Ensure child items are updated even if the parent item has no content

When a parent item had its visiblity toggled, then the child item would
not update if the parent item had ItemHasNoContents and
ItemClipsChildrenToShape set. This is a common use case in declarative as
the root item has ItemHasNoContents set.

Task-number: QTBUG-26846

Change-Id: Id6592ebc4ba2caa4331a4a71f7247e40993131b6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/widgets/graphicsview/qgraphicsitem.cpp

@@ -2297,7 +2297,8 @@ void QGraphicsItemPrivate::setVisibleHelper(bool newVisible, bool explicitly, bo
     }
 
     // Update children with explicitly = false.
-    const bool updateChildren = update && !(flags & QGraphicsItem::ItemClipsChildrenToShape);
+    const bool updateChildren = update && !((flags & QGraphicsItem::ItemClipsChildrenToShape)
+                                            && !(flags & QGraphicsItem::ItemHasNoContents));
     foreach (QGraphicsItem *child, children) {
         if (!newVisible || !child->d_ptr->explicitlyHidden)
             child->d_ptr->setVisibleHelper(newVisible, false, updateChildren);

tests/manual/manual.pro

@@ -9,6 +9,7 @@ network_remote_stresstest \
 network_stresstest \
 qcursor \
 qdesktopwidget \
+qgraphicsitem \
 qgraphicsitemgroup \
 qgraphicslayout/flicker \
 qhttpnetworkconnection \

tests/manual/qgraphicsitem/main.cpp

@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtWidgets/QApplication>
+#include <QtWidgets/QGraphicsView>
+#include <QtWidgets/QGraphicsScene>
+#include <QtWidgets/QGraphicsItem>
+#include <QtWidgets/QMessageBox>
+
+class MyObject : public QObject
+{
+public:
+    MyObject(QGraphicsItem *i, QObject *parent = 0) : QObject(parent), itemToToggle(i)
+    {
+        startTimer(500);
+    }
+protected:
+    void timerEvent(QTimerEvent *)
+    {
+        itemToToggle->setVisible(!itemToToggle->isVisible());
+    }
+private:
+    QGraphicsItem *itemToToggle;
+};
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+    QGraphicsView gv;
+    QGraphicsScene *scene = new QGraphicsScene(&gv);
+    gv.setScene(scene);
+    QGraphicsItem *rect = scene->addRect(0, 0, 200, 200, QPen(Qt::NoPen), QBrush(Qt::yellow));
+    rect->setFlag(QGraphicsItem::ItemHasNoContents);
+    rect->setFlag(QGraphicsItem::ItemClipsChildrenToShape);
+
+    QGraphicsItem *childRect = scene->addRect(0, 0, 100, 100, QPen(Qt::NoPen), QBrush(Qt::red));
+    childRect->setParentItem(rect);
+    gv.show();
+    MyObject o(rect);
+    QMessageBox::information(0, "What you should see",
+                             "The red rectangle should toggle visiblity, so you should see it flash on and off");
+    return a.exec();
+}

tests/manual/qgraphicsitem/qgraphicsitem.pro

@@ -0,0 +1,2 @@
+QT += widgets
+SOURCES += main.cpp