Don't accept all QTouchEvent::points unless the item accepts touch

An items that handles touch events can accept multiple touchpoints; but
after visiting an item that does not handle events at all, or that
relies on synth-mouse events, let the remaining touchpoints continue
propagating. Do not automatically accept all touchpoints just because
an item accepted a synth-mouse event, and do not auto-grab other
touchpoints besides the touchmouse point.

Done-with: Shawn Rutledge
Fixes: QTBUG-107867
Change-Id: I6c342487a4f8bacbd84e6d7e0e7c00884791a610
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 5ced8ec177fd730676eb854aea559a5f324a39b6)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 50 insertions, 8 deletions

diff --git a/src/quick/util/qquickdeliveryagent.cpp b/src/quick/util/qquickdeliveryagent.cpp
index ba16b4ab61..90d154ff5d 100644
--- a/src/quick/util/qquickdeliveryagent.cpp
+++ b/src/quick/util/qquickdeliveryagent.cpp
@@ -2147,18 +2147,16 @@ void QQuickDeliveryAgentPrivate::deliverMatchingPointsToItem(QQuickItem *item, b
         qCDebug(lcTouch) << "actually delivering" << &touchEvent << " to " << item;
         QCoreApplication::sendEvent(item, &touchEvent);
         eventAccepted = touchEvent.isAccepted();
-    } else if (Q_LIKELY(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents))) {
+    } else {
         // If the touch event wasn't accepted, synthesize a mouse event and see if the item wants it.
-        if (!eventAccepted && (itemPrivate->acceptedMouseButtons() & Qt::LeftButton)) {
-            // send mouse event
-            if (deliverTouchAsMouse(item, &touchEvent))
-                eventAccepted = true;
-        }
+        if (Q_LIKELY(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents)) &&
+                !eventAccepted && (itemPrivate->acceptedMouseButtons() & Qt::LeftButton))
+            deliverTouchAsMouse(item, &touchEvent);
+        return;
     }
 
+    Q_ASSERT(item->acceptTouchEvents()); // else we would've returned early above
     if (eventAccepted) {
-        // If the touch was accepted (regardless by whom or in what form),
-        // update accepted new points.
         bool isPressOrRelease = pointerEvent->isBeginEvent() || pointerEvent->isEndEvent();
         for (int i = 0; i < touchEvent.pointCount(); ++i) {
             auto &point = touchEvent.point(i);
diff --git a/tests/auto/quick/touchmouse/tst_touchmouse.cpp b/tests/auto/quick/touchmouse/tst_touchmouse.cpp
index e595175fee..f03af6660d 100644
--- a/tests/auto/quick/touchmouse/tst_touchmouse.cpp
+++ b/tests/auto/quick/touchmouse/tst_touchmouse.cpp
@@ -166,12 +166,14 @@ class GrabMonitor : public QObject
 {
 public:
     QObject *exclusiveGrabber = nullptr;
+    int transitionCount = 0;
     bool fromMouseEvent = false;
     bool canceled = false;
 
     void onGrabChanged(QObject *grabber, QPointingDevice::GrabTransition transition, const QPointerEvent *event, const QEventPoint &point)
     {
         qCDebug(lcTests) << grabber << transition << event << point << point.device();
+        ++transitionCount;
         switch (transition) {
         case QPointingDevice::GrabTransition::GrabExclusive:
             exclusiveGrabber = grabber;
@@ -232,6 +234,8 @@ private slots:
 
     void oneTouchInsideAndOneOutside();
 
+    void strayTouchDoesntAutograb();
+
 protected:
     bool eventFilter(QObject *, QEvent *event) override
     {
@@ -1600,6 +1604,46 @@ void tst_TouchMouse::oneTouchInsideAndOneOutside() // QTBUG-102996
     QQuickTouchUtils::flush(&window);
 }
 
+void tst_TouchMouse::strayTouchDoesntAutograb() // QTBUG-107867
+{
+    QQuickView window;
+    QVERIFY(QQuickTest::showView(window, testFileUrl("singleitem.qml")));
+    QQuickItem *root = window.rootObject();
+    QVERIFY(root);
+    EventItem *eventItem = root->findChild<EventItem*>();
+    QVERIFY(eventItem);
+    // This item accepts (synth-)mouse events but NOT touch
+    eventItem->acceptMouse = true;
+    QCOMPARE(eventItem->acceptTouchEvents(), false); // the default in Qt 6
+    QPoint p1(6, 6);
+
+    // Begin a new touch, that gets converted to a mouse press
+    QTest::touchEvent(&window, device).press(0, p1);
+    QQuickTouchUtils::flush(&window);
+    qCDebug(lcTests) << "after touch press:" << eventItem->eventList;
+    QCOMPARE(eventItem->eventList.size(), 1);
+    QCOMPARE(eventItem->eventList.at(0).type, QEvent::MouseButtonPress);
+    QCOMPARE(grabMonitor.exclusiveGrabber, eventItem);
+
+    // Drag
+    for (int i = 0; i < 3; ++i) {
+        QTest::touchEvent(&window, device).move(0, p1 + QPoint(i * 5, i * 5), &window);
+        QQuickTouchUtils::flush(&window);
+        QCOMPARE(grabMonitor.transitionCount, 1); // no new grab
+        QCOMPARE(eventItem->eventList.size(), i + 2);
+        QCOMPARE(eventItem->eventList.last().type, QEvent::MouseMove);
+    }
+
+    // Press an extra point: EventItem should see nothing
+    QTest::touchEvent(&window, device).stationary(0).press(1, p1);
+    QQuickTouchUtils::flush(&window);
+    qCDebug(lcTests) << "after press of second touchpoint:" << eventItem->eventList;
+    QCOMPARE(eventItem->eventList.size(), 4);
+    QCOMPARE(grabMonitor.transitionCount, 1); // no new grab
+
+    QTest::touchEvent(&window, device).release(0, p1).release(1, p1);
+}
+
 QTEST_MAIN(tst_TouchMouse)
 
 #include "tst_touchmouse.moc"