Qt Graphics View & Box2D

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = actor
TEMPLATE = app

SOURCES += main.cpp\
widget.cpp

HEADERS  += widget.h

FORMS    += widget.ui

win32{
Box2D = D:/Dev/Box2D
}
macx{
Box2D = /Users/spoon/Dev/Box2D
}
INCLUDEPATH += $$Box2D/include
LIBS += -L$$Box2D/lib \
-lBox2D

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <Box2D/Box2D.h>
#include <QVector>
namespace Ui {
class Widget;
}

class Widget : public QWidget
{
Q_OBJECT

public:
explicit Widget(QWidget *parent = 0);
~Widget();

protected:
void timerEvent(QTimerEvent *event);

private:
void createWall();
void createBall();

private:
Ui::Widget *ui;
QGraphicsScene* scene;
QGraphicsView* view;
b2World* world;
QVector<b2Body*> balls;
};

#endif // WIDGET_H

#include "widget.h"
#include "ui_widget.h"
#include <QTransform>
#include <QHBoxLayout>
#include <QGraphicsEllipseItem>
#include <QTimer>
Widget::Widget ( QWidget* parent ) :
QWidget ( parent ),
ui ( new Ui::Widget )
{
ui->setupUi ( this );
balls.resize(5);
QTransform transform;
scene = new QGraphicsScene;
scene->setSceneRect ( 0, 0, 800 , 600 );
scene->addRect(QRect(0,0,800,600),QPen(Qt::black));
view = new QGraphicsView ( scene );
view->setFixedSize ( 900, 700 );
transform.reset();
transform.scale ( 1  , -1 );
view->setTransform ( transform );

QHBoxLayout* layout = new QHBoxLayout;
layout->addWidget ( view );
this->setLayout ( layout );

b2Vec2 gravity ( 0.0f, -10.0f );
world = new b2World ( gravity );

createWall();
createBall();
this->startTimer ( 1000 / 60 );
}

Widget::~Widget()
{
delete world;
delete ui;
}

void Widget::timerEvent ( QTimerEvent* event )
{
world->Step ( 1.0f / 60.0f, 8, 3 );
for(int i = 0; i <= 4;i++){
QGraphicsEllipseItem* item =(QGraphicsEllipseItem* ) balls[i]->GetUserData();
item->setPos(balls[i]->GetPosition().x*30,balls[i]->GetPosition().y*30);
}
QWidget::timerEvent ( event );
}

void Widget::createWall()
{
b2BodyDef groundBodyDef;
groundBodyDef.position.Set ( scene->sceneRect().width()/2/30.0  , -5/30.0 );
b2Body* groundBody = world->CreateBody ( &groundBodyDef );
b2PolygonShape groundBox;
groundBox.SetAsBox ( scene->sceneRect().width()/2/30.0  , 5/30.0 );
groundBody->CreateFixture ( &groundBox, 0.0f );
QGraphicsRectItem* groundItem = new QGraphicsRectItem ( 0, 0, scene->sceneRect().width(), 10 );
groundItem->setBrush ( QBrush ( Qt::red ) );
groundBody->SetUserData ( groundItem );
scene->addItem ( groundItem );

}

void Widget::createBall()
{

QGraphicsEllipseItem * ballItem;
b2BodyDef ball;
for(int i = 0; i <= 4;i++){

ball.type = b2_dynamicBody;
ball.linearDamping = 0.1*i;
ball.position.Set ( (50+100*i)/30.0 , 600/30.0  );
balls [i] =  world->CreateBody ( &ball );
ballItem = new QGraphicsEllipseItem(0,0,1*30,1*30);
ballItem->setBrush(Qt::red);
ballItem->setPos(50+100*i,600);
scene->addItem(ballItem);
balls[i]->SetUserData(ballItem);

b2CircleShape ballShape;
ballShape.m_p.Set(0,0);
ballShape.m_radius = 1;
b2FixtureDef ballFixtureDef;
ballFixtureDef.restitution = 0.2*i;
ballFixtureDef.shape = &ballShape;
ballFixtureDef.density = 13.0f;
balls[i]->CreateFixture ( &ballFixtureDef );
}
}