[gtk/wip/synthetic-motion2: 4/4] scrolledwindow: Create a synthetic motion during scrolling

[Matthias Clasen <matthiasc src gnome org>]

commit 60038463ce17f7bb1126d1bf701387e9702cfe14
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Feb 21 16:40:10 2020 -0500

    scrolledwindow: Create a synthetic motion during scrolling
    
    We are not doing any layout here, so this is needed to fix
    the listbox demo in gtk4-demo.

 gtk/gtkscrolledwindow.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index fbc03039e4..179ebcf10c 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -52,6 +52,7 @@
 #include "gtktypebuiltins.h"
 #include "gtkviewport.h"
 #include "gtkwidgetprivate.h"
+#include "gtknative.h"
 
 #include <math.h>
 
@@ -3488,9 +3489,19 @@ gtk_scrolled_window_adjustment_value_changed (GtkAdjustment *adjustment,
 {
   GtkScrolledWindow *scrolled_window = user_data;
   GtkScrolledWindowPrivate *priv = gtk_scrolled_window_get_instance_private (scrolled_window);
+  GtkNative *native;
+  GdkSurface *surface;
 
   maybe_emit_edge_reached (scrolled_window, adjustment);
 
+  native = gtk_widget_get_native (GTK_WIDGET (scrolled_window));
+  if (native)
+    {
+      surface = gtk_native_get_surface (native);
+      if (surface)
+        gdk_surface_ensure_motion (surface);
+    }
+
   /* Allow overshooting for kinetic scrolling operations */
   if (priv->deceleration_id)
     return;