Marc Weichhold

That worked, thank you.

I second the concerns about jagged lines with Qwt 6.3.x while using an QwtPlotOpenGLCanvas. In the attachment there are two screenshots, the "good" one was created with Qwt 6.2.0 and Qt 5.14, the second one with Qwt 6.3.1 and Qt 5.14. Please note that the only difference is the different Qwt version, the code is exactly the same.

QwtPlotOpenGLCanvas changes curve color