On Friday 26 April 2024 21:52:48 CEST Christian Ehrlicher via Development
wrote:
> Hello,
>
> I'm currently trying to investigate a painting problem within the
> windowsvista / common style:
>
> QImage img(7, 7, QImage::Format_ARGB32_Premultiplied);
> QPolygon poly{ QPoint(1, 1), {5, 1}, {3, 5} };
> QPainter p(&img);
> p.setPen(Qt::NoPen);
> p.setBrush(QColor(Qt::black));
> p.drawPolygon(poly);
> p.setPen(QColor(0, 255, 0, 128));
> p.drawPoints(poly.data(), poly.size());
> p.end();
> img.save("output.png");
>
> This code should draw a small down arrow (e.g. for a QPushButton with a
> QMenu attached) and should look similar to this:
>
> 0123456
> 0
> 1 XXXXX
> 2 XXX
> 3 XXX
> 4 X
> 5 X
> 6
>
> But the outcome is this:
>
> 0123456
> 0
> 1 XXXX
> 2 XX
> 3 XX
> 4
> 5
> 6
>
> Setting a non-cosmetic pen at least result in painting of all three
> corners but gives a non-symmetric triangle:
>
> 0123456
> 0
> 1 XXXXX
> 2 XXXX
> 3 XXX
> 4 XX
> 5 X
> 6
>
I think the problem with the cosmetic pen is partly the need to be symmetric.
Years ago I tried cleaning up the cosmetic pen, but had to revert it because
it violated rules about symmetry.
https://codereview.qt-project.org/c/qt/qtbase/+/200383
Though perhaps the non-cosmetic painting could have the rounding adjusted so
it would look better for your example. Otherwise try offsetting the triangle
by 0.5
Best regards
Allan
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