1 files changed, 20 insertions, 10 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index 9be6d4ced7..bb349f08a7 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -77,6 +77,7 @@
 #include <QtCore/qoperatingsystemversion.h>
 #include <QtCore/qsysinfo.h>
 #include <QtCore/qscopedpointer.h>
+#include <QtCore/quuid.h>
 #include <QtCore/private/qsystemlibrary_p.h>
 
 #include <QtEventDispatcherSupport/private/qwindowsguieventdispatcher_p.h>
@@ -133,8 +134,8 @@ static inline bool useRTL_Extensions()
 #if QT_CONFIG(sessionmanager)
 static inline QWindowsSessionManager *platformSessionManager()
 {
-    QGuiApplicationPrivate *guiPrivate = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
-    QSessionManagerPrivate *managerPrivate = static_cast<QSessionManagerPrivate*>(QObjectPrivate::get(guiPrivate->session_manager));
+    auto *guiPrivate = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
+    auto *managerPrivate = static_cast<QSessionManagerPrivate*>(QObjectPrivate::get(guiPrivate->session_manager));
     return static_cast<QWindowsSessionManager *>(managerPrivate->platformSessionManager);
 }
 
@@ -317,6 +318,8 @@ QWindowsContext::~QWindowsContext()
         OleUninitialize();
 
     d->m_screenManager.clearScreens(); // Order: Potentially calls back to the windows.
+    if (d->m_displayContext)
+        ReleaseDC(nullptr, d->m_displayContext);
     m_instance = nullptr;
 }
 
@@ -542,10 +545,10 @@ QString QWindowsContext::registerWindowClass(QString cname,
     // each one has to have window class names with a unique name
     // The first instance gets the unmodified name; if the class
     // has already been registered by another instance of Qt then
-    // add an instance-specific ID, the address of the window proc.
+    // add a UUID.
     static int classExists = -1;
 
-    const HINSTANCE appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
+    const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
     if (classExists == -1) {
         WNDCLASS wcinfo;
         classExists = GetClassInfo(appInstance, reinterpret_cast<LPCWSTR>(cname.utf16()), &wcinfo);
@@ -553,7 +556,7 @@ QString QWindowsContext::registerWindowClass(QString cname,
     }
 
     if (classExists)
-        cname += QString::number(reinterpret_cast<quintptr>(proc));
+        cname += QUuid::createUuid().toString();
 
     if (d->m_registeredWindowClassNames.contains(cname))        // already registered in our list
         return cname;
@@ -598,7 +601,7 @@ QString QWindowsContext::registerWindowClass(QString cname,
 
 void QWindowsContext::unregisterWindowClasses()
 {
-    const HINSTANCE appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
+    const auto appInstance = static_cast<HINSTANCE>(GetModuleHandle(nullptr));
 
     for (const QString &name : qAsConst(d->m_registeredWindowClassNames)) {
         if (!UnregisterClass(reinterpret_cast<LPCWSTR>(name.utf16()), appInstance) && QWindowsContext::verbose)
@@ -749,6 +752,12 @@ QWindowsWindow *QWindowsContext::findPlatformWindowAt(HWND parent,
     QWindowsWindow *result = nullptr;
     const POINT screenPoint = { screenPointIn.x(), screenPointIn.y() };
     while (findPlatformWindowHelper(screenPoint, cwex_flags, this, &parent, &result)) {}
+    // QTBUG-40815: ChildWindowFromPointEx() can hit on special windows from
+    // screen recorder applications like ScreenToGif. Fall back to WindowFromPoint().
+    if (result == nullptr) {
+        if (const HWND window = WindowFromPoint(screenPoint))
+            result = findPlatformWindow(window);
+    }
     return result;
 }
 
@@ -925,7 +934,7 @@ bool QWindowsContext::systemParametersInfo(unsigned action, unsigned param, void
 bool QWindowsContext::systemParametersInfoForScreen(unsigned action, unsigned param, void *out,
                                                     const QPlatformScreen *screen)
 {
-    return systemParametersInfo(action, param, out, screen ? screen->logicalDpi().first : 0);
+    return systemParametersInfo(action, param, out, screen ? unsigned(screen->logicalDpi().first) : 0u);
 }
 
 bool QWindowsContext::systemParametersInfoForWindow(unsigned action, unsigned param, void *out,
@@ -944,7 +953,8 @@ bool QWindowsContext::nonClientMetrics(NONCLIENTMETRICS *ncm, unsigned dpi)
 bool QWindowsContext::nonClientMetricsForScreen(NONCLIENTMETRICS *ncm,
                                                 const QPlatformScreen *screen)
 {
-    return nonClientMetrics(ncm, screen ? screen->logicalDpi().first : 0);
+    const int dpi = screen ? qRound(screen->logicalDpi().first) : 0;
+    return nonClientMetrics(ncm, unsigned(dpi));
 }
 
 bool QWindowsContext::nonClientMetricsForWindow(NONCLIENTMETRICS *ncm, const QPlatformWindow *win)
@@ -1351,7 +1361,7 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
         sessionManager->blocksInteraction();
         sessionManager->clearCancellation();
 
-        QGuiApplicationPrivate *qGuiAppPriv = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
+        auto *qGuiAppPriv = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
         qGuiAppPriv->commitData();
 
         if (lParam & ENDSESSION_LOGOFF)
@@ -1369,7 +1379,7 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
 
         // we receive the message for each toplevel window included internal hidden ones,
         // but the aboutToQuit signal should be emitted only once.
-        QGuiApplicationPrivate *qGuiAppPriv = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
+        auto *qGuiAppPriv = static_cast<QGuiApplicationPrivate*>(QObjectPrivate::get(qApp));
         if (endsession && !qGuiAppPriv->aboutToQuitEmitted) {
             qGuiAppPriv->aboutToQuitEmitted = true;
             int index = QGuiApplication::staticMetaObject.indexOfSignal("aboutToQuit()");