Autoscale axis with QwtPlotTradingCurve and set min x axis value

Hi all,

I am new to Qwt. I am able to draw a simple candlestick plot and add some surves for my own indicators. To do so, I have started from the example stockchart.
As in the example, I also have a zoom:

Code:

class Zoomer: public QwtPlotZoomer
{
public:
    Zoomer( QWidget *canvas ): QwtPlotZoomer( canvas )
    {
        setRubberBandPen( QColor( Qt::darkGreen ) );
        setTrackerMode( QwtPlotPicker::AlwaysOn );
    }
 
protected:
    virtual QwtText trackerTextF( const QPointF &pos ) const
    {
        const QDateTime dt = QwtDate::toDateTime( pos.x() );
 
        QString s;
        s += QwtDate::toString( QwtDate::toDateTime( pos.x() ), "MMM dd hh:mm ", QwtDate::FirstThursday );
 
        QwtText text( s );
        text.setColor( Qt::white );
 
        QColor c = rubberBandPen().color();
        text.setBorderPen( QPen( c ) );
        text.setBorderRadius( 6 );
        c.setAlpha( 170 );
        text.setBackgroundBrush( c );
 
        return text;
    }
};

And in my Plot constructor:

Code:

PlotWidget::PlotWidget(QWidget *parent):
QwtPlot(parent)
{
    // LeftButton for the zooming
    // RightButton: zoom out by 1
    // Ctrl+RighButton: zoom out to full size
    Zoomer* zoomer = new Zoomer( canvas() );
    zoomer->setMousePattern( QwtEventPattern::MouseSelect2, Qt::RightButton, Qt::ControlModifier );
    zoomer->setMousePattern( QwtEventPattern::MouseSelect3, Qt::RightButton );
    zoomer->setKeyPattern( QwtEventPattern::KeyHome, Qt::Key_Home );
    // MidButton for the panning
    QwtPlotPanner *panner = new QwtPlotPanner( canvas() );
    panner->setMouseButton( Qt::MidButton );
 
    _scaleDraw = new DateScaleDraw( Qt::UTC );
    _scaleEngine = new QwtDateScaleEngine( Qt::UTC );
 
    setAxisScaleDraw( QwtPlot::xBottom, _scaleDraw );
    setAxisScaleEngine( QwtPlot::xBottom, _scaleEngine );
    setAxisLabelRotation( QwtPlot::xBottom, -50.0 );
    setAxisLabelAlignment( QwtPlot::xBottom, Qt::AlignLeft | Qt::AlignBottom );
}

OK. Nothing new ... The problems are with the zoom.

* If I press the home key, I go back to 1 january 1970 (begin of UTC time?). How can I say that the first date in my plot is for instance 1st april 2014 and disallow the user to go before?
* When I select a zoom region, the values on the y axis are not scaled according to the content, and thus, the plot display "flat" curves. How can I fix this? The same also applies to Ctrl+Right clic.

Hope you could help

Best regards