[goffice] Canvas: avoid notifying items of no-op canvas changes.

[Morten Welinder <mortenw src gnome org>]

commit 28c8cd3b28266e817744ddbcda76a752b2f857ea
Author: Morten Welinder <terra gnome org>
Date:   Tue Mar 26 09:18:25 2013 -0400

    Canvas: avoid notifying items of no-op canvas changes.

 ChangeLog                  |    3 +++
 goffice/canvas/goc-group.c |   15 ++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 35282d2..5e7fb04 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2013-03-26  Morten Welinder  <terra gnome org>
 
+       * goffice/canvas/goc-group.c (goc_group_add_child): Only notify of
+       canvas changes when the canvas actually does change.
+
        * goffice/canvas/goc-item.c (goc_item_get_style_context): Track
        parent changes.
 
diff --git a/goffice/canvas/goc-group.c b/goffice/canvas/goc-group.c
index fcbe086..389f1cb 100644
--- a/goffice/canvas/goc-group.c
+++ b/goffice/canvas/goc-group.c
@@ -334,17 +334,30 @@ goc_group_clear (GocGroup *group)
 void
 goc_group_add_child (GocGroup *parent, GocItem *item)
 {
+       GocCanvas *old_canvas;
+
        g_return_if_fail (GOC_IS_GROUP (parent));
        g_return_if_fail (GOC_IS_ITEM (item));
+
        if (item->parent == parent)
                return;
+
+       /* Remove from current group.  */
        if (item->parent != NULL)
                goc_group_remove_child (item->parent, item);
+
+       old_canvas = item->canvas;
+
+       /* Insert into new group.  */
        parent->children = g_list_append (parent->children, item);
        item->parent = parent;
        item->canvas = parent->base.canvas;
+
+       /* Notify of changes.  */
        g_object_notify (G_OBJECT (item), "parent");
-       g_object_notify (G_OBJECT (item), "canvas");
+       if (item->canvas != old_canvas)
+               g_object_notify (G_OBJECT (item), "canvas");
+
        if (GOC_ITEM (parent)->realized)
                _goc_item_realize (item);
        goc_item_bounds_changed (GOC_ITEM (parent));