How to do asynchronous points loading.?

[Uwe]

The problem is in access to the "low-level" QwtSeriesData from the parent Plot.
Should I do it like this (pseudo code)

The idea of QwtSeriesData is to have abstract API for the curve to retrieve data, but the application is free to organize the data itself according to what is best for the use case.
So why not simply load your data into some buffer - an operation unrelated to Qwt. Once this is done connect your curve data object to this buffer and call replot.

Uwe

[kuzulis]

Once this is done connect your curve data object to this buffer and call replot.

Do you mean to use the set of setSamples() methods?

If so, then it is not an optionn for me, because it causes an overheads:
it copies and re-creates the internal QwtSeriesData objects each time when calls setSamples() (as I can see).

The "right" way for me - it is to call the Curve::setData() once.

Let's me explain:

let's assume that an initial interval of interests data is: 2 second - 10 second (width is 8 second).

The next interval will be: 3 second - 11 second (width is 8 second too)..

So, I do not need to re-fill the whole buffer for 3 second - 11 second.
I need just to append to the buffer the points between 10-11 seconds,
and to remove the points from 2-3 second (to keep the width same 8 second).

But, of course, in case of changing of the width of interval, I will re-fill whole buffer with new points
(because in this case the detail level is changed, its like the zoom changed).

So, as I understand, it is better for me to have an *one* custom QwtSeriesData object with
"tricks", related to re-implementing of the setRectOfInterest() (where I will my buffer what I need).

UPD:

Maybe, even I can do not use the QwtSeriesData at all, and just override the dataSize(), dataRect() and
setRectOfInterest() of QwtPlotCurve class... But, I'm afraid that it is wrong..

[Uwe]

Do you mean to use the set of setSamples() methods?

No:

class YourData: public QwtSeriesData<QPointF>
{
    virtual size_t size() const override
    {
        return ...;
    }
 
    virtual QPointF sample( size_t i ) const override
    {
        return ...;
    }
 
    virtual QRectF boundingRect() const override
    {
         // be careful with not introdicing a performance bottleneck here
         // better calculate it in advance an cache it
         return ...;
    }
};
 
curve->setData( new YourData() );

class YourData: public QwtSeriesData<QPointF>
{
    virtual size_t size() const override
    {
        return ...;
    }

    virtual QPointF sample( size_t i ) const override
    {
        return ...;
    }

    virtual QRectF boundingRect() const override
    {
         // be careful with not introdicing a performance bottleneck here
         // better calculate it in advance an cache it
         return ...;
    }
};

curve->setData( new YourData() );

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It's totally up to you how these methods are implemented, but I guess they return values from some custom buffer. How these values come to this buffer is up the the application, Qwt does not see it.

setSamples()

Qt containers are implicitly shared: see http://doc.qt.io/qt-5/implicit-sharing.html.

So if you load your values only for the purpose of displaying it on the plot using a QPolygonF + setSamples is just fine. The only thing you could consider is to call setSamples( QPolygonF() ) before loading a new set of samples. Otherwise you need memory for 2 buffers until you can pass the new one in.

Uwe

[kuzulis]

Ok, many thanks for your help. I will think...