Disable mouse tracking in QGraphicsView if possible.

We don't need mouse tracking unless there are items in the
scene that either accept hover events or have a cursor set.
This cut-off is extremely efficient in the common case since
all items ignore hover events and use the standard cursor
by default.

We no longer dig for items and do lots of intersection and
calculating just for fun :-) We even get rid of the overhead
of 2 x QCoreApplication::sendEvent!

The next step is to optimize the items(*) functions to
simply check for hasCursor()/acceptsHoverEvents() before
we do complex checks like intersects/collidesWithPath() etc.

Auto test included.

Reviewed-by: Andreas

1 files changed, 100 insertions, 1 deletions

diff --git a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
index 412c6c5..6b3a9d4 100644
--- a/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
+++ b/tests/auto/qgraphicsview/tst_qgraphicsview.cpp
@@ -191,6 +191,7 @@ private slots:
     void scrollAfterResize_data();
     void scrollAfterResize();
     void centerOnDirtyItem();
+    void mouseTracking();
 
     // task specific tests below me
     void task172231_untransformableItems();
@@ -2515,7 +2516,8 @@ void tst_QGraphicsView::replayMouseMove()
 
     // One mouse event should be translated into one scene event.
     for (int i = 0; i < 3; ++i) {
-        sendMouseMove(view.viewport(), view.viewport()->rect().center());
+        sendMouseMove(view.viewport(), view.viewport()->rect().center(),
+                      Qt::LeftButton, Qt::MouseButtons(Qt::LeftButton));
         QCOMPARE(viewSpy.count(), i + 1);
         QCOMPARE(sceneSpy.count(), i + 1);
     }
@@ -2705,6 +2707,7 @@ void tst_QGraphicsView::task186827_deleteReplayedItem()
     MouseMoveCounter view;
     view.setScene(&scene);
     view.show();
+    view.viewport()->setMouseTracking(true);
 #ifdef Q_WS_X11
     qt_x11_wait_for_window_manager(&view);
 #endif
@@ -3048,6 +3051,102 @@ void tst_QGraphicsView::centerOnDirtyItem()
     QCOMPARE(before, after);
 }
 
+void tst_QGraphicsView::mouseTracking()
+{
+    // Mouse tracking should only be automatically enabled if items either accept hover events
+    // or have a cursor set. We never disable mouse tracking if it is already enabled.
+
+    { // Make sure mouse tracking is disabled by default.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+        QVERIFY(!view.viewport()->hasMouseTracking());
+    }
+
+    { // Make sure we don't disable mouse tracking in setupViewport/setScene.
+        QGraphicsView view;
+        QWidget *viewport = new QWidget;
+        viewport->setMouseTracking(true);
+        view.setViewport(viewport);
+        QVERIFY(viewport->hasMouseTracking());
+
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        view.setScene(&scene);
+        QVERIFY(viewport->hasMouseTracking());
+    }
+
+    // Make sure we enable mouse tracking when having items that accept hover events.
+    {
+        // Adding an item to the scene after the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        item->setAcceptHoverEvents(true);
+        scene.addItem(item);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+    {
+        // 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);
+        item->setAcceptHoverEvents(true);
+        scene.addItem(item);
+
+        QGraphicsView view(&scene);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+    {
+        // QGraphicsWidget implicitly accepts hover if it has window decoration.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+
+        QGraphicsWidget *widget = new QGraphicsWidget;
+        scene.addItem(widget);
+        QVERIFY(!view.viewport()->hasMouseTracking());
+        // Enable window decoraton.
+        widget->setWindowFlags(Qt::Window | Qt::WindowTitleHint);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    // Make sure we enable mouse tracking when having items with a cursor set.
+    {
+        // Adding an item to the scene after the scene is set on the view.
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view(&scene);
+
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        item->setCursor(Qt::CrossCursor);
+        scene.addItem(item);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+    {
+        // 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);
+        item->setCursor(Qt::CrossCursor);
+        scene.addItem(item);
+
+        QGraphicsView view(&scene);
+        QVERIFY(view.viewport()->hasMouseTracking());
+    }
+
+    // Make sure we propagate mouse tracking to all views.
+    {
+        QGraphicsScene scene(-10000, -10000, 20000, 20000);
+        QGraphicsView view1(&scene);
+        QGraphicsView view2(&scene);
+        QGraphicsView view3(&scene);
+
+        QGraphicsRectItem *item = new QGraphicsRectItem(10, 10, 10, 10);
+        item->setCursor(Qt::CrossCursor);
+        scene.addItem(item);
+
+        QVERIFY(view1.viewport()->hasMouseTracking());
+        QVERIFY(view2.viewport()->hasMouseTracking());
+        QVERIFY(view3.viewport()->hasMouseTracking());
+    }
+}
+
 QTEST_MAIN(tst_QGraphicsView)
 #include "tst_qgraphicsview.moc"
 #endif