removing space in the canvas at the top and bottom

[titanius]

Thanks for reading.

I am trying to plot a bar chart and i am not able to totally remove space (at the top and bottom) in the canvas, in a way that only the bar gets shown (when the value is maximum).

qwtplot_space.png

How do i remove the black portions at the top and bottom of the canvas?


My code as follows:

I promoted a QWidget to QwtPlot (ui->widget)

//contentsmagin reduces a pixel line or two but doesnot totally remove everything
    ui->widget->canvas()->setContentsMargins(0,0,0,0);
 
    QwtPlotBarChart* device_cri_bar_plot = new QwtPlotBarChart("Device");
    device_cri_bar_plot->attach(ui->widget);
 
    // removes the side (left & right) portions and the axes
    ui->widget->setAxisMaxMinor(QwtPlot::yLeft,0);
    ui->widget->setAxisMaxMajor(QwtPlot::xBottom,0);
    ui->widget->setAxisMaxMinor(QwtPlot::xBottom,0);
    ui->widget->setAxisAutoScale(QwtPlot::yLeft,true);
    ui->widget->setAxisAutoScale(QwtPlot::xBottom,false);
    ui->widget->setAxisScale(QwtPlot::yLeft,0,1);
    ui->widget->setAxisScale(QwtPlot::xBottom,-0.25,0.25);
    ui->widget->axisWidget( QwtPlot::yLeft )->setMargin( 0 );
    ui->widget->axisWidget( QwtPlot::xBottom )->setMargin( 0 );
    ui->widget->axisWidget( QwtPlot::xTop )->setMargin( 0 );
    ui->widget->enableAxis(QwtPlot::xBottom, false);
 
 
    ui->widget->setCanvasBackground(* new QBrush(Qt::black));
 
 
    //plot a green bar
    QwtColumnSymbol *ptr_to_bar_in_barchart = new QwtColumnSymbol( QwtColumnSymbol::Box );
    ptr_to_bar_in_barchart->setLineWidth( 0 );
    ptr_to_bar_in_barchart->setFrameStyle( QwtColumnSymbol::NoFrame );
    QColor barColor( 0,150,0 );
    QVector<QPointF> barpoints;
    barpoints<< QPointF(0,1) ;
    ptr_to_bar_in_barchart->setPalette( barColor );
    device_cri_bar_plot->setSymbol(ptr_to_bar_in_barchart);
    device_cri_bar_plot->setSamples(barpoints);

//contentsmagin reduces a pixel line or two but doesnot totally remove everything
    ui->widget->canvas()->setContentsMargins(0,0,0,0);

    QwtPlotBarChart* device_cri_bar_plot = new QwtPlotBarChart("Device");
    device_cri_bar_plot->attach(ui->widget);

    // removes the side (left & right) portions and the axes
    ui->widget->setAxisMaxMinor(QwtPlot::yLeft,0);
    ui->widget->setAxisMaxMajor(QwtPlot::xBottom,0);
    ui->widget->setAxisMaxMinor(QwtPlot::xBottom,0);
    ui->widget->setAxisAutoScale(QwtPlot::yLeft,true);
    ui->widget->setAxisAutoScale(QwtPlot::xBottom,false);
    ui->widget->setAxisScale(QwtPlot::yLeft,0,1);
    ui->widget->setAxisScale(QwtPlot::xBottom,-0.25,0.25);
    ui->widget->axisWidget( QwtPlot::yLeft )->setMargin( 0 );
    ui->widget->axisWidget( QwtPlot::xBottom )->setMargin( 0 );
    ui->widget->axisWidget( QwtPlot::xTop )->setMargin( 0 );
    ui->widget->enableAxis(QwtPlot::xBottom, false);


    ui->widget->setCanvasBackground(* new QBrush(Qt::black));

 
    //plot a green bar
    QwtColumnSymbol *ptr_to_bar_in_barchart = new QwtColumnSymbol( QwtColumnSymbol::Box );
    ptr_to_bar_in_barchart->setLineWidth( 0 );
    ptr_to_bar_in_barchart->setFrameStyle( QwtColumnSymbol::NoFrame );
    QColor barColor( 0,150,0 );
    QVector<QPointF> barpoints;
    barpoints<< QPointF(0,1) ;
    ptr_to_bar_in_barchart->setPalette( barColor );
    device_cri_bar_plot->setSymbol(ptr_to_bar_in_barchart);
    device_cri_bar_plot->setSamples(barpoints);

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any help would be most helpful.

[Uwe]

plot->plotLayout()->setAlignCanvasToScales( true );

plot->plotLayout()->setAlignCanvasToScales( true );

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Uwe

[titanius]

Uwe, thanks a lot!