Fill mode using QPainter

[lni]

Hi,

I am plotting a set of curves next to one another, amplitude vs. time (amplitudes are measured at different time), where time is in y axis and amplitude is in x axis.

I need to fill all curves whose amplitudes are over a certain amplitude, or those whose amplitudes are less than a certain amplitude.

In the attached example, I only fill positive amplitude, but eventually I need be able to fill negative amplitude too..

How can I effectively do this with good performance? QPainter::setClipPath is extremely slow...

Thanks