backend: Dispatch initial burst of events synchronously on init

This will consist of device-added events, meaning before init finishes,
we can derive some state that depends on the set of input devices
available on startup, such as cursor visibility.

This avoids cursor visibility switching between hidden and visibility
during startup.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3070>

clutter/clutter/clutter-stage.c

@@ -688,7 +688,7 @@ clutter_stage_compress_motion (ClutterStage       *stage,
   event->motion.dy_unaccel = dy_unaccel + dst_dy_unaccel;
 }
 
-void
+CLUTTER_EXPORT void
 _clutter_stage_process_queued_events (ClutterStage *stage)
 {
   ClutterStagePrivate *priv;

src/backends/meta-backend.c

@@ -154,6 +154,8 @@ struct _MetaBackendPrivate
   GList *gpus;
   GList *hw_cursor_inhibitors;
 
+  gboolean in_init;
+
   guint device_update_idle_id;
 
   ClutterInputDevice *current_device;
@@ -422,8 +424,9 @@ on_device_added (ClutterSeat        *seat,
 
   device_type = clutter_input_device_get_device_type (device);
 
-  if (device_type == CLUTTER_TOUCHSCREEN_DEVICE ||
-      device_type == CLUTTER_POINTER_DEVICE)
+  if (!priv->in_init &&
+      (device_type == CLUTTER_TOUCHSCREEN_DEVICE ||
+       device_type == CLUTTER_POINTER_DEVICE))
     {
       meta_cursor_tracker_set_pointer_visible (priv->cursor_tracker,
                                                determine_hotplug_pointer_visibility (seat));
@@ -446,6 +449,8 @@ on_device_removed (ClutterSeat        *seat,
   MetaBackend *backend = META_BACKEND (user_data);
   MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
 
+  g_warn_if_fail (!priv->in_init);
+
   if (clutter_input_device_get_device_mode (device) ==
       CLUTTER_INPUT_MODE_LOGICAL)
     return;
@@ -1032,6 +1037,8 @@ update_pointer_visibility_from_event (MetaBackend  *backend,
   ClutterInputDeviceType device_type;
   uint32_t time_ms;
 
+  g_warn_if_fail (!priv->in_init);
+
   device = clutter_event_get_source_device (event);
   device_type = clutter_input_device_get_device_type (device);
   time_ms = clutter_event_get_time (event);
@@ -1063,6 +1070,28 @@ update_pointer_visibility_from_event (MetaBackend  *backend,
     }
 }
 
+static gboolean
+dispatch_clutter_event (MetaBackend *backend)
+{
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+  ClutterEvent *event;
+
+  event = clutter_event_get ();
+  if (event)
+    {
+      g_warn_if_fail (!priv->in_init ||
+                      event->type == CLUTTER_DEVICE_ADDED);
+
+      event->any.stage = CLUTTER_STAGE (meta_backend_get_stage (backend));
+      clutter_do_event (event);
+      meta_backend_update_from_event (backend, event);
+      clutter_event_free (event);
+      return TRUE;
+    }
+
+  return FALSE;
+}
+
 /* Mutter is responsible for pulling events off the X queue, so Clutter
  * doesn't need (and shouldn't) run its normal event source which polls
  * the X fd, but we do have to deal with dispatching events that accumulate
@@ -1095,16 +1124,8 @@ clutter_source_dispatch (GSource     *source,
                          gpointer     user_data)
 {
   MetaBackendSource *backend_source = (MetaBackendSource *) source;
-  ClutterEvent *event = clutter_event_get ();
 
-  if (event)
-    {
-      event->any.stage =
-        CLUTTER_STAGE (meta_backend_get_stage (backend_source->backend));
-      clutter_do_event (event);
-      meta_backend_update_from_event (backend_source->backend, event);
-      clutter_event_free (event);
-    }
+  dispatch_clutter_event (backend_source->backend);
 
   return TRUE;
 }
@@ -1205,6 +1226,15 @@ meta_backend_initable_init (GInitable     *initable,
 
   meta_backend_post_init (backend);
 
+  while (TRUE)
+    {
+      if (!dispatch_clutter_event (backend))
+        break;
+    }
+  _clutter_stage_process_queued_events (CLUTTER_STAGE (priv->stage));
+
+  priv->in_init = FALSE;
+
   return TRUE;
 }
 
@@ -1217,6 +1247,9 @@ initable_iface_init (GInitableIface *initable_iface)
 static void
 meta_backend_init (MetaBackend *backend)
 {
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+
+  priv->in_init = TRUE;
 }
 
 /**
@@ -1708,8 +1741,12 @@ void
 meta_backend_update_from_event (MetaBackend  *backend,
                                 ClutterEvent *event)
 {
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+
   update_last_device_from_event (backend, event);
-  update_pointer_visibility_from_event (backend, event);
+
+  if (!priv->in_init)
+    update_pointer_visibility_from_event (backend, event);
 }
 
 /**

src/backends/native/meta-seat-impl.c

@@ -2841,6 +2841,8 @@ init_libinput (MetaSeatImpl  *seat_impl,
 
   seat_impl->libinput = libinput;
 
+  process_events (seat_impl);
+
   return TRUE;
 }
 
@@ -2877,18 +2879,6 @@ input_thread (MetaSeatImpl *seat_impl)
                            NULL,
                            (GDestroyNotify) meta_device_file_release);
 
-  if (!(seat_impl->flags & META_SEAT_NATIVE_FLAG_NO_LIBINPUT))
-    {
-      g_autoptr (GError) error = NULL;
-
-      if (!init_libinput (seat_impl, &error))
-        {
-          g_critical ("Failed to initialize seat: %s", error->message);
-          seat_impl->input_thread_initialized = TRUE;
-          return NULL;
-        }
-    }
-
   seat_impl->input_settings = meta_input_settings_native_new_in_impl (seat_impl);
   g_signal_connect_object (seat_impl->input_settings, "kbd-a11y-changed",
                            G_CALLBACK (kbd_a11y_changed_cb), seat_impl, 0);
@@ -2912,6 +2902,18 @@ input_thread (MetaSeatImpl *seat_impl)
   if (meta_input_settings_maybe_restore_numlock_state (seat_impl->input_settings))
     meta_seat_impl_set_keyboard_numlock_in_impl (seat_impl, TRUE);
 
+  if (!(seat_impl->flags & META_SEAT_NATIVE_FLAG_NO_LIBINPUT))
+    {
+      g_autoptr (GError) error = NULL;
+
+      if (!init_libinput (seat_impl, &error))
+        {
+          g_critical ("Failed to initialize seat: %s", error->message);
+          seat_impl->input_thread_initialized = TRUE;
+          return NULL;
+        }
+    }
+
   seat_impl->has_touchscreen = has_touchscreen (seat_impl);
   seat_impl->has_tablet_switch = has_tablet_switch (seat_impl);
   update_touch_mode (seat_impl);