QPainter and how to access the parent variables.

[wysota]

Why update 50 times per second? Why not update only when something actually changes?

You can access the parent though parent() and parentWidget(). Remember to cast the result to the proper class pointer (your QMainWindow descendant).

[Teuniz]

Why update 50 times per second? Why not update only when something actually changes?

There is a continu datastream arriving at the comport which need to be visualized, actually
the data is coming from a 4 channel analog/digital-converter which generates 100 samples
per second. So with 1200 pixels on the X-axe one trace takes 12 seconds (I paint one pixel
per sample).
Tnx for the tip, I'm going to try that.

Regards.

[Teuniz]

"mainwindow.h:140: error: ISO C++ forbids declaration of ‘PainterWidget’ with no type"

I can't include mainwindow.h in painterwidget.h because in mainwindow.h I have already
included painterwidget.h. If I don't include painterwidget.h in mainwindow.h I can not create
a class PainterWiget. If I can't include mainwindow.h in painter.h, how do I cast the parent
widget to the class used in mainwindow.cpp?

I guess I got lost in C++...

[jpn]

I guess I got lost in C++...

Use forward declaration in headers. Further explanation: Circular dependency

[wysota]

There is a continu datastream arriving at the comport which need to be visualized, actually
the data is coming from a 4 channel analog/digital-converter which generates 100 samples
per second.

But the human eye treats ~16fps as a smooth movement, so there is no point in refreshing the graph too often. I don't think a delay of several miliseconds will make you a difference in considering the data "real time".

[Teuniz]

I read the article on Wikipedia and now it works
I'm using a refreshrate of 16 fps as well

Tnx wysota and jpn!