Wrong caching of QGraphicsItem::childrenBoundingRect.

We cannot cache the bounding rect on the fly for children, because the
bounding rect is mapped to the callee's local coordinate system.

Auto-test included.

2 files changed, 44 insertions, 14 deletions

diff --git a/src/gui/graphicsview/qgraphicsitem.cpp b/src/gui/graphicsview/qgraphicsitem.cpp
index 07a063e..47f8a90 100644
--- a/src/gui/graphicsview/qgraphicsitem.cpp
+++ b/src/gui/graphicsview/qgraphicsitem.cpp
@@ -1016,11 +1016,6 @@ void QGraphicsItemPrivate::setParentItemHelper(QGraphicsItem *newParent)
 */
 void QGraphicsItemPrivate::childrenBoundingRectHelper(QTransform *x, QRectF *rect)
 {
-    if (!dirtyChildrenBoundingRect) {
-        *rect |= x->mapRect(childrenBoundingRect);
-        return;
-    }
-
     for (int i = 0; i < children.size(); ++i) {
         QGraphicsItem *child = children.at(i);
         QGraphicsItemPrivate *childd = child->d_ptr;
@@ -1028,19 +1023,20 @@ void QGraphicsItemPrivate::childrenBoundingRectHelper(QTransform *x, QRectF *rec
         if (hasPos || childd->transformData) {
             // COMBINE
             QTransform matrix = childd->transformToParent();
-            matrix *= *x;
+            if (x)
+                matrix *= *x;
             *rect |= matrix.mapRect(child->boundingRect());
             if (!childd->children.isEmpty())
                 childd->childrenBoundingRectHelper(&matrix, rect);
         } else {
-            *rect |= x->mapRect(child->boundingRect());
+            if (x)
+                *rect |= x->mapRect(child->boundingRect());
+            else
+                *rect |= child->boundingRect();
             if (!childd->children.isEmpty())
                 childd->childrenBoundingRectHelper(x, rect);
         }
     }
-
-    childrenBoundingRect = *rect;
-    dirtyChildrenBoundingRect = 0;
 }
 
 void QGraphicsItemPrivate::initStyleOption(QStyleOptionGraphicsItem *option, const QTransform &worldTransform,
@@ -3930,10 +3926,10 @@ QRectF QGraphicsItem::childrenBoundingRect() const
     if (!d_ptr->dirtyChildrenBoundingRect)
         return d_ptr->childrenBoundingRect;
 
-    QRectF childRect;
-    QTransform x;
-    d_ptr->childrenBoundingRectHelper(&x, &childRect);
-    return childRect;
+    d_ptr->childrenBoundingRect = QRectF();
+    d_ptr->childrenBoundingRectHelper(0, &d_ptr->childrenBoundingRect);
+    d_ptr->dirtyChildrenBoundingRect = 0;
+    return d_ptr->childrenBoundingRect;
 }
 
 /*!
diff --git a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
index ceb033e..d07c6fd 100644
--- a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -215,6 +215,7 @@ private slots:
     void childrenBoundingRect();
     void childrenBoundingRectTransformed();
     void childrenBoundingRect2();
+    void childrenBoundingRect3();
     void group();
     void setGroup();
     void nestedGroups();
@@ -3052,6 +3053,39 @@ void tst_QGraphicsItem::childrenBoundingRect2()
     QCOMPARE(box.childrenBoundingRect(), QRectF(0, 0, 100, 100));
 }
 
+void tst_QGraphicsItem::childrenBoundingRect3()
+{
+    QGraphicsScene scene;
+
+    QGraphicsRectItem *rect = scene.addRect(QRectF(0, 0, 100, 100));
+    QGraphicsRectItem *rect2 = scene.addRect(QRectF(0, 0, 100, 100));
+    QGraphicsRectItem *rect3 = scene.addRect(QRectF(0, 0, 100, 100));
+    QGraphicsRectItem *rect4 = scene.addRect(QRectF(0, 0, 100, 100));
+    QGraphicsRectItem *rect5 = scene.addRect(QRectF(0, 0, 100, 100));
+    rect2->setParentItem(rect);
+    rect3->setParentItem(rect2);
+    rect4->setParentItem(rect3);
+    rect5->setParentItem(rect4);
+
+    rect2->setTransform(QTransform().translate(50, 50).rotate(45));
+    rect2->setPos(25, 25);
+    rect3->setTransform(QTransform().translate(50, 50).rotate(45));
+    rect3->setPos(25, 25);
+    rect4->setTransform(QTransform().translate(50, 50).rotate(45));
+    rect4->setPos(25, 25);
+    rect5->setTransform(QTransform().translate(50, 50).rotate(45));
+    rect5->setPos(25, 25);
+
+    // Try to mess up the cached bounding rect.
+    (void)rect2->childrenBoundingRect();
+
+    QRectF subTreeRect = rect->childrenBoundingRect();
+    QCOMPARE(subTreeRect.left(), qreal(-206.0660171779821));
+    QCOMPARE(subTreeRect.top(), qreal(75.0));
+    QCOMPARE(subTreeRect.width(), qreal(351.7766952966369));
+    QCOMPARE(subTreeRect.height(), qreal(251.7766952966369));
+}
+
 void tst_QGraphicsItem::group()
 {
     QGraphicsScene scene;