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>

3 files changed, 35 insertions, 17 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);
 }
 
 /*!
diff --git a/src/widgets/graphicsview/qgraphicsitem_p.h b/src/widgets/graphicsview/qgraphicsitem_p.h
index bae38473f9..9fc6c0794a 100644
--- a/src/widgets/graphicsview/qgraphicsitem_p.h
+++ b/src/widgets/graphicsview/qgraphicsitem_p.h
@@ -190,6 +190,7 @@ public:
     void updateAncestorFlags();
     void setIsMemberOfGroup(bool enabled);
     void remapItemPos(QEvent *event, QGraphicsItem *item);
+    QTransform genericMapFromSceneTransform(const QWidget *viewport = nullptr) const;
     QPointF genericMapFromScene(const QPointF &pos, const QWidget *viewport) const;
     inline bool itemIsUntransformable() const
     {
diff --git a/src/widgets/graphicsview/qgraphicsscene.cpp b/src/widgets/graphicsview/qgraphicsscene.cpp
index 25b77aa02f..37c631483a 100644
--- a/src/widgets/graphicsview/qgraphicsscene.cpp
+++ b/src/widgets/graphicsview/qgraphicsscene.cpp
@@ -1286,10 +1286,11 @@ void QGraphicsScenePrivate::sendHoverEvent(QEvent::Type type, QGraphicsItem *ite
 {
     QGraphicsSceneHoverEvent event(type);
     event.setWidget(hoverEvent->widget());
-    event.setPos(item->d_ptr->genericMapFromScene(hoverEvent->scenePos(), hoverEvent->widget()));
+    const QTransform mapFromScene = item->d_ptr->genericMapFromSceneTransform(hoverEvent->widget());
+    event.setPos(mapFromScene.map(hoverEvent->scenePos()));
     event.setScenePos(hoverEvent->scenePos());
     event.setScreenPos(hoverEvent->screenPos());
-    event.setLastPos(item->d_ptr->genericMapFromScene(hoverEvent->lastScenePos(), hoverEvent->widget()));
+    event.setLastPos(mapFromScene.map(hoverEvent->lastScenePos()));
     event.setLastScenePos(hoverEvent->lastScenePos());
     event.setLastScreenPos(hoverEvent->lastScreenPos());
     event.setModifiers(hoverEvent->modifiers());
@@ -1312,14 +1313,16 @@ void QGraphicsScenePrivate::sendMouseEvent(QGraphicsSceneMouseEvent *mouseEvent)
     if (item->isBlockedByModalPanel())
         return;
 
+    const QTransform mapFromScene = item->d_ptr->genericMapFromSceneTransform(mouseEvent->widget());
+    const QPointF itemPos = mapFromScene.map(mouseEvent->scenePos());
     for (int i = 0x1; i <= 0x10; i <<= 1) {
         Qt::MouseButton button = Qt::MouseButton(i);
-        mouseEvent->setButtonDownPos(button, mouseGrabberButtonDownPos.value(button, item->d_ptr->genericMapFromScene(mouseEvent->scenePos(), mouseEvent->widget())));
+        mouseEvent->setButtonDownPos(button, mouseGrabberButtonDownPos.value(button, itemPos));
         mouseEvent->setButtonDownScenePos(button, mouseGrabberButtonDownScenePos.value(button, mouseEvent->scenePos()));
         mouseEvent->setButtonDownScreenPos(button, mouseGrabberButtonDownScreenPos.value(button, mouseEvent->screenPos()));
     }
-    mouseEvent->setPos(item->d_ptr->genericMapFromScene(mouseEvent->scenePos(), mouseEvent->widget()));
-    mouseEvent->setLastPos(item->d_ptr->genericMapFromScene(mouseEvent->lastScenePos(), mouseEvent->widget()));
+    mouseEvent->setPos(itemPos);
+    mouseEvent->setLastPos(mapFromScene.map(mouseEvent->lastScenePos()));
     sendEvent(item, mouseEvent);
 }
 
@@ -5858,10 +5861,17 @@ void QGraphicsScenePrivate::removeView(QGraphicsView *view)
 
 void QGraphicsScenePrivate::updateTouchPointsForItem(QGraphicsItem *item, QTouchEvent *touchEvent)
 {
+    const QTransform mapFromScene =
+        item->d_ptr->genericMapFromSceneTransform(static_cast<const QWidget *>(touchEvent->target()));
+
     for (auto &touchPoint : touchEvent->_touchPoints) {
-        touchPoint.setRect(item->mapFromScene(touchPoint.sceneRect()).boundingRect());
-        touchPoint.setStartPos(item->d_ptr->genericMapFromScene(touchPoint.startScenePos(), static_cast<QWidget *>(touchEvent->target())));
-        touchPoint.setLastPos(item->d_ptr->genericMapFromScene(touchPoint.lastScenePos(), static_cast<QWidget *>(touchEvent->target())));
+        // Deprecated TouchPoint::setRect clobbers ellipseDiameters, restore
+        const QSizeF ellipseDiameters = touchPoint.ellipseDiameters();
+        touchPoint.setRect(mapFromScene.map(touchPoint.sceneRect()).boundingRect());
+        touchPoint.setEllipseDiameters(ellipseDiameters);
+        touchPoint.setPos(mapFromScene.map(touchPoint.scenePos()));
+        touchPoint.setStartPos(mapFromScene.map(touchPoint.startScenePos()));
+        touchPoint.setLastPos(mapFromScene.map(touchPoint.lastScenePos()));
     }
 }