QwtPlotHistogram question

[fantom]

I want to set text on the rectangles of a QwtPlotHistogram. I attached an example how i want to look like. I took as a start the tv plot example and the set values function looks like this:

void Histogram::setValues(uint numValues, int*values)
{
    QVector<QwtIntervalSample> samples(numValues);
    for ( uint i = 0; i < numValues; i++ )
    {
        QwtInterval interval(double(i), i + 1.0);
        interval.setBorderFlags(QwtInterval::ExcludeMaximum);
 
        samples[i] = QwtIntervalSample(values[i], interval);
    }
 
    setData(new QwtIntervalSeriesData(samples));
}

void Histogram::setValues(uint numValues, int*values)
{
    QVector<QwtIntervalSample> samples(numValues);
    for ( uint i = 0; i < numValues; i++ )
    {
        QwtInterval interval(double(i), i + 1.0);
        interval.setBorderFlags(QwtInterval::ExcludeMaximum);
        
        samples[i] = QwtIntervalSample(values[i], interval);
    }

    setData(new QwtIntervalSeriesData(samples));
}

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Could you give me an example how it has to look like with the text?

Thank you

[Uwe]

Could you give me an example how it has to look like with the text?

When the text is available from the sample you can overload QwtPlotHistogram::drawColumn:

virtual void YourHistogram::drawColumn( QPainter *painter,
    const QwtColumnRect &rect, const QwtIntervalSample &sample ) const
{
    QwtPlotHistogram::drawColumn( painter, rect, sample );
 
    // now draw your text
    ...
}

virtual void YourHistogram::drawColumn( QPainter *painter,
    const QwtColumnRect &rect, const QwtIntervalSample &sample ) const
{
    QwtPlotHistogram::drawColumn( painter, rect, sample );

    // now draw your text
    ...
}

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Otherwise overload QwtPlotHistogram::drawColumns:

virtual void YourHistogram::drawColumns( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    int from, int to ) const
{
    QwtPlotHistogram::drawColumns( painter, xMap, yMap, from, to );
 
    for ( int i = from; i <= to; i++ )
    {
        const QwtIntervalSample sample = d_series->sample( i );
        const QwtColumnRect rect = columnRect( sample, xMap, yMap );
 
        // now draw your text 
    }
}

virtual void YourHistogram::drawColumns( QPainter *painter,
    const QwtScaleMap &xMap, const QwtScaleMap &yMap,
    int from, int to ) const
{
    QwtPlotHistogram::drawColumns( painter, xMap, yMap, from, to );

    for ( int i = from; i <= to; i++ )
    {
        const QwtIntervalSample sample = d_series->sample( i );
        const QwtColumnRect rect = columnRect( sample, xMap, yMap );

        // now draw your text 
    }
}

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Uwe

[hind]

I have a question which may be relevant to this thread. Forgive me if I chose the wrong place. Here's the pic based on the tvplot example:
图像 047.png
So how do I place labels displaying the value of each sample right on the top of each column? Or maybe some other reletive positions are fine too.
I thought the QwtPlotMarker might be the one but it seems not able to control the position of the label as I need.
Thanks in advance!

[Uwe]

Posting a question rbelow the answer for the same question ?

Uwe

PS: Qwt 6.1 offers new plot items for bar charts - something different than what QwtPlotHistogram is made for.