Fix MouseArea mouseX/mouseY coordinates while dragging

When MouseArea is not anchored with the usual anchors.fill: parent,
such that its position is not 0,0, calculating mouseX/mouseY as
d->lastScenePos - mapToScene(position()) was wrong.  It could be
d->lastScenePos - mapToScene(QPointF()), but instead we use
mapFromScene(d->lastScenePos) as in a few other places.

Amends 8068e7b98cde09565efe27585b84e120f9c5ea99.

Pick-to: 5.15
Fixes: QTBUG-85111
Task-number: QTBUG-75993
Change-Id: If1440d05ec3b75d9f9f4802fbc361756fadb559e
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 94 insertions, 3 deletions

diff --git a/tests/auto/quick/qquickmousearea/data/selfDrag.qml b/tests/auto/quick/qquickmousearea/data/selfDrag.qml
new file mode 100644
index 0000000000..98eaafbfcf
--- /dev/null
+++ b/tests/auto/quick/qquickmousearea/data/selfDrag.qml
@@ -0,0 +1,25 @@
+import QtQuick 2.0
+
+Rectangle {
+    width: 400
+    height: 400
+
+    MouseArea {
+        id: ma
+        objectName: "ma"
+        width: 200
+        height: 200
+
+        drag.target: ma
+        drag.minimumX: 0
+        drag.maximumX: 200
+
+        Rectangle {
+            objectName: "fill"
+            anchors.fill: parent
+            color: ma.drag.active ? "tomato" : "wheat"
+            border.color: ma.pressed ? "red" : "transparent"
+            Text { text: ma.mouseX + ", " + ma.mouseY }
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp b/tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp
index 1d22680261..c38ab72a7b 100644
--- a/tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp
+++ b/tests/auto/quick/qquickmousearea/tst_qquickmousearea.cpp
@@ -104,6 +104,7 @@ private slots:
     void resetDrag();
     void dragging_data() { acceptedButton_data(); }
     void dragging();
+    void selfDrag();
     void dragSmoothed();
     void dragThreshold_data();
     void dragThreshold();
@@ -389,10 +390,10 @@ void tst_QQuickMouseArea::dragging()
     for (int i = 0; i < 20; i++) {
         p += QPoint(1, 1);
         QTest::mouseMove(&window, p);
+        QTRY_COMPARE(mouseRegion->mouseX(), relativeX);
+        QCOMPARE(mouseRegion->mouseY(), relativeY);
     }
-    QTRY_VERIFY(drag->active());
-    QTRY_COMPARE(mouseRegion->mouseX(), relativeX);
-    QCOMPARE(mouseRegion->mouseY(), relativeY);
+    QVERIFY(drag->active());
 
     QTest::mouseRelease(&window, button, Qt::NoModifier, p);
     QTRY_VERIFY(!drag->active());
@@ -400,6 +401,71 @@ void tst_QQuickMouseArea::dragging()
     QCOMPARE(blackRect->y(), 81.0);
 }
 
+void tst_QQuickMouseArea::selfDrag() // QTBUG-85111
+{
+    QQuickView window;
+    QByteArray errorMessage;
+    QVERIFY2(QQuickTest::initView(window, testFileUrl("selfDrag.qml"), true, &errorMessage), errorMessage.constData());
+
+    window.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&window));
+    QVERIFY(window.rootObject() != nullptr);
+
+    QQuickMouseArea *ma = window.rootObject()->findChild<QQuickMouseArea*>("ma");
+    QVERIFY(ma != nullptr);
+    QQuickDrag *drag = ma->drag();
+    QVERIFY(drag != nullptr);
+    QCOMPARE(ma, drag->target());
+
+    QQuickItem *fillRect = window.rootObject()->findChild<QQuickItem*>("fill");
+    QVERIFY(fillRect != nullptr);
+
+    QVERIFY(!drag->active());
+
+    QPoint p = QPoint(100,100);
+    QTest::mousePress(&window, Qt::LeftButton, Qt::NoModifier, p);
+
+    QVERIFY(!drag->active());
+    QCOMPARE(ma->x(), 0);
+    QCOMPARE(ma->y(), 0);
+
+    int dragThreshold = QGuiApplication::styleHints()->startDragDistance();
+
+    // First move event triggers drag, second is acted upon.
+    // move the minimum distance to activate drag
+    p += QPoint(dragThreshold + 1, dragThreshold + 1);
+    QTest::mouseMove(&window, p);
+    QVERIFY(!drag->active());
+
+    // from here on move the item
+    p += QPoint(1, 1);
+    QTest::mouseMove(&window, p);
+    QTRY_VERIFY(drag->active());
+    QTRY_COMPARE(ma->x(), 1);
+    QCOMPARE(ma->y(), 1);
+
+    p += QPoint(10, 10);
+    QTest::mouseMove(&window, p);
+    QTRY_VERIFY(drag->active());
+    QTRY_COMPARE(ma->x(), 11);
+    QCOMPARE(ma->y(), 11);
+
+    qreal relativeX = ma->mouseX();
+    qreal relativeY = ma->mouseY();
+    for (int i = 0; i < 20; i++) {
+        p += QPoint(1, 1);
+        QTest::mouseMove(&window, p);
+        QVERIFY(drag->active());
+        QTRY_COMPARE(ma->mouseX(), relativeX);
+        QCOMPARE(ma->mouseY(), relativeY);
+    }
+
+    QTest::mouseRelease(&window, Qt::LeftButton, Qt::NoModifier, p);
+    QTRY_VERIFY(!drag->active());
+    QTRY_COMPARE(ma->x(), 31);
+    QCOMPARE(ma->y(), 31);
+}
+
 void tst_QQuickMouseArea::dragSmoothed()
 {
     QQuickView window;