Extend selections in QGraphicsView when selection extension key down

If the user has some objects selected and holds down the "extend selection"
key (Control on Windows, Command on Mac OS X), clicking and dragging a
rubber band selection deselects the current selection.  This is
counter-intuitive and confusing for users.

This commit fixes the behavior so users can extend selections using the
rubber band when the proper key is held down.

Task-number: QTBUG-6523
Change-Id: Ieda4aaa50adb351c0405f5cb8aae23332eec58a9
Reviewed-by: Andreas Aardal Hanssen <andreas@hanssen.name>

8 files changed, 132 insertions, 7 deletions

diff --git a/src/corelib/global/qnamespace.h b/src/corelib/global/qnamespace.h
index e239a11cda..fccb0d5421 100644
--- a/src/corelib/global/qnamespace.h
+++ b/src/corelib/global/qnamespace.h
@@ -73,6 +73,7 @@ Qt {
     Q_ENUMS(TextInteractionFlag)
     Q_FLAGS(TextInteractionFlags)
     Q_ENUMS(ItemSelectionMode)
+    Q_ENUMS(ItemSelectionOperation)
     Q_FLAGS(ItemFlags)
     Q_ENUMS(CheckState)
     Q_ENUMS(SortOrder CaseSensitivity)
@@ -1298,6 +1299,11 @@ public:
         IntersectsItemBoundingRect = 0x3
     };
 
+    enum ItemSelectionOperation {
+        ReplaceSelection,
+        AddToSelection
+    };
+
     enum TransformationMode {
         FastTransformation,
         SmoothTransformation
diff --git a/src/corelib/global/qnamespace.qdoc b/src/corelib/global/qnamespace.qdoc
index 04055a3308..4b582642f3 100644
--- a/src/corelib/global/qnamespace.qdoc
+++ b/src/corelib/global/qnamespace.qdoc
@@ -2234,6 +2234,21 @@
 */
 
 /*!
+    \enum Qt::ItemSelectionOperation
+
+    This enum is used in QGraphicsScene to specify what to do with currently selected
+    items when setting a selection area.
+
+    \value ReplaceSelection The currently selected items are replaced by items
+           in the selection area.
+
+    \value AddToSelection The items in the selection area are added to the currently
+           selected items.
+
+    \sa QGraphicsScene::setSelectionArea()
+*/
+
+/*!
     \enum Qt::FillRule
 
     Specifies which method should be used to fill the paths and polygons.
diff --git a/src/widgets/graphicsview/qgraphicsscene.cpp b/src/widgets/graphicsview/qgraphicsscene.cpp
index 8765b8114d..aa42445b2a 100644
--- a/src/widgets/graphicsview/qgraphicsscene.cpp
+++ b/src/widgets/graphicsview/qgraphicsscene.cpp
@@ -1468,6 +1468,8 @@ void QGraphicsScenePrivate::mousePressEventHandler(QGraphicsSceneMouseEvent *mou
 
         QGraphicsView *view = mouseEvent->widget() ? qobject_cast<QGraphicsView *>(mouseEvent->widget()->parentWidget()) : 0;
         bool dontClearSelection = view && view->dragMode() == QGraphicsView::ScrollHandDrag;
+        bool extendSelection = (mouseEvent->modifiers() & Qt::ControlModifier) != 0;
+        dontClearSelection |= extendSelection;
         if (!dontClearSelection) {
             // Clear the selection if the originating view isn't in scroll
             // hand drag mode. The view will clear the selection if no drag
@@ -2263,6 +2265,28 @@ void QGraphicsScene::setSelectionArea(const QPainterPath &path, const QTransform
 void QGraphicsScene::setSelectionArea(const QPainterPath &path, Qt::ItemSelectionMode mode,
                                       const QTransform &deviceTransform)
 {
+    setSelectionArea(path, Qt::ReplaceSelection, mode, deviceTransform);
+}
+
+/*!
+    \overload
+    \since 5.5
+
+    Sets the selection area to \a path using \a mode to determine if items are
+    included in the selection area.
+
+    \a deviceTransform is the transformation that applies to the view, and needs to
+    be provided if the scene contains items that ignore transformations.
+
+    \a selectionOperation determines what to do with the currently selected items.
+
+    \sa clearSelection(), selectionArea()
+*/
+void QGraphicsScene::setSelectionArea(const QPainterPath &path,
+                                      Qt::ItemSelectionOperation selectionOperation,
+                                      Qt::ItemSelectionMode mode,
+                                      const QTransform &deviceTransform)
+{
     Q_D(QGraphicsScene);
 
     // Note: with boolean path operations, we can improve performance here
@@ -2287,10 +2311,16 @@ void QGraphicsScene::setSelectionArea(const QPainterPath &path, Qt::ItemSelectio
         }
     }
 
-    // Unselect all items outside path.
-    foreach (QGraphicsItem *item, unselectItems) {
-        item->setSelected(false);
-        changed = true;
+    switch (selectionOperation) {
+    case Qt::ReplaceSelection:
+        // Deselect all items outside path.
+        foreach (QGraphicsItem *item, unselectItems) {
+            item->setSelected(false);
+            changed = true;
+        }
+        break;
+    default:
+        break;
     }
 
     // Reenable emitting selectionChanged() for individual items.
diff --git a/src/widgets/graphicsview/qgraphicsscene.h b/src/widgets/graphicsview/qgraphicsscene.h
index 6cd5da00c8..03df18fbce 100644
--- a/src/widgets/graphicsview/qgraphicsscene.h
+++ b/src/widgets/graphicsview/qgraphicsscene.h
@@ -177,6 +177,8 @@ public:
     QPainterPath selectionArea() const;
     void setSelectionArea(const QPainterPath &path, const QTransform &deviceTransform);
     void setSelectionArea(const QPainterPath &path, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, const QTransform &deviceTransform = QTransform());
+    void setSelectionArea(const QPainterPath &path, Qt::ItemSelectionOperation selectionOperation, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape, const QTransform &deviceTransform = QTransform());
+    // ### Qt6 merge the last 2 functions and add a default: Qt::ItemSelectionOperation selectionOperation = Qt::ReplaceSelection
 
     QGraphicsItemGroup *createItemGroup(const QList<QGraphicsItem *> &items);
     void destroyItemGroup(QGraphicsItemGroup *group);
diff --git a/src/widgets/graphicsview/qgraphicsview.cpp b/src/widgets/graphicsview/qgraphicsview.cpp
index 5484ecb96e..b92655013e 100644
--- a/src/widgets/graphicsview/qgraphicsview.cpp
+++ b/src/widgets/graphicsview/qgraphicsview.cpp
@@ -350,6 +350,7 @@ QGraphicsViewPrivate::QGraphicsViewPrivate()
 #ifndef QT_NO_RUBBERBAND
       rubberBanding(false),
       rubberBandSelectionMode(Qt::IntersectsItemShape),
+      rubberBandSelectionOperation(Qt::ReplaceSelection),
 #endif
       handScrollMotions(0), cacheMode(0),
 #ifndef QT_NO_CURSOR
@@ -735,6 +736,7 @@ void QGraphicsViewPrivate::updateRubberBand(const QMouseEvent *event)
     // if we didn't get the release events).
     if (!event->buttons()) {
         rubberBanding = false;
+        rubberBandSelectionOperation = Qt::ReplaceSelection;
         if (!rubberBandRect.isNull()) {
             rubberBandRect = QRect();
             emit q->rubberBandChanged(rubberBandRect, QPointF(), QPointF());
@@ -768,7 +770,7 @@ void QGraphicsViewPrivate::updateRubberBand(const QMouseEvent *event)
     selectionArea.addPolygon(q->mapToScene(rubberBandRect));
     selectionArea.closeSubpath();
     if (scene)
-        scene->setSelectionArea(selectionArea, rubberBandSelectionMode, q->viewportTransform());
+        scene->setSelectionArea(selectionArea, rubberBandSelectionOperation, rubberBandSelectionMode, q->viewportTransform());
 }
 #endif
 
@@ -3289,8 +3291,14 @@ void QGraphicsView::mousePressEvent(QMouseEvent *event)
             d->rubberBanding = true;
             d->rubberBandRect = QRect();
             if (d->scene) {
-                // Initiating a rubber band always clears the selection.
-                d->scene->clearSelection();
+                bool extendSelection = (event->modifiers() & Qt::ControlModifier) != 0;
+
+                if (extendSelection) {
+                    d->rubberBandSelectionOperation = Qt::AddToSelection;
+                } else {
+                    d->rubberBandSelectionOperation = Qt::ReplaceSelection;
+                    d->scene->clearSelection();
+                }
             }
         }
     } else
@@ -3347,6 +3355,7 @@ void QGraphicsView::mouseReleaseEvent(QMouseEvent *event)
                     d->updateAll();
             }
             d->rubberBanding = false;
+            d->rubberBandSelectionOperation = Qt::ReplaceSelection;
             if (!d->rubberBandRect.isNull()) {
                 d->rubberBandRect = QRect();
                 emit rubberBandChanged(d->rubberBandRect, QPointF(), QPointF());
diff --git a/src/widgets/graphicsview/qgraphicsview_p.h b/src/widgets/graphicsview/qgraphicsview_p.h
index ca87b932e2..546f34ba81 100644
--- a/src/widgets/graphicsview/qgraphicsview_p.h
+++ b/src/widgets/graphicsview/qgraphicsview_p.h
@@ -134,6 +134,7 @@ public:
     void updateRubberBand(const QMouseEvent *event);
     bool rubberBanding;
     Qt::ItemSelectionMode rubberBandSelectionMode;
+    Qt::ItemSelectionOperation rubberBandSelectionOperation;
 #endif
     int handScrollMotions;
 
diff --git a/tests/auto/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp b/tests/auto/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
index 51efc47094..44d06c6244 100644
--- a/tests/auto/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
+++ b/tests/auto/widgets/graphicsview/qgraphicsitem/tst_qgraphicsitem.cpp
@@ -1799,6 +1799,12 @@ void tst_QGraphicsItem::selected_multi()
     // Ctrl-click on scene
     QTest::mouseClick(view.viewport(), Qt::LeftButton, Qt::ControlModifier, view.mapFromScene(0, 0));
     QTest::qWait(20);
+    QVERIFY(item1->isSelected());
+    QVERIFY(!item2->isSelected());
+
+    // Click on scene
+    QTest::mouseClick(view.viewport(), Qt::LeftButton, 0, view.mapFromScene(0, 0));
+    QTest::qWait(20);
     QVERIFY(!item1->isSelected());
     QVERIFY(!item2->isSelected());
 
diff --git a/tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.cpp b/tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.cpp
index 04852721db..c051f38ffb 100644
--- a/tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.cpp
+++ b/tests/auto/widgets/graphicsview/qgraphicsview/tst_qgraphicsview.cpp
@@ -164,6 +164,7 @@ private slots:
     void dragMode_scrollHand();
     void dragMode_rubberBand();
     void rubberBandSelectionMode();
+    void rubberBandExtendSelection();
     void rotated_rubberBand();
     void backgroundBrush();
     void foregroundBrush();
@@ -941,6 +942,61 @@ void tst_QGraphicsView::rubberBandSelectionMode()
     QCOMPARE(scene.selectedItems(), QList<QGraphicsItem *>() << rect);
 }
 
+void tst_QGraphicsView::rubberBandExtendSelection()
+{
+   QWidget toplevel;
+   setFrameless(&toplevel);
+
+   QGraphicsScene scene(0, 0, 1000, 1000);
+
+   QGraphicsView view(&scene, &toplevel);
+   view.setDragMode(QGraphicsView::RubberBandDrag);
+   toplevel.show();
+
+   // Disable mouse tracking to prevent the window system from sending mouse
+   // move events to the viewport while we are synthesizing events. If
+   // QGraphicsView gets a mouse move event with no buttons down, it'll
+   // terminate the rubber band.
+   view.viewport()->setMouseTracking(false);
+
+   QGraphicsItem *item1 = scene.addRect(10, 10, 100, 100);
+   QGraphicsItem *item2 = scene.addRect(10, 120, 100, 100);
+   QGraphicsItem *item3 = scene.addRect(10, 230, 100, 100);
+
+   item1->setFlag(QGraphicsItem::ItemIsSelectable);
+   item2->setFlag(QGraphicsItem::ItemIsSelectable);
+   item3->setFlag(QGraphicsItem::ItemIsSelectable);
+
+   // select first item
+   item1->setSelected(true);
+   QCOMPARE(scene.selectedItems(), QList<QGraphicsItem *>() << item1);
+
+   // first rubberband without modifier key
+   sendMousePress(view.viewport(), view.mapFromScene(20, 115), Qt::LeftButton);
+   sendMouseMove(view.viewport(), view.mapFromScene(20, 300), Qt::LeftButton, Qt::LeftButton);
+   QVERIFY(!item1->isSelected());
+   QVERIFY(item2->isSelected());
+   QVERIFY(item3->isSelected());
+   sendMouseRelease(view.viewport(), QPoint(), Qt::LeftButton);
+
+   scene.clearSelection();
+
+   // select first item
+   item1->setSelected(true);
+   QVERIFY(item1->isSelected());
+
+   // now rubberband with modifier key
+   {
+      QPoint clickPoint = view.mapFromScene(20, 115);
+      QMouseEvent event(QEvent::MouseButtonPress, clickPoint, view.viewport()->mapToGlobal(clickPoint), Qt::LeftButton, 0, Qt::ControlModifier);
+      QApplication::sendEvent(view.viewport(), &event);
+   }
+   sendMouseMove(view.viewport(), view.mapFromScene(20, 300), Qt::LeftButton, Qt::LeftButton);
+   QVERIFY(item1->isSelected());
+   QVERIFY(item2->isSelected());
+   QVERIFY(item3->isSelected());
+}
+
 void tst_QGraphicsView::rotated_rubberBand()
 {
     QWidget toplevel;