Windows Platform: Redirect wheel event to a window under mouse cursor

Revert a part of af5c8d04fb0c9ddda58925e4862e857c78a5e563
which affected mouse wheel event redirection.

Task-number: QTBUG-63979
Change-Id: Ice88675aadbb8a7477b3758a607db5979d62562c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Alexandra Cherdantseva <neluhus.vagus@gmail.com>
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

1 files changed, 17 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowsmousehandler.cpp b/src/plugins/platforms/windows/qwindowsmousehandler.cpp
index 814291c54a..17851618b4 100644
--- a/src/plugins/platforms/windows/qwindowsmousehandler.cpp
+++ b/src/plugins/platforms/windows/qwindowsmousehandler.cpp
@@ -395,10 +395,24 @@ static bool isValidWheelReceiver(QWindow *candidate)
 static void redirectWheelEvent(QWindow *window, const QPoint &globalPos, int delta,
                                Qt::Orientation orientation, Qt::KeyboardModifiers mods)
 {
+    // Redirect wheel event to one of the following, in order of preference:
+    // 1) The window under mouse
+    // 2) The window receiving the event
     // If a window is blocked by modality, it can't get the event.
-    if (isValidWheelReceiver(window)) {
-        QWindowSystemInterface::handleWheelEvent(window,
-                                                 QWindowsGeometryHint::mapFromGlobal(window, globalPos),
+
+    QWindow *receiver = QWindowsScreen::windowAt(globalPos, CWP_SKIPINVISIBLE);
+    while (receiver && receiver->flags().testFlag(Qt::WindowTransparentForInput))
+        receiver = receiver->parent();
+    bool handleEvent = true;
+    if (!isValidWheelReceiver(receiver)) {
+        receiver = window;
+        if (!isValidWheelReceiver(receiver))
+            handleEvent = false;
+    }
+
+    if (handleEvent) {
+        QWindowSystemInterface::handleWheelEvent(receiver,
+                                                 QWindowsGeometryHint::mapFromGlobal(receiver, globalPos),
                                                  globalPos, delta, orientation, mods);
     }
 }