Curve legend doesn't show a symbol entirely

[AnnaP]

Hello all,

I faced with a problem that using QwtPlotCurve::LegendShowSymbol doesn't show a symbol (a circle in my case) in a legend entirely:
legend1.png

Here is an example code:

class TestPlot: public QwtPlot
{
 
public:
 
    TestPlot(QWidget * parent = NULL);
 
private:
 
    QwtPlotCurve    _curve;
 
};
 
TestPlot::TestPlot(QWidget * parent) : QwtPlot(parent)
{
 
    QwtSymbol *sym = new QwtSymbol(QwtSymbol::Ellipse);
    sym->setSize(5);
    sym->setPen(QColor(Qt::blue));
 
    _curve.setSymbol(sym);
    _curve.setStyle(QwtPlotCurve::NoCurve);
    _curve.setTitle(tr ("Curve"));
    _curve.setLegendAttribute(QwtPlotCurve::LegendShowSymbol);
    _curve.attach(this);
 
    QVector <double> x;
 
    for (unsigned i = 0; i < 10; ++i)
    {
        x.push_back(i);
    }
 
    _curve.setSamples(x, x);
 
    QwtLegend *legend = new QwtLegend(this);
    insertLegend(legend, QwtPlot::BottomLegend);
}

class TestPlot: public QwtPlot
{

public:

    TestPlot(QWidget * parent = NULL);

private:

    QwtPlotCurve    _curve;

};

TestPlot::TestPlot(QWidget * parent) : QwtPlot(parent)
{

    QwtSymbol *sym = new QwtSymbol(QwtSymbol::Ellipse);
    sym->setSize(5);
    sym->setPen(QColor(Qt::blue));

    _curve.setSymbol(sym);
    _curve.setStyle(QwtPlotCurve::NoCurve);
    _curve.setTitle(tr ("Curve"));
    _curve.setLegendAttribute(QwtPlotCurve::LegendShowSymbol);
    _curve.attach(this);

    QVector <double> x;

    for (unsigned i = 0; i < 10; ++i)
    {
        x.push_back(i);
    }

    _curve.setSamples(x, x);

    QwtLegend *legend = new QwtLegend(this);
    insertLegend(legend, QwtPlot::BottomLegend);
}

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If I change a symbol size from 5 to 10 everything looks nice:
legend2.png

Does anybody know why this can happen?
Thanks for any help!

[Uwe]

I can't confirm this on my box.

What version of Qwt/Qt on which platform do you have. Does it still happen with Qwt from SVN trunk ?

Uwe

[AnnaP]

Yes, it happens with the last Qwt version from SVN trunk.

I use Qt 4.7.0 and platform is Windows 7 Professional.

[AnnaP]

I've figured it out!

The problem is in using even/odd QwtSymbol sizes.
E.g. it is better to set an even size using a circle (QwtSymbol::Ellipse), and odd size using QwtSymbol::Star1.

[Uwe]

Ah o.k. but then the odd size of the ellipse should be also bad on the plot itself ?

Unfortunately I had to rewrite much of the symbol code for Qwt 6 because of the floating point based render engine ( + symbols can be cached in a pixmap, what is sometimes faster ). So I might have introduced bugs in this version.

Uwe

[AnnaP]

The ellipse with an odd side looks ok by itself. But if I put a circle with an odd size in a circe with an even size there is a problem that the inner circle looks asymmetrical:

legend3.png

QwtSymbol *sym1 = new QwtSymbol(QwtSymbol::Ellipse);
    sym1->setSize(14);
    sym1->setPen(QColor(Qt::blue));
 
    _curve1.setSymbol(sym1);
    _curve1.setStyle(QwtPlotCurve::NoCurve);
    _curve1.attach(this);
 
    QwtSymbol *sym2 = new QwtSymbol(QwtSymbol::Ellipse, Qt::black, QColor(Qt::black), QSize(7, 7));
 
    _curve2.setSymbol(sym2);
    _curve2.setStyle(QwtPlotCurve::NoCurve);
    _curve2.attach(this);
 
    QVector <double> x;
 
    for (unsigned i = 0; i < 10; ++i)
    {
        x.push_back(i);
    }
 
    _curve1.setSamples(x, x);
    _curve2.setSamples(x, x);

QwtSymbol *sym1 = new QwtSymbol(QwtSymbol::Ellipse);
    sym1->setSize(14);
    sym1->setPen(QColor(Qt::blue));

    _curve1.setSymbol(sym1);
    _curve1.setStyle(QwtPlotCurve::NoCurve);
    _curve1.attach(this);

    QwtSymbol *sym2 = new QwtSymbol(QwtSymbol::Ellipse, Qt::black, QColor(Qt::black), QSize(7, 7));

    _curve2.setSymbol(sym2);
    _curve2.setStyle(QwtPlotCurve::NoCurve);
    _curve2.attach(this);

    QVector <double> x;

    for (unsigned i = 0; i < 10; ++i)
    {
        x.push_back(i);
    }

    _curve1.setSamples(x, x);
    _curve2.setSamples(x, x);

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