wayland: Simplify wl_touch.frame handling

We want to coalesce multiple touch events into the same wl_touch.frame
event. Instead of poking internals to peek the touch events (and their
slots) coming at us before we handle them, simplify things by queueing
the event at a slightly lower priority than events, so we are ensured
to handle all pending input events before sending the event.

If there's no pending events, we can just send the frame event. As it
doesn't make sense to hold any longer.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1486

src/wayland/meta-wayland-touch.c

@@ -401,35 +401,34 @@ touch_send_frame_event (MetaWaylandTouch *touch)
   g_list_free (surfaces);
 }
 
-static void
+static gboolean
-check_send_frame_event (MetaWaylandTouch   *touch,
+queue_frame_event_cb (MetaWaylandTouch *touch)
-                        const ClutterEvent *event)
 {
-  gboolean send_frame_event;
-#ifdef HAVE_NATIVE_BACKEND
-  MetaBackend *backend = meta_get_backend ();
-  ClutterEventSequence *sequence;
-  gint32 slot;
-
-  if (META_IS_BACKEND_NATIVE (backend))
-    {
-      sequence = clutter_event_get_event_sequence (event);
-      slot = meta_event_native_sequence_get_slot (sequence);
-      touch->frame_slots &= ~(1 << slot);
-
-      if (touch->frame_slots == 0)
-        send_frame_event = TRUE;
-      else
-        send_frame_event = FALSE;
-    }
-  else
-#endif /* HAVE_NATIVE_BACKEND */
-    {
-      send_frame_event = TRUE;
-    }
-
-  if (send_frame_event)
   touch_send_frame_event (touch);
+  touch->queued_frame_id = 0;
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+send_or_queue_frame_event (MetaWaylandTouch *touch)
+{
+  if (clutter_events_pending ())
+    {
+      if (touch->queued_frame_id == 0)
+        {
+          touch->queued_frame_id =
+            g_idle_add_full (CLUTTER_PRIORITY_EVENTS + 1,
+                             (GSourceFunc) queue_frame_event_cb,
+                             touch, NULL);
+        }
+    }
+  else
+    {
+      /* There's no more events */
+      g_clear_handle_id (&touch->queued_frame_id, g_source_remove);
+      touch_send_frame_event (touch);
+    }
 }
 
 gboolean
@@ -454,7 +453,7 @@ meta_wayland_touch_handle_event (MetaWaylandTouch   *touch,
       return FALSE;
     }
 
-  check_send_frame_event (touch, event);
+  send_or_queue_frame_event (touch);
   return FALSE;
 }
 
@@ -520,21 +519,6 @@ evdev_filter_func (struct libinput_event *event,
 
   switch (libinput_event_get_type (event))
     {
-    case LIBINPUT_EVENT_TOUCH_DOWN:
-    case LIBINPUT_EVENT_TOUCH_UP:
-    case LIBINPUT_EVENT_TOUCH_MOTION: {
-      struct libinput_event_touch *touch_event;
-      int32_t slot;
-
-      touch_event = libinput_event_get_touch_event (event);
-      slot = libinput_event_touch_get_slot (touch_event);
-
-      /* XXX: Could theoretically overflow, 64 slots should be
-       * enough for most hw/usecases though.
-       */
-      touch->frame_slots |= (1 << slot);
-      break;
-    }
     case LIBINPUT_EVENT_TOUCH_CANCEL:
       /* Clutter translates this into individual CLUTTER_TOUCH_CANCEL events,
        * which are not so useful when sending a global signal as the protocol

src/wayland/meta-wayland-touch.h

@@ -41,10 +41,9 @@ struct _MetaWaylandTouch
 
   struct wl_list resource_list;
 
+  guint queued_frame_id;
   GHashTable *touch_surfaces; /* HT of MetaWaylandSurface->MetaWaylandTouchSurface */
   GHashTable *touches; /* HT of sequence->MetaWaylandTouchInfo */
-
-  guint64 frame_slots;
 };
 
 void meta_wayland_touch_enable (MetaWaylandTouch *touch);