vtkcharxy with rectangles


I have a plot on vtkcharXY and i have a qslider (from qt).
the slider is a double slider ( or a range slider).

The idea is the user can set the double slider to select a window on the plot. To show this window on the plot i would like to put two rectangles( one from 0 to the minimum of the window and one from the maximum of the window to the extremity of the chart.) with grey color and little bit transparent.

I checked the pain function from vtkcharxy and vtkContext2D but i have a problem with vtkContextDevice2D which is not initialize.

I don’t really know what is vtkContextDevice2D. i don’t even know if this is the good way to put transparent rectangles.

what is the best way to do this?

thank you in advance!

no one?