send touch update when more points begin after single touch is ignored

Otherwise, a widget can't detect pinches if the points don't start
simultaneously unless it sets WA_TouchPadAcceptSingleTouchEvents.
The use case is for a widget that doesn't actually want the single
touch events, but only when there are two or more touchpoints.

Task-number: QTBUG-42389
Change-Id: I5269d9acb93a0001c4fde02b1f7b9e0dfcc0032f
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

2 files changed, 11 insertions, 3 deletions

diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 8f6c5d748c..269fe452c1 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -4230,8 +4230,9 @@ bool QApplicationPrivate::shouldSetFocus(QWidget *w, Qt::FocusPolicy policy)
     return true;
 }
 
-void QApplicationPrivate::updateTouchPointsForWidget(QWidget *widget, QTouchEvent *touchEvent)
+bool QApplicationPrivate::updateTouchPointsForWidget(QWidget *widget, QTouchEvent *touchEvent)
 {
+    bool containsPress = false;
     for (int i = 0; i < touchEvent->touchPoints().count(); ++i) {
         QTouchEvent::TouchPoint &touchPoint = touchEvent->_touchPoints[i];
 
@@ -4244,7 +4245,11 @@ void QApplicationPrivate::updateTouchPointsForWidget(QWidget *widget, QTouchEven
         touchPoint.d->rect = rect;
         touchPoint.d->startPos = widget->mapFromGlobal(touchPoint.startScreenPos().toPoint()) + delta;
         touchPoint.d->lastPos = widget->mapFromGlobal(touchPoint.lastScreenPos().toPoint()) + delta;
+
+        if (touchPoint.state() == Qt::TouchPointPressed)
+            containsPress = true;
     }
+    return containsPress;
 }
 
 void QApplicationPrivate::initializeMultitouch()
@@ -4391,11 +4396,14 @@ bool QApplicationPrivate::translateRawTouchEvent(QWidget *window,
                                QApplication::keyboardModifiers(),
                                it.value().first,
                                it.value().second);
-        updateTouchPointsForWidget(widget, &touchEvent);
+        bool containsPress = updateTouchPointsForWidget(widget, &touchEvent);
         touchEvent.setTimestamp(timestamp);
         touchEvent.setWindow(window->windowHandle());
         touchEvent.setTarget(widget);
 
+        if (containsPress)
+            widget->setAttribute(Qt::WA_WState_AcceptedTouchBeginEvent);
+
         switch (touchEvent.type()) {
         case QEvent::TouchBegin:
         {
diff --git a/src/widgets/kernel/qapplication_p.h b/src/widgets/kernel/qapplication_p.h
index 156bf34194..7d97235c66 100644
--- a/src/widgets/kernel/qapplication_p.h
+++ b/src/widgets/kernel/qapplication_p.h
@@ -275,7 +275,7 @@ public:
     QPixmap *ignore_cursor;
 #endif
 
-    static void updateTouchPointsForWidget(QWidget *widget, QTouchEvent *touchEvent);
+    static bool updateTouchPointsForWidget(QWidget *widget, QTouchEvent *touchEvent);
     void initializeMultitouch();
     void initializeMultitouch_sys();
     void cleanupMultitouch();