Fix bugs in QGraphicsItem::childrenBoundingRect()

While working on layering in Graphics View I stumbled over this bug. The
QGraphicsItem::childrenBoundingRect() function had an accumulating error
caused by recursive adding of rectangles that individually were mapped to
the local parent using QGraphicsItem::mapRectToParent() /
QTransform::mapRect. This caused the brect to be way too large for items
with children that are rotated (fex, alternating 45 and -45 degrees).

The new version should be just as fast, but with no loss of precision.

Reviewed-by: bnilsen

1 files changed, 49 insertions, 0 deletions

diff --git a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
index 57e441b..88c64d3 100644
--- a/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/auto/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -172,6 +172,7 @@ private slots:
     void boundingRects2();
     void sceneBoundingRect();
     void childrenBoundingRect();
+    void childrenBoundingRectTransformed();
     void group();
     void setGroup();
     void nestedGroups();
@@ -2917,9 +2918,57 @@ void tst_QGraphicsItem::childrenBoundingRect()
     childChild->setParentItem(child);
     childChild->setPos(500, 500);
     child->rotate(90);
+
+
+    scene.addPolygon(parent->mapToScene(parent->boundingRect() | parent->childrenBoundingRect()))->setPen(QPen(Qt::red));;
+
+    QGraphicsView view(&scene);
+    view.show();
+
+    QTest::qWait(5000);
+
     QCOMPARE(parent->childrenBoundingRect(), QRectF(-500, -100, 600, 800));
 }
 
+void tst_QGraphicsItem::childrenBoundingRectTransformed()
+{
+    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);
+
+    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));
+
+    rect->rotate(45);
+    rect2->rotate(-45);
+    rect3->rotate(45);
+    rect4->rotate(-45);
+    rect5->rotate(45);
+
+    subTreeRect = rect->childrenBoundingRect();
+    QCOMPARE(rect->childrenBoundingRect(), QRectF(-100, 75, 275, 250));
+}
+
 void tst_QGraphicsItem::group()
 {
     QGraphicsScene scene;