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#include <QtGui>

class DesktopView : public QGraphicsView

{

    Q_OBJECT

public:

    DesktopView()

        : that(0)

    {

        scene = new QGraphicsScene;

        setScene(scene);

        QDesktopWidget *desktop = QApplication::desktop();

        connect(desktop, SIGNAL(resized(int)), this, SLOT(updateScene()));

        connect(desktop, SIGNAL(resized(int)), this, SLOT(desktopResized(int)));

        connect(desktop, SIGNAL(workAreaResized(int)), this, SLOT(updateScene()));

        connect(desktop, SIGNAL(workAreaResized(int)), this, SLOT(desktopWorkAreaResized(int)));

        connect(desktop, SIGNAL(screenCountChanged(int)), this, SLOT(updateScene()));

        connect(desktop, SIGNAL(screenCountChanged(int)), this, SLOT(desktopScreenCountChanged(int)));

        updateScene();

        QTransform transform;

        transform.scale(0.25, 0.25);

        setTransform(transform);

        setBackgroundBrush(Qt::darkGray);

        desktopScreenCountChanged(-1);

    }

protected:

    void moveEvent(QMoveEvent *e)

    {

        if (that) {

            that->setRect(appRect());

            scene->update();

        }

        QGraphicsView::moveEvent(e);

    }

    void resizeEvent(QResizeEvent *e)

    {

        if (that) {

            that->setRect(appRect());

        }

        QGraphicsView::resizeEvent(e);

    }

private slots:

    void updateScene()

    {

        scene->clear();

        const QDesktopWidget *desktop = QApplication::desktop();

        const bool isVirtualDesktop = desktop->isVirtualDesktop();

        const int homeScreen = desktop->screenNumber(this);

        QRect sceneRect;

        int screenCount = desktop->screenCount();

        for (int s = 0; s < screenCount; ++s) {

            const bool isPrimary = desktop->primaryScreen() == s;

            const QRect screenRect = desktop->screenGeometry(s);

            const QRect workRect = desktop->availableGeometry(s);

            const QBrush fillBrush = palette().brush(isPrimary ? QPalette::Active : QPalette::Inactive, QPalette::Highlight);

            QGraphicsRectItem *screen = new QGraphicsRectItem(0, 0, screenRect.width(), screenRect.height());

            if (isVirtualDesktop) {

                thatRoot = QPoint();

                screen->setPos(screenRect.x(), screenRect.y());

            } else {

               // for non-virtual desktops we assume that screens are

               // simply next to each other

                if (s)

                    screen->setPos(sceneRect.right(), 0);

                if (s == homeScreen)

                    thatRoot = screen->pos().toPoint();

            }

            screen->setBrush(fillBrush);

            scene->addItem(screen);

            sceneRect.setLeft(qMin(sceneRect.left(), screenRect.left()));

            sceneRect.setRight(qMax(sceneRect.right(), screenRect.right()));

            sceneRect.setTop(qMin(sceneRect.top(), screenRect.top()));

            sceneRect.setBottom(qMax(sceneRect.bottom(), screenRect.bottom()));

            QGraphicsRectItem *workArea = new QGraphicsRectItem(screen);

            workArea->setRect(0, 0, workRect.width(), workRect.height());

            workArea->setPos(workRect.x() - screenRect.x(), workRect.y() - screenRect.y());

            workArea->setBrush(Qt::white);

            QGraphicsSimpleTextItem *screenNumber = new QGraphicsSimpleTextItem(workArea);

            screenNumber->setText(QString::number(s));

            screenNumber->setPen(QPen(Qt::black, 1));

            screenNumber->setBrush(fillBrush);

            screenNumber->setFont(QFont("Arial Black", 18));

            screenNumber->setTransform(QTransform().scale(10, 10));

            screenNumber->setTransformOriginPoint(screenNumber->boundingRect().center());

            QSizeF center = (workRect.size() - screenNumber->boundingRect().size()) / 2;

            screenNumber->setPos(center.width(), center.height());

            screen->show();

            screen->setZValue(1);

        }

        if (isVirtualDesktop) {

            QGraphicsRectItem *virtualDesktop = new QGraphicsRectItem;

            virtualDesktop->setRect(sceneRect);

            virtualDesktop->setPen(QPen(Qt::black));

            virtualDesktop->setBrush(Qt::DiagCrossPattern);

            scene->addItem(virtualDesktop);

            virtualDesktop->setZValue(-1);

            virtualDesktop->show();

        }

        that = new QGraphicsRectItem;

        that->setBrush(Qt::red);

        that->setOpacity(0.5);

        that->setZValue(2);

        that->setRect(appRect());

        that->show();

        scene->addItem(that);

        scene->setSceneRect(sceneRect);

        scene->update();

    }

    QRect appRect() const

    {

        QRect rect = frameGeometry();

        if (!QApplication::desktop()->isVirtualDesktop()) {

            rect.translate(thatRoot);

        }

        return rect;

    }

    void desktopResized(int screen)

    {

        qDebug() << "Screen was resized: " << screen

                << ", new size =" << QApplication::desktop()->screenGeometry(screen);

    }

    void desktopWorkAreaResized(int screen)

    {

        qDebug() << "Screen workarea was resized: " << screen

                << ", new size =" << QApplication::desktop()->availableGeometry(screen);

    }

    void desktopScreenCountChanged(int screenCount)

    {

        QDesktopWidget *desktop = QApplication::desktop();

        qDebug() << "";

        if (screenCount != -1) {

            qDebug() << "Screen count was changed to " << screenCount;

        } else {

            screenCount = desktop->screenCount();

            qDebug() << "Screen count: " << screenCount;

        }

        for (int i = 0; i < screenCount; ++i) {

            qDebug() << "  #" << i << ": geometry =" << desktop->screenGeometry(i)

                    << "; available geometry =" << desktop->availableGeometry(i);

        }

        qDebug() << "";

    }

private:

    QGraphicsScene *scene;

    QGraphicsRectItem *that;

    QPoint thatRoot;

};

#include "main.moc"

int main(int argc, char **argv)

{

    QApplication app(argc, argv);

    DesktopView view;

    view.show();

    return app.exec();

}