Treat a double-click event as an update event with stationary point

The sequence is still press, release, press, double-click, release.
isBeginEvent() should not be true for a double-click event: the second
click began with a normal MouseButtonPress, and the MouseButtonDblClick
event is a way of sending updated state to tell the recipient that the
second click was special, occurring within such spatial and temporal
constraints that it can be interpreted as a double-click.
It never has a different position either, because MouseButtonDblClick
is a synthetic event occurring at the same position as the second press;
so we might as well say its QEventPoint is Stationary.

Together, these changes fix tst_controls::Basic::DelayButton::test_mouse
in Controls 2, without any changes in qtdeclarative.
In QQuickWindowPrivate::deliverPointerEvent(), if isBeginEvent() == true,
it delivers to all items under the point position(s) first, and then if
all _updated_ points were not accepted, it continues delivery to grabbers;
whereas if isBeginEvent() == false, it delivers only to grabbers.
isBeginEvent() and QEventPoint::state() are important to that algorithm.

Amends 6d6ed64d6ca27c1b5fec305e6ed9b923b5bb1037

Task-number: QTBUG-87018
Change-Id: I95def9704652147540df5cc065354a0fe04ed626
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 12 insertions, 4 deletions

diff --git a/src/gui/kernel/qevent.cpp b/src/gui/kernel/qevent.cpp
index 2772ca6fe2..087873d67e 100644
--- a/src/gui/kernel/qevent.cpp
+++ b/src/gui/kernel/qevent.cpp
@@ -851,8 +851,10 @@ QSinglePointEvent::QSinglePointEvent(QEvent::Type type, const QPointingDevice *d
     mut.setGlobalPosition(globalPos);
     if (isWheel && mut.state() != QEventPoint::State::Updated)
         mut.setGlobalPressPosition(globalPos);
-    if (button == Qt::NoButton || isWheel)
-        mut.setState(QEventPoint::State::Updated); // stationary only happens with touch events, not single-point events
+    if (type == MouseButtonDblClick)
+        mut.setState(QEventPoint::State::Stationary);
+    else if (button == Qt::NoButton || isWheel)
+        mut.setState(QEventPoint::State::Updated);
     else if (isPress)
         mut.setState(QEventPoint::State::Pressed);
     else
@@ -890,7 +892,11 @@ QSinglePointEvent::QSinglePointEvent(QEvent::Type type, const QPointingDevice *d
 */
 bool QSinglePointEvent::isBeginEvent() const
 {
-    return m_button != Qt::NoButton && m_mouseState.testFlag(m_button);
+    // A double-click event does not begin a sequence: it comes after a press event,
+    // and while it tells which button caused the double-click, it doesn't represent
+    // a change of button state. So it's an update event.
+    return m_button != Qt::NoButton && m_mouseState.testFlag(m_button)
+            && type() != QEvent::MouseButtonDblClick;
 }
 
 /*!
@@ -898,7 +904,9 @@ bool QSinglePointEvent::isBeginEvent() const
 */
 bool QSinglePointEvent::isUpdateEvent() const
 {
-    return m_button == Qt::NoButton;
+    // A double-click event is an update event even though it tells which button
+    // caused the double-click, because a MouseButtonPress event was sent right before it.
+    return m_button == Qt::NoButton || type() == QEvent::MouseButtonDblClick;
 }
 
 /*!