[Interest] differences in drawing round(ed)/elliptical objects in Qt5 w.r.t. Qt4?

René J.V. Bertin rjvbertin at gmail.com
Thu Dec 31 12:28:44 CET 2015


Hello,

I'm seeing differences in the appearance of round/elliptical and rounded objects in Qt4 code ported to Qt5, differences that suggest that either a rather crude polygon approximation is being used, or that some part of the drawing procedure doesn't use anti-aliasing properly.
This is code from a Qt/KDE theme, not exactly a minimal test case, which doesn't make it easy to figure out what exactly is happening. I'm hoping someone here has seen similar glitches before and can give some suggestions what I ought to look for.

Examples of the correct appearance:
https://bugsfiles.kde.org/attachment.cgi?id=96376
https://bugs.kde.org/attachment.cgi?id=96377

Same elements drawn under Qt5 (it doesn't matter whether any KDE code is involved or not)
https://bugs.kde.org/attachment.cgi?id=96378
https://bugs.kde.org/attachment.cgi?id=96379

The code has a large number of AA renderhint calls; the Qt5 snapshots were taken with AA turned on by all those calls. Turning it off in certain places almost makes the result look better (as in "AA is not used here" rather than "that looks weird").

Apologies if I asked about this before; I don't think I ever got an answer.

(cf. also https://bugs.kde.org/show_bug.cgi?id=357365)

Thanks!
René



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