MouseArea shouldn't grab the mouse until there is an effective drag.

A MouseArea shouldn't prevent a parent MouseArea or Flickable from
handling a drag event unless it is going to do something useful with
it.

(cherry picked from commit 67db779665b1d95a20720c0dee058c47f7df8726)

Task-number: QTBUG-29717
Change-Id: I17caa51ebc2e547e73e727fd185e60644591ad2b
Reviewed-by: Alan Alpert <aalpert@rim.com>

3 files changed, 136 insertions, 22 deletions

diff --git a/src/declarative/graphicsitems/qdeclarativemousearea.cpp b/src/declarative/graphicsitems/qdeclarativemousearea.cpp
index 242bf79..e17c42c 100644
--- a/src/declarative/graphicsitems/qdeclarativemousearea.cpp
+++ b/src/declarative/graphicsitems/qdeclarativemousearea.cpp
@@ -529,37 +529,32 @@ void QDeclarativeMouseArea::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
             curLocalPos = event->scenePos();
         }
 
-        const int dragThreshold = QApplication::startDragDistance();
-        qreal dx = qAbs(curLocalPos.x() - startLocalPos.x());
-        qreal dy = qAbs(curLocalPos.y() - startLocalPos.y());
-
         if (keepMouseGrab() && d->stealMouse)
             d->drag->setActive(true);
 
         bool dragX = drag()->axis() & QDeclarativeDrag::XAxis;
         bool dragY = drag()->axis() & QDeclarativeDrag::YAxis;
 
-        if (dragX && d->drag->active()) {
-            qreal x = (curLocalPos.x() - startLocalPos.x()) + d->startX;
-            if (x < drag()->xmin())
-                x = drag()->xmin();
-            else if (x > drag()->xmax())
-                x = drag()->xmax();
-            drag()->target()->setX(x);
-        }
-        if (dragY && d->drag->active()) {
-            qreal y = (curLocalPos.y() - startLocalPos.y()) + d->startY;
-            if (y < drag()->ymin())
-                y = drag()->ymin();
-            else if (y > drag()->ymax())
-                y = drag()->ymax();
-            drag()->target()->setY(y);
+        const qreal x = dragX
+                ? qBound(d->drag->xmin(), d->startX + curLocalPos.x() - startLocalPos.x(), d->drag->xmax())
+                : d->startX;
+        const qreal y = dragY
+                ? qBound(d->drag->ymin(), d->startY + curLocalPos.y() - startLocalPos.y(), d->drag->ymax())
+                : d->startY;
+
+        if (d->drag->active()) {
+            if (dragX && dragY)
+                d->drag->target()->setPos(x, y);
+            else if (dragX)
+                d->drag->target()->setX(x);
+            else if (dragY)
+                d->drag->target()->setY(y);
         }
 
         if (!keepMouseGrab()) {
-            if ((!dragY && dy < dragThreshold && dragX && dx > dragThreshold)
-                || (!dragX && dx < dragThreshold && dragY && dy > dragThreshold)
-                || (dragX && dragY && (dx > dragThreshold || dy > dragThreshold))) {
+            const int dragThreshold = QApplication::startDragDistance();
+
+            if (qAbs(x - d->startX) > dragThreshold || qAbs(y - d->startY) > dragThreshold) {
                 setKeepMouseGrab(true);
                 d->stealMouse = true;
             }
diff --git a/tests/auto/declarative/qdeclarativemousearea/data/nestedStopAtBounds.qml b/tests/auto/declarative/qdeclarativemousearea/data/nestedStopAtBounds.qml
new file mode 100644
index 0000000..0379964
--- /dev/null
+++ b/tests/auto/declarative/qdeclarativemousearea/data/nestedStopAtBounds.qml
@@ -0,0 +1,44 @@
+import QtQuick 1.1
+
+Rectangle {
+    width: 400
+    height: 400
+
+    MouseArea {
+        id: outer
+        objectName: "outer"
+        x: 50
+        y: 50
+        width: 300
+        height: 300
+
+        drag.target: outer
+        drag.filterChildren: true
+
+        Rectangle {
+            anchors.fill: parent
+            color: "yellow"
+        }
+
+        MouseArea {
+            id: inner
+            objectName: "inner"
+
+            x: 0
+            y: 0
+            width: 200
+            height: 200
+
+            drag.target: inner
+            drag.minimumX: 0
+            drag.maximumX: 100
+            drag.minimumY: 0
+            drag.maximumY: 100
+
+            Rectangle {
+                anchors.fill: parent
+                color: "blue"
+            }
+        }
+    }
+}
diff --git a/tests/auto/declarative/qdeclarativemousearea/tst_qdeclarativemousearea.cpp b/tests/auto/declarative/qdeclarativemousearea/tst_qdeclarativemousearea.cpp
index fc5353c..41dcc81 100644
--- a/tests/auto/declarative/qdeclarativemousearea/tst_qdeclarativemousearea.cpp
+++ b/tests/auto/declarative/qdeclarativemousearea/tst_qdeclarativemousearea.cpp
@@ -75,6 +75,8 @@ private slots:
     void preventContextMenu();
 #endif // QT_NO_CONTEXTMENU
     void changeAxis();
+    void nestedStopAtBounds();
+    void nestedStopAtBounds_data();
 
 private:
     QDeclarativeView *createView();
@@ -782,6 +784,79 @@ void tst_QDeclarativeMouseArea::changeAxis()
     delete canvas;
 }
 
+void tst_QDeclarativeMouseArea::nestedStopAtBounds_data()
+{
+    QTest::addColumn<bool>("transpose");
+    QTest::addColumn<bool>("invert");
+
+    QTest::newRow("left") << false << false;
+    QTest::newRow("right") << false << true;
+    QTest::newRow("top") << true << false;
+    QTest::newRow("bottom") << true << true;
+}
+
+void tst_QDeclarativeMouseArea::nestedStopAtBounds()
+{
+    QFETCH(bool, transpose);
+    QFETCH(bool, invert);
+
+    QDeclarativeView view;
+    view.setSource(QUrl::fromLocalFile(SRCDIR "/data/nestedStopAtBounds.qml"));
+    view.show();
+    QTest::qWaitForWindowShown(&view);
+    QVERIFY(view.rootObject());
+
+    QDeclarativeMouseArea *outer =  view.rootObject()->findChild<QDeclarativeMouseArea*>("outer");
+    QVERIFY(outer);
+
+    QDeclarativeMouseArea *inner = outer->findChild<QDeclarativeMouseArea*>("inner");
+    QVERIFY(inner);
+    inner->drag()->setAxis(transpose ? QDeclarativeDrag::YAxis : QDeclarativeDrag::XAxis);
+    inner->setX(invert ? 100 : 0);
+    inner->setY(invert ? 100 : 0);
+
+    const int threshold = QApplication::startDragDistance();
+
+    QPoint position(200, 200);
+    int &axis = transpose ? position.ry() : position.rx();
+
+    QGraphicsSceneMouseEvent moveEvent(QEvent::GraphicsSceneMouseMove);
+    moveEvent.setButton(Qt::LeftButton);
+    moveEvent.setButtons(Qt::LeftButton);
+
+    // drag toward the aligned boundary.  Outer mouse area dragged.
+    QTest::mousePress(view.viewport(), Qt::LeftButton, 0, position);
+    QTest::qWait(10);
+    axis += invert ? threshold * 2 : -threshold * 2;
+    moveEvent.setScenePos(position);
+    QApplication::sendEvent(view.scene(), &moveEvent);
+    axis += invert ? threshold : -threshold;
+    moveEvent.setScenePos(position);
+    QApplication::sendEvent(view.scene(), &moveEvent);
+    QCOMPARE(outer->drag()->active(), true);
+    QCOMPARE(inner->drag()->active(), false);
+    QTest::mouseRelease(view.viewport(), Qt::LeftButton, 0, position);
+
+    QVERIFY(!outer->drag()->active());
+
+    axis = 200;
+    outer->setX(50);
+    outer->setY(50);
+
+    // drag away from the aligned boundary.  Inner mouse area dragged.
+    QTest::mousePress(view.viewport(), Qt::LeftButton, 0, position);
+    QTest::qWait(10);
+    axis += invert ? -threshold * 2 : threshold * 2;
+    moveEvent.setScenePos(position);
+    QApplication::sendEvent(view.scene(), &moveEvent);
+    axis += invert ? -threshold : threshold;
+    moveEvent.setScenePos(position);
+    QApplication::sendEvent(view.scene(), &moveEvent);
+    QCOMPARE(outer->drag()->active(), false);
+    QCOMPARE(inner->drag()->active(), true);
+    QTest::mouseRelease(view.viewport(), Qt::LeftButton, 0, position);
+}
+
 QTEST_MAIN(tst_QDeclarativeMouseArea)
 
 #include "tst_qdeclarativemousearea.moc"