Fix MouseButtonDblClick synthesis from touch double-tap

When QGuiApplicationPrivate::processTouchEvent() sees that the
touch event was not handled, and calls processMouseEvent(), the latter
uses the QEventPoint with pointId 0 regardless of the original
touchpoint ID. Now it updates the persistent QEventPoint from the
original touchpoint so that a double-click event will not be ruled out
because of the timestamp delta or position delta (movement since press)
being too large.

Fixes: QTBUG-125993
Pick-to: 6.7 6.5
Change-Id: I8e9b007818107ac2329454e0ccfb2ac9e506b617
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 2a0b907f11b9c0ad46322ba06482861423246d93)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/kernel/qguiapplication.cpp

@@ -2271,7 +2271,7 @@ void QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::Mo
         QWindowSystemInterfacePrivate::MouseEvent moveEvent(window, e->timestamp,
             e->localPos, e->globalPos, e->buttons ^ button, e->modifiers, Qt::NoButton,
             e->nonClientArea ? QEvent::NonClientAreaMouseMove : QEvent::MouseMove,
-            e->source, e->nonClientArea);
+            e->source, e->nonClientArea, device, e->eventPointId);
         if (e->synthetic())
             moveEvent.flags |= QWindowSystemInterfacePrivate::WindowSystemEvent::Synthetic;
         processMouseEvent(&moveEvent); // mouse move excluding state change
@@ -2291,6 +2291,9 @@ void QGuiApplicationPrivate::processMouseEvent(QWindowSystemInterfacePrivate::Mo
     bool doubleClick = false;
     auto persistentEPD = devPriv->pointById(0);
 
+    if (e->synthetic(); auto *originalDeviceEPD = devPriv->queryPointById(e->eventPointId))
+        QMutableEventPoint::update(originalDeviceEPD->eventPoint, persistentEPD->eventPoint);
+
     if (mouseMove) {
         QGuiApplicationPrivate::lastCursorPosition = globalPoint;
         const auto doubleClickDistance = (e->device && e->device->type() == QInputDevice::DeviceType::Mouse ?
@@ -3207,7 +3210,8 @@ void QGuiApplicationPrivate::processTouchEvent(QWindowSystemInterfacePrivate::To
                         }
                         // All touch events that are not accepted by the application will be translated to
                         // left mouse button events instead (see AA_SynthesizeMouseForUnhandledTouchEvents docs).
-                        // TODO why go through QPA?  Why not just send a QMouseEvent right from here?
+                        // Sending a QPA event (rather than simply sending a QMouseEvent) takes care of
+                        // side-effects such as double-click synthesis.
                         QWindowSystemInterfacePrivate::MouseEvent fake(window, e->timestamp,
                                                                        window->mapFromGlobal(touchPoint->globalPosition().toPoint()),
                                                                        touchPoint->globalPosition(),
@@ -3217,7 +3221,8 @@ void QGuiApplicationPrivate::processTouchEvent(QWindowSystemInterfacePrivate::To
                                                                        mouseEventType,
                                                                        Qt::MouseEventSynthesizedByQt,
                                                                        false,
-                                                                       device);
+                                                                       device,
+                                                                       touchPoint->id());
                         fake.flags |= QWindowSystemInterfacePrivate::WindowSystemEvent::Synthetic;
                         processMouseEvent(&fake);
                     }

src/gui/kernel/qwindowsysteminterface_p.h

@@ -224,9 +224,11 @@ public:
                    Qt::MouseButtons state, Qt::KeyboardModifiers mods,
                    Qt::MouseButton b, QEvent::Type type,
                    Qt::MouseEventSource src = Qt::MouseEventNotSynthesized, bool frame = false,
-                   const QPointingDevice *device = QPointingDevice::primaryPointingDevice())
+                   const QPointingDevice *device = QPointingDevice::primaryPointingDevice(),
+                   int evPtId = -1)
             : PointerEvent(w, time, Mouse, mods, device), localPos(local), globalPos(global),
-              buttons(state), source(src), nonClientArea(frame), button(b), buttonType(type) { }
+              buttons(state), source(src), nonClientArea(frame), button(b), buttonType(type),
+              eventPointId(evPtId) { }
 
         QPointF localPos;
         QPointF globalPos;
@@ -235,6 +237,7 @@ public:
         bool nonClientArea;
         Qt::MouseButton button;
         QEvent::Type buttonType;
+        int eventPointId; // from the original device if synth-mouse, otherwise -1
     };
 
     class WheelEvent : public PointerEvent {

tests/auto/widgets/graphicsview/qgraphicsproxywidget/tst_qgraphicsproxywidget.cpp

@@ -3872,6 +3872,7 @@ void tst_QGraphicsProxyWidget::touchEventPropagation()
                 break;
             }
             case QEvent::MouseButtonPress:
+            case QEvent::MouseButtonDblClick:
                 mousePressReceiver = qobject_cast<QWidget*>(receiver);
                 break;
             default:

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

@@ -432,6 +432,7 @@ private slots:
     void touchUpdateOnNewTouch();
     void touchCancel();
     void touchEventsForGesturePendingWidgets();
+    void synthMouseDoubleClick();
 
     void styleSheetPropagation();
 
@@ -12257,7 +12258,24 @@ protected:
         case QEvent::MouseMove:
         case QEvent::MouseButtonRelease:
             ++m_mouseEventCount;
-            m_lastMouseEventPos = static_cast<QMouseEvent *>(e)->position();
+            {
+                QMouseEvent *me = static_cast<QMouseEvent *>(e);
+                m_lastMouseEventPos = me->position();
+                m_lastMouseTimestamp = me->timestamp();
+            }
+            if (m_acceptMouse)
+                e->accept();
+            else
+                e->ignore();
+            return true;
+
+        case QEvent::MouseButtonDblClick:
+            ++m_mouseEventCount;
+            {
+                QMouseEvent *me = static_cast<QMouseEvent *>(e);
+                m_lastMouseEventPos = me->position();
+                m_doubleClickTimestamp = me->timestamp();
+            }
             if (m_acceptMouse)
                 e->accept();
             else
@@ -12283,6 +12301,8 @@ public:
     int m_mouseEventCount = 0;
     bool m_acceptMouse = true;
     QPointF m_lastMouseEventPos;
+    quint64 m_lastMouseTimestamp = 0;
+    quint64 m_doubleClickTimestamp = 0;
 };
 
 void tst_QWidget::touchEventSynthesizedMouseEvent()
@@ -12524,6 +12544,50 @@ void tst_QWidget::touchEventsForGesturePendingWidgets()
     QVERIFY(parent.m_gestureEventCount > 0);
 }
 
+void tst_QWidget::synthMouseDoubleClick()
+{
+    TouchMouseWidget widget;
+    widget.setWindowTitle(QLatin1String(QTest::currentTestFunction()));
+    widget.show();
+    QWindow* window = widget.windowHandle();
+    QVERIFY(QTest::qWaitForWindowExposed(window));
+
+    // tap once; move slightly from press to release
+    QPoint p(20, 20);
+    int expectedMouseEventCount = 0;
+    QTest::touchEvent(window, m_touchScreen).press(1, p, window);
+    QCOMPARE(widget.m_touchBeginCount, 0);
+    QCOMPARE(widget.m_mouseEventCount, ++expectedMouseEventCount);
+    QCOMPARE(widget.m_lastMouseEventPos.toPoint(), p);
+    quint64 mouseTimestamp = widget.m_lastMouseTimestamp;
+    p += {1, 0};
+    QTest::touchEvent(window, m_touchScreen).move(1, p, window);
+    QCOMPARE(widget.m_mouseEventCount, ++expectedMouseEventCount);
+    QCOMPARE(widget.m_lastMouseEventPos.toPoint(), p);
+    QCOMPARE_GT(widget.m_lastMouseTimestamp, mouseTimestamp);
+    mouseTimestamp = widget.m_lastMouseTimestamp;
+    QTest::touchEvent(window, m_touchScreen).release(1, p, window);
+    QCOMPARE(widget.m_mouseEventCount, ++expectedMouseEventCount);
+    QCOMPARE(widget.m_lastMouseEventPos.toPoint(), p);
+    QCOMPARE_GT(widget.m_lastMouseTimestamp, mouseTimestamp);
+    mouseTimestamp = widget.m_lastMouseTimestamp;
+
+    // tap again nearby: a double-click event should be synthesized
+    p += {0, 1};
+    QTest::touchEvent(window, m_touchScreen).press(2, p, window);
+    QCOMPARE(widget.m_touchBeginCount, 0);
+    QCOMPARE(widget.m_mouseEventCount, ++expectedMouseEventCount);
+    QCOMPARE(widget.m_lastMouseEventPos.toPoint(), p);
+    QCOMPARE_GT(widget.m_doubleClickTimestamp, mouseTimestamp);
+    mouseTimestamp = widget.m_doubleClickTimestamp;
+
+    QTest::touchEvent(window, m_touchScreen).release(2, p, window);
+    QCOMPARE(widget.m_mouseEventCount, ++expectedMouseEventCount);
+    QCOMPARE(widget.m_lastMouseEventPos.toPoint(), p);
+    QCOMPARE_GT(widget.m_lastMouseTimestamp, mouseTimestamp);
+    mouseTimestamp = widget.m_lastMouseTimestamp;
+}
+
 void tst_QWidget::styleSheetPropagation()
 {
     QTableView tw;