QQuickWindow: Higher z-order items now steal drop target

Previously, an active drop target would remain the drop target until the
drag left it's area, or entered a child item that accepted a
DragEnterEvent, even if the drag entered a drop target with a globally
higher z-order from a different subtree.

When moving to an item with a higher z-order, the DragEnterEvent is
now sent to the new drop target before DragLeaveEvent is sent to the old
drop target.  There can now only be one drop target.  If an item is the
current drop target and a higher z-order child accepts the DragEnterEvent,
the parent is no longer a drop target.

Fixes: QTBUG-30305
Change-Id: I7b985d6317be70867e7727222a4cd44ace7559e6
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

2 files changed, 186 insertions, 0 deletions

diff --git a/tests/auto/quick/qquickdroparea/data/nested1.qml b/tests/auto/quick/qquickdroparea/data/nested1.qml
new file mode 100644
index 0000000000..de6ac70d08
--- /dev/null
+++ b/tests/auto/quick/qquickdroparea/data/nested1.qml
@@ -0,0 +1,93 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+import QtQuick 2.0
+
+Item {
+    width: 200; height: 200
+    property int outerEnterEvents: 0
+    property int outerExitEvents: 0
+    property int innerEnterEvents: 0
+    property int innerExitEvents: 0
+
+    DropArea {
+        objectName: "outerDropArea"
+        x: 75; y: 75
+        width: 100; height: 100
+        Rectangle {
+            anchors.fill: parent
+            color: "green"
+        }
+        onEntered: ++outerEnterEvents
+        onExited: ++outerExitEvents
+
+        DropArea {
+            objectName: "innerDropArea"
+            width: 50; height: 50
+            Rectangle {
+                anchors.fill: parent
+                color: "blue"
+            }
+            onEntered: ++innerEnterEvents
+            onExited: ++innerExitEvents
+        }
+    }
+
+    Rectangle {
+        width: 20; height: 20
+        color: dragArea.pressed ? "red" : "brown"
+        Drag.active: dragArea.drag.active
+        MouseArea {
+            id: dragArea
+            objectName: "dragArea"
+            anchors.fill: parent
+            drag.target: parent
+        }
+    }
+}
diff --git a/tests/auto/quick/qquickdroparea/data/nested2.qml b/tests/auto/quick/qquickdroparea/data/nested2.qml
new file mode 100644
index 0000000000..93630c3779
--- /dev/null
+++ b/tests/auto/quick/qquickdroparea/data/nested2.qml
@@ -0,0 +1,93 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+import QtQuick 2.0
+
+Item {
+    width: 200; height: 200
+    property int outerEnterEvents: 0
+    property int outerExitEvents: 0
+    property int innerEnterEvents: 0
+    property int innerExitEvents: 0
+
+    Rectangle {
+        x: 75; y: 75
+        width: 100; height: 100
+        color: "green"
+        DropArea {
+            objectName: "outerDropArea"
+            anchors.fill: parent
+            onEntered: ++outerEnterEvents
+            onExited: ++outerExitEvents
+        }
+
+        Rectangle {
+            width: 50; height: 50
+            color: "blue"
+            DropArea {
+                objectName: "innerDropArea"
+                anchors.fill: parent
+                onEntered: ++innerEnterEvents
+                onExited: ++innerExitEvents
+            }
+        }
+    }
+
+    Rectangle {
+        width: 20; height: 20
+        color: dragArea.pressed ? "red" : "brown"
+        Drag.active: dragArea.drag.active
+        MouseArea {
+            id: dragArea
+            objectName: "dragArea"
+            anchors.fill: parent
+            drag.target: parent
+        }
+    }
+}