xrt: Send compositor state change timestamp with event

Currently unused.

Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2647>

src/xrt/compositor/multi/comp_multi_system.c

@@ -592,7 +592,8 @@ thread_func(void *ptr)
  */
 
 static xrt_result_t
-system_compositor_set_state(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible, bool focused)
+system_compositor_set_state(
+    struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible, bool focused, int64_t timestamp_ns)
 {
 	struct multi_system_compositor *msc = multi_system_compositor(xsc);
 	struct multi_compositor *mc = multi_compositor(xc);
@@ -607,6 +608,7 @@ system_compositor_set_state(struct xrt_system_compositor *xsc, struct xrt_compos
 		xse.type = XRT_SESSION_EVENT_STATE_CHANGE;
 		xse.state.visible = visible;
 		xse.state.focused = focused;
+		xse.state.timestamp_ns = timestamp_ns;
 
 		return multi_compositor_push_event(mc, &xse);
 	}

src/xrt/include/xrt/xrt_compositor.h

@@ -2391,7 +2391,8 @@ struct xrt_multi_compositor_control
 	xrt_result_t (*set_state)(struct xrt_system_compositor *xsc,
 	                          struct xrt_compositor *xc,
 	                          bool visible,
-	                          bool focused);
+	                          bool focused,
+	                          int64_t timestamp_ns);
 
 	/*!
 	 * Set the rendering Z order for rendering, visible has higher priority
@@ -2491,13 +2492,14 @@ struct xrt_system_compositor
  * @public @memberof xrt_system_compositor
  */
 static inline xrt_result_t
-xrt_syscomp_set_state(struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible, bool focused)
+xrt_syscomp_set_state(
+    struct xrt_system_compositor *xsc, struct xrt_compositor *xc, bool visible, bool focused, int64_t timestamp_ns)
 {
 	if (xsc->xmcc == NULL) {
 		return XRT_ERROR_MULTI_SESSION_NOT_IMPLEMENTED;
 	}
 
-	return xsc->xmcc->set_state(xsc, xc, visible, focused);
+	return xsc->xmcc->set_state(xsc, xc, visible, focused, timestamp_ns);
 }
 
 /*!

src/xrt/include/xrt/xrt_session.h

@@ -80,6 +80,7 @@ struct xrt_session_event_state_change
 	enum xrt_session_event_type type;
 	bool visible;
 	bool focused;
+	int64_t timestamp_ns;
 };
 
 /*!

src/xrt/ipc/server/ipc_server_handler.c

@@ -461,7 +461,7 @@ ipc_handle_session_create(volatile struct ipc_client_state *ics,
 	ics->xc = &xcn->base;
 
 	xrt_syscomp_set_state(ics->server->xsysc, ics->xc, ics->client_state.session_visible,
-	                      ics->client_state.session_focused);
+	                      ics->client_state.session_focused, os_monotonic_get_ns());
 	xrt_syscomp_set_z_order(ics->server->xsysc, ics->xc, ics->client_state.z_order);
 
 	return XRT_SUCCESS;

src/xrt/ipc/server/ipc_server_process.c

@@ -615,7 +615,7 @@ handle_focused_client_events(volatile struct ipc_client_state *ics, int active_i
 	ics->client_state.z_order = z_order;
 
 	if (ics->xc != NULL) {
-		xrt_syscomp_set_state(ics->server->xsysc, ics->xc, visible, focused);
+		xrt_syscomp_set_state(ics->server->xsysc, ics->xc, visible, focused, os_monotonic_get_ns());
 		xrt_syscomp_set_z_order(ics->server->xsysc, ics->xc, z_order);
 	}
 }

src/xrt/state_trackers/oxr/oxr_session.c

@@ -551,6 +551,11 @@ oxr_session_poll(struct oxr_logger *log, struct oxr_session *sess)
 		case XRT_SESSION_EVENT_STATE_CHANGE:
 			sess->compositor_visible = xse.state.visible;
 			sess->compositor_focused = xse.state.focused;
+
+			// Do not use xse.state.timestamp_ns, server side focused / visible state does not correspond
+			// 1:1 to the cycle we tell the app. In particular the compositor may have become focused /
+			// visible much earlier than what we tell the app when it became so.
+
 			break;
 		case XRT_SESSION_EVENT_OVERLAY_CHANGE:
 #ifdef OXR_HAVE_EXTX_overlay
@@ -1162,7 +1167,7 @@ oxr_create_xrt_session_and_native_compositor(struct oxr_logger *log,
 		                 "Failed to create xrt_session and xrt_compositor_native! '%i'", xret);
 	}
 	if (sess->sys->xsysc->xmcc != NULL) {
-		xrt_syscomp_set_state(sess->sys->xsysc, &sess->xcn->base, true, true);
+		xrt_syscomp_set_state(sess->sys->xsysc, &sess->xcn->base, true, true, os_monotonic_get_ns());
 		xrt_syscomp_set_z_order(sess->sys->xsysc, &sess->xcn->base, 0);
 	}
 	return XR_SUCCESS;