clutter-seat: Handle device events and emit signals

Clutter device events are special events coming from the backend when an
input device is added or removed.

When such events are processed, we should make the seat to handle them by
calling vfunc that can be implemented by each backend and eventually
emitting the appropriate signal.

If a device is removed, we can also safely dispose it, as it can be
considered stale at this point.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1371

clutter/clutter/clutter-main.c

@@ -1954,6 +1954,17 @@ _clutter_process_event_details (ClutterActor        *stage,
       case CLUTTER_CLIENT_MESSAGE:
         break;
 
+      case CLUTTER_DEVICE_ADDED:
+      case CLUTTER_DEVICE_REMOVED:
+        if (!_clutter_event_process_filters (event))
+          {
+            ClutterSeat *seat;
+
+            seat = clutter_backend_get_default_seat (context->backend);
+            clutter_seat_handle_device_event (seat, event);
+          }
+        break;
+
       case CLUTTER_EVENT_LAST:
         break;
     }

clutter/clutter/clutter-seat.c

@@ -674,6 +674,46 @@ clutter_seat_compress_motion (ClutterSeat        *seat,
     seat_class->compress_motion (seat, event, to_discard);
 }
 
+gboolean
+clutter_seat_handle_device_event (ClutterSeat  *seat,
+                                  ClutterEvent *event)
+{
+  ClutterSeatClass *seat_class;
+  ClutterInputDevice *device;
+
+  g_return_val_if_fail (CLUTTER_IS_SEAT (seat), FALSE);
+  g_return_val_if_fail (event, FALSE);
+
+  g_assert (event->type == CLUTTER_DEVICE_ADDED ||
+            event->type == CLUTTER_DEVICE_REMOVED);
+
+  seat_class = CLUTTER_SEAT_GET_CLASS (seat);
+
+  if (seat_class->handle_device_event)
+    {
+      if (!seat_class->handle_device_event (seat, event))
+        return FALSE;
+    }
+
+  device = clutter_event_get_source_device (event);
+  g_assert_true (CLUTTER_IS_INPUT_DEVICE (device));
+
+  switch (event->type)
+    {
+      case CLUTTER_DEVICE_ADDED:
+        g_signal_emit (seat, signals[DEVICE_ADDED], 0, device);
+        break;
+      case CLUTTER_DEVICE_REMOVED:
+        g_signal_emit (seat, signals[DEVICE_REMOVED], 0, device);
+        g_object_run_dispose (G_OBJECT (device));
+        break;
+      default:
+        break;
+    }
+
+  return TRUE;
+}
+
 void
 clutter_seat_warp_pointer (ClutterSeat *seat,
                            int          x,

clutter/clutter/clutter-seat.h

@@ -106,6 +106,9 @@ struct _ClutterSeatClass
                             ClutterEvent       *event,
                             const ClutterEvent *to_discard);
 
+  gboolean (* handle_device_event) (ClutterSeat  *seat,
+                                    ClutterEvent *event);
+
   void (* warp_pointer) (ClutterSeat *seat,
                          int          x,
                          int          y);
@@ -181,6 +184,9 @@ void clutter_seat_compress_motion (ClutterSeat        *seat,
                                    ClutterEvent       *event,
                                    const ClutterEvent *to_discard);
 
+gboolean clutter_seat_handle_device_event (ClutterSeat  *seat,
+                                           ClutterEvent *event);
+
 CLUTTER_EXPORT
 void clutter_seat_warp_pointer (ClutterSeat *seat,
                                 int          x,