QQuickWindow: obey AA_SynthesizeMouseForUnhandledTouchEvents

Until now, AA_SynthesizeMouseForUnhandledTouchEvents has only affected
behavior of QGuiApplicationPrivate::processTouchEvent, but had no
effect in Qt Quick.  QQuickWindow also accepts the touch event
just to make sure that QGuiApplication will not synthesize mouse
from touch, because it would be redundant: QQuickWindow does that
for itself.

Now we make it have an effect in Qt Quick too: skip mouse synthesis
if it is set to false.  This provides a way to simplify the
event delivery.  If you set it false, then you cannot manipulate old
mouse-only items like MouseArea and Flickable on a touchscreen.
(You can of course use event handlers for that.)

[ChangeLog][QtQuick][QQuickWindow] You can now disable touch->mouse
event synthesis in QtQuick by calling
qGuiApp.setAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents, false);
This will simplify and speed up event delivery, and it will also prevent
any and all interaction with mouse-only items like MouseArea and
Flickable on a touchscreen.

Task-number: QTBUG-52748
Change-Id: I71f1731b5abaeabd9dbce1112cd23bc97d24c12a
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 9 insertions, 5 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index 39aebf7992..804d82a212 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -615,6 +615,7 @@ QQmlListProperty<QObject> QQuickWindowPrivate::data()
 
 static QMouseEvent *touchToMouseEvent(QEvent::Type type, const QTouchEvent::TouchPoint &p, QTouchEvent *event, QQuickItem *item, bool transformNeeded = true)
 {
+    Q_ASSERT(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents));
     // The touch point local position and velocity are not yet transformed.
     QMouseEvent *me = new QMouseEvent(type, transformNeeded ? item->mapFromScene(p.scenePos()) : p.pos(), p.scenePos(), p.screenPos(),
                                       Qt::LeftButton, (type == QEvent::MouseButtonRelease ? Qt::NoButton : Qt::LeftButton), event->modifiers());
@@ -656,6 +657,7 @@ bool QQuickWindowPrivate::checkIfDoubleClicked(ulong newPressEventTimestamp)
 
 bool QQuickWindowPrivate::deliverTouchAsMouse(QQuickItem *item, QQuickPointerEvent *pointerEvent)
 {
+    Q_ASSERT(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents));
     Q_Q(QQuickWindow);
     auto device = pointerEvent->device();
 
@@ -2622,10 +2624,12 @@ void QQuickWindowPrivate::deliverMatchingPointsToItem(QQuickItem *item, QQuickPo
     eventAccepted = touchEvent->isAccepted();
 
     // 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, ptEvent))
-            eventAccepted = true;
+    if (Q_LIKELY(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents))) {
+        if (!eventAccepted && (itemPrivate->acceptedMouseButtons() & Qt::LeftButton)) {
+            //  send mouse event
+            if (deliverTouchAsMouse(item, ptEvent))
+                eventAccepted = true;
+        }
     }
 
     if (eventAccepted) {
@@ -2886,7 +2890,7 @@ bool QQuickWindowPrivate::sendFilteredPointerEventImpl(QQuickPointerEvent *event
                             pt->setGrabberItem(filteringParent);
                         }
                         return true;
-                    } else {
+                    } else if (Q_LIKELY(QCoreApplication::testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents))) {
                         // filteringParent didn't filter the touch event.  Give it a chance to filter a synthetic mouse event.
                         for (int i = 0; i < filteringParentTouchEvent->touchPoints().size(); ++i) {
                             const QTouchEvent::TouchPoint &tp = filteringParentTouchEvent->touchPoints().at(i);