[konsole] [Bug 373232] Horizontal lines with fractional HiDPI scaling

[Lucas Pires Camargo]

https://bugs.kde.org/show_bug.cgi?id=373232

--- Comment #184 from Lucas Pires Camargo <lucaspcamargo at gmail.com> ---
I'm not quite sure. For painting the background, it seems like the clip region
is always null or the entire area inside the borders. Figured that out by
printing out the QRegion via qDebug().

So there seems to be a rounding problem also when rendering rectangles,
unrelated to the clip region.  My patch fixes it for me. And after adjusting it
just now, it's "much less wrong" by expanding the rectangle to be painted as
the background like so:

QRect expandedRect{ rect.x(), rect.y(), rect.width(), rect.height()+1 };

So, only 1px of added height is needed to get rid of the spurious horizontal
lines. If I figured out a way to calculate when this is going to happen, it'd
be pixel-perfect, I guess.

I still get spurious artifacts when selecting/deselecting text, but not
scrolling. I can't test the Qt 5.15 fix right now with my current setup. After
playing around with it a bit, I figured the only solution to this whole shebang
if figuring out how to adjust the coordinates on bounding rects of the lines in
a way that after scaling, they align perfectly with the physical pixel grid,
not overlapping not leaving gaps. I'm trying to figure that out, but I'm not at
all familiar with Konsole's codebase, so this might take a while.

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