Problem with selecting qwtplotcurve and points on qwtplotcurve

[tangtao_xp]

The event_filter example does this more or less - even if this example is outdated and I wouldn't recommend to copy its code. But at least CanvasPicker::select shows how to identify a curve and its point corresponding to a mouse position.

Also similar - and more up to date - is the curvetracker example in Qwt 6.1. The itemeditor example might also be of interest, showing how to select and drag plot items on the canvas.

Uwe

Hi, Uwe

I greatly appreciate your reply.

I had read the example code. I still have a small confusion:

code from CanvasPicker

const QwtPlotItemList& itmList = plot()->itemList();
    for ( QwtPlotItemIterator it = itmList.begin();
        it != itmList.end(); ++it )
    {
        if ( ( *it )->rtti() == QwtPlotItem::Rtti_PlotCurve )
        {
            QwtPlotCurve *c = static_cast<QwtPlotCurve *>( *it );
            double d;
            int idx = c->closestPoint( pos, &d );
            if ( d < dist )
            {
                curve = c;
                index = idx;
                dist = d;
            }
        }
    }

const QwtPlotItemList& itmList = plot()->itemList();
    for ( QwtPlotItemIterator it = itmList.begin();
        it != itmList.end(); ++it )
    {
        if ( ( *it )->rtti() == QwtPlotItem::Rtti_PlotCurve )
        {
            QwtPlotCurve *c = static_cast<QwtPlotCurve *>( *it );
            double d;
            int idx = c->closestPoint( pos, &d );
            if ( d < dist )
            {
                curve = c;
                index = idx;
                dist = d;
            }
        }
    }

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the for loop efficency is very low. In my situation, there will be as many curves as the user want (large number of curves) and meanwhile, I was told that closestPoint() is also low efficent. Any better ideas?

Considering the problem of curve crossing, this loop only can return one curve.(I think I am able to fix this problem by return a vector or sth like that)

Thank you in advance.