How to obtain values of a zoomed curve ?

I need to obtain the values of a part of a curve, determined by a zoom.
I could achieve this by obtaining the indexes of the curve,determining the curve segment being shown, to use the sample function of QwtPlotSeriesItem and assuming that the curve values ​​were inserted in order, according to the passage of time. So far I could not do that. I know I could use the function QwtPlotZoomer::zoomRect(), and others but all efforts have been unsuccessful. I'm ussing Qwt 6.0
I know this has been asked before, but maybe in qwt 6.0 is easier to achieve this or there is another way.
Any help is welcome.

pd: sorry my english.

Assuming that data in vector is in function of time then you can easily get first and last index of vector points on the edges of visible area:

Code:

---

QwtPlotCurve* curve = new QwtPlotCurve();
curve->setSamples( x_vector.data(), y_vector.data(), qMin( x_vector.size(), y_vector.size() ) );
int idx_start = findIndex( zoomer->zoomRect().left(), curve );
int idx_end = findIndex( zoomer->zoomRect().right(), curve );
 
QVector< double > data = x_vector.mid( idx_start, idx_end );
 
int     findIndex( double worldX, const QwtPlotCurve& curve ) const
{
    int idx = 0;
 
    int low = 0;
    int high = curve.dataSize() - 1;
 
    while( true )
    {
        int size = high-low;
        int mid = low+size/2;
        double mid_value = curve.sample( mid ).x();
 
        if( size <= 1 || worldX == mid_value )
        {
            idx = mid;
            break;
        }
        else
        {
            if( worldX < mid_value )
            {
                high -= size/2;
            }
            else
            {
                low += size/2;
            }
        }
    }
 
    return idx;
}

---

First of all thanks for responding
Your fuction partially solves what I need, because it works correctly if the curve does not have points with the same x values, otherwise it is not. My curve values ​​were inserted in order, according to the passage of time, but, at the same time maybe I need to insert more than one value.
Moreover, not necessarily all points of the curve are inside of the segment determinated by the x values of the rectangle [zoomer->zoomRect() ( left() and right() fuctions )],
because it may have points above or below the zoomed rectangle. I hope to explain myself.
Actually, I want to implement a function that allows me to get all the points within the zoomed area, because in the near future I will need it, but, for the time being, I will continue assuming that the values are inserted in order, according to the passage of time.
Any help is welcome.
Thanks again for your answer

pd: Sorry my English

The function above is just a start.
I didn't account for the case when at single x vaule there's more than one y value but that can be easily remedied.
Simple validation of returned indexes would solve the issue:

Code:

---

int prev = idx_start-1;
while( prev >= 0 && curve.sample( idx_start ) == curve.sample( prev ) )
{
    --prev;
    --idx_start;
}
 
int next = idx_end+1;
while( next < curve.dataSize() && curve.sample( idx_end ) == curve.sample( next ) )
{
    ++next;
    ++idx_end;
}

---

As to your second issue.
If you want all points acroos x axis regardless if they fit on y axis in current zoom rectangle - above function can be used.
If you want points acroos x axis only if they fit on y axis in current zoom rectangle - above function can be used.

In the second case only work required on your part is to remove from the cut-out *data* segment points that overshoot upper and lower values of the zoom rectangle.