Add widget support for requestUpdate() and improve its docs and tests

We must do something when requestUpdate() is called on a QWidgetWindow.
The semantics of UpdateRequest for QWindow and QWidget are unfortunately
different: for widgets an UpdateRequest means "sync the backing store".
For QWindow it also involves marking as dirty.

Change-Id: Idf40b3fc0873652dc081edeb12c96b3007a126ef
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

src/gui/kernel/qwindow.cpp

@@ -2078,11 +2078,16 @@ void QWindowPrivate::deliverUpdateRequest()
     Calling this function multiple times will result in a single event
     being delivered to the window.
 
-    Subclasses of QWindow should reimplement QWindow::event(), intercept
-    the event and call the application's rendering code, then call the
-    base class implementation.
-*/
+    Subclasses of QWindow should reimplement event(), intercept the event and
+    call the application's rendering code, then call the base class
+    implementation.
 
+    \note The subclass' reimplementation of event() must invoke the base class
+    implementation, unless it is absolutely sure that the event does not need to
+    be handled by the base class. For example, the default implementation of
+    this function relies on QEvent::Timer events. Filtering them away would
+    therefore break the delivery of the update events.
+*/
 void QWindow::requestUpdate()
 {
     Q_D(QWindow);

src/widgets/kernel/qwidgetwindow.cpp

@@ -292,11 +292,21 @@ bool QWidgetWindow::event(QEvent *event)
     case QEvent::WindowBlocked:
         qt_button_down = 0;
         break;
+
+    case QEvent::UpdateRequest:
+        // This is not the same as an UpdateRequest for a QWidget. That just
+        // syncs the backing store while here we also must mark as dirty.
+        m_widget->repaint();
+        return true;
+
     default:
         break;
     }
 
-    return m_widget->event(event) || QWindow::event(event);
+    if (m_widget->event(event) && event->type() != QEvent::Timer)
+        return true;
+
+    return QWindow::event(event);
 }
 
 QPointer<QWidget> qt_last_mouse_receiver = 0;

tests/auto/gui/kernel/qwindow/tst_qwindow.cpp

@@ -91,6 +91,7 @@ private slots:
     void modalWindowModallity();
     void modalWindowPosition();
     void windowsTransientChildren();
+    void requestUpdate();
     void initTestCase();
     void cleanup();
 
@@ -1666,6 +1667,25 @@ void tst_QWindow::windowsTransientChildren()
     QVERIFY(isNativeWindowVisible(&child)); // Real children should be visible.
 }
 
+void tst_QWindow::requestUpdate()
+{
+    QRect geometry(m_availableTopLeft + QPoint(80, 80), m_testWindowSize);
+
+    Window window;
+    window.setGeometry(geometry);
+    window.show();
+    QCoreApplication::processEvents();
+    QTRY_VERIFY(window.isExposed());
+
+    QVERIFY(window.received(QEvent::UpdateRequest) == 0);
+
+    window.requestUpdate();
+    QTRY_VERIFY(window.received(QEvent::UpdateRequest) == 1);
+
+    window.requestUpdate();
+    QTRY_VERIFY(window.received(QEvent::UpdateRequest) == 2);
+}
+
 #include <tst_qwindow.moc>
 QTEST_MAIN(tst_QWindow)
 

tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp

@@ -55,6 +55,7 @@ private slots:
     void reparentToAlreadyCreated();
     void reparentToNotYetCreated();
     void asViewport();
+    void requestUpdate();
 };
 
 void tst_QOpenGLWidget::create()
@@ -305,6 +306,29 @@ void tst_QOpenGLWidget::asViewport()
     QVERIFY(view->paintCount() == 0);
 }
 
+class PaintCountWidget : public QOpenGLWidget
+{
+public:
+    PaintCountWidget() : m_count(0) { }
+    void reset() { m_count = 0; }
+    void paintGL() Q_DECL_OVERRIDE { ++m_count; }
+    int m_count;
+};
+
+void tst_QOpenGLWidget::requestUpdate()
+{
+    PaintCountWidget w;
+    w.resize(640, 480);
+    w.show();
+    QTest::qWaitForWindowExposed(&w);
+
+    w.reset();
+    QCOMPARE(w.m_count, 0);
+
+    w.windowHandle()->requestUpdate();
+    QTRY_VERIFY(w.m_count > 0);
+}
+
 QTEST_MAIN(tst_QOpenGLWidget)
 
 #include "tst_qopenglwidget.moc"