wayland: add gdk_event_is_scroll_stop_event()

And use it to handle kinetic scrolling in the GtkScrolledWindow.

However, dropping the delta check causes the X11-based kinetic
scroll to break since we don't have the stop event here. Correct handling of
xf86-input-libinput-based scroll events is still being discussed.

https://bugzilla.gnome.org/show_bug.cgi?id=756729

1 files changed, 23 insertions, 0 deletions

diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 9ed43176aa..83f8ab11f2 100644
--- a/gdk/gdkevents.c
+++ b/gdk/gdkevents.c
@@ -562,6 +562,7 @@ gdk_event_new (GdkEventType type)
       new_event->scroll.y_root = 0.;
       new_event->scroll.delta_x = 0.;
       new_event->scroll.delta_y = 0.;
+      new_event->scroll.is_stop = FALSE;
       break;
     case GDK_ENTER_NOTIFY:
     case GDK_LEAVE_NOTIFY:
@@ -1419,6 +1420,28 @@ gdk_event_get_scroll_deltas (const GdkEvent *event,
 }
 
 /**
+ * gdk_event_is_scroll_stop_event
+ * @event: a #GdkEvent
+ *
+ * Check whether a scroll event is a stop scroll event. Scroll sequences
+ * with smooth scroll information may provide a stop scroll event once the
+ * interaction with the device finishes, e.g. by lifting a finger. This
+ * stop scroll event is the signal that a widget may trigger kinetic
+ * scrolling based on the current velocity.
+ *
+ * Stop scroll events always have a a delta of 0/0.
+ *
+ * Returns: %TRUE if the event is a scroll stop event
+ *
+ * Since: 3.20
+ */
+gboolean
+gdk_event_is_scroll_stop_event (const GdkEvent *event)
+{
+  return event->scroll.is_stop;
+}
+
+/**
  * gdk_event_get_axis:
  * @event: a #GdkEvent
  * @axis_use: the axis use to look for