Performance issue in QGraphicsItem::addParentItem while building the

scene bottom-up.

When adding n items, the depth was computed n² times. Adding lazy computation
fixes this performance issue.

Reviewed-by: Andreas

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/benchmarks/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/benchmarks/qgraphicsitem/tst_qgraphicsitem.cpp
index 923838a..91dd28b 100644
--- a/tests/benchmarks/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/benchmarks/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -61,6 +61,7 @@ public slots:
 private slots:
     void setParentItem();
     void setParentItem_deep();
+    void setParentItem_deep_reversed();
     void deleteItemWithManyChildren();
     void setPos_data();
     void setPos();
@@ -113,6 +114,19 @@ void tst_QGraphicsItem::setParentItem_deep()
     }
 }
 
+void tst_QGraphicsItem::setParentItem_deep_reversed()
+{
+    QBENCHMARK {
+        QGraphicsRectItem *lastRect = new QGraphicsRectItem;
+        for (int i = 0; i < 100; ++i) {
+            QGraphicsRectItem *parentRect = new QGraphicsRectItem;
+            lastRect->setParentItem(parentRect);
+            lastRect = parentRect;
+        }
+        delete lastRect;
+    }
+}
+
 void tst_QGraphicsItem::deleteItemWithManyChildren()
 {
     QBENCHMARK {