[Interest] High DPI support in QT (Windows)

Pavlo Dyachenko upavlo at gmail.com
Fri Sep 18 10:38:38 CEST 2015

Hi QT team, I posted a question on the forum about high DPI support but
then was recommended this mailing list instead:
According to documentation here http://doc.qt.io/qt-5/highdpi.html QT 5.4+
introduces high DPI support. However, either I’m missing something
fundamental or the current support is still in very early stages. I’m
writing a brand new application so I have a chance to do it right from the
ground up. I understand that I would have to use layouts instead of fixed
positioning etc, but there always going to be cases in which I would have
to specify, for example a minimum/maximum size of a control. I can specify
them in the editor, but these are device pixels. So if I change my Windows
settings to use 150% DPI then min/max values in the editor would be too
small. Of course I can obtain that ratio and adjust all the required values
in code, but then what kind of high DPI support does QT give for me if I
have to do everything by hand? I mean how is it different to pre QT 5.4?

Then an interesting one is QT_DEVICE_PIXEL_RATIO environment variable. It
does exactly what I need, it multiplies all pixels set in editor by a
factor. But why is it an environment variable and not a per application
setting? Why does it only support integer values of 2, 3 etc, since we know
that Windows has settings like 125, 150% etc. and why couldn’t it
automatically read the Windows setting and set itself to that value?

Thanks in advance.
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