Check perfomance of QwtPlotCurve with setPaintAttribute for displaying large data

[Uwe]

I think in QWT spectrogram with big data could be useful also.

The impact of the data size depends on the type of resampling being used - for example with nearest neighbor ( = default ) the performance does not depend on the data size.
But the opposite is true: when the resolution of the data is smaller, than the one on screen rendering will be faster as in situations, where you have to calculate all pixels.

Probably that is not so necessary but depending on plotted data each curve may have up to 5000 points (usually it is 2000-5000 points but may vary). In this case QwtPlotCurve::FilterPointsAggressive may be useful I think (or at least it should not consume much time to execute if number of points is small, less than 1000, I'm going to test it).

The algo calculates 4 points for each pixel: enter, min, max, leave. So when having 5K points and 1K pixels you will have almost no effect in reducing the number of lines to be painted.
But the algo is fast and should not hurt that much.

HTH,
Uwe