Fix performance issue with drag retrigger events for qtquick items

The items that reject drag events (specifically onEntered in DropArea)
should not be retriggered with DragEnter event until entered once again.

Fixes: QTBUG-74496
Pick-to: 6.4 6.3 6.2 5.15
Change-Id: I241a6004da6382685be89fe8a001b98dfde5c8a2
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/quick/items/qquickdrag_p.h

@@ -72,9 +72,12 @@ public:
     void grab(QQuickItem *item) { m_items.insert(new Item(item)); }
     iterator release(iterator at) { Item *item = *at; at = at.erase(); delete item; return at; }
 
+    auto& ignoreList() { return m_ignoreDragItems; }
+
 private:
 
     ItemList m_items;
+    QVarLengthArray<QQuickItem *, 4> m_ignoreDragItems;
     QObject *m_target;
 };
 

src/quick/util/qquickdeliveryagent.cpp

@@ -2231,6 +2231,7 @@ void QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QE
             QDragLeaveEvent leaveEvent;
             for (; grabItem != grabber->end(); grabItem = grabber->release(grabItem))
                 QCoreApplication::sendEvent(**grabItem, &leaveEvent);
+            grabber->ignoreList().clear();
             return;
         } else {
             QDragMoveEvent *moveEvent = static_cast<QDragMoveEvent *>(event);
@@ -2288,6 +2289,8 @@ void QQuickDeliveryAgentPrivate::deliverDragEvent(QQuickDragGrabber *grabber, QE
                 e->modifiers());
         QQuickDropEventEx::copyActions(&enterEvent, *e);
         event->setAccepted(deliverDragEvent(grabber, rootItem, &enterEvent));
+    } else {
+        grabber->ignoreList().clear();
     }
 }
 
@@ -2301,8 +2304,13 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(
     QPointF p = item->mapFromScene(event->position().toPoint());
     bool itemContained = item->contains(p);
 
-    if (!itemContained && itemPrivate->flags & QQuickItem::ItemClipsChildrenToShape) {
-        return false;
+    const int itemIndex = grabber->ignoreList().indexOf(item);
+    if (!itemContained) {
+        if (itemIndex >= 0)
+            grabber->ignoreList().remove(itemIndex);
+
+        if (itemPrivate->flags & QQuickItem::ItemClipsChildrenToShape)
+            return false;
     }
 
     QDragEnterEvent enterEvent(
@@ -2332,15 +2340,19 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(
         }
 
         if (event->type() == QEvent::DragMove || itemPrivate->flags & QQuickItem::ItemAcceptsDrops) {
-            if (event->type() == QEvent::DragEnter && formerTarget) {
-                QQuickItem *formerTargetItem = qobject_cast<QQuickItem *>(formerTarget);
-                if (formerTargetItem && currentGrabItems) {
-                    QDragLeaveEvent leaveEvent;
-                    QCoreApplication::sendEvent(formerTarget, &leaveEvent);
+            if (event->type() == QEvent::DragEnter) {
+                if (formerTarget) {
+                    QQuickItem *formerTargetItem = qobject_cast<QQuickItem *>(formerTarget);
+                    if (formerTargetItem && currentGrabItems) {
+                        QDragLeaveEvent leaveEvent;
+                        QCoreApplication::sendEvent(formerTarget, &leaveEvent);
 
-                    // Remove the item from the currentGrabItems so a leave event won't be generated
-                    // later on
-                    currentGrabItems->removeAll(formerTarget);
+                        // Remove the item from the currentGrabItems so a leave event won't be generated
+                        // later on
+                        currentGrabItems->removeAll(formerTarget);
+                    }
+                } else if (itemIndex >= 0) {
+                    return false;
                 }
             }
 
@@ -2356,6 +2368,8 @@ bool QQuickDeliveryAgentPrivate::deliverDragEvent(
                     grabber->grab(item);
                     grabber->setTarget(item);
                     return true;
+                } else if (itemIndex < 0) {
+                    grabber->ignoreList().append(item);
                 }
             } else {
                 return true;

tests/auto/quick/qquickdroparea/data/ignoreRetriggerEvent.qml

@@ -0,0 +1,15 @@
+import QtQuick 2.0
+
+DropArea {
+    property int enterEvents: 0
+    property int exitEvents: 0
+    width: 100; height: 100
+    objectName: "dropArea"
+    onEntered: function (drag) { ++enterEvents; drag.accepted = false }
+    onExited: {++exitEvents}
+        Item {
+        objectName: "dragItem"
+        x: 50; y: 50
+        width: 10; height: 10
+    }
+}

tests/auto/quick/qquickdroparea/tst_qquickdroparea.cpp

@@ -45,6 +45,9 @@ public:
 private slots:
     void containsDrag_internal();
     void containsDrag_external();
+
+    void ignoreRetriggerEvent();
+
     void keys_internal();
     void keys_external();
     void source_internal();
@@ -807,6 +810,32 @@ void tst_QQuickDropArea::competingDrags()
     QCOMPARE(evaluate<QString>(dropArea1, "statuslol"), QStringLiteral("parent"));
 }
 
+void tst_QQuickDropArea::ignoreRetriggerEvent()
+{
+    QQuickView window;
+    QByteArray errorMessage;
+    QVERIFY2(QQuickTest::initView(window, testFileUrl("ignoreRetriggerEvent.qml"), true, &errorMessage), errorMessage.constData());
+
+    QQuickItem *dropArea = window.rootObject();
+    QVERIFY(dropArea);
+    QQuickItem *dragItem = dropArea->findChild<QQuickItem *>("dragItem");
+    QVERIFY(dragItem);
+
+    evaluate<void>(dragItem, "Drag.active = true");
+    // Drag the item within the drop area
+    dragItem->setPosition(QPointF(25, 25));
+    QCoreApplication::processEvents();
+    dragItem->setPosition(QPointF(50, 50));
+    QCoreApplication::processEvents();
+    dragItem->setPosition(QPointF(75, 75));
+    QCoreApplication::processEvents();
+
+    QCOMPARE(evaluate<bool>(dropArea, "containsDrag"), false);
+    QCOMPARE(evaluate<int>(dropArea, "enterEvents"), 1);
+    QCOMPARE(evaluate<int>(dropArea, "exitEvents"), 0);
+}
+
+
 void tst_QQuickDropArea::simultaneousDrags()
 {
     QQuickWindow window;