Can I use QwtPlot to plot while data is created?

[Ole Jacob]

Hi,

I'm planning on using QwtPlot to create a graph while the data is created,
meaning I will add one and one point and have the QwtPlot continously update.

Is QwtPlot up to this, or will it not work/be very slow?

Regards,
Ole Jacob

[Uwe Rathmann]

Post by Ole Jacob
I'm planning on using QwtPlot to create a graph while the data is created,
meaning I will add one and one point and have the QwtPlot continously update.
Is QwtPlot up to this, or will it not work/be very slow?

Have a look at the realtime example: it generates and paints random points one
by one. ( For X11 some optimizations are missing in Qwt 5.0.2. So better take
the code from qwt-5.0 SVN, or wait for the Qwt 5.0.3 maintenance release,
what is planned for next week )

The example does an incremental painting of points, what should work fine with
Qt3 on all platforms. With Qt4 you will see a similar performance on X11, on
Windows the performance is worse, but also ok. But on the Mac incremental
painting is not possible, what makes the performance lousy.

Uwe

[Houssem BDIOUI]

Uwe,

Post by Uwe Rathmann
With Qt4 you will see a similar performance on X11, on
Windows the performance is worse,

Is there any plan to improve the performance on Windows? Or is
it related to Qt itself?

Best regards,
Houssem

Post by Uwe Rathmann

Post by Ole Jacob
I'm planning on using QwtPlot to create a graph while the data is

created,

Post by Ole Jacob
meaning I will add one and one point and have the QwtPlot continously update.
Is QwtPlot up to this, or will it not work/be very slow?

Have a look at the realtime example: it generates and paints random points one
by one. ( For X11 some optimizations are missing in Qwt 5.0.2. So better take
the code from qwt-5.0 SVN, or wait for the Qwt 5.0.3 maintenance release,
what is planned for next week )
The example does an incremental painting of points, what should work fine with
Qt3 on all platforms. With Qt4 you will see a similar performance on X11, on
Windows the performance is worse, but also ok. But on the Mac incremental
painting is not possible, what makes the performance lousy.
Uwe
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[Uwe Rathmann]

Post by Houssem BDIOUI
Is there any plan to improve the performance on Windows? Or is
it related to Qt itself?

It is related to Qt4:

a) X11

On X11 you can paint outside of paint events ( QwtPlotCurve does it, when
Qt::WA_PaintOutsidePaintEvent is enabled for the canvas ).

b) Windows

On Windows Qt::WA_PaintOutsidePaintEvent is not supported. So QwtPlotCurve
needs to send a dummy paint event to draw the points from inside the paint
event ( running through Qt4 render pipeline ).

c) Mac

On the Mac incremental painting is not supported at all and the pixmap cache
of the canvas needs to be repainted for each paint operation.

Something we have to pay for the exciting new world of transparent desktops,

Uwe