Change to enter/leave policy while grabbing.

Sending enter and leave events to other windows than the grabbing
window is not logical. The policy should be that only the grabbing
window receives enter and leave events.

Changed the documentation accordingly and provided the necessary
changes to Windows implementation.

Also removed explicit leave event generation for widgets when
popup is opened as that is now redundant.

tst_QWidget::underMouse() test was changed to behave according to
new logic.

Task-number: QTBUG-27871
Change-Id: I127fb8685b4a4206d1a319f42cba491ec02bc8ca
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/gui/kernel/qplatformwindow.cpp

@@ -466,12 +466,18 @@ bool QPlatformWindow::frameStrutEventsEnabled() const
         \li Mouse grab: Qt expects windows to automatically grab the mouse if the user presses
             a button until the button is released.
             Automatic grab should be released if some window is explicitly grabbed.
-        \li Enter/Leave events: Enter and leave events should be sent independently of
+        \li Enter/Leave events: If there is a window explicitly grabbing mouse events
-            explicit mouse grabs (\c{setMouseGrabEnabled()}). That is, if the mouse leaves
+            (\c{setMouseGrabEnabled()}), enter and leave events should only be sent to the
-            a window that has explicit mouse grab, a leave event should be sent and other
+            grabbing window when mouse cursor passes over the grabbing window boundary.
-            windows should get enter/leave events as well as the mouse traverses them.
+            Other windows will not receive enter or leave events while the grab is active.
-            For automatic mouse grab, however, a leave event should be sent when the
+            While an automatic mouse grab caused by a mouse button press is active, no window
-            button is released.
+            will receive enter or leave events. When the last mouse button is released, the
+            autograbbing window will receive leave event if mouse cursor is no longer within
+            the window boundary.
+            When any grab starts, the window under cursor will receive a leave event unless
+            it is the grabbing window.
+            When any grab ends, the window under cursor will receive an enter event unless it
+            was the grabbing window.
         \li Window positioning: When calling \c{QWindow::setFramePos()}, the flag
             \c{QWindowPrivate::positionPolicy} is set to \c{QWindowPrivate::WindowFrameInclusive}.
             This means the position includes the window frame, whose size is at this point

src/plugins/platforms/windows/qwindowsmousehandler.cpp

@@ -130,7 +130,8 @@ QWindowsMouseHandler::QWindowsMouseHandler() :
     m_windowUnderMouse(0),
     m_trackedWindow(0),
     m_touchDevice(0),
-    m_leftButtonDown(false)
+    m_leftButtonDown(false),
+    m_previousCaptureWindow(0)
 {
 }
 
@@ -212,6 +213,7 @@ bool QWindowsMouseHandler::translateMouseEvent(QWindow *window, HWND hwnd,
                 if (QWindowsContext::verboseEvents)
                     qDebug() << "Automatic mouse capture for missing buttondown event" << window;
             }
+            m_previousCaptureWindow = window;
             return true;
         } else if (m_leftButtonDown && !actualLeftDown) {
             m_leftButtonDown = false;
@@ -253,12 +255,13 @@ bool QWindowsMouseHandler::translateMouseEvent(QWindow *window, HWND hwnd,
         }
     }
 
+    const bool hasCapture = platformWindow->hasMouseCapture();
+    const bool currentNotCapturing = hasCapture && currentWindowUnderMouse != window;
 #ifndef Q_OS_WINCE
     // Enter new window: track to generate leave event.
-    // If there is an active capture, we must track the actual capture window instead of window
+    // If there is an active capture, only track if the current window is capturing,
-    // under cursor or leaves will trigger constantly, so always track the window we got
+    // so we don't get extra leave when cursor leaves the application.
-    // native mouse event for.
+    if (window != m_trackedWindow && !currentNotCapturing) {
-    if (window != m_trackedWindow) {
         TRACKMOUSEEVENT tme;
         tme.cbSize = sizeof(TRACKMOUSEEVENT);
         tme.dwFlags = TME_LEAVE;
@@ -270,39 +273,53 @@ bool QWindowsMouseHandler::translateMouseEvent(QWindow *window, HWND hwnd,
     }
 #endif // !Q_OS_WINCE
 
-    // Qt expects enter/leave events for windows even when some window is capturing mouse input,
+    // No enter or leave events are sent as long as there is an autocapturing window.
-    // except for automatic capture when mouse button is pressed - in that case enter/leave
+    if (!hasCapture || !platformWindow->testFlag(QWindowsWindow::AutoMouseCapture)) {
-    // should be sent only after the last button is released.
+        // Leave is needed if:
-    // We need to track m_windowUnderMouse separately from m_trackedWindow, as
+        // 1) There is no capture and we move from a window to another window.
-    // Windows mouse tracking will not trigger WM_MOUSELEAVE for leaving window when
+        //    Note: Leaving the application entirely is handled in WM_MOUSELEAVE case.
-    // mouse capture is set.
+        // 2) There is capture and we move out of the capturing window.
-    if (!platformWindow->hasMouseCapture()
+        // 3) There is a new capture and we were over another window.
-        || !platformWindow->testFlag(QWindowsWindow::AutoMouseCapture)) {
+        if ((m_windowUnderMouse && m_windowUnderMouse != currentWindowUnderMouse
-        if (m_windowUnderMouse != currentWindowUnderMouse) {
+                && (!hasCapture || window == m_windowUnderMouse))
-            if (m_windowUnderMouse) {
+            || (hasCapture && m_previousCaptureWindow != window && m_windowUnderMouse
-                if (QWindowsContext::verboseEvents)
+                && m_windowUnderMouse != window)) {
-                    qDebug() << "Synthetic leave for " << m_windowUnderMouse;
+            if (QWindowsContext::verboseEvents)
-                QWindowSystemInterface::handleLeaveEvent(m_windowUnderMouse);
+                qDebug() << "Synthetic leave for " << m_windowUnderMouse;
-                // Clear tracking if we are no longer over application,
+            QWindowSystemInterface::handleLeaveEvent(m_windowUnderMouse);
-                // since we have already sent the leave.
+            if (currentNotCapturing) {
-                if (!currentWindowUnderMouse)
+                // Clear tracking if capturing and current window is not the capturing window
-                    m_trackedWindow = 0;
+                // to avoid leave when mouse actually leaves the application.
-            }
+                m_trackedWindow = 0;
-
+                // We are not officially in any window, but we need to set some cursor to clear
-            if (currentWindowUnderMouse) {
+                // whatever cursor the left window had, so apply the cursor of the capture window.
-                if (QWindowsContext::verboseEvents)
+                QWindowsWindow::baseWindowOf(window)->applyCursor();
-                    qDebug() << "Entering " << currentWindowUnderMouse;
-                QWindowsWindow::baseWindowOf(currentWindowUnderMouse)->applyCursor();
-                QWindowSystemInterface::handleEnterEvent(currentWindowUnderMouse,
-                                                         currentWindowUnderMouse->mapFromGlobal(globalPosition),
-                                                         globalPosition);
             }
         }
+        // Enter is needed if:
+        // 1) There is no capture and we move to a new window.
+        // 2) There is capture and we move into the capturing window.
+        // 3) The capture just ended and we are over non-capturing window.
+        if ((currentWindowUnderMouse && m_windowUnderMouse != currentWindowUnderMouse
+                && (!hasCapture || currentWindowUnderMouse == window))
+            || (m_previousCaptureWindow && window != m_previousCaptureWindow && currentWindowUnderMouse
+                && currentWindowUnderMouse != m_previousCaptureWindow)) {
+            if (QWindowsContext::verboseEvents)
+                qDebug() << "Entering " << currentWindowUnderMouse;
+            QWindowsWindow::baseWindowOf(currentWindowUnderMouse)->applyCursor();
+            QWindowSystemInterface::handleEnterEvent(currentWindowUnderMouse,
+                                                     currentWindowUnderMouse->mapFromGlobal(globalPosition),
+                                                     globalPosition);
+        }
+        // We need to track m_windowUnderMouse separately from m_trackedWindow, as
+        // Windows mouse tracking will not trigger WM_MOUSELEAVE for leaving window when
+        // mouse capture is set.
         m_windowUnderMouse = currentWindowUnderMouse;
     }
 
     QWindowSystemInterface::handleMouseEvent(window, winEventPosition, globalPosition, buttons,
                                              QWindowsKeyMapper::queryKeyboardModifiers());
+    m_previousCaptureWindow = hasCapture ? window : 0;
     return true;
 }
 

src/plugins/platforms/windows/qwindowsmousehandler.h

@@ -82,6 +82,7 @@ private:
     QHash<DWORD, int> m_touchInputIDToTouchPointID;
     QTouchDevice *m_touchDevice;
     bool m_leftButtonDown;
+    QWindow *m_previousCaptureWindow;
 };
 
 Qt::MouseButtons QWindowsMouseHandler::keyStateToMouseButtons(int wParam)

src/widgets/kernel/qapplication_qpa.cpp

@@ -250,13 +250,6 @@ void QApplicationPrivate::openPopup(QWidget *popup)
             QApplication::sendEvent(fw, &e);
         }
     }
-
-    // Dispatch leave for last mouse receiver to update undermouse states
-    if (qt_last_mouse_receiver && !QWidget::mouseGrabber()) {
-        QApplicationPrivate::dispatchEnterLeave(0, qt_last_mouse_receiver.data(),
-                                                QGuiApplicationPrivate::lastCursorPosition);
-        qt_last_mouse_receiver = 0;
-    }
 }
 
 void QApplicationPrivate::initializeMultitouch_sys()

tests/auto/widgets/kernel/qwidget/tst_qwidget.cpp

@@ -9665,6 +9665,11 @@ void tst_QWidget::underMouse()
     QVERIFY(popupWindow);
     QVERIFY(QApplication::activePopupWidget() == &popupWidget);
 
+    // Send an artificial leave event for window, as it won't get generated automatically
+    // due to cursor not actually being over the window.
+    QWindowSystemInterface::handleLeaveEvent(window);
+    QApplication::processEvents();
+
     // If there is an active popup, undermouse should not be reported (QTBUG-27478),
     // but opening a popup causes leave for widgets under mouse.
     QVERIFY(!topLevelWidget.underMouse());
@@ -9682,13 +9687,8 @@ void tst_QWidget::underMouse()
     topLevelWidget.resetCounts();
     childWidget2.resetCounts();
 
-    // Note about commented out compares below:
+    // Moving around while popup active should not change undermouse or cause
-    // Widgets are not receiving enter/leave events properly when there is a popup up,
+    // enter and leave events for widgets.
-    // so all enter and leave counts are not correct yet.
-    // Fix this test when QTBUG-27800 is fixed (i.e. uncomment commented out compares).
-
-    // Moving around while popup active should not change undermouse either,
-    // but should send enter and leave events for widgets
     QTest::mouseMove(popupWindow, popupWindow->mapFromGlobal(window->mapToGlobal(child2PointB)));
     QVERIFY(!topLevelWidget.underMouse());
     QVERIFY(!childWidget1.underMouse());
@@ -9696,14 +9696,12 @@ void tst_QWidget::underMouse()
     QVERIFY(!popupWidget.underMouse());
     QCOMPARE(popupWidget.enters, 0);
     QCOMPARE(popupWidget.leaves, 0);
-    //QCOMPARE(topLevelWidget.enters, 1); // QTBUG-27800
+    QCOMPARE(topLevelWidget.enters, 0);
     QCOMPARE(topLevelWidget.leaves, 0);
     QCOMPARE(childWidget1.enters, 0);
     QCOMPARE(childWidget1.leaves, 0);
-    //QCOMPARE(childWidget2.enters, 1); // QTBUG-27800
+    QCOMPARE(childWidget2.enters, 0);
     QCOMPARE(childWidget2.leaves, 0);
-    topLevelWidget.resetCounts();
-    childWidget2.resetCounts();
 
     QTest::mouseMove(popupWindow, popupWindow->mapFromGlobal(window->mapToGlobal(inWindowPoint)));
     QVERIFY(!topLevelWidget.underMouse());
@@ -9717,8 +9715,7 @@ void tst_QWidget::underMouse()
     QCOMPARE(childWidget1.enters, 0);
     QCOMPARE(childWidget1.leaves, 0);
     QCOMPARE(childWidget2.enters, 0);
-    //QCOMPARE(childWidget2.leaves, 1); // QTBUG-27800
+    QCOMPARE(childWidget2.leaves, 0);
-    childWidget2.resetCounts();
 
     QTest::mouseMove(popupWindow, popupWindow->mapFromGlobal(window->mapToGlobal(child1Point)));
     QVERIFY(!topLevelWidget.underMouse());
@@ -9729,68 +9726,19 @@ void tst_QWidget::underMouse()
     QCOMPARE(popupWidget.leaves, 0);
     QCOMPARE(topLevelWidget.enters, 0);
     QCOMPARE(topLevelWidget.leaves, 0);
-    //QCOMPARE(childWidget1.enters, 1); // QTBUG-27800
-    QCOMPARE(childWidget1.leaves, 0);
-    QCOMPARE(childWidget2.enters, 0);
-    QCOMPARE(childWidget2.leaves, 0);
-    childWidget1.resetCounts();
-
-    // Mouse moves off-application, should cause leaves for currently entered widgets
-    QWindowSystemInterface::handleLeaveEvent(window);
-    QApplication::processEvents();
-    QVERIFY(!topLevelWidget.underMouse());
-    QVERIFY(!childWidget1.underMouse());
-    QVERIFY(!childWidget2.underMouse());
-    QVERIFY(!popupWidget.underMouse());
-    QCOMPARE(popupWidget.enters, 0);
-    QCOMPARE(popupWidget.leaves, 0);
-    QCOMPARE(topLevelWidget.enters, 0);
-    QCOMPARE(topLevelWidget.leaves, 1);
-    QCOMPARE(childWidget1.enters, 0);
-    //QCOMPARE(childWidget1.leaves, 1); // QTBUG-27800
-    QCOMPARE(childWidget2.enters, 0);
-    QCOMPARE(childWidget2.leaves, 0);
-    topLevelWidget.resetCounts();
-    childWidget1.resetCounts();
-
-    // Mouse enters back in, should cause enter to topLevelWidget
-    QWindowSystemInterface::handleEnterEvent(window, inWindowPoint, window->mapToGlobal(inWindowPoint));
-    QApplication::processEvents();
-    QVERIFY(!topLevelWidget.underMouse());
-    QVERIFY(!childWidget1.underMouse());
-    QVERIFY(!childWidget2.underMouse());
-    QVERIFY(!popupWidget.underMouse());
-    QCOMPARE(popupWidget.enters, 0);
-    QCOMPARE(popupWidget.leaves, 0);
-    QCOMPARE(topLevelWidget.enters, 1);
-    QCOMPARE(topLevelWidget.leaves, 0);
     QCOMPARE(childWidget1.enters, 0);
     QCOMPARE(childWidget1.leaves, 0);
     QCOMPARE(childWidget2.enters, 0);
     QCOMPARE(childWidget2.leaves, 0);
-    topLevelWidget.resetCounts();
 
-    // Mouse moves to child widget, should cause enter to child
+    // Note: Mouse moving off-application while there is an active popup cannot be simulated
-    QTest::mouseMove(popupWindow, popupWindow->mapFromGlobal(window->mapToGlobal(child2PointB)));
+    // without actually moving the cursor so it is not tested.
-    QVERIFY(!topLevelWidget.underMouse());
-    QVERIFY(!childWidget1.underMouse());
-    QVERIFY(!childWidget2.underMouse());
-    QVERIFY(!popupWidget.underMouse());
-    QCOMPARE(popupWidget.enters, 0);
-    QCOMPARE(popupWidget.leaves, 0);
-    QCOMPARE(topLevelWidget.enters, 0);
-    QCOMPARE(topLevelWidget.leaves, 0);
-    QCOMPARE(childWidget1.enters, 0);
-    QCOMPARE(childWidget1.leaves, 0);
-    //QCOMPARE(childWidget2.enters, 1); // QTBUG-27800
-    QCOMPARE(childWidget2.leaves, 0);
-    childWidget2.resetCounts();
 
-    // Mouse enters popup, should cause enter to popup and leave to current widgets under mouse
+    // Mouse enters popup, should cause enter to popup.
-    QWindowSystemInterface::handleLeaveEvent(window);
+    // Once again, need to create artificial enter event.
     const QPoint popupCenter = popupWindow->geometry().center();
     QWindowSystemInterface::handleEnterEvent(popupWindow, popupWindow->mapFromGlobal(popupCenter), popupCenter);
-    QApplication::processEvents();
+    QTest::mouseMove(popupWindow, popupCenter);
     QVERIFY(!topLevelWidget.underMouse());
     QVERIFY(!childWidget1.underMouse());
     QVERIFY(!childWidget2.underMouse());
@@ -9798,14 +9746,12 @@ void tst_QWidget::underMouse()
     QCOMPARE(popupWidget.enters, 1);
     QCOMPARE(popupWidget.leaves, 0);
     QCOMPARE(topLevelWidget.enters, 0);
-    QCOMPARE(topLevelWidget.leaves, 1);
+    QCOMPARE(topLevelWidget.leaves, 0);
     QCOMPARE(childWidget1.enters, 0);
     QCOMPARE(childWidget1.leaves, 0);
     QCOMPARE(childWidget2.enters, 0);
-    //QCOMPARE(childWidget2.leaves, 1); // QTBUG-27800
+    QCOMPARE(childWidget2.leaves, 0);
     popupWidget.resetCounts();
-    topLevelWidget.resetCounts();
-    childWidget2.resetCounts();
 
     // Mouse moves around inside popup, no changes
     QTest::mouseMove(popupWindow, QPoint(5, 5));
@@ -9822,9 +9768,10 @@ void tst_QWidget::underMouse()
     QCOMPARE(childWidget2.enters, 0);
     QCOMPARE(childWidget2.leaves, 0);
 
-    // Mouse leaves popup and enters topLevelWidget, should cause enter to topLevelWidget and leave for popup
+    // Mouse leaves popup and enters topLevelWidget, should cause leave for popup
+    // but no enter to topLevelWidget. Again, artificial leave event needed.
     QWindowSystemInterface::handleLeaveEvent(popupWindow);
-    QWindowSystemInterface::handleEnterEvent(window, inWindowPoint, window->mapToGlobal(inWindowPoint));
+    QTest::mouseMove(popupWindow, popupWindow->mapFromGlobal(window->mapToGlobal(inWindowPoint)));
     QApplication::processEvents();
     QVERIFY(!topLevelWidget.underMouse());
     QVERIFY(!childWidget1.underMouse());
@@ -9832,7 +9779,7 @@ void tst_QWidget::underMouse()
     QVERIFY(!popupWidget.underMouse());
     QCOMPARE(popupWidget.enters, 0);
     QCOMPARE(popupWidget.leaves, 1);
-    QCOMPARE(topLevelWidget.enters, 1);
+    QCOMPARE(topLevelWidget.enters, 0);
     QCOMPARE(topLevelWidget.leaves, 0);
     QCOMPARE(childWidget1.enters, 0);
     QCOMPARE(childWidget1.leaves, 0);