text on QwtPlot

[Kamran I. <kam...@gm...>]

Hi

I have QwtPlot with a time indexed x-axis

What I need is to display the exact time of the rendered
curves in the plot while the user moves the cursor inside,
that is a text string following the cursor and being upddated.
The text is like 2005-082:15.45.36 (year-day_of_year, hour,
minutes, seconds, millisecons)
What I have done (patching from examples) in the following
displays the text but it leaves a trail behind which eventually 
leaves a messy screen:

--------------------------------------------------

 
 
 class dataPlot: public QwtPlot
 {
 public:
 	dataPlot(...)
 	{
             canvas()->setMouseTracking(TRUE);
             canvas()->installEventFilter(this);
 	}
 
 virtual bool eventFilter(QObject *object, QEvent *e)
         {
         if ( object != (QObject *)this->canvas() )
        return FALSE;

        switch(e->type())
       {
	  case QEvent::MouseButtonPress:
          {
             ....
           }
	case QEvent::MouseButtonRelease:
         {
         ....
        }
        case QEvent::MouseMove:
        {
           x = ((QMouseEvent *)e)->x();
           y = ((QMouseEvent *)e)->y();
	   xposition = this->invTransform(this->xBottom, x); 
	   yposition = this->invTransform(this->yLeft, y); 
	   millisecs = int((xposition - double((int)xposition))*1000);
	   dt = dt.addSecs((int)xposition);
	   d = dt.date(); 
	   t = dt.time();
           ds.sprintf("%d-%03d:%02d.%02d.%02d.%03d",d.year(),d.dayOfYear(),
                           t.hour(),t.minute(),t.second(),millisecs);
           p.setClipping(TRUE);
	   p.setRasterOp(XorROP);
           p_pen.setColor(QColor((bg.rgb() ^ pen.color().rgb())));
	   p.setPen(p_pen);
	   p.drawText(x, y, ds);
	   dt = dt.addSecs((int)(-1.0*xposition));  
        }
    default:
      break;
    }
    return QwtPlot::eventFilter(object, e);
}

---------------------------------

what am I doing wrong ?

Thanks in advance

Kamran