Fix touch point positions of non-transformable QGraphicsItems

TouchEvent::TouchPoint::pos was not updated in
QGraphicsScenePrivate::updateTouchPointsForItem().

To prevent the transformation being calculated repeatedly for each touch
point member, extract a function genericMapFromSceneTransform()
from genericMapFromScene() returning the transformation and use
that whereever multiple points are transformed.

Add a test, extracting helper functionality from
tst_QGraphicsItem::touchEventPropagation().
In addition, fold tst_QGraphicsScene::checkTouchPointsEllipseDiameters() from
c48f4bde0044bd5b23af231f3639d0779ecbdb03 into this test, so that
it is testing all transformations.

Task-number: QTBUG-66192
Change-Id: If71886d2c14c4e216f7781ea2f22f1adc444e6cf
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

1 files changed, 16 insertions, 9 deletions

diff --git a/src/widgets/graphicsview/qgraphicsitem.cpp b/src/widgets/graphicsview/qgraphicsitem.cpp
index 0bc3af2f77..cef1d1b6da 100644
--- a/src/widgets/graphicsview/qgraphicsitem.cpp
+++ b/src/widgets/graphicsview/qgraphicsitem.cpp
@@ -1134,19 +1134,26 @@ void QGraphicsItemPrivate::remapItemPos(QEvent *event, QGraphicsItem *item)
     is untransformable, this function will correctly map \a pos from the scene using the
     view's transformation.
 */
-QPointF QGraphicsItemPrivate::genericMapFromScene(const QPointF &pos,
-                                                  const QWidget *viewport) const
+
+QTransform QGraphicsItemPrivate::genericMapFromSceneTransform(const QWidget *viewport) const
 {
     Q_Q(const QGraphicsItem);
     if (!itemIsUntransformable())
-        return q->mapFromScene(pos);
-    QGraphicsView *view = 0;
-    if (viewport)
-        view = qobject_cast<QGraphicsView *>(viewport->parentWidget());
-    if (!view)
-        return q->mapFromScene(pos);
+       return sceneTransform.inverted();
+    const QGraphicsView *view = viewport
+        ? qobject_cast<QGraphicsView *>(viewport->parentWidget())
+        : nullptr;
+    if (view == nullptr)
+        return sceneTransform.inverted();
     // ### More ping pong than needed.
-    return q->deviceTransform(view->viewportTransform()).inverted().map(view->mapFromScene(pos));
+    const QTransform viewportTransform = view->viewportTransform();
+    return viewportTransform * q->deviceTransform(viewportTransform).inverted();
+}
+
+QPointF QGraphicsItemPrivate::genericMapFromScene(const QPointF &pos,
+                                                  const QWidget *viewport) const
+{
+    return genericMapFromSceneTransform(viewport).map(pos);
 }
 
 /*!