Qwt, Align content to center

[Asting]

Hello everyone,
My question is, how to locate the content of QwtPlot in the center? Normaly after axisAutoscale, content pushed to left-bottom corner, and end of scale setted at nearest bigger division after end on contet, so it already lookn not in the middle. Also, I use rescaler by Y-axis to keep equal-scale and make content looks in real scale. In this case, my content can occupy whole range of Y-axis, but only half of X-axis, and it will still pushed to leftBottom corner (pictures take left half of QwtPlot, and right side is empty), look not good. Is awailable to set align-center content of plot by x-axis, or for both axises?
If describtion is not clear, I can attach pictures for example.
Sorry if question is lame, I didnt found usefull info at internet.
I would appreciate any help.

[Asting]

I will try show what I looking for.
Like that I have now, with QwtPlotRescaler/axisAutoScale
pic1.jpg
And like that I wants to get automaticaly:
pic2.jpg
Is it generaly possible?

[Uwe]

Isn't your question about how to configure the auto scaler to adjust the scale being symmetric according to the center of the given range ?

Maybe setting the QwtScaleEngine::Floating flag is already good enough - if not you can try the code below:

class MyScaleEngine: public QwtLinearScaleEngine
{
public:
    MyScaleEngine()
    {
        setAttribute( QwtScaleEngine::Symmetric, true );
    }
 
    virtual void autoScale( int maxNumSteps, double &x1, double &x2, double &stepSize ) const
    {
        MyScaleEngine *that = const_cast<MyScaleEngine *>( this );
        that->setReference( 0.5 * ( x1 + x2 ) );
 
        QwtLinearScaleEngine::autoScale( maxNumSteps, x1, x2, stepSize );
    }
};

class MyScaleEngine: public QwtLinearScaleEngine
{
public:
    MyScaleEngine()
    {
        setAttribute( QwtScaleEngine::Symmetric, true );
    }

    virtual void autoScale( int maxNumSteps, double &x1, double &x2, double &stepSize ) const
    {
        MyScaleEngine *that = const_cast<MyScaleEngine *>( this );
        that->setReference( 0.5 * ( x1 + x2 ) );

        QwtLinearScaleEngine::autoScale( maxNumSteps, x1, x2, stepSize );
    }
};

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Uwe

[Asting]

Thanks for advice Uwe. Tip about "floating" flag was very usefull. Unfortunately the proposed class did not work in my case
But suddenly, I found solution in QwtPlotRescaler::setExpandingDirection(axisID, QwtPlotRescaler::ExpandBoth);