Add QGraphicsView::isTransformed(), and use it to avoid view transforms.

Ensure that we don't ask for or multiply with the view transform if the
view is not transformed.

3 files changed, 19 insertions, 4 deletions

diff --git a/src/gui/graphicsview/qgraphicsscene.cpp b/src/gui/graphicsview/qgraphicsscene.cpp
index 2773bdd..7bf58c3 100644
--- a/src/gui/graphicsview/qgraphicsscene.cpp
+++ b/src/gui/graphicsview/qgraphicsscene.cpp
@@ -5314,10 +5314,12 @@ void QGraphicsScenePrivate::processDirtyItemsRecursive(QGraphicsItem *item)
                     viewPrivate->updateRect(item->d_ptr->paintedViewBoundingRects.value(viewPrivate->viewport));
 
                 QTransform deviceTransform = item->d_ptr->sceneTransform;
-                if (!untransformableItem)
-                    deviceTransform *= view->viewportTransform();
-                else
-                    deviceTransform = item->deviceTransform(view->viewportTransform());
+                if (view->isTransformed()) {
+                    if (!untransformableItem)
+                        deviceTransform *= view->viewportTransform();
+                    else
+                        deviceTransform = item->deviceTransform(view->viewportTransform());
+                }
                 if (item->d_ptr->hasBoundingRegionGranularity)
                     viewPrivate->updateRegion(deviceTransform.map(QRegion(dirtyRect.toRect())));
                 else
diff --git a/src/gui/graphicsview/qgraphicsview.cpp b/src/gui/graphicsview/qgraphicsview.cpp
index e9a432e..c91e0d1 100644
--- a/src/gui/graphicsview/qgraphicsview.cpp
+++ b/src/gui/graphicsview/qgraphicsview.cpp
@@ -3555,6 +3555,18 @@ QTransform QGraphicsView::viewportTransform() const
 }
 
 /*!
+    Returns true if the view is transformed (i.e., a non-identity transform
+    has been assigned, or the scrollbars are adjusted).
+
+    \sa setTransform(), horizontalScrollBar(), verticalScrollBar()
+*/
+bool QGraphicsView::isTransformed() const
+{
+    Q_D(const QGraphicsView);
+    return !d->identityMatrix || d->horizontalScroll() || d->verticalScroll();
+}
+
+/*!
     Sets the view's current transformation matrix to \a matrix.
 
     If \a combine is true, then \a matrix is combined with the current matrix;
diff --git a/src/gui/graphicsview/qgraphicsview.h b/src/gui/graphicsview/qgraphicsview.h
index b7a9906..387fa01 100644
--- a/src/gui/graphicsview/qgraphicsview.h
+++ b/src/gui/graphicsview/qgraphicsview.h
@@ -170,6 +170,7 @@ public:
     void resetMatrix();
     QTransform transform() const;
     QTransform viewportTransform() const;
+    bool isTransformed() const;
     void setTransform(const QTransform &matrix, bool combine = false);
     void resetTransform();
     void rotate(qreal angle);