Forward touchEvents to children inside QGraphicsProxyWidget

This reapplies the fix from 1ecf2212fae176b78c9951a37df9e33eb24d4f2d,
using QApplication::translateRawTouchEvent to dispatch the touch event
received by the QGraphicsProxyWidget to the relevant child widgets
under each touch point.

In addition, limit the implicit grabbing of each touch point before
sending the event to those cases where we have to: touch pads, and
if the target widget comes from a closest-widget matching. And don't
call the QTouchEvent override of QEvent::setAccepted() on QTouchEvent
instances in QGraphicsView classes, as this will override each event
point's acceptance state.

This way, we can identify which touch points have been accepted after
event delivery, any only implicitly grab those points that were.
Otherwise, touch points not accepted by a proxied widget hierarchy
will still be part of an accepted event, and be grabbed by the
viewport of the QGraphicsView. This would then lead to infinite
recursion when the QGraphicsProxyWidget passes the TouchUpdate event
on to each touch point's grabber.

Re-activate the test case, and extend it with more combinations.
Refactor touch-event recording to make it easier to test multi-touch
scenarios.

Task-number: QTBUG-45737
Fixes: QTBUG-67819
Pick-to: 6.2
Change-Id: Id5611f4feecb43b9367d9c2c71ad863b117efbcb
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 19 insertions, 5 deletions

diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 4c704f3946..de450923ff 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -3911,8 +3911,13 @@ void QApplicationPrivate::activateImplicitTouchGrab(QWidget *widget, QTouchEvent
     if (touchEvent->type() != QEvent::TouchBegin)
         return;
 
-    for (int i = 0; i < touchEvent->pointCount(); ++i)
-        QMutableEventPoint::from(touchEvent->point(i)).setTarget(widget);
+    // If the widget dispatched the event further (see QGraphicsProxyWidget), then
+    // there might already be an implicit grabber. Don't override that.
+    for (int i = 0; i < touchEvent->pointCount(); ++i) {
+        auto &mep = QMutableEventPoint::from(touchEvent->point(i));
+        if (!mep.target() && mep.isAccepted())
+            mep.setTarget(widget);
+    }
     // TODO setExclusiveGrabber() to be consistent with Qt Quick?
 }
 
@@ -3946,16 +3951,21 @@ bool QApplicationPrivate::translateRawTouchEvent(QWidget *window, const QTouchEv
                     target = window;
             }
 
+            bool usingClosestWidget = false;
             if (device->type() == QInputDevice::DeviceType::TouchScreen) {
                 QWidget *closestWidget = d->findClosestTouchPointTarget(device, touchPoint);
                 QWidget *widget = static_cast<QWidget *>(target.data());
                 if (closestWidget
                         && (widget->isAncestorOf(closestWidget) || closestWidget->isAncestorOf(widget))) {
                     target = closestWidget;
+                    usingClosestWidget = true;
                 }
             }
 
-            QMutableEventPoint::from(touchPoint).setTarget(target);
+            // on touch pads, implicitly grab all touch points
+            // on touch screens, grab touch points that are redirected to the closest widget
+            if (device->type() == QInputDevice::DeviceType::TouchPad || usingClosestWidget)
+                QMutableEventPoint::from(touchPoint).setTarget(target);
         } else {
             target = QMutableEventPoint::from(touchPoint).target();
             if (!target)
@@ -4020,7 +4030,9 @@ bool QApplicationPrivate::translateRawTouchEvent(QWidget *window, const QTouchEv
         {
             // if the TouchBegin handler recurses, we assume that means the event
             // has been implicitly accepted and continue to send touch events
-            if (QApplication::sendSpontaneousEvent(widget, &touchEvent) && touchEvent.isAccepted()) {
+            bool res = te->spontaneous() ? QApplication::sendSpontaneousEvent(widget, &touchEvent)
+                                         : QApplication::sendEvent(widget, &touchEvent);
+            if (res && touchEvent.isAccepted()) {
                 accepted = true;
                 if (!widget.isNull())
                     widget->setAttribute(Qt::WA_WState_AcceptedTouchBeginEvent);
@@ -4033,7 +4045,9 @@ bool QApplicationPrivate::translateRawTouchEvent(QWidget *window, const QTouchEv
                 || QGestureManager::gesturePending(widget)
 #endif
                 ) {
-                if (QApplication::sendSpontaneousEvent(widget, &touchEvent) && touchEvent.isAccepted())
+                bool res = te->spontaneous() ? QApplication::sendSpontaneousEvent(widget, &touchEvent)
+                                            : QApplication::sendEvent(widget, &touchEvent);
+                if (res && touchEvent.isAccepted())
                     accepted = true;
                 // widget can be deleted on TouchEnd
                 if (touchEvent.type() == QEvent::TouchEnd && !widget.isNull())