Fix crash when handling WM_PAINT during COM operations

Synchronous expose corrupts painter state if it is done during existing
paint operation, which can happen e.g. when requesting some value from
dumpcpp generated wrapper inside a slot.

Fixed by setting platform native interface property "asyncExpose"
when application uses ActiveQt. This allows Windows QPA plugin to
do an asynchronous exposes instead of synchronous.

Task-number: QTBUG-27209
Change-Id: I93595c1d1dc01601f7a8c4562a145bebb29268b6
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/activeqt/container/qaxbase.cpp b/src/activeqt/container/qaxbase.cpp
index 6930c80..70ad8b3 100644
--- a/src/activeqt/container/qaxbase.cpp
+++ b/src/activeqt/container/qaxbase.cpp
@@ -56,6 +56,8 @@
 #include <qmetaobject.h>
 #include <qsettings.h>
 #include <qdebug.h>
+#include <QGuiApplication>
+#include <qpa/qplatformnativeinterface.h>
 
 #ifndef QT_NO_THREAD
 #   include <qmutex.h>
@@ -1221,6 +1223,16 @@ bool QAxBase::initialize(IUnknown **ptr)
     if (*ptr || control().isEmpty())
         return false;
 
+    // Request asynchronous expose events to be used when application uses ActiveQt objects.
+    // Otherwise painter can get corrupted if Invoke or some other COM method that cause Windows
+    // messages to be processed is called during an existing paint operation when WM_PAINT is
+    // also in the queue.
+    static bool asyncExposeSet = false;
+    if (!asyncExposeSet) {
+        QGuiApplication::platformNativeInterface()->setProperty("asyncExpose", QVariant(true));
+        asyncExposeSet = true;
+    }
+
     *ptr = 0;
 
     bool res = false;