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:

Qt Code: 
  1. void fastReplot(const int updatePos)
  2.     {
  3.         if (updatePos == 0)
  4.             replot();
  5.         else //if (!canvas()->testAttribute(Qt::WA_PaintOnScreen))
  6.         {
  7.             foreach(QwtPlotCurveSpecial* poCurve, curveList)
  8.             {
  9.                 if (!poCurve->isVisible())
  10.                     continue;
  11.  
  12.                 const QwtScaleMap xMap = canvasMap(poCurve->xAxis());
  13.                 const QwtScaleMap yMap = canvasMap(poCurve->yAxis());
  14.  
  15.                 QRegion clipRegion;
  16.                 QRect rect(0,0,1.0,axisScaleDiv(poCurve->yAxis()).interval().width());
  17.  
  18.                 const QPointF center = QwtScaleMap::transform(xMap, yMap, QPointF(updatePos,axisScaleDiv(poCurve->yAxis()).interval().width()/2.0));
  19.                 rect.moveCenter(center.toPoint());
  20.  
  21.                 clipRegion += rect;
  22.  
  23.                 directPainter->setClipRegion(clipRegion);
  24.  
  25.                 directPainter->drawSeries(poCurve, updatePos, updatePos);
  26.             }
  27.         }
  28.     }
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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:

Screenshot from 2014-05-06 10:03:50.png

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