Only send QGraphicsItem::ParentChange(d) notifications from setParentItem.

QmlGraphicsItem doesn't need any parent change notifactions so we can
call the helper class (QGraphicsItemPrivate::setParentItemHelper)
direclty from QmlGraphicsItem::setParentItem. This avoids a lot of unnecessary
instructions related to QVariant constructions as well as virtual
function calls.

I've made the variant pointers explicit in the declaration of
setParentItemHelper so that we don't accidentally call setParentItemHelper
from places where we need parent change notifications.

Task-number: QTBUG-6877
Reviewed-by: alexis

3 files changed, 28 insertions, 20 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 5c7ea76..d43176b 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -1012,19 +1012,10 @@ QVariant QGraphicsItemPrivate::inputMethodQueryHelper(Qt::InputMethodQuery query
     prepareGeometryChange) if the item is in its destructor, i.e.
     inDestructor is 1.
 */
-void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
+void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent, const QVariant *newParentVariant,
+                                               const QVariant *thisPointerVariant)
 {
     Q_Q(QGraphicsItem);
-    if (newParent == q) {
-        qWarning("QGraphicsItem::setParentItem: cannot assign %p as a parent of itself", this);
-        return;
-    }
-    if (newParent == parent)
-        return;
-
-    const QVariant newParentVariant(q->itemChange(QGraphicsItem::ItemParentChange,
-                                                  qVariantFromValue<QGraphicsItem *>(newParent)));
-    newParent = qVariantValue<QGraphicsItem *>(newParentVariant);
     if (newParent == parent)
         return;
 
@@ -1049,11 +1040,11 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
     if (!inDestructor)
         q_ptr->prepareGeometryChange();
 
-    const QVariant thisPointerVariant(qVariantFromValue<QGraphicsItem *>(q));
     if (parent) {
         // Remove from current parent
         parent->d_ptr->removeChild(q);
-        parent->itemChange(QGraphicsItem::ItemChildRemovedChange, thisPointerVariant);
+        if (thisPointerVariant)
+            parent->itemChange(QGraphicsItem::ItemChildRemovedChange, *thisPointerVariant);
     }
 
     // Update toplevelitem list. If this item is being deleted, its parent
@@ -1129,7 +1120,8 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
         }
 
         parent->d_ptr->addChild(q);
-        parent->itemChange(QGraphicsItem::ItemChildAddedChange, thisPointerVariant);
+        if (thisPointerVariant)
+            parent->itemChange(QGraphicsItem::ItemChildAddedChange, *thisPointerVariant);
         if (scene) {
             if (!implicitUpdate)
                 scene->d_func()->markDirty(q_ptr);
@@ -1184,7 +1176,8 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
     }
 
     // Deliver post-change notification
-    q->itemChange(QGraphicsItem::ItemParentHasChanged, newParentVariant);
+    if (newParentVariant)
+        q->itemChange(QGraphicsItem::ItemParentHasChanged, *newParentVariant);
 
     if (isObject)
         emit static_cast<QGraphicsObject *>(q)->parentChanged();
@@ -1373,7 +1366,7 @@ QGraphicsItem::~QGraphicsItem()
         d_ptr->scene->d_func()->removeItemHelper(this);
     } else {
         d_ptr->resetFocusProxy();
-        d_ptr->setParentItemHelper(0);
+        setParentItem(0);
     }
 
 #ifndef QT_NO_GRAPHICSEFFECT
@@ -1578,9 +1571,23 @@ const QGraphicsObject *QGraphicsItem::toGraphicsObject() const
 
     \sa parentItem(), childItems()
 */
-void QGraphicsItem::setParentItem(QGraphicsItem *parent)
+void QGraphicsItem::setParentItem(QGraphicsItem *newParent)
 {
-    d_ptr->setParentItemHelper(parent);
+    if (newParent == this) {
+        qWarning("QGraphicsItem::setParentItem: cannot assign %p as a parent of itself", this);
+        return;
+    }
+    if (newParent == d_ptr->parent)
+        return;
+
+    const QVariant newParentVariant(itemChange(QGraphicsItem::ItemParentChange,
+                                               qVariantFromValue<QGraphicsItem *>(newParent)));
+    newParent = qVariantValue<QGraphicsItem *>(newParentVariant);
+    if (newParent == d_ptr->parent)
+        return;
+
+    const QVariant thisPointerVariant(qVariantFromValue<QGraphicsItem *>(this));
+    d_ptr->setParentItemHelper(newParent, &newParentVariant, &thisPointerVariant);
 }
 
 /*!
diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index cfdd382..ac10aa7 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -230,7 +230,8 @@ public:
     void resolveDepth();
     void addChild(QGraphicsItem *child);
     void removeChild(QGraphicsItem *child);
-    void setParentItemHelper(QGraphicsItem *parent);
+    void setParentItemHelper(QGraphicsItem *parent, const QVariant *newParentVariant,
+                             const QVariant *thisPointerVariant);
     void childrenBoundingRectHelper(QTransform *x, QRectF *rect);
     void initStyleOption(QStyleOptionGraphicsItem *option, const QTransform &worldTransform,
                          const QRegion &exposedRegion, bool allItems = false) const;
diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index fa9f794..088a6b9 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -599,7 +599,7 @@ void QGraphicsScenePrivate::removeItemHelper(QGraphicsItem *item)
         if (parentItem->scene()) {
             Q_ASSERT_X(parentItem->scene() == q, "QGraphicsScene::removeItem",
                        "Parent item's scene is different from this item's scene");
-            item->d_ptr->setParentItemHelper(0);
+            item->setParentItem(0);
         }
     } else {
         unregisterTopLevelItem(item);