QwtPlot with many curves and QwtPlotOVerlay

Hello.

I have QwtPlot at which I have f.e. 6 curves and each curve consist of many points ( f.e. near 1000 samples )...

Than I want to draw when I move mouse some rectangle with information, for this I use QwtPlotOverlay at which I draw this info...

But there is some lags when I move mouse and draw info. If I chagne number of sampels for each curve f.e. to 500, than it work good...
All my info and rectangle I draw with help of QPainter...

Why there is so bad performance? In example ItemEditor in Qwt all is good even if I set more shapes, but in my case performance depends on what are drawing at QwtPlot. What can be wrong?

High sample graphs take a lot of calculation power for drawing
you can try using a Curvefitter, it reduces the amout of points (removing points that share a pixel) I use the QwtSplineCurveFitter the most

also check post Qwt curve fitting takes a lot of time

Show us some code. I have a plot with several thousands of samples and I don't have any significant slowdowns.

Sorry, it was my bug...
Thanks to all