[Qt-interest] Qt Charting Component - Feedback Request

[Uwe Rathmann]

Malyushytsky, Alex wrote:

>>> Qwt supports incremental painting - check the oscilloscope example in
>>> Qwt 6. Isn't this "super-fast" ?
> 
> As far as I recall this had some issues, ...

Of course incremental painting is no solution for all type of plots. But if 
it is possible you can display very close to realtime with almost no CPU 
load.

Unfortunately there is a lot of FUD written ( also in this thread ) about 
the performance of Qwt. That's why I wrote a demo called refreshtest, that 
does performance tests how long it takes to do full replots and shows the 
effect of different parameters.

On my box ( a single core Atom ) it measures the following:

a) For a curve with 10000 points: 135 fps
b) For a curve with 1000 points: 406 fps

When I limit the refreshrate to 50 fps for a curve with 10000 points my CPU 
load for X-Server + application is about 50%.

There are a lot of factors, that affect the painting performance. f.e. with 
antialiasing the refresh rate drastically breaks down. No surprise - but 
there are also effects you wouldn't expect: f.e. filling a QPixmap ( 
1000x1000 ) with a gradient takes 300ms on my box ( X11 ). Filling an QImage 
of the same size only needs 20ms and even filling the image + converting it 
into a pixmap is much faster ( ~100ms ).

So take care, when using gradients as widget background on X11 !

Uwe