How to draw a cruve with increasing data?

[Uwe]

I use linux-2.6.13 kernel on arm9 board. Qt version is qt-core-4.3.2, and qwt is 5.20

Qt has been renamed so often - I can't remember if qt-core was Qt Embedded or Qt X11. This is important as on X11 you can paint outside of paint events - while on Qt embedded ( and all platforms with the raster paint engine like Windows ) QwtPlotCurve::draw is implemented using internal dummy paint events.

Also Qt 4.3 is pretty old - better upgrade if possible.

the realtime example can work,...

Then check all the flags that are temporarily enabled in IncrementalPlot::appendData.

You could also have a look at the new spectrogram example in Qwt SVN trunk. Maybe this is closer to your use case ( but I'm not sure if it works with Qt 4.3 ).

Uwe