Axis yLeft cuts of numbers

[Uwe]

I know this is an old thread but was this issue ever resolved?

Nobody ever sent me a demo for debugging the problem,

Uwe

[d_stranz]

Here you go Uwe:

#include <QtGui/QApplication>
#include <QMainWindow>
#include <qwt_plot.h>
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	QMainWindow w;
	QwtPlot * pPlot = new QwtPlot;
	pPlot->setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
	w.setCentralWidget( pPlot );
	w.resize( 500, 500 );
	w.show();
	return a.exec();
}

#include <QtGui/QApplication>
#include <QMainWindow>
#include <qwt_plot.h>

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	QMainWindow w;
	QwtPlot * pPlot = new QwtPlot;
	pPlot->setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
	w.setCentralWidget( pPlot );
	w.resize( 500, 500 );
	w.show();
	return a.exec();
}

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All of the x.5e7 labels are clipped on the left side by a couple of pixels. If the screenshot I will try to attach shows up, you can easily see this. This is Windows XP, Qt 4.5, Qwt 5.2.0, Visual C++ 2008. i have no way to test on another platform.

David

[Uwe]

Well, your code works fine in my environment. The main problem of this bug is, that it seems to be platform and font depending. Unfortunately the font is derived from your environment ( or depends on the font matching algo ) and not known from your code. So please do the following in your environment: assign a scale draw object to the left axis, where you return text labels with a frame. ( QwtText::setBackgroundPen() ).

When the frame is cut off it should be a problem of the layout code - if not ( what I expect ), there is a mismatch between calculating the bounding rect for the text and what is used for painting. The next step would be to strip down the code from QwtText::draw() and QwtPlainTextEngine::textSize() and QwtPlainTextEngine::textMargins() to a small demo, that paints a text to a QWidget without using Qwt.

Uwe

PS: subclassing QwtPlainTextEngine + returning left/right margins in YourPlainTextEngine::textMargins() might be a workaround for the bug.

[d_stranz]

Hi Uwe,

OK, a little bigger example, with a custom QwtAxisScaleDraw for the yLeft axis. As you can see from the screenshot, the left side of most of the boxes is clippped.

What next?

Regards,
David

#include <QtGui/QApplication>
#include <QMainWindow>
#include <QPainter>
#include <QPen>
#include <qwt_plot.h>
#include <qwt_scale_draw.h>
#include <qwt_text.h>
#include <qwt_painter.h>
#include	<qwt_math.h>
 
#if QT_VERSION < 0x040000
#include <qwmatrix.h>
#define QwtMatrix QWMatrix
#else
#include <qmatrix.h>
#define QwtMatrix QMatrix
#endif
 
class MyScaleDraw
	:	public QwtScaleDraw
{
public:
	MyScaleDraw()	{}
 
protected:
	virtual void drawLabel( QPainter * painter, double value ) const
	{
		QwtText lbl = tickLabel(painter->font(), value);
		if ( lbl.isEmpty() )
			return; 
 
		lbl.setBackgroundPen( QPen( Qt::black ) );
		QPoint pos = labelPosition(value);
 
		QSize labelSize = lbl.textSize(painter->font());
		if ( labelSize.height() % 2 )
			labelSize.setHeight(labelSize.height() + 1);
 
		const QwtMetricsMap metricsMap = QwtPainter::metricsMap();
		QwtPainter::resetMetricsMap();
 
		labelSize = metricsMap.layoutToDevice(labelSize);
		pos = metricsMap.layoutToDevice(pos);
 
		const QwtMatrix m = labelMatrix( pos, labelSize);
 
		painter->save();
#if QT_VERSION < 0x040000
		painter->setWorldMatrix(m, true);
#else
		painter->setMatrix(m, true);
#endif
 
		lbl.draw (painter, QRect(QPoint(0, 0), labelSize) );
 
		QwtPainter::setMetricsMap(metricsMap); // restore metrics map
 
		painter->restore();
	}
 
private:
};
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	QwtPlot * pPlot = new QwtPlot;
	pPlot->setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
	pPlot->setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );
 
	QMainWindow w;
	w.setCentralWidget( pPlot );
	w.resize( 500, 500 );
	w.show();
	return a.exec();
}

#include <QtGui/QApplication>
#include <QMainWindow>
#include <QPainter>
#include <QPen>
#include <qwt_plot.h>
#include <qwt_scale_draw.h>
#include <qwt_text.h>
#include <qwt_painter.h>
#include	<qwt_math.h>

#if QT_VERSION < 0x040000
#include <qwmatrix.h>
#define QwtMatrix QWMatrix
#else
#include <qmatrix.h>
#define QwtMatrix QMatrix
#endif

class MyScaleDraw
	:	public QwtScaleDraw
{
public:
	MyScaleDraw()	{}

protected:
	virtual void drawLabel( QPainter * painter, double value ) const
	{
		QwtText lbl = tickLabel(painter->font(), value);
		if ( lbl.isEmpty() )
			return; 

		lbl.setBackgroundPen( QPen( Qt::black ) );
		QPoint pos = labelPosition(value);

		QSize labelSize = lbl.textSize(painter->font());
		if ( labelSize.height() % 2 )
			labelSize.setHeight(labelSize.height() + 1);

		const QwtMetricsMap metricsMap = QwtPainter::metricsMap();
		QwtPainter::resetMetricsMap();

		labelSize = metricsMap.layoutToDevice(labelSize);
		pos = metricsMap.layoutToDevice(pos);

		const QwtMatrix m = labelMatrix( pos, labelSize);

		painter->save();
#if QT_VERSION < 0x040000
		painter->setWorldMatrix(m, true);
#else
		painter->setMatrix(m, true);
#endif

		lbl.draw (painter, QRect(QPoint(0, 0), labelSize) );

		QwtPainter::setMetricsMap(metricsMap); // restore metrics map

		painter->restore();
	}

private:
};

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	QwtPlot * pPlot = new QwtPlot;
	pPlot->setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
	pPlot->setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );

	QMainWindow w;
	w.setCentralWidget( pPlot );
	w.resize( 500, 500 );
	w.show();
	return a.exec();
}

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[Uwe]

I tried the following code on my Linux box:

#include <QApplication>
#include <QPen>
#include <qwt_plot.h>
#include <qwt_scale_draw.h>
 
class MyScaleDraw: public QwtScaleDraw
{
public:
    virtual QwtText label(double value) const
    {
        QwtText lbl = QwtScaleDraw::label(value);
        lbl.setBackgroundPen(QPen(Qt::red));
        return lbl;
    }
};
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    QwtPlot pPlot;
    pPlot.setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
    pPlot.setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );
 
    pPlot.resize( 500, 500 );
    pPlot.show();
 
    return a.exec();
}

#include <QApplication>
#include <QPen>
#include <qwt_plot.h>
#include <qwt_scale_draw.h>

class MyScaleDraw: public QwtScaleDraw
{
public:
    virtual QwtText label(double value) const
    {
        QwtText lbl = QwtScaleDraw::label(value);
        lbl.setBackgroundPen(QPen(Qt::red));
        return lbl;
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QwtPlot pPlot;
    pPlot.setAxisScale( QwtPlot::yLeft, 0.0, 1.0e8, 5.0e6 );
    pPlot.setAxisScaleDraw( QwtPlot::yLeft, new MyScaleDraw() );

    pPlot.resize( 500, 500 );
    pPlot.show();

    return a.exec();
}

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Most of the rectangles are visible, but 2 of them are cut off too, what indicates a bug in the Qwt layout code.

So the next steps are on my side,

Uwe

[d_stranz]

Hi Uwe,

Thanks. And thanks for showing me an easier way to demonstrate the problem.

And by the way, this bug only occurs when the left axis title is null.

Cheers,

David

[Uwe]

The layout code in QwtScaleDraw seems to be wrong by 1 pixel for the left top and right axes. On the left axis it has the effect, that the left axis is cut off by 1 pixel. At least on Linux/X11 the demo seems to be o.k. now.

Fixed in SVN ( 5.2 + trunk ),

Uwe

[d_stranz]

Thanks, Uwe.

[Ban-chan]

Thanks Uwe, works great!