Performance of Polar plot vs. Rectangular plot

I developed a wireless antenna pattern viewer that plots points from 0-360 degrees in rectangular form and in polar form. We noticed that the performance of the polar plot is much slower than the rectangular plot. Displaying, re-sizing and showing/hiding points in the rectangular plot is nearly instantaneous. With the polar plot, every action takes 5+ seconds to respond.

Does this sound normal? Does anyone have any suggestions to improve the performance of the polar plot?

I'm running with Solaris 9 on a SUN E3000 server with multiple 496 MHz cpu’s.

QT version:
qt4.4.0
qwt-5.1.1
qwtPolar-0.0.2

Thanks,

Please start the polardemo example and check its replot performance on your box ( f.e move the canvas with the mouse ).
If it is slow too please play with the check boxes at the left and try to identify which options have a significant effect.

Uwe

I tested a bit myself and detected at least one serious performance hog: painting with a clipping region from an ellipse. The penalty for each replot is about 500ms on my box ( Linux/X11 + Qt 4.1.1 ). Surprisingly the effect is much worse when antialiasing is disabled: ~4500ms.

If you don't need clipping ( the values of your curves, markers are inside the ranges of your scales ) you can avoid this problem by removing the line "painter->setClipRegion(..)" in QwtPolarPlot::drawItems.

Uwe

Many thanks Uwe. I work with the original poster. We'll give your suggestions a try and will report back soon...

Uwe - we commented out the clipping section of the code and rebuilt the library. The performance of the Polar plot increased a lot ! It went from taking 5-7 seconds to display to about 1 second.

Many thanks !

Obviously a problem inside Qt. I have already contacted Trolltech support. I will try to introduce a workaround in the next QwtPolar release ( next month ).

Uwe

Comparing the performance of Qt 4.4.1 vs. Qt 4.4.2 with the QwtPolar example:

A) With clipping and antialiasing

4.4.1: ~610 ms
4.4.2: ~340 ms

B) With clipping, no antialiasing

4.4.1: ~2180 ms
4.4.2: ~220 ms

C) No clipping, with antialiasing

4.4.1: ~155 ms
4.4.2: ~150 ms

D) No clipping, no antialiasing

4.4.1: ~15 ms
4.4.2: ~9 ms

Looks like it's worth to upgrade to 4.4.2.

But the fact, that clipping takes longer than antialiasing doesn't sound reasonable to me and needs further investigations.

Uwe

We will give it a try, thanks Uwe!