PinchHandler: scale incrementally when new pinch gesture begins

When the gesture begins, we begin multiplying the target item's scale
by 1.0 at first; it doesn't make sense to start immediately with
the accumulated scale remembered from previous pinch gestures, because
the target item remembers its own scale.

When QQuickPinchHandler::wantsPointerEvent() returns false because
some irrelevant gesture was received (for example a PanNativeGesture),
that's not a good reason to deactivate.  Deactivating and re-activating
with each ZoomNativeGesture event results in extreme behavior, because
PinchHandler depends on the BeginNativeGesture and EndNativeGesture
events to reset internal state.  Likewise, the fact that the button
state is NoButton is not a good reason for wantsPointerEvent() to
return false.

Added an autotest: the first of its kind that actually simulates the
native gesture events.

Fixes: QTBUG-92064
Change-Id: I3a9b92d70f99497ee58ad8557d90d521fbe16d41
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit fc636af3a723ee8b4ee42cf71864ae0df5ca4621)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 7 insertions, 4 deletions

diff --git a/src/quick/handlers/qquickpinchhandler.cpp b/src/quick/handlers/qquickpinchhandler.cpp
index b1dca9a905..fffcc2f848 100644
--- a/src/quick/handlers/qquickpinchhandler.cpp
+++ b/src/quick/handlers/qquickpinchhandler.cpp
@@ -91,6 +91,8 @@ Q_LOGGING_CATEGORY(lcPinchHandler, "qt.quick.handler.pinch")
 QQuickPinchHandler::QQuickPinchHandler(QQuickItem *parent)
     : QQuickMultiPointHandler(parent, 2)
 {
+    // Tell QQuickPointerDeviceHandler::wantsPointerEvent() to ignore button state
+    d_func()->acceptedButtons = Qt::NoButton;
 }
 
 /*!
@@ -235,7 +237,7 @@ void QQuickPinchHandler::onActiveChanged()
             m_startRotation = t->rotation();
             m_startPos = t->position();
         } else {
-            m_startScale = m_accumulatedScale;
+            m_startScale = 1;
             m_startRotation = 0;
         }
         qCDebug(lcPinchHandler) << "activated with starting scale" << m_startScale << "rotation" << m_startRotation;
@@ -448,7 +450,7 @@ void QQuickPinchHandler::handlePointerEventImpl(QPointerEvent *event)
 
     qCDebug(lcPinchHandler) << "centroid" << centroid().scenePressPosition() << "->"  << centroid().scenePosition()
                             << ", distance" << m_startDistance << "->" << dist
-                            << ", startScale" << m_startScale << "->" << m_accumulatedScale
+                            << ", scale" << m_startScale << "->" << m_accumulatedScale
                             << ", activeRotation" << m_activeRotation
                             << ", rotation" << rotation
                             << " from " << event->device()->type();
diff --git a/src/quick/handlers/qquickpointerdevicehandler.cpp b/src/quick/handlers/qquickpointerdevicehandler.cpp
index a838f46d83..27f9c3fc36 100644
--- a/src/quick/handlers/qquickpointerdevicehandler.cpp
+++ b/src/quick/handlers/qquickpointerdevicehandler.cpp
@@ -305,7 +305,7 @@ bool QQuickPointerDeviceHandler::wantsPointerEvent(QPointerEvent *event)
         return false;
     if (d->acceptedModifiers != Qt::KeyboardModifierMask && event->modifiers() != d->acceptedModifiers)
         return false;
-    // HoverHandler sets acceptedButtons to Qt::NoButton to indicate that button state is irrelevant.
+    // Some handlers (HoverHandler, PinchHandler) set acceptedButtons to Qt::NoButton to indicate that button state is irrelevant.
     if (event->pointingDevice()->pointerType() != QPointingDevice::PointerType::Finger &&
             acceptedButtons() != Qt::NoButton && event->type() != QEvent::Wheel &&
             (static_cast<QSinglePointEvent *>(event)->buttons() & acceptedButtons()) == 0 &&
diff --git a/src/quick/handlers/qquickpointerhandler.cpp b/src/quick/handlers/qquickpointerhandler.cpp
index cae700b1c8..bcebf2c2ec 100644
--- a/src/quick/handlers/qquickpointerhandler.cpp
+++ b/src/quick/handlers/qquickpointerhandler.cpp
@@ -622,7 +622,8 @@ void QQuickPointerHandler::handlePointerEvent(QPointerEvent *event)
     if (wants) {
         handlePointerEventImpl(event);
     } else {
-        setActive(false);
+        if (event->type() != QEvent::NativeGesture)
+            setActive(false);
         for (int i = 0; i < event->pointCount(); ++i) {
             auto &pt = event->point(i);
             if (event->exclusiveGrabber(pt) == this && pt.state() != QEventPoint::Stationary) {