Click on a marker

Hello! The plot (QwtPlot) contains many markers (QwtPlotMarker). How to determine which marker was clicked?

To solve this problem, I changed the standard example of "event filter". After each click of the mouse, I check all the markers.
If the marker is located close to the click, this marker has been pressed.

Code:

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void Plot::mousePressEvent(QMouseEvent *e)
{
    QwtPlot::mousePressEvent(e);
 
    const QwtPlotItemList& items = itemList();
    for ( QwtPlotItemIterator i = items.begin(); i != items.end(); ++i )
    {
        if ( (*i)->rtti() == QwtPlotItem::Rtti_PlotMarker )
        {
            QwtPlotMarker *m = static_cast<QwtPlotMarker*>(*i);
 
	    // The distance from the marker to the place a clicked
            float distance = sqrt( pow( (transform(QwtPlot::xBottom, m->value().x()) - e->pos().x()), 2 ) + pow( (transform(QwtPlot::yLeft, m->value().y()) - e->pos().y()), 2 ) );
 
            if (distance <= 5)
            {
		qDebug() << "YEAP!";
            }
        }
    }
}

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Is there a better solution?

Quote:

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Originally Posted by d1mbarus

Is there a better solution?

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Not out of the box - if you have to deal with many, many markers you might need to introduce some spatial ordered index ( f.e a quadtree ).

Uwe

PS: Using x * x is faster than pow(x, 2 ) and you can avoid the sqrt by comparing x * x + y * y against 25.

Quote:

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Originally Posted by Uwe

Not out of the box - if you have to deal with many, many markers you might need to introduce some spatial ordered index ( f.e a quadtree ).

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The number of markers is less than 10. Can you tell us more about the quadtree? I have not found information about quadtree.

Quote:

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Originally Posted by d1mbarus

The number of markers is less than 10.

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Then iterating over the complete list will never be a problem.

Quote:

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Originally Posted by d1mbarus

Can you tell us more about the quadtree? I have not found information about quadtree.

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https://en.wikipedia.org/wiki/Quadtree

Uwe