Problem Q3Scrollview along with Q3Painter while porting

Hi,
I am in the process of porting my code from qt3.3 to qt4.7, and am facing a issue while drawing a line using Q3painter over Q3Scrollview.
In my application all the paintings are done on viewport widget of QScrollView(Q3ScrollView in support class).
i have class graphview which is inherited from Q3Scrollview, and i have widgets for x & y axis on it. i want to draw a line parallel to x-axis with regular interval on y-axis.

Code:

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GraphView::GraphView(
        int min, int max, QWidget* parent, const char* name, Qt::WFlags f
        ) : Q3ScrollView(parent,name,f|Qt::WResizeNoErase|Qt::WStaticContents),
        vscale(1.0),
        hscale(1.0),
        oVscale(1.0),
        oHscale(1.0),
        hZoom(1.0),
        vZoom(1.0), manscale(false), marker(100),
        zoomPop(this),
        crossCursor(Qt::CrossCursor),waitCursor(Qt::WaitCursor)
        {
    leftMark=0; rightMark=0; doingStatistics=false;statsInProgress=0;
    if(max < min) max = min;
    minval = min;
    maxval = max;
    setDragAutoScroll(true);
    valsPerReport=1;
    xLine = 0;
    viewport()->setEraseColor(QColor("white"));
    update_from_move = false; 
    yAxis = new Axis(minval, maxval, true, this);
    xAxis = new Axis(this); 
    xAxisHeight = ((QWidget*)xAxis)->sizeHint().height();
    yAxisWidth = ((QWidget*)yAxis)->sizeHint().width();
    //hide - the rectangle outside the axis - down and left
    hide = new QWidget(this);
    hide->setBackgroundColor(QColor("white"));
    hide->lower();  
    hide->stackUnder(yAxis);
    hide->stackUnder(xAxis);
    setMargins(yAxisWidth,0,0,xAxisHeight);
    QRect r = viewport()->geometry();
    yAxis->setGeometry(r.x()-yAxisWidth,r.y(),yAxisWidth,r.height());
    hide->setGeometry(r.x()-yAxisWidth,r.y()+r.height(),yAxisWidth-1,xAxisHeight);
    xAxis->setGeometry(r.x()-1,r.y()+r.height(),r.width()+1,xAxisHeight);
    conX = contentsX();
    conY = contentsY();
    resizeContents(1, (int)((maxval-minval)*vscale)); 
    center(0,0); //ensureVisible
    size = 0;
    visibleSize = visibleWidth();
    newScrolling= false;
    updSize = 1;
    connect(this, SIGNAL( horizontalSliderReleased() ), this,  SLOT(processNewXPosition() ) );
    viewport()->setCursor(Qt::CrossCursor);
    reloadCounter=0;
    gVector.push_back(this);
}
 
//in resize event i am trying to draw line on yaxis, but i don't see the output.
 
void GraphView::viewportResizeEvent( QResizeEvent* re) {
 
   // resize the axis widgets
   QRect r = viewport()->geometry();
   yAxis->setOffset(contentsY());
   yAxis->setGeometry(r.x()-yAxisWidth,r.y(),yAxisWidth,r.height());
   xAxis->setOffset(contentsX());
   xAxis->setGeometry(r.x()-1,r.y()+r.height(),r.width()+1,xAxisHeight);
   hide->setGeometry(r.x()-yAxisWidth,r.y()+r.height(),yAxisWidth-1,xAxisHeight);
   QSize os = re->oldSize();
 
   if(os.width() < r.width() && r.width() > ((int)size/hscale-contentsX())) {
      QPainter painter(viewport());
      int y = ((int)((double)maxval - (double)contentsY()/vscale))%marker;
      if(marker*vscale>5){
         painter.setPen(QColor("grey"));
         for(; y < r.height(); y+=marker) {
            double yd = y * vscale;
            painter.drawLine(os.width(),(int)yd,r.width()-1,(int)yd);
            update();//added newly for graph issue
         }
 
      }
   }
   setContentsPos ( contentsX(), contentsY()+os.height()-r.height() );
}

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i am getting the window with x and y axis but not the grey lines on y axis.
Please let me what am missing here, is anything needs to be considered while using Qpainter on Q3Scrollview?

Thx
Dav