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#include <QtGui>

class EditArea : public QAbstractScrollArea
{
    Q_OBJECT
//
public:
 EditArea( QWidget *parent = 0 , int dimension = 800 )
  : QAbstractScrollArea(0),workArea(dimension,dimension),
    scaleFaktor(0.8),mesure(dimension)
{
  mcurrent  = QTransform(scaleFaktor,0.,0.,scaleFaktor,0.,0.);
  dotChain << mcurrent.map(QPointF(44,55)) << mcurrent.map(QPointF(100,155));
  adjustScrollbars();
}
int xOffset() const { return horizontalScrollBar()->value(); }
int yOffset() const { return verticalScrollBar()->value(); }

protected:
    
void paintEvent( QPaintEvent *Event )
{
  const int y = yOffset();
  const int x = xOffset();
  QTransform mati(scaleFaktor,0.,0.,scaleFaktor,0.,0.);
  QPainter *p = new QPainter( viewport() );
  p->setRenderHint(QPainter::Antialiasing, true);
  p->setPen(Qt::NoPen);
  p->setBrush(Qt::lightGray);
  p->drawRect(Event->rect());
  p->setWorldTransform(mati,false);
  p->translate(-x,-y);
    
    QFont fontText("Verdana",12,QFont::StyleItalic);
    fontText.setStyleStrategy(QFont::PreferBitmap);
    
  p->setBrush(Qt::yellow);
  p->drawRect(QRect(QPoint(1,11),workArea));
    for (int i = 0; i < dotChain.size(); ++i) {
        QPainterPath textPath;
        textPath.addText (dotChain.at(i),
                          fontText,QString("Click here. DoubleClick clear."));
        textPath.addText (dotChain.at(i) + QPointF(0,1 * 15),
                         fontText,QString("Scale Faktor = %1 (mouse wheel).").arg(scaleFaktor));
        textPath.addText (dotChain.at(i) + QPointF(0,2 * 15),
                         fontText,QString("Area  yellow = %1x%1.").arg(mesure * mcurrent.m11()));
        p->setBrush(Qt::darkGreen);
        p->drawPath(textPath);  
    }
  mcurrent = mati;
  p->end();
}

void mousePressEvent ( QMouseEvent *e )
{
    QPointF newpos = mcurrent.map(e->pos());
    dotChain << newpos;
    viewport()->update();
}
void mouseDoubleClickEvent ( QMouseEvent *e )   
{
    dotChain.clear();
    viewport()->update();
}
void resizeEvent(QResizeEvent *e)
{
    adjustScrollbars();
}

void adjustScrollbars()
{
     mcurrent  = QTransform(scaleFaktor,0.,0.,scaleFaktor,0.,0.);
     workArea = QSize(mesure * mcurrent.m11() , mesure * mcurrent.m11() );
     QSize areaSize = viewport()->size();
     QSize  widgetSize = workArea;
     setHorizontalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );
     verticalScrollBar()->setPageStep(widgetSize.height());
     horizontalScrollBar()->setPageStep(widgetSize.width());
     verticalScrollBar()->setRange(0, widgetSize.height() - areaSize.height());
     horizontalScrollBar()->setRange(0, widgetSize.width() - areaSize.width());
     setHorizontalScrollBarPolicy ( Qt::ScrollBarAlwaysOn );
}

void wheelEvent (QWheelEvent * event)
{
  qreal docksscale = scaleFaktor;
  if (event->delta() > 1) {
      docksscale = docksscale + 0.05; 
  } else {
      docksscale = docksscale - 0.05; 
  }
  if (docksscale < 0.45 || docksscale > 5) {
   return;
  } else {
      scaleFaktor = docksscale;
      adjustScrollbars();
      viewport()->update();
  }
 
}

private:
    int mesure;
    QTransform mcurrent;
    QList<QPointF> dotChain;
    QSize workArea;
    qreal scaleFaktor;
signals:
public slots:
};


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

#include "main.moc"