Change previoux revision 44999: QGraphicsView::matrix returns a *copy* of

its matrix! Hopefully, QGraphicsView has a member function scale(), similar
to the one of QMatrix.

GraphicsView/demo/Triangulation_2/Constrained_Delaunay_triangulation_2.cpp

@@ -246,7 +246,7 @@ MainWindow::MainWindow()
   this->graphicsView->setMouseTracking(true);
 
   // Turn the vertical axis upside down
-  this->graphicsView->matrix().scale(1, -1);
+  this->graphicsView->scale(1, -1);
                                                       
   // The navigation adds zooming and translation functionality to the
   // QGraphicsView