создание маштабированного окна с элементами

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsItem>
 
class CircleItem : public QGraphicsItem
{
public:
 CircleItem( qreal radius, QGraphicsItem* parent = 0 )
 : QGraphicsItem( parent )
 , radius_( radius ) {}
 virtual ~CircleItem() {}
 void paint( QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = 0 )
 {
  painter->drawEllipse( QRectF( -radius_ / 2, -radius_ / 2, radius_, radius_ ) );
 }
 QRectF boundingRect() const
 {
  return QRectF( -radius_ / 2, -radius_ / 2, radius_, radius_ );
 }
private:
 qreal radius_;
};
 
class GraphicsView : public QGraphicsView
{
public:
 GraphicsView( QWidget* p = 0 ) : QGraphicsView( p ) {}
 void resizeEvent( QResizeEvent* e )
 {
  fitInView( scene()->sceneRect() );
 }
};
 
int main( int argc, char** argv )
{
 QApplication app( argc, argv );
 
 GraphicsView gv;
 QGraphicsScene scene( -150, -150, 300, 300 );
 
 gv.setScene( &scene );
 gv.setRenderHint( QPainter::Antialiasing );
 
 for( qreal r = 20; r < 300; r += 10 )
  scene.addItem( new CircleItem( r ) );
 
 gv.show();
 
 return app.exec();
}