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>

2 files changed, 20 insertions, 5 deletions

diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 1fbb67fb8a..4a88988322 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/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);
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 11dfe8a6d5..6c7dc070d5 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/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;