From 2923f69d3cc3a3518b847c8d91e5003584cb50f9 Mon Sep 17 00:00:00 2001
From: Carlos Garnacho <carlosg@gnome.org>
Date: Wed, 9 Mar 2016 17:00:31 +0100
Subject: [PATCH] gdkdnd: Add private means to commit the drag status

The way gdk_drag_status() may be called multiple times during the
processing of drag and drop events throughout the widget hierarchy
brings some superfluous messaging going in, esp. when it's the last
request the one we want to honor, yet we emit messaging requests on
all.

This is barely appreciable in the X11 backend, but due to the design
of the wayland protocol, quick series of changes like this it have
some self-amplificating consequences which may end up flooding the
connection.

We can delegate this to a late "commit" call, performed within GDK
event management. This way gdk_drag_status() calls may be cached
and only result in windowing messaging once per ::drag-motion or
::drag-data-received event. Emitting the final status will also
avoid spurious action changes on the compositor and the other peer.

https://bugzilla.gnome.org/show_bug.cgi?id=763298
---
 gdk/gdkdnd.c                 | 50 ++++++++++++++++++++++++++++++++++++
 gdk/gdkdndprivate.h          |  3 +++
 gdk/gdkevents.c              |  3 +++
 gdk/wayland/gdkdnd-wayland.c |  3 +--
 4 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/gdk/gdkdnd.c b/gdk/gdkdnd.c
index 02d8d53420..3cbd5312ca 100644
--- a/gdk/gdkdnd.c
+++ b/gdk/gdkdnd.c
@@ -764,3 +764,53 @@ gdk_drag_get_cursor (GdkDragAction action)
                                                        drag_cursors[i].name);
   return drag_cursors[i].cursor;
 }
+
+static void
+gdk_drag_context_commit_drag_status (GdkDragContext *context)
+{
+  GdkDragContextClass *context_class;
+
+  g_return_if_fail (GDK_IS_DRAG_CONTEXT (context));
+  g_return_if_fail (!context->is_source);
+
+  context_class = GDK_DRAG_CONTEXT_GET_CLASS (context);
+
+  if (context_class->commit_drag_status)
+    context_class->commit_drag_status (context);
+}
+
+gboolean
+gdk_drag_context_handle_dest_event (GdkEvent *event)
+{
+  GdkDragContext *context = NULL;
+  GList *l;
+
+  switch (event->type)
+    {
+    case GDK_DRAG_MOTION:
+    case GDK_DROP_START:
+      context = event->dnd.context;
+      break;
+    case GDK_SELECTION_NOTIFY:
+      for (l = contexts; l; l = l->next)
+        {
+          GdkDragContext *c = l->data;
+
+          if (!c->is_source &&
+              event->selection.selection == gdk_drag_get_selection (c))
+            {
+              context = c;
+              break;
+            }
+        }
+      break;
+    default:
+      return FALSE;
+    }
+
+  if (!context)
+    return FALSE;
+
+  gdk_drag_context_commit_drag_status (context);
+  return TRUE;;
+}
diff --git a/gdk/gdkdndprivate.h b/gdk/gdkdndprivate.h
index c66de32d85..283dba2b85 100644
--- a/gdk/gdkdndprivate.h
+++ b/gdk/gdkdndprivate.h
@@ -84,6 +84,8 @@ struct _GdkDragContextClass {
                                  const GdkEvent  *event);
   void        (*action_changed) (GdkDragContext  *context,
                                  GdkDragAction    action);
+
+  void        (*commit_drag_status) (GdkDragContext  *context);
 };
 
 struct _GdkDragContext {
@@ -116,6 +118,7 @@ void     gdk_drag_context_set_cursor          (GdkDragContext *context,
 void     gdk_drag_context_cancel              (GdkDragContext      *context,
                                                GdkDragCancelReason  reason);
 gboolean gdk_drag_context_handle_source_event (GdkEvent *event);
+gboolean gdk_drag_context_handle_dest_event   (GdkEvent *event);
 GdkCursor * gdk_drag_get_cursor (GdkDragAction action);
 
 G_END_DECLS
diff --git a/gdk/gdkevents.c b/gdk/gdkevents.c
index 6a6771cf0a..2eb249e776 100644
--- a/gdk/gdkevents.c
+++ b/gdk/gdkevents.c
@@ -71,6 +71,9 @@ _gdk_event_emit (GdkEvent *event)
 
   if (_gdk_event_func)
     (*_gdk_event_func) (event, _gdk_event_data);
+
+  if (gdk_drag_context_handle_dest_event (event))
+    return;
 }
 
 /*********************************************
diff --git a/gdk/wayland/gdkdnd-wayland.c b/gdk/wayland/gdkdnd-wayland.c
index 1d71d90f34..2a2bad51e6 100644
--- a/gdk/wayland/gdkdnd-wayland.c
+++ b/gdk/wayland/gdkdnd-wayland.c
@@ -287,8 +287,6 @@ gdk_wayland_drag_context_drag_status (GdkDragContext *context,
 
   wayland_context = GDK_WAYLAND_DRAG_CONTEXT (context);
   wayland_context->selected_action = action;
-
-  gdk_wayland_drag_context_commit_status (context);
 }
 
 static void
@@ -471,6 +469,7 @@ gdk_wayland_drag_context_class_init (GdkWaylandDragContextClass *klass)
   context_class->action_changed = gdk_wayland_drag_context_action_changed;
   context_class->drop_performed = gdk_wayland_drag_context_drop_performed;
   context_class->cancel = gdk_wayland_drag_context_cancel;
+  context_class->commit_drag_status = gdk_wayland_drag_context_commit_status;
 }
 
 GdkDragProtocol