gmane.comp.graphics.qwt.general

Problem in QwtPlotCurve

Hi All,

    I am newbie to qwt and qt. I am trying to alter the example data_plot so that a mark will appear on the graphs at some particular point.

        For this i used the following code

iValX = cRight->x(x);
        iValY = cLeft->y(x);
        printf("\n X & Y Val = %d %d\n",iValX,iValY);

        //if((x%10) == 0)
        if(iValX == 15)
        {
                 mY->setXValue(x);
            QPen p;
             const QColor oldcc = p.color();
        cRight->setSymbol(QwtSymbol(QwtSymbol::VLine,
            QBrush(c), QPen(c), QSize(1, 10)) );
        }
        if(iValY == 15)
        {
        cLeft->setSymbol(QwtSymbol(QwtSymbol::VLine,
            QBrush(c), QPen(c), QSize(1, 10)) );
              }

           I am also attaching the graph i am able to plot .

            Can any one help me out to solve this problem.

         I am expecting a vertical lines on the curve when the value == 15 but, i am getting multiple vertical lines.

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Uwe Rathmann | 16 Apr 07:52

Re: Problem in QwtPlotCurve

Hi Vikram,

>     I am newbie to qwt and qt. I am trying to alter the example data_plot
> so that a mark will appear on the graphs at some particular point.

If these marks are not too many you can use QwtPlotMarker.

If you need to display symbols at particular curve points only you have to 
derive your own curve class and implement YourCurve::drawSymbols.

void YourCurve::drawSymbols(QPainter *painter, const QwtSymbol &symbol,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    int from, int to) const
{
    painter->setBrush(symbol.brush());
    painter->setPen(symbol.pen());

    QRect rect;
    rect.setSize(QwtPainter::metricsMap().screenToLayout(symbol.size()));

    for (int i = from; i <= to; i++)
    {
         if ( ... )
         {
             const int xi = xMap.transform(x(i));
             const int yi = yMap.transform(y(i));

             rect.moveCenter(QPoint(xi, yi));
             symbol.draw(painter, rect);
         }
     }
}

Uwe

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