#include <QtGui>#include <cmath>#include "cityview.h"CityView::CityView(QWidget *parent)    : QGraphicsView(parent){    setDragMode(ScrollHandDrag);}void CityView::wheelEvent(QWheelEvent *event){    double numDegrees = -event->delta() / 8.0;    double numSteps = numDegrees / 15.0;    double factor = std::pow(1.125, numSteps);    scale(factor, factor);}