Revert "glib dispatcher: ensure all window system events are flushed"

This reverts commit 341bfcd1ea.

As it turns out there might be use cases where we want to have proper
windowing system event integration with glib dispatcher via g_source_attach().
For example with gtk_dialog_run, where GTK blocks in a recursive main loop.
We want to continue dispatcing our windowing system events during this nested
event loop. Not having a proper glib integration can result in rendering issues,
e.g. when resizing parent window via mouse while GTK-based dialog is shown. Can
be seen on examples/widgets/richtext/textedit/ -> Format (from menu) -> "Color..."

The issue from 341bfcd1ea actually should be fixed inside XCB platform plugin,
by improving integration with event dispatcher. That is handled in follow-up patches.

Change-Id: Icabc6d841a554aefbdd460765a3165d22e65f651
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/platformsupport/eventdispatchers/qeventdispatcher_glib.cpp

@@ -48,26 +48,78 @@
 
 QT_BEGIN_NAMESPACE
 
+struct GUserEventSource
+{
+    GSource source;
+    QPAEventDispatcherGlib *q;
+};
+
+static gboolean userEventSourcePrepare(GSource *source, gint *timeout)
+{
+    Q_UNUSED(timeout)
+    GUserEventSource *userEventSource = reinterpret_cast<GUserEventSource *>(source);
+    QPAEventDispatcherGlib *dispatcher = userEventSource->q;
+    if (dispatcher->m_flags & QEventLoop::ExcludeUserInputEvents)
+        return QWindowSystemInterface::nonUserInputEventsQueued();
+    else
+        return QWindowSystemInterface::windowSystemEventsQueued() > 0;
+}
+
+static gboolean userEventSourceCheck(GSource *source)
+{
+    return userEventSourcePrepare(source, 0);
+}
+
+static gboolean userEventSourceDispatch(GSource *source, GSourceFunc, gpointer)
+{
+    GUserEventSource *userEventSource = reinterpret_cast<GUserEventSource *>(source);
+    QPAEventDispatcherGlib *dispatcher = userEventSource->q;
+    QWindowSystemInterface::sendWindowSystemEvents(dispatcher->m_flags);
+    return true;
+}
+
+static GSourceFuncs userEventSourceFuncs = {
+    userEventSourcePrepare,
+    userEventSourceCheck,
+    userEventSourceDispatch,
+    NULL,
+    NULL,
+    NULL
+};
+
 QPAEventDispatcherGlibPrivate::QPAEventDispatcherGlibPrivate(GMainContext *context)
     : QEventDispatcherGlibPrivate(context)
 {
+    Q_Q(QPAEventDispatcherGlib);
+    userEventSource = reinterpret_cast<GUserEventSource *>(g_source_new(&userEventSourceFuncs,
+                                                                       sizeof(GUserEventSource)));
+    userEventSource->q = q;
+    g_source_set_can_recurse(&userEventSource->source, true);
+    g_source_attach(&userEventSource->source, mainContext);
 }
 
+
 QPAEventDispatcherGlib::QPAEventDispatcherGlib(QObject *parent)
     : QEventDispatcherGlib(*new QPAEventDispatcherGlibPrivate, parent)
     , m_flags(QEventLoop::AllEvents)
 {
+    Q_D(QPAEventDispatcherGlib);
+    d->userEventSource->q = this;
 }
 
 QPAEventDispatcherGlib::~QPAEventDispatcherGlib()
 {
+    Q_D(QPAEventDispatcherGlib);
+
+    g_source_destroy(&d->userEventSource->source);
+    g_source_unref(&d->userEventSource->source);
+    d->userEventSource = 0;
 }
 
 bool QPAEventDispatcherGlib::processEvents(QEventLoop::ProcessEventsFlags flags)
 {
     m_flags = flags;
-    const bool didSendEvents = QEventDispatcherGlib::processEvents(m_flags);
-    return QWindowSystemInterface::sendWindowSystemEvents(m_flags) || didSendEvents;
+    return QEventDispatcherGlib::processEvents(m_flags);
 }
 
 QT_END_NAMESPACE

src/platformsupport/eventdispatchers/qeventdispatcher_glib_p.h

@@ -71,11 +71,14 @@ public:
     QEventLoop::ProcessEventsFlags m_flags;
 };
 
+struct GUserEventSource;
+
 class QPAEventDispatcherGlibPrivate : public QEventDispatcherGlibPrivate
 {
     Q_DECLARE_PUBLIC(QPAEventDispatcherGlib)
 public:
     QPAEventDispatcherGlibPrivate(GMainContext *context = 0);
+    GUserEventSource *userEventSource;
 };