Getting size of a QGraphicsScene

[sedi]

Thank you amleto, nice to see you over here, too! Well, I don't know how to get the area - that's kind of my problem ;-). I thought the viewable size might be exactly that of the view. I've changed "view" to view->viewport():

rectItem->setRect(this->view->mapToScene(this->view->viewport()->rect()).boundingRect());

rectItem->setRect(this->view->mapToScene(this->view->viewport()->rect()).boundingRect());

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But it didn't change the result.

I have never set any translation on scene or view, thus I hadn't checked that and I'm not quite sure if I did it correctly now:

qDebug()<<this->view->transform();

qDebug()<<this->view->transform();

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yields this:

QTransform(type=TxNone, 11=1 12=0 13=0 21=0 22=1 23=0 31=0 32=0 33=1)

Because of "type=TxNone" I think this should be a non-transforming matrix. Thinking about it... it's a 3x3 matrix with diagonal "1"s, that's identity, of course. Long time since I last thought about that stuff... :-)

As for the compilable code: it's a >6000 lines project by now, so I have built a new project here that is compilable and seems the smallest size possible to reproduce my problem:
main.cpp:

#include <QtGui>
#include <QApplication>
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWin;
    mainWin.show();
    return app.exec();
}

#include <QtGui>
#include <QApplication>
#include "mainwindow.h"

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

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mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QGraphicsScene>
#include <QMainWindow>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    MainWindow();
    ~MainWindow();
private:
    QGraphicsView *view;
    QGraphicsScene *scene;
};
 
 
#endif // MAINWINDOW_H

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QGraphicsScene>
#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();
    ~MainWindow();
private:
    QGraphicsView *view;
    QGraphicsScene *scene;
};


#endif // MAINWINDOW_H

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mainwindow.cpp:

#include <QtGui>
#include "mainwindow.h"
#include <qdebug.h>
 
MainWindow::MainWindow()
{
    this->showMaximized();
    scene=new QGraphicsScene(this);
    view = new QGraphicsView(scene);
    QHBoxLayout *layout = new QHBoxLayout;
    QWidget *widget = new QWidget;
 
    setCentralWidget(widget);
    widget->setLayout(layout);
 
    layout->addWidget(view);
    this->scene->setSceneRect(this->view->viewport()->rect());
 
    QGraphicsRectItem* rectItem = new QGraphicsRectItem();
    rectItem->setRect(this->view->mapToScene(this->view->viewport()->rect()).boundingRect());
    qDebug()<<this->view->transform();
 
    scene->addItem(rectItem);
    rectItem->setBrush(QBrush(Qt::black,Qt::SolidPattern));
}
MainWindow::~MainWindow()
{
    delete scene;
}

#include <QtGui>
#include "mainwindow.h"
#include <qdebug.h>

MainWindow::MainWindow()
{
    this->showMaximized();
    scene=new QGraphicsScene(this);
    view = new QGraphicsView(scene);
    QHBoxLayout *layout = new QHBoxLayout;
    QWidget *widget = new QWidget;

    setCentralWidget(widget);
    widget->setLayout(layout);

    layout->addWidget(view);
    this->scene->setSceneRect(this->view->viewport()->rect());

    QGraphicsRectItem* rectItem = new QGraphicsRectItem();
    rectItem->setRect(this->view->mapToScene(this->view->viewport()->rect()).boundingRect());
    qDebug()<<this->view->transform();

    scene->addItem(rectItem);
    rectItem->setBrush(QBrush(Qt::black,Qt::SolidPattern));
}
MainWindow::~MainWindow()
{
    delete scene;
}

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Instead of the scene being filled entirely by the black QGraphicsRectItem (as expected) the result of this "naked" example is this one:
tryoutResult.jpg
I've tried to follow this thread, but my result doesn't change, when I do the correspondend changes in my mainwindow.cpp:

QMatrix const matrix = view->matrix().inverted();
    QRect visibleRect = matrix.mapRect(view->viewport()->rect());
    // when the viewport is scrolled, then the top left point of the visible rectangle needs to be moved
    // according to the scroll bar positions
    visibleRect.moveTopLeft(matrix.map(QPoint(view->horizontalScrollBar()->value(),
                                                    view->verticalScrollBar()->value())));
 
    QGraphicsRectItem* rectItem = new QGraphicsRectItem();
    rectItem->setRect(visibleRect);

QMatrix const matrix = view->matrix().inverted();
    QRect visibleRect = matrix.mapRect(view->viewport()->rect());
    // when the viewport is scrolled, then the top left point of the visible rectangle needs to be moved
    // according to the scroll bar positions
    visibleRect.moveTopLeft(matrix.map(QPoint(view->horizontalScrollBar()->value(),
                                                    view->verticalScrollBar()->value())));

    QGraphicsRectItem* rectItem = new QGraphicsRectItem();
    rectItem->setRect(visibleRect);

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I am quite desperate now. It seemed to work for shad0w, why not for me?
Thank you for your time!