graphicsview: use std::sort instead of qSort

In almost all cases, std::sort is wildly faster than qSort - but especially in
the case where the input data is already sorted. in some stress tests which ran
through the index with a lot of items, this commit provides huge speedup (684ms
down to 10ms for painting 15001 empty items on the provided benchmark), for me.

Task-number: QTBUG-11022
Change-Id: I5551f8e320c33ba13d464bf22047a665c81f3b74
Reviewed-by: Peter Kümmel <syntheticpp@gmx.net>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>

src/widgets/graphicsview/qgraphicsitem.cpp

@@ -4578,7 +4578,7 @@ void QGraphicsItem::setZValue(qreal z)
 void QGraphicsItemPrivate::ensureSequentialSiblingIndex()
 {
     if (!sequentialOrdering) {
-        qSort(children.begin(), children.end(), insertionOrder);
+        std::sort(children.begin(), children.end(), insertionOrder);
         sequentialOrdering = 1;
         needSortChildren = 1;
     }

src/widgets/graphicsview/qgraphicsitem_p.h

@@ -826,7 +826,7 @@ inline void QGraphicsItemPrivate::ensureSortedChildren()
         sequentialOrdering = 1;
         if (children.isEmpty())
             return;
-        qSort(children.begin(), children.end(), qt_notclosestLeaf);
+        std::sort(children.begin(), children.end(), qt_notclosestLeaf);
         for (int i = 0; i < children.size(); ++i) {
             if (children.at(i)->d_ptr->siblingIndex != i) {
                 sequentialOrdering = 0;

src/widgets/graphicsview/qgraphicsscene.cpp

@@ -1465,7 +1465,7 @@ void QGraphicsScenePrivate::mousePressEventHandler(QGraphicsSceneMouseEvent *mou
 void QGraphicsScenePrivate::ensureSequentialTopLevelSiblingIndexes()
 {
     if (!topLevelSequentialOrdering) {
-        qSort(topLevelItems.begin(), topLevelItems.end(), QGraphicsItemPrivate::insertionOrder);
+        std::sort(topLevelItems.begin(), topLevelItems.end(), QGraphicsItemPrivate::insertionOrder);
         topLevelSequentialOrdering = true;
         needSortTopLevelItems = 1;
     }
@@ -6055,7 +6055,7 @@ void QGraphicsScenePrivate::gestureEventHandler(QGestureEvent *event)
         gestureTargetsAtHotSpots(startedGestures, Qt::GestureFlag(0), &cachedItemGestures, 0,
                                  &normalGestures, &conflictedGestures);
         cachedTargetItems = cachedItemGestures.keys();
-        qSort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
+        std::sort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
         DEBUG() << "QGraphicsScenePrivate::gestureEventHandler:"
                 << "Normal gestures:" << normalGestures
                 << "Conflicting gestures:" << conflictedGestures;
@@ -6148,7 +6148,7 @@ void QGraphicsScenePrivate::gestureEventHandler(QGestureEvent *event)
                     << gesture->hotSpot() << gesture->d_func()->sceneHotSpot;
         }
     }
-    qSort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
+    std::sort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
     for (int i = 0; i < cachedTargetItems.size(); ++i) {
         QPointer<QGraphicsObject> receiver = cachedTargetItems.at(i);
         QSet<QGesture *> gestures =
@@ -6228,7 +6228,7 @@ void QGraphicsScenePrivate::gestureEventHandler(QGestureEvent *event)
                                      &cachedItemGestures, &targetsSet, 0, 0);
 
             cachedTargetItems = targetsSet.toList();
-            qSort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
+            std::sort(cachedTargetItems.begin(), cachedTargetItems.end(), qt_closestItemFirst);
             DEBUG() << "QGraphicsScenePrivate::gestureEventHandler:"
                     << "new targets:" << cachedTargetItems;
             i = -1; // start delivery again

src/widgets/graphicsview/qgraphicsscene_p.h

@@ -271,7 +271,7 @@ public:
     inline void ensureSortedTopLevelItems()
     {
         if (needSortTopLevelItems) {
-            qSort(topLevelItems.begin(), topLevelItems.end(), qt_notclosestLeaf);
+            std::sort(topLevelItems.begin(), topLevelItems.end(), qt_notclosestLeaf);
             topLevelSequentialOrdering = false;
             needSortTopLevelItems = false;
         }

src/widgets/graphicsview/qgraphicsscenebsptreeindex.cpp

@@ -243,7 +243,7 @@ void QGraphicsSceneBspTreeIndexPrivate::climbTree(QGraphicsItem *item, int *stac
 {
     if (!item->d_ptr->children.isEmpty()) {
         QList<QGraphicsItem *> childList = item->d_ptr->children;
-        qSort(childList.begin(), childList.end(), qt_closestLeaf);
+        std::sort(childList.begin(), childList.end(), qt_closestLeaf);
         for (int i = 0; i < childList.size(); ++i) {
             QGraphicsItem *item = childList.at(i);
             if (!(item->flags() & QGraphicsItem::ItemStacksBehindParent))
@@ -282,7 +282,7 @@ void QGraphicsSceneBspTreeIndexPrivate::_q_updateSortCache()
             topLevels << item;
     }
 
-    qSort(topLevels.begin(), topLevels.end(), qt_closestLeaf);
+    std::sort(topLevels.begin(), topLevels.end(), qt_closestLeaf);
     for (int i = 0; i < topLevels.size(); ++i)
         climbTree(topLevels.at(i), &stackingOrder);
 }
@@ -417,23 +417,23 @@ void QGraphicsSceneBspTreeIndexPrivate::sortItems(QList<QGraphicsItem *> *itemLi
 
     if (onlyTopLevelItems) {
         if (order == Qt::DescendingOrder)
-            qSort(itemList->begin(), itemList->end(), qt_closestLeaf);
+            std::sort(itemList->begin(), itemList->end(), qt_closestLeaf);
         else if (order == Qt::AscendingOrder)
-            qSort(itemList->begin(), itemList->end(), qt_notclosestLeaf);
+            std::sort(itemList->begin(), itemList->end(), qt_notclosestLeaf);
         return;
     }
 
     if (sortCacheEnabled) {
         if (order == Qt::DescendingOrder) {
-            qSort(itemList->begin(), itemList->end(), closestItemFirst_withCache);
+            std::sort(itemList->begin(), itemList->end(), closestItemFirst_withCache);
         } else if (order == Qt::AscendingOrder) {
-            qSort(itemList->begin(), itemList->end(), closestItemLast_withCache);
+            std::sort(itemList->begin(), itemList->end(), closestItemLast_withCache);
         }
     } else {
         if (order == Qt::DescendingOrder) {
-            qSort(itemList->begin(), itemList->end(), qt_closestItemFirst);
+            std::sort(itemList->begin(), itemList->end(), qt_closestItemFirst);
         } else if (order == Qt::AscendingOrder) {
-            qSort(itemList->begin(), itemList->end(), qt_closestItemLast);
+            std::sort(itemList->begin(), itemList->end(), qt_closestItemLast);
         }
     }
 }