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.

gdk/gdkdisplay.c

@@ -515,6 +515,54 @@ generate_grab_broken_event (GdkDisplay *display,
     }
 }
 
+void
+gdk_surface_ensure_motion (GdkSurface *surface)
+{
+  GList *list, *l;
+  GdkDisplay *display;
+  GdkSeat *seat;
+  GdkDevice *device;
+  GdkEvent *event;
+  GdkFrameClock *frame_clock;
+
+  display = gdk_surface_get_display (surface);
+
+  for (l = g_queue_peek_head_link (&display->queued_events); l; l = l->next)
+    {
+      event = l->data;
+
+      if (event->any.type == GDK_MOTION_NOTIFY)
+        return;
+  }
+
+  seat = gdk_display_get_default_seat (display);
+  device = gdk_seat_get_pointer (seat);
+  list = gdk_seat_get_slaves (seat, GDK_SEAT_CAPABILITY_POINTER);
+  for (l = list; l; l = l->next)
+    {
+      GdkDevice *source_device = l->data;
+      double x, y;
+      GdkModifierType state;
+
+      gdk_surface_get_device_position (surface, device, &x, &y, &state);
+      event = gdk_event_motion_new (surface,
+                                    device,
+                                    source_device,
+                                    NULL,
+                                    GDK_CURRENT_TIME,
+                                    state,
+                                    x, y,
+                                    NULL);
+      _gdk_event_queue_append (display, event);
+    }
+
+  g_list_free (list);
+
+  frame_clock = gdk_surface_get_frame_clock (surface);
+  if (frame_clock)
+    gdk_frame_clock_request_phase (frame_clock, GDK_FRAME_CLOCK_PHASE_FLUSH_EVENTS);
+}
+
 GdkDeviceGrabInfo *
 _gdk_display_get_last_device_grab (GdkDisplay *display,
                                    GdkDevice  *device)

gdk/gdksurface.h

@@ -614,6 +614,9 @@ GdkVulkanContext *
                gdk_surface_create_vulkan_context(GdkSurface     *surface,
                                                  GError        **error);
 
+GDK_AVAILABLE_IN_ALL
+void           gdk_surface_ensure_motion (GdkSurface *surface);
+
 G_END_DECLS
 
 #endif /* __GDK_SURFACE_H__ */

gtk/gtkcontainer.c

@@ -372,7 +372,10 @@ gtk_container_idle_sizer (GdkFrameClock *clock,
   if (gtk_widget_needs_allocate (GTK_WIDGET (container)))
     {
       if (GTK_IS_ROOT (container))
-        gtk_native_check_resize (GTK_NATIVE (container));
+        {
+          gtk_native_check_resize (GTK_NATIVE (container));
+          gdk_surface_ensure_motion (gtk_native_get_surface (GTK_NATIVE (container)));
+        }
       else
         g_warning ("gtk_container_idle_sizer() called on a non-native non-window");
     }

gtk/gtkscrolledwindow.c

@@ -51,6 +51,7 @@
 #include "gtktypebuiltins.h"
 #include "gtkviewport.h"
 #include "gtkwidgetprivate.h"
+#include "gtknative.h"
 
 #include "a11y/gtkscrolledwindowaccessible.h"
 
@@ -3470,9 +3471,22 @@ 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)
+        {
+          g_print ("adjustment value changed\n");
+          //gdk_surface_ensure_motion (surface);
+        }
+    }
+
   /* Allow overshooting for kinetic scrolling operations */
   if (priv->deceleration_id)
     return;