compositor: Sync pointer after begin/end modal on X11

Ensure we issue a motion event for the current pointer position,
as there might be situations where compositor modals get X grabs
from other clients stacked on top, or missed events in between
otherwise.

Ensure the Clutter state is still up-to-date afterwards here. This
replaces some sync_pointer() calls done in GNOME Shell code, always
done after modality changes.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1659>

3 files changed, 33 insertions, 0 deletions

diff --git a/src/backends/x11/meta-backend-x11.c b/src/backends/x11/meta-backend-x11.c
index 722d7b3d9..9c40ada2c 100644
--- a/src/backends/x11/meta-backend-x11.c
+++ b/src/backends/x11/meta-backend-x11.c
@@ -921,3 +921,28 @@ meta_backend_x11_reload_cursor (MetaBackendX11 *x11)
 
   meta_cursor_renderer_force_update (cursor_renderer);
 }
+
+void
+meta_backend_x11_sync_pointer (MetaBackendX11 *backend_x11)
+{
+  MetaBackend *backend = META_BACKEND (backend_x11);
+  ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
+  ClutterSeat *seat = clutter_backend_get_default_seat (clutter_backend);
+  ClutterInputDevice *pointer = clutter_seat_get_pointer (seat);
+  ClutterStage *stage = CLUTTER_STAGE (meta_backend_get_stage (backend));
+  ClutterModifierType modifiers;
+  ClutterEvent *event;
+  graphene_point_t pos;
+
+  event = clutter_event_new (CLUTTER_MOTION);
+  clutter_seat_query_state (seat, pointer, NULL, &pos, &modifiers);
+  clutter_event_set_flags (event, CLUTTER_EVENT_FLAG_SYNTHETIC);
+  clutter_event_set_coords (event, pos.x, pos.y);
+  clutter_event_set_device (event, pointer);
+  clutter_event_set_state (event, modifiers);
+  clutter_event_set_source_device (event, NULL);
+  clutter_event_set_stage (event, stage);
+
+  clutter_event_put (event);
+  clutter_event_free (event);
+}
diff --git a/src/backends/x11/meta-backend-x11.h b/src/backends/x11/meta-backend-x11.h
index 526bf0caa..2815015d1 100644
--- a/src/backends/x11/meta-backend-x11.h
+++ b/src/backends/x11/meta-backend-x11.h
@@ -58,4 +58,6 @@ uint8_t meta_backend_x11_get_xkb_event_base (MetaBackendX11 *x11);
 
 void meta_backend_x11_reload_cursor (MetaBackendX11 *x11);
 
+void meta_backend_x11_sync_pointer (MetaBackendX11 *backend_x11);
+
 #endif /* META_BACKEND_X11_H */
diff --git a/src/compositor/meta-compositor-x11.c b/src/compositor/meta-compositor-x11.c
index 6cfdef52b..27999fbae 100644
--- a/src/compositor/meta-compositor-x11.c
+++ b/src/compositor/meta-compositor-x11.c
@@ -442,11 +442,17 @@ meta_compositor_x11_monotonic_to_high_res_xserver_time (MetaCompositor *composit
 static void
 meta_compositor_x11_grab_begin (MetaCompositor *compositor)
 {
+  MetaBackendX11 *backend_x11 = META_BACKEND_X11 (meta_get_backend ());
+
+  meta_backend_x11_sync_pointer (backend_x11);
 }
 
 static void
 meta_compositor_x11_grab_end (MetaCompositor *compositor)
 {
+  MetaBackendX11 *backend_x11 = META_BACKEND_X11 (meta_get_backend ());
+
+  meta_backend_x11_sync_pointer (backend_x11);
 }
 
 Window