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, 3 insertions, 0 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene_p.h b/src/gui/graphicsview/qgraphicsscene_p.h
index 8af8b28..9ace725 100644
--- a/src/gui/graphicsview/qgraphicsscene_p.h
+++ b/src/gui/graphicsview/qgraphicsscene_p.h
@@ -168,6 +168,9 @@ public:
     Qt::DropAction lastDropAction;
     QList<QGraphicsItem *> cachedItemsUnderMouse;
     QList<QGraphicsItem *> hoverItems;
+    bool allItemsIgnoreHoverEvents;
+    bool allItemsUseDefaultCursor;
+    void enableMouseTrackingOnViews();
     QMap<Qt::MouseButton, QPointF> mouseGrabberButtonDownPos;
     QMap<Qt::MouseButton, QPointF> mouseGrabberButtonDownScenePos;
     QMap<Qt::MouseButton, QPoint> mouseGrabberButtonDownScreenPos;