Windows QPA: Fix multi-touch support in some devices

Some multi-touch devices send touch information for each finger using
different WM_POINTER messages/frames, instead of a single one with
a list of touches, like most devices. This would result in the generation
of multiple touch events, which can cause unexpected behavior in
applications (the QTouchEvent documentation specifies that it should
contain all simultaneous touches). This patch adds a workaround to
ensure all simultaneous touches are included in the events, to comply
with the expected behavior.

Pick-to: 6.2 5.15
Change-Id: I12a2f84b35a6bdd49ee53d25de580c0941a9aea6
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

2 files changed, 37 insertions, 9 deletions

diff --git a/src/plugins/platforms/windows/qwindowspointerhandler.cpp b/src/plugins/platforms/windows/qwindowspointerhandler.cpp
index efe02139f1..7f8d0e54de 100644
--- a/src/plugins/platforms/windows/qwindowspointerhandler.cpp
+++ b/src/plugins/platforms/windows/qwindowspointerhandler.cpp
@@ -460,6 +460,8 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
 {
     Q_UNUSED(hwnd);
 
+    auto *touchInfo = static_cast<POINTER_TOUCH_INFO *>(vTouchInfo);
+
     if (et & QtWindows::NonClientEventFlag)
         return false; // Let DefWindowProc() handle Non Client messages.
 
@@ -469,10 +471,19 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
     if (msg.message == WM_POINTERCAPTURECHANGED) {
         QWindowSystemInterface::handleTouchCancelEvent(window, m_touchDevice.data(),
                                                        QWindowsKeyMapper::queryKeyboardModifiers());
-        m_lastTouchPositions.clear();
+        m_lastTouchPoints.clear();
         return true;
     }
 
+    if (msg.message == WM_POINTERLEAVE) {
+        for (quint32 i = 0; i < count; ++i) {
+            const quint32 pointerId = touchInfo[i].pointerInfo.pointerId;
+            int id = m_touchInputIDToTouchPointID.value(pointerId, -1);
+            if (id != -1)
+                m_lastTouchPoints.remove(id);
+        }
+    }
+
     // Only handle down/up/update, ignore others like WM_POINTERENTER, WM_POINTERLEAVE, etc.
     if (msg.message > WM_POINTERUP)
         return false;
@@ -483,8 +494,6 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
     if (!screen)
         return false;
 
-    auto *touchInfo = static_cast<POINTER_TOUCH_INFO *>(vTouchInfo);
-
     const QRect screenGeometry = screen->geometry();
 
     QList<QWindowSystemInterface::TouchPoint> touchPoints;
@@ -496,6 +505,7 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
                 << " count=" << Qt::dec << count;
 
     QEventPoint::States allStates;
+    QSet<int> inputIds;
 
     for (quint32 i = 0; i < count; ++i) {
         if (QWindowsContext::verbose > 1)
@@ -508,14 +518,17 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
         const quint32 pointerId = touchInfo[i].pointerInfo.pointerId;
         int id = m_touchInputIDToTouchPointID.value(pointerId, -1);
         if (id == -1) {
+            // Start tracking after fingers touch the screen. Ignore bogus updates after touch is released.
+            if ((touchInfo[i].pointerInfo.pointerFlags & POINTER_FLAG_DOWN) == 0)
+                continue;
             id = m_touchInputIDToTouchPointID.size();
             m_touchInputIDToTouchPointID.insert(pointerId, id);
         }
         touchPoint.id = id;
         touchPoint.pressure = (touchInfo[i].touchMask & TOUCH_MASK_PRESSURE) ?
                     touchInfo[i].pressure / 1024.0 : 1.0;
-        if (m_lastTouchPositions.contains(touchPoint.id))
-            touchPoint.normalPosition = m_lastTouchPositions.value(touchPoint.id);
+        if (m_lastTouchPoints.contains(touchPoint.id))
+            touchPoint.normalPosition = m_lastTouchPoints.value(touchPoint.id).normalPosition;
 
         const QPointF screenPos = QPointF(touchInfo[i].pointerInfo.ptPixelLocation.x,
                                           touchInfo[i].pointerInfo.ptPixelLocation.y);
@@ -531,22 +544,36 @@ bool QWindowsPointerHandler::translateTouchEvent(QWindow *window, HWND hwnd,
 
         if (touchInfo[i].pointerInfo.pointerFlags & POINTER_FLAG_DOWN) {
             touchPoint.state = QEventPoint::State::Pressed;
-            m_lastTouchPositions.insert(touchPoint.id, touchPoint.normalPosition);
+            m_lastTouchPoints.insert(touchPoint.id, touchPoint);
         } else if (touchInfo[i].pointerInfo.pointerFlags & POINTER_FLAG_UP) {
             touchPoint.state = QEventPoint::State::Released;
-            m_lastTouchPositions.remove(touchPoint.id);
+            m_lastTouchPoints.remove(touchPoint.id);
         } else {
             touchPoint.state = stationaryTouchPoint ? QEventPoint::State::Stationary : QEventPoint::State::Updated;
-            m_lastTouchPositions.insert(touchPoint.id, touchPoint.normalPosition);
+            m_lastTouchPoints.insert(touchPoint.id, touchPoint);
         }
         allStates |= touchPoint.state;
 
         touchPoints.append(touchPoint);
+        inputIds.insert(touchPoint.id);
 
         // Avoid getting repeated messages for this frame if there are multiple pointerIds
         QWindowsContext::user32dll.skipPointerFrameMessages(touchInfo[i].pointerInfo.pointerId);
     }
 
+    // Some devices send touches for each finger in a different message/frame, instead of consolidating
+    // them in the same frame as we were expecting. We account for missing unreleased touches here.
+    for (auto tp : qAsConst(m_lastTouchPoints)) {
+        if (!inputIds.contains(tp.id)) {
+            tp.state = QEventPoint::State::Stationary;
+            allStates |= tp.state;
+            touchPoints.append(tp);
+        }
+    }
+
+    if (touchPoints.count() == 0)
+        return false;
+
     // all touch points released, forget the ids we've seen.
     if (allStates == QEventPoint::State::Released)
         m_touchInputIDToTouchPointID.clear();
diff --git a/src/plugins/platforms/windows/qwindowspointerhandler.h b/src/plugins/platforms/windows/qwindowspointerhandler.h
index 5b6179b7fa..376902c530 100644
--- a/src/plugins/platforms/windows/qwindowspointerhandler.h
+++ b/src/plugins/platforms/windows/qwindowspointerhandler.h
@@ -48,6 +48,7 @@
 #include <QtCore/qsharedpointer.h>
 #include <QtCore/qhash.h>
 #include <QtGui/qevent.h>
+#include <qpa/qwindowsysteminterface.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -88,7 +89,7 @@ private:
     QList<QPointingDevicePtr> m_tabletDevices;
     QPointingDevicePtr m_activeTabletDevice;
 #endif
-    QHash<int, QPointF> m_lastTouchPositions;
+    QHash<int, QWindowSystemInterface::TouchPoint> m_lastTouchPoints;
     QHash<DWORD, int> m_touchInputIDToTouchPointID;
     QPointer<QWindow> m_windowUnderPointer;
     QPointer<QWindow> m_currentWindow;