MultiPointHandler::wantsPointerEvent: reset if different cand count

We always intended to "start over" with event delivery when the number
of touchpoints changes. Change 48011c2dfeb83b4fe717034d4b3c353714fead48
began this process, but in addition to QQuickWindow delivering the
event to all items and their handlers in reverse paint order, ignoring
existing grabs, the handlers themselves have responsibility to act
as if it was an initial press whenever the number of relevant
touchpoints changes; and because QQuickWindow starts over, handlers do
not need to rely on passive grabs to retain interest in one point at
the time when a transition to a different number of points occurs.

For example, DragHandler by default handles just one point, so if you
press one point such that it takes a passive grab and adds that point
to m_currentPoints, then you press a second finger within the bounds
of the same parentItem, the DragHandler should not go on "wanting" the
first point anymore, because a two-finger gesture is different, and
not suitable for the DragHandler unless its maximumPointCount >= 2.
Even if the second point is released, QQuickWindow will "start over"
with delivery, so a multi-point handler does not need to rely on
retaining a passive grab to handle the transition from two points back
to one again.

This also helps enable smoother transitions between different
gestures: e.g. in the map.qml manual test, you can drag one finger and
transition from dragging to pinching and back while the second finger
is pressed, dragged and released.

Change-Id: Id9b8f30029ed1ff9fd2d64a5e413a47055622083
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 18 insertions, 14 deletions

diff --git a/tests/auto/quick/pointerhandlers/multipointtoucharea_interop/tst_multipointtoucharea_interop.cpp b/tests/auto/quick/pointerhandlers/multipointtoucharea_interop/tst_multipointtoucharea_interop.cpp
index 1c95bb57b4..5959db0c5a 100644
--- a/tests/auto/quick/pointerhandlers/multipointtoucharea_interop/tst_multipointtoucharea_interop.cpp
+++ b/tests/auto/quick/pointerhandlers/multipointtoucharea_interop/tst_multipointtoucharea_interop.cpp
@@ -213,26 +213,26 @@ void tst_MptaInterop::touchesThenPinch()
     // Press one more point (pinkie finger)
     QPoint p4 = mpta->mapToScene(QPointF(300, 200)).toPoint();
     touch.move(1, p1).move(2, p2).move(3, p3).press(4, p4).commit();
-    // MPTA grabs the newly pressed point
-    QTRY_COMPARE(pointerEvent->point(0)->exclusiveGrabber(), pinch);
-    QCOMPARE(pointerEvent->point(1)->exclusiveGrabber(), pinch);
-    QCOMPARE(pointerEvent->point(2)->exclusiveGrabber(), pinch);
+    // PinchHandler deactivates, which lets MPTA grab all the points
+    QTRY_COMPARE(pointerEvent->point(0)->exclusiveGrabber(), mpta);
+    QCOMPARE(pointerEvent->point(1)->exclusiveGrabber(), mpta);
+    QCOMPARE(pointerEvent->point(2)->exclusiveGrabber(), mpta);
     QCOMPARE(pointerEvent->point(3)->exclusiveGrabber(), mpta);
-    // Move some more... PinchHandler and MPTA both keep reacting
+    // Move some more... MPTA keeps reacting
     for (int i = 0; i < 8; ++i) {
         p1 += QPoint(4, 4);
         p2 += QPoint(4, 4);
         p3 += QPoint(-4, 4);
         p4 += QPoint(-4, -4);
         touch.move(1, p1).move(2, p2).move(3, p3).move(4, p4).commit();
-        QCOMPARE(pointerEvent->point(0)->exclusiveGrabber(), pinch);
-        QCOMPARE(pointerEvent->point(1)->exclusiveGrabber(), pinch);
-        QCOMPARE(pointerEvent->point(2)->exclusiveGrabber(), pinch);
+        QCOMPARE(pointerEvent->point(0)->exclusiveGrabber(), mpta);
+        QCOMPARE(pointerEvent->point(1)->exclusiveGrabber(), mpta);
+        QCOMPARE(pointerEvent->point(2)->exclusiveGrabber(), mpta);
         QCOMPARE(pointerEvent->point(3)->exclusiveGrabber(), mpta);
         QCOMPARE(tp.at(0)->property("pressed").toBool(), true);
-        QCOMPARE(tp.at(1)->property("pressed").toBool(), false);
-        QCOMPARE(tp.at(2)->property("pressed").toBool(), false);
-        QCOMPARE(tp.at(3)->property("pressed").toBool(), false);
+        QCOMPARE(tp.at(1)->property("pressed").toBool(), true);
+        QCOMPARE(tp.at(2)->property("pressed").toBool(), true);
+        QCOMPARE(tp.at(3)->property("pressed").toBool(), true);
     }
 
     // Release the pinkie: PinchHandler acquires passive grabs on the 3 remaining points
@@ -263,13 +263,17 @@ void tst_MptaInterop::touchesThenPinch()
 
     // Release another finger
     touch.stationary(2).release(3, p3).commit();
-    // Move some more: DragHandler reacts.
-    // It had a passive grab this whole time; now it activates and gets an exclusive grab.
+    // Move some more: DragHandler eventually reacts.
+    int dragTookGrab = 0;
     for (int i = 0; i < 8; ++i) {
         p2 += QPoint(8, -8);
         touch.move(2, p2).commit();
-        QTRY_COMPARE(pointerEvent->point(0)->exclusiveGrabber(), drag);
+        if (!dragTookGrab && pointerEvent->point(0)->exclusiveGrabber() == drag)
+            dragTookGrab = i;
     }
+    qCDebug(lcPointerTests) << "drag started after" << dragTookGrab << "moves; ended with translation" << drag->translation();
+    QCOMPARE(pointerEvent->point(0)->exclusiveGrabber(), drag);
+    QTRY_VERIFY(drag->translation().x() > 0);
 
     touch.release(2, p2).commit();
     QQuickTouchUtils::flush(window);