setAxisScale become invalid to xTop Axis？

hi, all.
i meet a problem with setAxisScale . when i use setAxisScale to set xTop axis , it can't work as i expect ，however , when i set xBottom , it works fine..

I try to change the curve by setting the xTop axis ,but the curve can't change! the code is as follow:

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->qwtPlot->setCanvasBackground( Qt::white );

ui->qwtPlot->enableAxis(QwtPlot::xBottom,false);
ui->qwtPlot->enableAxis(QwtPlot::xTop,true);

ui->qwtPlot->setAxisScale( QwtPlot::yLeft, 0.0, 10.0 );
ui->qwtPlot->setAxisScale( QwtPlot::xTop, 0.0, 10.0 );

QwtPlotCurve *curve= new QwtPlotCurve();

curve->setPen( Qt::blue );
curve->setRenderHint( QwtPlotItem::RenderAntialiased, true );

QPolygonF points;
points << QPointF( 0.0, 4.4 ) << QPointF( 1.0, 3.0 )
<< QPointF( 2.0, 4.5 ) << QPointF( 3.0, 6.8 )
<< QPointF( 4.0, 7.9 ) << QPointF( 5.0, 7.1 );
curve->setSamples( points );

curve->attach(ui->qwtPlot);


ui->qwtPlot->resize( 600, 400 );
}


however . i can set the xBottom AXIS scale and th program works well, the key part of code is as follow:

//ui->qwtPlot->enableAxis(QwtPlot::xBottom,false);
//ui->qwtPlot->enableAxis(QwtPlot::xTop,true);

ui->qwtPlot->setAxisScale( QwtPlot::yLeft, 0.0, 10.0 );
ui->qwtPlot->setAxisScale( QwtPlot::xBottom, 0.0, 100.0 );


i want to know a way to set the xTop axis scale correctly ,can u help me?

Micky Jhon.

Quote:

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it can't work as i expect

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Run the code below... Are the scales drawn as expected?

Code:

---

int main(int argc, char *argv[])
{
     QApplication a(argc, argv);
 
     QwtPlot plot;
 
     plot.setCanvasBackground( Qt::white );
 
     plot.enableAxis(QwtPlot::xBottom,false);
     plot.enableAxis(QwtPlot::xTop,true);
 
     plot.setAxisScale( QwtPlot::yLeft, 0.0, 10.0 );
     plot.setAxisScale( QwtPlot::xTop, 0.0, 10.0 );
 
     QwtPlotCurve *curve= new QwtPlotCurve();
 
     curve->setPen( Qt::blue );
     curve->setRenderHint( QwtPlotItem::RenderAntialiased, true );
 
     QPolygonF points;
     points << QPointF( 0.0, 4.4 ) << QPointF( 1.0, 3.0 )
     << QPointF( 2.0, 4.5 ) << QPointF( 3.0, 6.8 )
     << QPointF( 4.0, 7.9 ) << QPointF( 5.0, 7.1 );
     curve->setSamples( points );
     curve->attach(&plot);
     plot.resize( 600, 400 );
 
     plot.show();
 
    return a.exec();
}

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Attachment 9983, sorry, the problem is still, and the result is wrong! it looks like setAxisScale function is invalid to xTop? please help me.

Quote:

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Originally Posted by Cah

Run the code below... Are the scales drawn as expected?

Code:

---

int main(int argc, char *argv[])
{
     QApplication a(argc, argv);
 
     QwtPlot plot;
 
     plot.setCanvasBackground( Qt::white );
 
     plot.enableAxis(QwtPlot::xBottom,false);
     plot.enableAxis(QwtPlot::xTop,true);
 
     plot.setAxisScale( QwtPlot::yLeft, 0.0, 10.0 );
     plot.setAxisScale( QwtPlot::xTop, 0.0, 10.0 );
 
     QwtPlotCurve *curve= new QwtPlotCurve();
 
     curve->setPen( Qt::blue );
     curve->setRenderHint( QwtPlotItem::RenderAntialiased, true );
 
     QPolygonF points;
     points << QPointF( 0.0, 4.4 ) << QPointF( 1.0, 3.0 )
     << QPointF( 2.0, 4.5 ) << QPointF( 3.0, 6.8 )
     << QPointF( 4.0, 7.9 ) << QPointF( 5.0, 7.1 );
     curve->setSamples( points );
     curve->attach(&plot);
     plot.resize( 600, 400 );
 
     plot.show();
 
    return a.exec();
}

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---

The coordinate systems spanned by the 4 axes are always present - independent from the visibility of an axis. A plot item is always related to one x/y combination, different plot items on the same plot might be related to different combinations ( see the bode example, where you have 2 y axes ). In your code the curve is related to the invisible xBottom scale - because xBottom/yleft is the default setting.

The following line is missing:

Code:

---

curve->setXAxis( QwtPlot::xTop ):

---

Uwe

thank you very much,that's the answer!:D

Quote:

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Originally Posted by Uwe

The coordinate systems spanned by the 4 axes are always present - independent from the visibility of an axis. A plot item is always related to one x/y combination, different plot items on the same plot might be related to different combinations ( see the bode example, where you have 2 y axes ). In your code the curve is related to the invisible xBottom scale - because xBottom/yleft is the default setting.

The following line is missing:

Code:

---

curve->setXAxis( QwtPlot::xTop ):

---

Uwe

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Yes

Thanks