Add imageSource property to attached Drag property

This property holds a URL which is loaded into a QPixmap via
QQuickPixmap, and subsequently set on the QDrag object.

This is especially important for drag and drop to external applications,
where of course a QQuickItem cannot be dragged; however, combined with
QQuickItem::grabToImage(), this change allows setting a QQuickItem's
contents as the drag pixmap.

[ChangeLog][QtQuick][Drag] Added imageSource property to attached Drag
object: this allows drag sources to specify the pixmap to be drawn next
to the mouse cursor when starting a drag and drop operation.

Task-number: QTBUG-37366
Change-Id: Ibcf1d888c525e50976a116ec743ce6fca4c31525
Reviewed-by: Michael Brasser <michael.brasser@live.com>

3 files changed, 125 insertions, 3 deletions

diff --git a/src/quick/doc/snippets/qml/externaldrag.qml b/src/quick/doc/snippets/qml/externaldrag.qml
new file mode 100644
index 0000000000..096a7702b4
--- /dev/null
+++ b/src/quick/doc/snippets/qml/externaldrag.qml
@@ -0,0 +1,76 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** 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."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//![0]
+import QtQuick 2.8
+
+Item {
+    width: 200; height: 200
+
+    Rectangle {
+        anchors.centerIn: parent
+        width: text.implicitWidth + 20; height: text.implicitHeight + 10
+        color: "green"
+        radius: 5
+
+        Drag.active: dragArea.drag.active
+        Drag.dragType: Drag.Automatic
+        Drag.supportedActions: Qt.CopyAction
+        Drag.mimeData: {
+            "text/plain": "Copied text"
+        }
+
+        Text {
+            id: text
+            anchors.centerIn: parent
+            text: "Drag me"
+        }
+
+        MouseArea {
+            id: dragArea
+            anchors.fill: parent
+
+            drag.target: parent
+            onPressed: parent.grabToImage(function(result) {
+                parent.Drag.imageSource = result.url
+            })
+        }
+    }
+}
+//![0]
diff --git a/src/quick/items/qquickdrag.cpp b/src/quick/items/qquickdrag.cpp
index 4aa54b71df..76e13bc985 100644
--- a/src/quick/items/qquickdrag.cpp
+++ b/src/quick/items/qquickdrag.cpp
@@ -45,6 +45,7 @@
 #include <private/qquickitem_p.h>
 #include <QtQuick/private/qquickevents_p_p.h>
 #include <private/qquickitemchangelistener_p.h>
+#include <private/qquickpixmapcache_p.h>
 #include <private/qv8engine_p.h>
 #include <private/qv4scopedvalue_p.h>
 #include <QtCore/qmimedata.h>
@@ -110,6 +111,8 @@ public:
     bool eventQueued : 1;
     bool overrideActions : 1;
     QPointF hotSpot;
+    QUrl imageSource;
+    QQuickPixmap pixmapLoader;
     QStringList keys;
     QVariantMap externalMimeData;
     QQuickDrag::DragType dragType;
@@ -408,6 +411,43 @@ void QQuickDragAttached::setHotSpot(const QPointF &hotSpot)
 }
 
 /*!
+    \qmlattachedproperty QUrl QtQuick::Drag::imageSource
+    \since 5.8
+
+    This property holds the URL of the image which will be used to represent
+    the data during the drag and drop operation. Changing this property after
+    the drag operation has started will have no effect.
+
+    The example below uses an item's contents as a drag image:
+
+    \snippet qml/externaldrag.qml 0
+
+    \sa Item::grabToImage()
+*/
+
+QUrl QQuickDragAttached::imageSource() const
+{
+    Q_D(const QQuickDragAttached);
+    return d->imageSource;
+}
+
+void QQuickDragAttached::setImageSource(const QUrl &url)
+{
+    Q_D(QQuickDragAttached);
+    if (d->imageSource != url) {
+        d->imageSource = url;
+
+        if (url.isEmpty()) {
+            d->pixmapLoader.clear();
+        } else {
+            d->pixmapLoader.load(qmlEngine(this), url);
+        }
+
+        Q_EMIT imageSourceChanged();
+    }
+}
+
+/*!
     \qmlattachedproperty stringlist QtQuick::Drag::keys
 
     This property holds a list of keys that can be used by a DropArea to filter drag events.
@@ -726,9 +766,9 @@ Qt::DropAction QQuickDragAttachedPrivate::startDrag(Qt::DropActions supportedAct
         mimeData->setData(it.key(), it.value().toString().toUtf8());
 
     drag->setMimeData(mimeData);
-
-    // TODO: how to handle drag image?
-    // drag->setPixmap(iconPixmap);
+    if (pixmapLoader.isReady()) {
+        drag->setPixmap(QPixmap::fromImage(pixmapLoader.image()));
+    }
 
     emit q->dragStarted();
 
diff --git a/src/quick/items/qquickdrag_p.h b/src/quick/items/qquickdrag_p.h
index c1695e49f0..17721251d9 100644
--- a/src/quick/items/qquickdrag_p.h
+++ b/src/quick/items/qquickdrag_p.h
@@ -58,6 +58,7 @@
 
 #include <QtCore/qmimedata.h>
 #include <QtCore/qstringlist.h>
+#include <QtCore/qurl.h>
 
 #ifndef QT_NO_DRAGANDDROP
 
@@ -247,6 +248,7 @@ class QQuickDragAttached : public QObject
     Q_PROPERTY(QObject *source READ source WRITE setSource NOTIFY sourceChanged RESET resetSource)
     Q_PROPERTY(QObject *target READ target NOTIFY targetChanged)
     Q_PROPERTY(QPointF hotSpot READ hotSpot WRITE setHotSpot NOTIFY hotSpotChanged)
+    Q_PROPERTY(QUrl imageSource READ imageSource WRITE setImageSource NOTIFY imageSourceChanged REVISION 8)
     Q_PROPERTY(QStringList keys READ keys WRITE setKeys NOTIFY keysChanged)
     Q_PROPERTY(QVariantMap mimeData READ mimeData WRITE setMimeData NOTIFY mimeDataChanged)
     Q_PROPERTY(Qt::DropActions supportedActions READ supportedActions WRITE setSupportedActions NOTIFY supportedActionsChanged)
@@ -268,6 +270,9 @@ public:
     QPointF hotSpot() const;
     void setHotSpot(const QPointF &hotSpot);
 
+    QUrl imageSource() const;
+    void setImageSource(const QUrl &url);
+
     QStringList keys() const;
     void setKeys(const QStringList &keys);
 
@@ -300,6 +305,7 @@ Q_SIGNALS:
     void sourceChanged();
     void targetChanged();
     void hotSpotChanged();
+    void imageSourceChanged();
     void keysChanged();
     void mimeDataChanged();
     void supportedActionsChanged();