[neon] [Bug 362767] High DPI is messed up after Qt 5.6 update

[Greg Varsanyi via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=362767

--- Comment #8 from Greg Varsanyi <gvarsanyi at gmail.com> ---
(In reply to David Edmundson from comment #5)
> For Case #1:
>  - qt now scales up font DPI for some reason, you can counter that by
> explicitly also setting
> QT_FONT_DPI to be half/double (not sure which way round it is) 
> 
> For Case #3
> 
> Since Plasma 5.5 we do have code to disable internal high DPI managing on
> Qt5.6
> 
> However, it requires kwin/plasma also be *compiled* with Qt5.6
> 
> #if (QT_VERSION >= QT_VERSION_CHECK(5, 6, 0))
>     QCoreApplication::setAttribute(Qt::AA_DisableHighDpiScaling);
> #endif

playing with QT_FONT_DPI gets me the closest.
a combination of QT_FONT_DPI=96 and QT_DEVICE_PIXEL_RATIO=2 (and not
setting/unsetting any new Qt 5.6 env vars) gives me consistent look and feel
across the *apps*, but not plasmashell and kwin - they go half sized.
it would seem that plasmashell and kwin read the font dpi value and apply that
literally as pixels.
that can also be mitigated by starting these two (and only these two) with
QT_FONT_DPI=192.

So, using a deprecated and a falsified env var - with some exception handling -
mostly gets us there.

--

i wonder why did you guys decided to disable the native scaling.

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