OS X: Fix pan gestures.

The QPanGesture recognizer requires single-point touch events. The touch
implementation in Qt 4 would test Qt::WA_TouchPadAcceptSingleTouchEvents
and forward single touch events if set.

Making this work in Qt 5 is a little bit more involved since the platform
plugins don't know about widgets.

Change the Cocoa touch implementation to send single-point touch events
to QWidgetWindow windows only. Make QApplication forward single-point
touch events only if the target widget has the
Qt::WA_TouchPadAcceptSingleTouchEvents attribute set.

Task-number: QTBUG-35893
Change-Id: I68712a5e3efb4ece7a81ca42f49c412e525eeb3a
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>

src/plugins/platforms/cocoa/qnsview.mm

@@ -1124,10 +1124,17 @@ static QTabletEvent::TabletDevice wacomTabletDevice(NSEvent *theEvent)
     }
 }
 
+- (bool) shouldSendSingleTouch
+{
+    // QtWidgets expects single-point touch events, QtDeclarative does not.
+    // Until there is an API we solve this by looking at the window class type.
+    return m_window->inherits("QWidgetWindow");
+}
+
 - (void)touchesBeganWithEvent:(NSEvent *)event
 {
     const NSTimeInterval timestamp = [event timestamp];
-    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, /*acceptSingleTouch= ### true or false?*/false);
+    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, [self shouldSendSingleTouch]);
     qCDebug(lcQpaTouch) << "touchesBeganWithEvent" << points;
     QWindowSystemInterface::handleTouchEvent(m_window, timestamp * 1000, touchDevice, points);
 }
@@ -1135,7 +1142,7 @@ static QTabletEvent::TabletDevice wacomTabletDevice(NSEvent *theEvent)
 - (void)touchesMovedWithEvent:(NSEvent *)event
 {
     const NSTimeInterval timestamp = [event timestamp];
-    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, /*acceptSingleTouch= ### true or false?*/false);
+    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, [self shouldSendSingleTouch]);
     qCDebug(lcQpaTouch) << "touchesMovedWithEvent" << points;
     QWindowSystemInterface::handleTouchEvent(m_window, timestamp * 1000, touchDevice, points);
 }
@@ -1143,7 +1150,7 @@ static QTabletEvent::TabletDevice wacomTabletDevice(NSEvent *theEvent)
 - (void)touchesEndedWithEvent:(NSEvent *)event
 {
     const NSTimeInterval timestamp = [event timestamp];
-    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, /*acceptSingleTouch= ### true or false?*/false);
+    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, [self shouldSendSingleTouch]);
     qCDebug(lcQpaTouch) << "touchesEndedWithEvent" << points;
     QWindowSystemInterface::handleTouchEvent(m_window, timestamp * 1000, touchDevice, points);
 }
@@ -1151,7 +1158,7 @@ static QTabletEvent::TabletDevice wacomTabletDevice(NSEvent *theEvent)
 - (void)touchesCancelledWithEvent:(NSEvent *)event
 {
     const NSTimeInterval timestamp = [event timestamp];
-    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, /*acceptSingleTouch= ### true or false?*/false);
+    const QList<QWindowSystemInterface::TouchPoint> points = QCocoaTouch::getCurrentTouchPointList(event, [self shouldSendSingleTouch]);
     qCDebug(lcQpaTouch) << "touchesCancelledWithEvent" << points;
     QWindowSystemInterface::handleTouchEvent(m_window, timestamp * 1000, touchDevice, points);
 }

src/widgets/kernel/qapplication.cpp

@@ -4343,7 +4343,16 @@ bool QApplicationPrivate::translateRawTouchEvent(QWidget *window,
         }
         Q_ASSERT(target.data() != 0);
 
-        StatesAndTouchPoints &maskAndPoints = widgetsNeedingEvents[static_cast<QWidget *>(target.data())];
+        QWidget *targetWidget = static_cast<QWidget *>(target.data());
+
+#ifdef Q_OS_OSX
+        // Single-touch events are normally not sent unless WA_TouchPadAcceptSingleTouchEvents is set.
+        // In Qt 4 this check was in OS X-only coode. That behavior is preserved here by the #ifdef.
+        if (touchPoints.count() == 1 && !targetWidget->testAttribute(Qt::WA_TouchPadAcceptSingleTouchEvents))
+            continue;
+#endif
+
+        StatesAndTouchPoints &maskAndPoints = widgetsNeedingEvents[targetWidget];
         maskAndPoints.first |= touchPoint.state();
         maskAndPoints.second.append(touchPoint);
     }

tests/auto/widgets/kernel/qapplication/tst_qapplication.cpp

@@ -1976,7 +1976,9 @@ public:
 
     TouchEventPropagationTestWidget(QWidget *parent = 0)
         : QWidget(parent), seenTouchEvent(false), acceptTouchEvent(false), seenMouseEvent(false), acceptMouseEvent(false)
-    { }
+    {
+        setAttribute(Qt::WA_TouchPadAcceptSingleTouchEvents);
+    }
 
     void reset()
     {