Fixes bug when using AnchorUnderMouse for GraphicsView transformation.

We now automatically enable mouse tracking on the viewport of the
GraphicsView when setting AnchorUnderMouse as transformationAnchor or
resizeAnchor.

Autotest included.

Task-number: QTBUG-6835
Reviewed-by: bnilsen

2 files changed, 113 insertions, 3 deletions

diff --git a/src/gui/graphicsview/qgraphicsview.cpp b/src/gui/graphicsview/qgraphicsview.cpp
index ffe64aa..3bb40fb 100644
--- a/src/gui/graphicsview/qgraphicsview.cpp
+++ b/src/gui/graphicsview/qgraphicsview.cpp
@@ -1208,6 +1208,11 @@ void QGraphicsView::setTransformationAnchor(ViewportAnchor anchor)
 {
     Q_D(QGraphicsView);
     d->transformationAnchor = anchor;
+
+    // Ensure mouse tracking is enabled in the case we are using AnchorUnderMouse
+    // in order to have up-to-date information for centering the view.
+    if (d->transformationAnchor == AnchorUnderMouse)
+        d->viewport->setMouseTracking(true);
 }
 
 /*!
@@ -1235,6 +1240,11 @@ void QGraphicsView::setResizeAnchor(ViewportAnchor anchor)
 {
     Q_D(QGraphicsView);
     d->resizeAnchor = anchor;
+
+    // Ensure mouse tracking is enabled in the case we are using AnchorUnderMouse
+    // in order to have up-to-date information for centering the view.
+    if (d->resizeAnchor == AnchorUnderMouse)
+        d->viewport->setMouseTracking(true);
 }
 
 /*!
@@ -2597,9 +2607,12 @@ void QGraphicsView::setupViewport(QWidget *widget)
     }
 
     // We are only interested in mouse tracking if items
-    // accept hover events or use non-default cursors.
-    if (d->scene && (!d->scene->d_func()->allItemsIgnoreHoverEvents
-                     || !d->scene->d_func()->allItemsUseDefaultCursor)) {
+    // accept hover events or use non-default cursors or if
+    // AnchorUnderMouse is used as transformation or resize anchor.
+    if ((d->scene && (!d->scene->d_func()->allItemsIgnoreHoverEvents
+                     || !d->scene->d_func()->allItemsUseDefaultCursor))
+        || d->transformationAnchor == AnchorUnderMouse
+        || d->resizeAnchor == AnchorUnderMouse) {
         widget->setMouseTracking(true);
     }
 
diff --git a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
index 69df39b..9e4321b 100644
--- a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
+++ b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
@@ -211,6 +211,7 @@ private slots:
     void centerOnDirtyItem();
     void mouseTracking();
     void mouseTracking2();
+    void mouseTracking3();
     void render();
     void exposeRegion();
     void update_data();
@@ -3403,6 +3404,102 @@ void tst_QGraphicsView::mouseTracking2()
     QCOMPARE(spy.count(), 1);
 }
 
+void tst_QGraphicsView::mouseTracking3()
+{
+    // Mouse tracking should be automatically enabled if AnchorUnderMouse is used for
+    // view transform or resize. We never disable mouse tracking if it is already enabled.
+
+    { // Make sure we enable mouse tracking when using AnchorUnderMouse for view transformation.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+        QVERIFY(!view.viewport()->hasMouseTracking());
+
+        view.setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    { // Make sure we enable mouse tracking when using AnchorUnderMouse for view resizing.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+        QVERIFY(!view.viewport()->hasMouseTracking());
+
+        view.setResizeAnchor(QGraphicsView::AnchorUnderMouse);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    { // Make sure we don't disable mouse tracking in setViewport/setScene (transformation anchor).
+        QGraphicsView view;
+        view.setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+        QVERIFY(view.viewport()->hasMouseTracking());
+
+        QWidget *viewport = new QWidget;
+        view.setViewport(viewport);
+        QVERIFY(viewport->hasMouseTracking());
+
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        view.setScene(&scene);
+        QVERIFY(viewport->hasMouseTracking());
+    }
+
+    { // Make sure we don't disable mouse tracking in setViewport/setScene (resize anchor).
+        QGraphicsView view;
+        view.setResizeAnchor(QGraphicsView::AnchorUnderMouse);
+        QVERIFY(view.viewport()->hasMouseTracking());
+
+        QWidget *viewport = new QWidget;
+        view.setViewport(viewport);
+        QVERIFY(viewport->hasMouseTracking());
+
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        view.setScene(&scene);
+        QVERIFY(viewport->hasMouseTracking());
+    }
+
+    // Make sure we don't disable mouse tracking when adding an item (transformation anchor).
+    { // Adding an item to the scene before the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        scene.addItem(item);
+
+        QGraphicsView view;
+        view.setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+        view.setScene(&scene);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    { // Adding an item to the scene after the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+        view.setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
+
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        scene.addItem(item);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    // Make sure we don't disable mouse tracking when adding an item (resize anchor).
+    { // Adding an item to the scene before the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        scene.addItem(item);
+
+        QGraphicsView view;
+        view.setResizeAnchor(QGraphicsView::AnchorUnderMouse);
+        view.setScene(&scene);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    { // Adding an item to the scene after the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+        view.setResizeAnchor(QGraphicsView::AnchorUnderMouse);
+
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        scene.addItem(item);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+}
+
 class RenderTester : public QGraphicsRectItem
 {
 public: