QwtPlotDirectPainter not plotting correctly

Hello!

I'm trying to use QwtPlotDirectPainter to improve the plotting of a embedded device-based Qt interface using Qwt. I used one of the Qwt example implementations of the QwtPlotDirectPainter class and the code I wrote was:

Code:

---

void fastReplot(const int updatePos)
    {
        if (updatePos == 0)
            replot();
        else //if (!canvas()->testAttribute(Qt::WA_PaintOnScreen))
        {
            foreach(QwtPlotCurveSpecial* poCurve, curveList)
            {
                if (!poCurve->isVisible())
                    continue;
 
                const QwtScaleMap xMap = canvasMap(poCurve->xAxis());
                const QwtScaleMap yMap = canvasMap(poCurve->yAxis());
 
                QRegion clipRegion;
                QRect rect(0,0,1.0,axisScaleDiv(poCurve->yAxis()).interval().width());
 
                const QPointF center = QwtScaleMap::transform(xMap, yMap, QPointF(updatePos,axisScaleDiv(poCurve->yAxis()).interval().width()/2.0));
                rect.moveCenter(center.toPoint());
 
                clipRegion += rect;
 
                directPainter->setClipRegion(clipRegion);
 
                directPainter->drawSeries(poCurve, updatePos, updatePos);
            }
        }
    }

---

To explain better: a data package is received by a socket connection with the Y coordinates which are put inside a static sized QVector<double>. A int value coordinates the position in the QVector where the new data should be placed. When this new data arrives, a signal connected to fastReplot(int) is emitted with the position in the vector where the new data was stored. My desire was to repaint only a small part of the plot which corresponds with the coordinate of the last updated data in the vector. The problem, though, is that the image is coming with some error:

Attachment 10336

In the image above, the curve should all be like it is on the left.

How to solve this? What is wrong in my code?

Thanks,

Momergil




Note: QwtPlotCurveSpecial is a variant of QwtPlotCurve