need */
diff --git a/servers/xr_server.cpp b/servers/xr_server.cpp
index 69f4c69b53..dbfe76a127 100644
--- a/servers/xr_server.cpp
+++ b/servers/xr_server.cpp
@@ -65,10 +65,6 @@ void XRServer::_bind_methods() {
 
 	ADD_PROPERTY(PropertyInfo(Variant::OBJECT, "primary_interface"), "set_primary_interface", "get_primary_interface");
 
-	ClassDB::bind_method(D_METHOD("get_last_process_usec"), &XRServer::get_last_process_usec);
-	ClassDB::bind_method(D_METHOD("get_last_commit_usec"), &XRServer::get_last_commit_usec);
-	ClassDB::bind_method(D_METHOD("get_last_frame_usec"), &XRServer::get_last_frame_usec);
-
 	BIND_ENUM_CONSTANT(TRACKER_HEAD);
 	BIND_ENUM_CONSTANT(TRACKER_CONTROLLER);
 	BIND_ENUM_CONSTANT(TRACKER_BASESTATION);
@@ -351,24 +347,9 @@ PackedStringArray XRServer::get_suggested_pose_names(const StringName &p_tracker
 	return arr;
 }
 
-uint64_t XRServer::get_last_process_usec() {
-	return last_process_usec;
-};
-
-uint64_t XRServer::get_last_commit_usec() {
-	return last_commit_usec;
-};
-
-uint64_t XRServer::get_last_frame_usec() {
-	return last_frame_usec;
-};
-
 void XRServer::_process() {
 	/* called from renderer_viewport.draw_viewports right before we start drawing our viewports */
 
-	/* mark for our frame timing */
-	last_process_usec = OS::get_singleton()->get_ticks_usec();
-
 	/* process all active interfaces */
 	for (int i = 0; i < interfaces.size(); i++) {
 		if (!interfaces[i].is_valid()) {
@@ -379,13 +360,32 @@ void XRServer::_process() {
 	};
 };
 
-void XRServer::_mark_commit() {
-	/* time this */
-	last_commit_usec = OS::get_singleton()->get_ticks_usec();
+void XRServer::pre_render() {
+	// called from RendererViewport.draw_viewports right before we start drawing our viewports
+	// note that we can have multiple interfaces active if we have interfaces that purely handle tracking
 
-	/* now store our difference as we may overwrite last_process_usec before this is accessed */
-	last_frame_usec = last_commit_usec - last_process_usec;
-};
+	// process all active interfaces
+	for (int i = 0; i < interfaces.size(); i++) {
+		if (!interfaces[i].is_valid()) {
+			// ignore, not a valid reference
+		} else if (interfaces[i]->is_initialized()) {
+			interfaces.write[i]->pre_render();
+		};
+	};
+}
+
+void XRServer::end_frame() {
+	// called from RenderingServerDefault after Vulkan queues have been submitted
+
+	// process all active interfaces
+	for (int i = 0; i < interfaces.size(); i++) {
+		if (!interfaces[i].is_valid()) {
+			// ignore, not a valid reference
+		} else if (interfaces[i]->is_initialized()) {
+			interfaces.write[i]->end_frame();
+		};
+	};
+}
 
 XRServer::XRServer() {
 	singleton = this;
diff --git a/servers/xr_server.h b/servers/xr_server.h
index a820634bd9..d9188d2de1 100644
--- a/servers/xr_server.h
+++ b/servers/xr_server.h
@@ -84,10 +84,6 @@ private:
 	Transform3D world_origin; /* our world origin point, maps a location in our virtual world to the origin point in our real world tracking volume */
 	Transform3D reference_frame; /* our reference frame */
 
-	uint64_t last_process_usec; /* for frame timing, usec when we did our processing */
-	uint64_t last_commit_usec; /* for frame timing, usec when we finished committing both eyes */
-	uint64_t last_frame_usec; /* time it took between process and committing, we should probably average this over the last x frames */
-
 protected:
 	static XRServer *singleton;
 
@@ -175,12 +171,16 @@ public:
 	PackedStringArray get_suggested_pose_names(const StringName &p_tracker_name) const;
 	// Q: Should we add get_suggested_input_names and get_suggested_haptic_names even though we don't use them for the IDE?
 
-	uint64_t get_last_process_usec();
-	uint64_t get_last_commit_usec();
-	uint64_t get_last_frame_usec();
-
+	// Process is called before we handle our physics process and game process. This is where our interfaces will update controller data and such.
 	void _process();
-	void _mark_commit();
+
+	// Pre-render is called right before we're rendering our viewports.
+	// This is where interfaces such as OpenVR and OpenXR will update positioning data.
+	// Many of these interfaces will also do a predictive sync which ensures we run at a steady framerate.
+	void pre_render();
+
+	// End-frame is called right after Godot has finished its rendering bits.
+	void end_frame();
 
 	XRServer();
 	~XRServer();