Custom CurveStyle for qwt_plot_curve

[jmsbc]

Hi,

I needed to inherit from qwt_plot_curve to add another CurveStyle (DottedLines) to the enum:

/*          
           - UserCurve
           Styles >= UserCurve are reserved for derived
           classes of QwtPlotCurve that overload drawCurve() with
           additional application specific curve types.
*/
    enum CurveStyle
    {
        NoCurve,
 
        Lines,
        Sticks,
        Steps,
        Dots,
 
        UserCurve = 100
    };

/*          
           - UserCurve
           Styles >= UserCurve are reserved for derived
           classes of QwtPlotCurve that overload drawCurve() with
           additional application specific curve types.
*/
    enum CurveStyle
    {
        NoCurve,

        Lines,
        Sticks,
        Steps,
        Dots,

        UserCurve = 100
    };

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I wanted to make a style called DottedLine, which connects every other point with a line. I need to derive a class and then redefine DrawCurve:

void QwtPlotCurve::drawCurve(QPainter *painter, int style,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
    switch (style)
    {
        case Lines:
            if ( testCurveAttribute(Fitted) )
            {
                // we always need the complete 
                // curve for fitting
                from = 0;
                to = dataSize() - 1;
            }
            drawLines(painter, xMap, yMap, from, to);
            break;
        case Sticks:
            drawSticks(painter, xMap, yMap, from, to);
            break;
        case Steps:
            drawSteps(painter, xMap, yMap, from, to);
            break;
        case Dots:
            drawDots(painter, xMap, yMap, from, to);
            break;
        case DottedLines:
            drawDottedLines(painter, xMap, yMap, from, to);
            break;
        case NoCurve:
        default:
            break;
    }
}

void QwtPlotCurve::drawCurve(QPainter *painter, int style,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
    switch (style)
    {
        case Lines:
            if ( testCurveAttribute(Fitted) )
            {
                // we always need the complete 
                // curve for fitting
                from = 0;
                to = dataSize() - 1;
            }
            drawLines(painter, xMap, yMap, from, to);
            break;
        case Sticks:
            drawSticks(painter, xMap, yMap, from, to);
            break;
        case Steps:
            drawSteps(painter, xMap, yMap, from, to);
            break;
        case Dots:
            drawDots(painter, xMap, yMap, from, to);
            break;
        case DottedLines:
            drawDottedLines(painter, xMap, yMap, from, to);
            break;
        case NoCurve:
        default:
            break;
    }
}

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(I added drawDottedLines at the bottom). How can I inherit the enum CurveStyles such that I can set the style using:

void QwtPlotCurve::setStyle(CurveStyle style)?

I can't inherit the enum right? Do I need to redefine setStyle to:

void MyPlotCurve::setStyle(MyCurveStyle style)? And if so, how do I define MyCurveStyle?

I hope this is not too confusing, thanks

[Uwe]

class YourCurve: public QwtPlotCurve
{
   enum YourStyle
   {
       DottedLines = QwtPlotCurve::UserStyle + 1000
   }
 
   ....
 
   virtual void drawCurve(QPainter *painter, int style,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    int from, int to) const
   {
      if ( style < QwtPlotCurve::UserStyle )
        QwtPlotCurve::drawCurve(painter, style, xMap, yMap, from, to);
     else
         drawYourCurve(painter, style, xMap, yMap, from, to);
   }
};

class YourCurve: public QwtPlotCurve
{
   enum YourStyle
   {
       DottedLines = QwtPlotCurve::UserStyle + 1000
   }

   ....

   virtual void drawCurve(QPainter *painter, int style,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    int from, int to) const
   {
      if ( style < QwtPlotCurve::UserStyle )
        QwtPlotCurve::drawCurve(painter, style, xMap, yMap, from, to);
     else
         drawYourCurve(painter, style, xMap, yMap, from, to);
   }
};

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HTH,
Uwe

[jmsbc]

Thanks Uwe!

Now that I got that problem solved, I'm trying to connect every other point in the QwtPlotCurve. I added a function for drawing DottedLines, which looks like this:

void MyQwtPlotCurve::drawDottedLines(QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
  if (!connectLine)
  {
    prevX = xMap.transform(to);
    prevY = yMap.transform(to);
    connectLine = true;
  } else
  {
    const int xi = xMap.transform(x(to));
    const int yi = yMap.transform(y(to));
 
    QwtPainter::drawLine(painter, prevX, prevY, xi, yi);
    connectLine = false;
  }

void MyQwtPlotCurve::drawDottedLines(QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
  if (!connectLine)
  {
    prevX = xMap.transform(to);
    prevY = yMap.transform(to);
    connectLine = true;
  } else
  {
    const int xi = xMap.transform(x(to));
    const int yi = yMap.transform(y(to));

    QwtPainter::drawLine(painter, prevX, prevY, xi, yi);
    connectLine = false;
  }

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The bool connectLine is just a counter to keep track of drawing for every other point. Also, the parameters "from" and "to" are always equal to each other. I was trying to implement something like DrawSticks, but this isn't quite working correctly. A line keeps getting drawn from the last point to some crazy point. What am I doing wrong, please help!

Thanks a lot again

[Uwe]

prevX = xMap.transform(to);
prevY = yMap.transform(to);

prevX = xMap.transform(to);
prevY = yMap.transform(to);

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Mapping an index - did you look at your code yourself ?

But if "from" is always the same as "to" you have degenerated curves consisting of one point ( what is a marker ). Don't do this.

Uwe

[jmsbc]

prevX = xMap.transform(to);
prevY = yMap.transform(to);

prevX = xMap.transform(to);
prevY = yMap.transform(to);

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Mapping an index - did you look at your code yourself ?

But if "from" is always the same as "to" you have degenerated curves consisting of one point ( what is a marker ). Don't do this.

Uwe

Sorry about that, I was testing a bunch of different code in that function, so I didn't catch that mistake.

After going back to debug the code, I realized that drawDottedLines is not only called when I explicitly call draw(int from, int to), but it is called to repaint the canvas each time the canvas changes from a paintevent. So then I realized every point or line in the curve need to be re-drawn each time drawDottedLines(...) gets called. (When I was debugging before, for some reason I saw that "from" and "to" were always the same number so I thought one point was being painted at a time)

Here's the code which works now:

void MyQwtPlotCurve::drawDottedLines(QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
  for (int i = from; i <= to; i++)
  {
    if (((i+1) % 2) == 0)
    {
      const int prevX = xMap.transform(x(i - 1));
      const int prevY = yMap.transform(y(i - 1));
      const int xi = xMap.transform(x(i));
      const int yi = yMap.transform(y(i));
 
      QwtPainter::drawLine(painter, prevX, prevY, xi, yi);
    }
  }

void MyQwtPlotCurve::drawDottedLines(QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap, 
    int from, int to) const
{
  for (int i = from; i <= to; i++)
  {
    if (((i+1) % 2) == 0)
    {
      const int prevX = xMap.transform(x(i - 1));
      const int prevY = yMap.transform(y(i - 1));
      const int xi = xMap.transform(x(i));
      const int yi = yMap.transform(y(i));

      QwtPainter::drawLine(painter, prevX, prevY, xi, yi);
    }
  }

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Thanks again Uwe