#include <QApplication>
#include <QGraphicsRectItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QMainWindow>
#include <QPainter>
#include <QSlider>
#include <QVBoxLayout>
#include <QWidget>

class QStyleOptionGraphicsItem;

class GraphicsRectItem : public QGraphicsRectItem {
public:
    GraphicsRectItem(int x, int y, int w, int h) : QGraphicsRectItem(x, y, w, h, 0) { }
    virtual void paint(QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget* widget);
};

void GraphicsRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *) {
    if ( isSelected() ) {
        painter->setBrush(Qt::red);
    } else {
        painter->setBrush(Qt::blue);
    }
    painter->drawRect(rect());
}

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
private slots:
    void rotate(int value);
private:
    QGraphicsView *m_graphicsView;
    QGraphicsScene *m_scene;
    void populateScene();
    double m_currentRotation;
};

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
    resize(600, 700);
    m_graphicsView = new QGraphicsView();
    m_graphicsView->setRenderHint(QPainter::HighQualityAntialiasing, true);
    m_graphicsView->setRenderHint(QPainter::SmoothPixmapTransform, true);
    m_graphicsView->setDragMode(QGraphicsView::RubberBandDrag);
    m_graphicsView->setRubberBandSelectionMode(Qt::IntersectsItemShape);
    //m_graphicsView->setRubberBandSelectionMode(Qt::ContainsItemShape);

    QSlider *zoomSlider = new QSlider(Qt::Horizontal, this);
    zoomSlider->setMinimum(-45);
    zoomSlider->setMaximum(45);
    zoomSlider->setValue(0);
    zoomSlider->setTickPosition(QSlider::TicksBelow);
    zoomSlider->setTickInterval(5);
    zoomSlider->setPageStep(10);

    QVBoxLayout *layout = new QVBoxLayout();
    layout->addWidget(m_graphicsView);
    layout->addWidget(zoomSlider);

    QWidget *centralWidget = new QWidget;
    centralWidget->setLayout(layout);
    setCentralWidget(centralWidget);

    m_scene = new QGraphicsScene;
    m_graphicsView->setScene(m_scene);
    populateScene();
    connect(zoomSlider, SIGNAL(valueChanged(int)), this, SLOT(rotate(int)));
}

void MainWindow::populateScene() {
    for (int i = 0; i < 20; i++) {
        for (int j = 0; j < 20; j ++) {
            GraphicsRectItem *rect = new GraphicsRectItem(i*20, j*20, 10, 10);
            rect->setFlag(QGraphicsItem::ItemIsSelectable, true);
            m_scene->addItem(rect);
        }
    }
}

void MainWindow::rotate(int value) {
    if (m_currentRotation  != (double)value) {
        m_graphicsView->rotate(m_currentRotation - (double)value);
        m_currentRotation = (double)value;
    }
}

int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

#include "main.moc"