Problem with the reimplementation of the zoom function of a QwtPlotZoomer

[Valsylver]

Thanks Uwe for your answer.

I don't understand very well how the setRectOfInterest(QRectF) method works.
Am I supposed to subclass the QwtSeriesData class and to reimplement the setRectOfInterest method to set the data of my QwtPlotCurve ? In this case, is this setRectOfInterest function called every time the user zooms on the plot ?

[Uwe]

Am I supposed to subclass the QwtSeriesData class and to reimplement the setRectOfInterest method to set the data of my QwtPlotCurve ?

Guess you want to derive from one of the available subclasses of QwtSeriesData ( depending on which you are using today ) - and yes, then overload setRectOfInterest.

In this case, is this setRectOfInterest function called every time the user zooms on the plot ?

Better - it is called every time the scales are modified, where zooming is only one of the many possible reasons. Note that you could also overload QwtPlotCurve::updateScaleDiv(), if this is easier for your implementation.

I don't know how your samples are organized, but maybe all you need to do is to adjust a start and an end index in your data object having an effect on what points are returned from the data object. It's worth to spend some time on the idea of the QwtSeriesData class !

HTH,
Uwe

[Valsylver]

Thanks Uwe, it worked very well.

I have another question.

On my plot, I put 2 cursors (instance of QwtPlotMarker), and make them movable by overloading the MouseMoveEvent of the plot. In the label of these cursors, I write the x and y position. When the data size of my Curve is higher than the pixels available on the canvas, it's not a problem to find the y position. But, when the user zooms in such a way that there are less points than the number of pixels of the canvas, I'd like the cursors to be able to move between points and make a linear regression to find the y position in this case.

So, Is there a means of knowing where the points are drawn on the canvas (a kind of map of pixels) ?

Thanks

[Valsylver]

I finally found another way to do that.

Thanks again Uwe