End touch->mouse synthesis when the chosen touchpoint is released

During delivery of a TouchBegin event, if no widget accepts it,
we begin treating the first touchpoint as a synth-mouse, as before.
If a second touchpoint is pressed or released in any order, it's
irrelevant: the fake mouse button is released as soon as the first
touchpoint is released.  This fixes the bug that such a scenario
caused the mouse release not to be sent, so that a widget could get
"stuck" in pressed state.

Done-with: Tang Haixiang <tanghaixiang@uniontech.com>
Fixes: QTBUG-86253
Change-Id: I7fbbe120539d8ded8ef5e7cf712a27bd69391e02
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit f51e6552e361c0716f6301b4c5b03b12e8bfe0fe)
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 49 insertions, 23 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 72e1b16e55..a95331e246 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -201,7 +201,7 @@ static bool force_reverse = false;
 
 QGuiApplicationPrivate *QGuiApplicationPrivate::self = nullptr;
 QTouchDevice *QGuiApplicationPrivate::m_fakeTouchDevice = nullptr;
-int QGuiApplicationPrivate::m_fakeMouseSourcePointId = 0;
+int QGuiApplicationPrivate::m_fakeMouseSourcePointId = -1;
 
 #ifndef QT_NO_CLIPBOARD
 QClipboard *QGuiApplicationPrivate::qt_clipboard = nullptr;
@@ -3057,32 +3057,32 @@ void QGuiApplicationPrivate::processTouchEvent(QWindowSystemInterfacePrivate::To
         if (!e->synthetic() && !touchEvent.isAccepted() && qApp->testAttribute(Qt::AA_SynthesizeMouseForUnhandledTouchEvents)) {
             // exclude devices which generate their own mouse events
             if (!(touchEvent.device()->capabilities() & QTouchDevice::MouseEmulation)) {
-
-                if (eventType == QEvent::TouchEnd)
-                    self->synthesizedMousePoints.clear();
-
                 const QList<QTouchEvent::TouchPoint> &touchPoints = touchEvent.touchPoints();
-                if (eventType == QEvent::TouchBegin)
+                QEvent::Type mouseEventType = QEvent::MouseMove;
+                Qt::MouseButton button = Qt::NoButton;
+                Qt::MouseButtons buttons = Qt::LeftButton;
+                if (eventType == QEvent::TouchBegin && m_fakeMouseSourcePointId < 0)
                     m_fakeMouseSourcePointId = touchPoints.first().id();
-
-                const QEvent::Type mouseType = [&]() {
-                    switch (eventType) {
-                    case QEvent::TouchBegin:  return QEvent::MouseButtonPress;
-                    case QEvent::TouchUpdate: return QEvent::MouseMove;
-                    case QEvent::TouchEnd:    return QEvent::MouseButtonRelease;
-                    default: Q_UNREACHABLE();
-                    }
-                }();
-
-                Qt::MouseButton button = mouseType == QEvent::MouseMove ? Qt::NoButton : Qt::LeftButton;
-                Qt::MouseButtons buttons = mouseType == QEvent::MouseButtonRelease ? Qt::NoButton : Qt::LeftButton;
-
-                for (int i = 0; i < touchPoints.count(); ++i) {
-                    const QTouchEvent::TouchPoint &touchPoint = touchPoints.at(i);
+                for (const auto &touchPoint : touchPoints) {
                     if (touchPoint.id() == m_fakeMouseSourcePointId) {
-                        if (eventType != QEvent::TouchEnd)
+                        switch (touchPoint.state()) {
+                        case Qt::TouchPointPressed:
+                            mouseEventType = QEvent::MouseButtonPress;
+                            button = Qt::LeftButton;
+                            break;
+                        case Qt::TouchPointReleased:
+                            mouseEventType = QEvent::MouseButtonRelease;
+                            button = Qt::LeftButton;
+                            buttons = Qt::NoButton;
+                            m_fakeMouseSourcePointId = -1;
+                            break;
+                        default:
+                            break;
+                        }
+                        if (touchPoint.state() != Qt::TouchPointReleased) {
                             self->synthesizedMousePoints.insert(w, SynthesizedMouseData(
                                                                     touchPoint.pos(), touchPoint.screenPos(), w));
+                        }
                         // All touch events that are not accepted by the application will be translated to
                         // left mouse button events instead (see AA_SynthesizeMouseForUnhandledTouchEvents docs).
                         QWindowSystemInterfacePrivate::MouseEvent fake(w, e->timestamp,
@@ -3091,13 +3091,15 @@ void QGuiApplicationPrivate::processTouchEvent(QWindowSystemInterfacePrivate::To
                                                                        buttons,
                                                                        e->modifiers,
                                                                        button,
-                                                                       mouseType,
+                                                                       mouseEventType,
                                                                        Qt::MouseEventSynthesizedByQt);
                         fake.flags |= QWindowSystemInterfacePrivate::WindowSystemEvent::Synthetic;
                         processMouseEvent(&fake);
                         break;
                     }
                 }
+                if (eventType == QEvent::TouchEnd)
+                    self->synthesizedMousePoints.clear();
             }
         }
     }
diff --git a/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp b/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
index 34de756ab5..2292462046 100644
--- a/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
+++ b/tests/auto/gui/kernel/qwindow/tst_qwindow.cpp
@@ -1176,6 +1176,30 @@ void tst_QWindow::touchToMouseTranslation()
     // mouse event synthesizing disabled
     QTRY_COMPARE(window.mousePressButton, 0);
     QTRY_COMPARE(window.mouseReleaseButton, 0);
+
+    points.clear();
+    points.append(tp2);
+    points[0].state = Qt::TouchPointPressed;
+    QWindowSystemInterface::handleTouchEvent(&window, touchDevice, points);
+    QCoreApplication::processEvents();
+    points.clear();
+    points.append(tp1);
+    points[0].state = Qt::TouchPointPressed;
+    QWindowSystemInterface::handleTouchEvent(&window, touchDevice, points);
+    QCoreApplication::processEvents();
+    QTRY_COMPARE(window.mousePressButton, 1);
+
+    points.clear();
+    points.append(tp2);
+    points[0].state = Qt::TouchPointReleased;
+    QWindowSystemInterface::handleTouchEvent(&window, touchDevice, points);
+    QCoreApplication::processEvents();
+    points.clear();
+    points.append(tp1);
+    points[0].state = Qt::TouchPointReleased;
+    QWindowSystemInterface::handleTouchEvent(&window, touchDevice, points);
+    QCoreApplication::processEvents();
+    QTRY_COMPARE(window.mouseReleaseButton, 1);
 }
 
 void tst_QWindow::touchToMouseTranslationForDevices()