QwtPlotCurve update problem

[knarfS]

Hi there,

I have a problem with a QwtPlotCurve not updating correctly.
This could be observed with the oscilloscope example. The only thing i changed in the example code is the line color and width, so the problem is more highlighted:

d_curve->setPen( Qt::red, 4.0, Qt::SolidLine );

d_curve->setPen( Qt::red, 4.0, Qt::SolidLine );

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The curve is plotted with a line width of approximately 1px until the canvas is replotted by changing the window size or changing the displayed seconds. Only then the curve line has the desired 4px width.
Here are 2 pictures that show the problem: https://imgur.com/a/z9EoL

I'm using Debian testing with Qt 5.10 and Qwt 6.1.3. But I stumbled across the same issue 2 years ago with Qt 4.? and Qwt 6.? under Linux and Windows (I can't remember exactly which versions).
Is this a know problem? Am I doing something wrong? Couldn't find any problem like that.

Frank

[Uwe]

The oscilloscope example is painting incrementally, so you won't have any updates of the previously rendered content only by changing the pen. You probably have to call replot manually once after changing the pen.

Uwe