Add QGraphicsItem::itemChangeEnabled().

This function allows the user to disable notifications for item changes.
In QSimpleCanvasItem, all notifications are disabled by default, and
you can enable them one at a time. QGraphicsItem's behavior is to by
default enable all notifications.

A side effect of this change is that I've removed one optimization in
favor of another: by not constructing a QVariant at all when there's no
notification we get maximum performance, at the expense of constructing
it twice if there is a notification.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index b0b940b..2752056 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -147,6 +147,7 @@ public:
         dirtyChildrenBoundingRect(1),
         paintedViewBoundingRectsNeedRepaint(0),
         dirtySceneTransform(1),
+        itemChangesEnabled(0xffff),
         globalStackingOrder(-1),
         q_ptr(0)
     {
@@ -396,7 +397,8 @@ public:
     quint32 dirtyChildrenBoundingRect : 1;
     quint32 paintedViewBoundingRectsNeedRepaint : 1;
     quint32 dirtySceneTransform  : 1;
-    quint32 padding : 18; // feel free to use
+    quint32 itemChangesEnabled : 16;
+    quint32 padding : 3; // feel free to use
 
     // Optional stacking order
     int globalStackingOrder;