Improve performance of QGraphicsItem::setParentItem.

The biggest optimization here is "updateAncestorFlags()". It's much
faster to update all the flags rather than trying to enable/disable
certain flags according to the current state.

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

3 files changed, 62 insertions, 35 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 1ea69fb..9008be3 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -800,8 +800,36 @@ void QGraphicsItemPrivate::updateAncestorFlag(QGraphicsItem::GraphicsItemFlag ch
             return;
     }
 
-    foreach (QGraphicsItem *child, children)
-        child->d_ptr->updateAncestorFlag(childFlag, flag, enabled, false);
+    for (int i = 0; i < children.size(); ++i)
+        children.at(i)->d_ptr->updateAncestorFlag(childFlag, flag, enabled, false);
+}
+
+void QGraphicsItemPrivate::updateAncestorFlags()
+{
+    int flags = 0;
+    if (parent) {
+        // Inherit the parent's ancestor flags.
+        QGraphicsItemPrivate *pd = parent->d_ptr.data();
+        flags = pd->ancestorFlags;
+
+        // Add in flags from the parent.
+        if (pd->filtersDescendantEvents)
+            flags |= AncestorFiltersChildEvents;
+        if (pd->handlesChildEvents)
+            flags |= AncestorHandlesChildEvents;
+        if (pd->flags & QGraphicsItem::ItemClipsChildrenToShape)
+            flags |= AncestorClipsChildren;
+        if (pd->flags & QGraphicsItem::ItemIgnoresTransformations)
+            flags |= AncestorIgnoresTransformations;
+    }
+
+    if (ancestorFlags == flags)
+        return; // No change; stop propagation.
+    ancestorFlags = flags;
+
+    // Propagate to children recursively.
+    for (int i = 0; i < children.size(); ++i)
+        children.at(i)->d_ptr->updateAncestorFlags();
 }
 
 /*!
@@ -1004,7 +1032,8 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
 
     if (scene) {
         // Deliver the change to the index
-        scene->d_func()->index->itemChange(q, QGraphicsItem::ItemParentChange, newParentVariant);
+        if (scene->d_func()->indexMethod != QGraphicsScene::NoIndex)
+            scene->d_func()->index->itemChange(q, QGraphicsItem::ItemParentChange, newParentVariant);
 
         // Disable scene pos notifications for old ancestors
         if (scenePosDescendants || (flags & QGraphicsItem::ItemSendsScenePositionChanges))
@@ -1044,7 +1073,7 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
     QGraphicsItem *p = parent;
     QGraphicsItem *parentFocusScopeItem = 0;
     while (p) {
-        if (p->flags() & QGraphicsItem::ItemIsFocusScope) {
+        if (p->d_ptr->flags & QGraphicsItem::ItemIsFocusScope) {
             // If this item's focus scope's focus scope item points
             // to this item or a descendent, then clear it.
             QGraphicsItem *fsi = p->d_ptr->focusScopeItem;
@@ -1065,11 +1094,11 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
             QGraphicsItem *ancestorScope = 0;
             QGraphicsItem *p = subFocusItem->d_ptr->parent;
             while (p) {
-                if (p->flags() & QGraphicsItem::ItemIsFocusScope)
+                if (p->d_ptr->flags & QGraphicsItem::ItemIsFocusScope)
                     ancestorScope = p;
-                if (p->isPanel())
+                if (p->d_ptr->flags & QGraphicsItem::ItemIsPanel)
                     break;
-                p = p->parentItem();
+                p = p->d_ptr->parent;
             }
             if (ancestorScope)
                 newFocusScopeItem = ancestorScope;
@@ -1077,7 +1106,7 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
 
         QGraphicsItem *p = newParent;
         while (p) {
-            if (p->flags() & QGraphicsItem::ItemIsFocusScope) {
+            if (p->d_ptr->flags & QGraphicsItem::ItemIsFocusScope) {
                 p->d_ptr->focusScopeItem = newFocusScopeItem;
                 // Ensure the new item is no longer the subFocusItem. The
                 // only way to set focus on a child of a focus scope is
@@ -1113,30 +1142,24 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
         }
 
         // Inherit ancestor flags from the new parent.
-        updateAncestorFlag(QGraphicsItem::GraphicsItemFlag(-2));
-        updateAncestorFlag(QGraphicsItem::GraphicsItemFlag(-1));
-        updateAncestorFlag(QGraphicsItem::ItemClipsChildrenToShape);
-        updateAncestorFlag(QGraphicsItem::ItemIgnoresTransformations);
+        updateAncestorFlags();
 
         // Update item visible / enabled.
-        if (parent->isVisible() != visible) {
-            if (!parent->isVisible() || !explicitlyHidden)
-                setVisibleHelper(parent->isVisible(), /* explicit = */ false, /* update = */ !implicitUpdate);
+        if (parent->d_ptr->visible != visible) {
+            if (!parent->d_ptr->visible || !explicitlyHidden)
+                setVisibleHelper(parent->d_ptr->visible, /* explicit = */ false, /* update = */ !implicitUpdate);
         }
         if (parent->isEnabled() != enabled) {
-            if (!parent->isEnabled() || !explicitlyDisabled)
-                setEnabledHelper(parent->isEnabled(), /* explicit = */ false, /* update = */ !implicitUpdate);
+            if (!parent->d_ptr->enabled || !explicitlyDisabled)
+                setEnabledHelper(parent->d_ptr->enabled, /* explicit = */ false, /* update = */ !implicitUpdate);
         }
 
         // Auto-activate if visible and the parent is active.
-        if (q->isVisible() && parent->isActive())
+        if (visible && parent->isActive())
             q->setActive(true);
     } else {
         // Inherit ancestor flags from the new parent.
-        updateAncestorFlag(QGraphicsItem::GraphicsItemFlag(-2));
-        updateAncestorFlag(QGraphicsItem::GraphicsItemFlag(-1));
-        updateAncestorFlag(QGraphicsItem::ItemClipsChildrenToShape);
-        updateAncestorFlag(QGraphicsItem::ItemIgnoresTransformations);
+        updateAncestorFlags();
 
         if (!inDestructor) {
             // Update item visible / enabled.
diff --git a/src/gui/graphicsview/qgraphicsitem_p.h b/src/gui/graphicsview/qgraphicsitem_p.h
index 2d34b80..cfdd382 100644
--- a/src/gui/graphicsview/qgraphicsitem_p.h
+++ b/src/gui/graphicsview/qgraphicsitem_p.h
@@ -153,7 +153,7 @@ public:
         dirtyChildren(0),
         localCollisionHack(0),
         inSetPosHelper(0),
-        needSortChildren(1), // ### can be 0 by default?
+        needSortChildren(0),
         allChildrenDirty(0),
         fullUpdatePending(0),
         flags(0),
@@ -197,6 +197,7 @@ public:
 
     void updateAncestorFlag(QGraphicsItem::GraphicsItemFlag childFlag,
                             AncestorFlag flag = NoFlag, bool enabled = false, bool root = true);
+    void updateAncestorFlags();
     void setIsMemberOfGroup(bool enabled);
     void remapItemPos(QEvent *event, QGraphicsItem *item);
     QPointF genericMapFromScene(const QPointF &pos, const QWidget *viewport) const;
@@ -721,11 +722,13 @@ inline QTransform QGraphicsItemPrivate::transformToParent() const
 inline void QGraphicsItemPrivate::ensureSortedChildren()
 {
     if (needSortChildren) {
-        qSort(children.begin(), children.end(), qt_notclosestLeaf);
         needSortChildren = 0;
         sequentialOrdering = 1;
+        if (children.isEmpty())
+            return;
+        qSort(children.begin(), children.end(), qt_notclosestLeaf);
         for (int i = 0; i < children.size(); ++i) {
-            if (children[i]->d_ptr->siblingIndex != i) {
+            if (children.at(i)->d_ptr->siblingIndex != i) {
                 sequentialOrdering = 0;
                 break;
             }
diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index cea723c..49925e1 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -2482,12 +2482,12 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
         qWarning("QGraphicsScene::addItem: cannot add null item");
         return;
     }
-    if (item->scene() == this) {
+    if (item->d_ptr->scene == this) {
         qWarning("QGraphicsScene::addItem: item has already been added to this scene");
         return;
     }
     // Remove this item from its existing scene
-    if (QGraphicsScene *oldScene = item->scene())
+    if (QGraphicsScene *oldScene = item->d_ptr->scene)
         oldScene->removeItem(item);
 
     // Notify the item that its scene is changing, and allow the item to
@@ -2496,15 +2496,15 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
                                                     qVariantFromValue<QGraphicsScene *>(this)));
     QGraphicsScene *targetScene = qVariantValue<QGraphicsScene *>(newSceneVariant);
     if (targetScene != this) {
-        if (targetScene && item->scene() != targetScene)
+        if (targetScene && item->d_ptr->scene != targetScene)
             targetScene->addItem(item);
         return;
     }
 
     // Detach this item from its parent if the parent's scene is different
     // from this scene.
-    if (QGraphicsItem *itemParent = item->parentItem()) {
-        if (itemParent->scene() != this)
+    if (QGraphicsItem *itemParent = item->d_ptr->parent) {
+        if (itemParent->d_ptr->scene != this)
             item->setParentItem(0);
     }
 
@@ -2534,7 +2534,7 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
         d->enableMouseTrackingOnViews();
     }
 #ifndef QT_NO_CURSOR
-    if (d->allItemsUseDefaultCursor && item->hasCursor()) {
+    if (d->allItemsUseDefaultCursor && item->d_ptr->hasCursor) {
         d->allItemsUseDefaultCursor = false;
         if (d->allItemsIgnoreHoverEvents) // already enabled otherwise
             d->enableMouseTrackingOnViews();
@@ -2542,7 +2542,7 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
 #endif //QT_NO_CURSOR
 
     // Enable touch events if the item accepts touch events.
-    if (d->allItemsIgnoreTouchEvents && item->acceptTouchEvents()) {
+    if (d->allItemsIgnoreTouchEvents && item->d_ptr->acceptTouchEvents) {
         d->allItemsIgnoreTouchEvents = false;
         d->enableTouchEventsOnViews();
     }
@@ -2575,8 +2575,9 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
     }
 
     // Add all children recursively
-    foreach (QGraphicsItem *child, item->children())
-        addItem(child);
+    item->d_ptr->ensureSortedChildren();
+    for (int i = 0; i < item->d_ptr->children.size(); ++i)
+        addItem(item->d_ptr->children.at(i));
 
     // Resolve font and palette.
     item->d_ptr->resolveFont(d->font.resolve());
@@ -2619,7 +2620,7 @@ void QGraphicsScene::addItem(QGraphicsItem *item)
         }
     }
 
-    if (item->flags() & QGraphicsItem::ItemSendsScenePositionChanges)
+    if (item->d_ptr->flags & QGraphicsItem::ItemSendsScenePositionChanges)
         d->registerScenePosItem(item);
 
     // Ensure that newly added items that have subfocus set, gain