[Interest] Changes in Qt 5.6 on Windows HiDPI

[Adam Light]

On Fri, Nov 13, 2015 at 1:00 AM, Julius Bullinger <
Julius.Bullinger at asctec.de> wrote:

> Hello Adam,
>
>
>
> do you use the new environment variables QT_AUTO_SCREEN_SCALE_FACTOR=1 ?
>
> Additionally, make sure to unset the deprecated  QT_DEVICE_PIXEL_RATIO.
>
>
>
> You can do this in your shell for testing, and programmatically with
> qputenv [1].
>
>
>
We are not setting any environment variables whatsoever.

I have read through the documentation at
https://doc-snapshots.qt.io/qt5-5.6/highdpi.html several times now and I'm
having a hard time figuring out what our application needs to do.

I did try setting  QT_AUTO_SCREEN_SCALE_FACTOR=1, both with and without
calling QApplication::setAttribute(Qt::AA_EnableHighDpiScaling) before the
QApplication is constructed, and I get the same results: that is, with the
Windows "set a custom scaling level" setting set to 200%,
QApplication::desktop()->logicalDpiX() returns 96, whereas with Qt 5.5 it
returned 192.

We can live with either value that's returned, I'm just trying to figure
out if this particular change in behavior with Qt 5.6 is intentional or not.

The second problem is that when I set the system "set a custom scaling
level" to 250%, which is the factory value for the 15" Dell Inspiron laptop
we purchased, QApplication::desktop()->devicePixelRatioF() returns 3, which
is wrong--it should be 2.5. I'm happy to file a bug report about this, but
I'm hoping to make sure that I understand what the intended behavior is
before I call this a bug.

Thanks
Adam
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