Start over with event delivery when touchpoint releases occur

The new rule is that when the number of touchpoints changes, we start
over with event delivery as if the touch had just begun, to give more
opportunities to hand off processing from one item or handler to
another.  And MultiPointTouchArea can now handle the handoff:
for example in tests/manual/pointer/pinchDragFlingMPTA.qml when the
user is pressing three fingers, the PinchHandler is active; when the
user then lifts one finger, the MPTA can resume handling the two
remaining touchpoints as if they were just pressed.

The change in QQuickMultiPointerHandler::wantsPointerEvent is both
a behavior change and an optimization: released points aren't eligible;
but if some points are released, then pressed, updated and stationary
points are all eligible. And, figure this out without looping over the
points twice.

Change-Id: I26b7593de8e72b471adfec4a4482dd87a8288442
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/quick/items/qquickevents_p_p.h b/src/quick/items/qquickevents_p_p.h
index 72d5be54c9..4b3587f18c 100644
--- a/src/quick/items/qquickevents_p_p.h
+++ b/src/quick/items/qquickevents_p_p.h
@@ -272,7 +272,8 @@ public:
         Released    = Qt::TouchPointReleased
         // Canceled    = Qt::TouchPointReleased << 1 // 0x10 // TODO maybe
     };
-    Q_ENUM(State)
+    Q_DECLARE_FLAGS(States, State)
+    Q_FLAG(States)
 
     enum GrabState {
         GrabPassive = 0,
@@ -406,6 +407,8 @@ public: // helpers for C++ only (during event delivery)
     virtual void localize(QQuickItem *target) = 0;
 
     virtual bool isPressEvent() const = 0;
+    virtual bool isUpdateEvent() const = 0;
+    virtual bool isReleaseEvent() const = 0;
     virtual QQuickPointerMouseEvent *asPointerMouseEvent() { return nullptr; }
     virtual QQuickPointerTouchEvent *asPointerTouchEvent() { return nullptr; }
     virtual QQuickPointerTabletEvent *asPointerTabletEvent() { return nullptr; }
@@ -448,6 +451,8 @@ public:
     QQuickPointerEvent *reset(QEvent *) override;
     void localize(QQuickItem *target) override;
     bool isPressEvent() const override;
+    bool isUpdateEvent() const override;
+    bool isReleaseEvent() const override;
     QQuickPointerMouseEvent *asPointerMouseEvent() override { return this; }
     const QQuickPointerMouseEvent *asPointerMouseEvent() const override { return this; }
     int pointCount() const override { return 1; }
@@ -481,6 +486,8 @@ public:
     QQuickPointerEvent *reset(QEvent *) override;
     void localize(QQuickItem *target) override;
     bool isPressEvent() const override;
+    bool isUpdateEvent() const override;
+    bool isReleaseEvent() const override;
     QQuickPointerTouchEvent *asPointerTouchEvent() override { return this; }
     const QQuickPointerTouchEvent *asPointerTouchEvent() const override { return this; }
     int pointCount() const override { return m_pointCount; }