Incorrect UI scale on high-resolution desktop

What Qt version do you have installed?

Hey,
this is weird. Would you be able to open a terminal and run the following command:

xargs -n 1 -0 < /proc/`pidof unity8`/environ | ag GRID_UNIT

(it prints all the environment variables that the unity8 process has, and just returns the GRID_UNIT_PX one)
Thanks
-G

Contents of $HOME/.cache/upstart/unity8.log might be handy too

Oops, safer to use grep:

xargs -n 1 -0 < /proc/`pidof unity8`/environ | grep GRID_UNIT

Could you also share hte output of

xargs -n 1 -0 < /proc/`pidof unity8`/enviro | grep QT_

in case there are Qt dynamic scaling env vars set in your environment too. (e.g. QT_DEVICE_PIXEL_RATIO, QT_AUTO_SCREEN_SCALE_FACTOR, QT_SCALE_FACTOR, QT_SCREEN_SCALE_FACTORS)

Please also attach these logs (the second one requires sudo to access):
   ~/.cache/upstart/unity8.log*
   /var/log/lightdm/unity-system-compositor.log

We need them to check that Mir is getting sane physical dimensions for your screen and not reporting crazy information like "this is a 4-inch tablet".

I have Qt 5.6.1 installed (and ppa:convergent-apps/testing).

xargs -n 1 -0 < /proc/`pidof unity8`/environ | grep GRID_UNIT
GRID_UNIT_PX=20

xargs -n 1 -0 < /proc/`pidof unity8`/environ | grep QT_
QT_DEVICE_PIXEL_RATIO=2
QT_IM_MODULE=ibus
QT_QPA_PLATFORM=ubuntumirclient

Thanks. Not a Mir bug. Mir is reporting correct display information all the way to unity8.log at least:

[2016-11-21 04:31:38.606047] mirserver: Initial display configuration:
[2016-11-21 04:31:38.606590] mirserver: 0.37: eDP 13,2" 290x170mm
[2016-11-21 04:31:38.606600] mirserver: Current mode 3200x1800 59,99Hz
[2016-11-21 04:31:38.606619] mirserver: Preferred mode 3200x1800 59,99Hz
[2016-11-21 04:31:38.606625] mirserver: Logical position +0+0

Status changed to 'Confirmed' because the bug affects multiple users.

I discovered: Initially, I had set environment variables in .bashrc for manually triggering the UI scaling of Qt5, Java, etc. During debugging of this issue (as instructed above) I **commented them out** and after loout/login, the incorrect UI scale persisted.

Now I noticed that QT_DEVICE_PIXEL_RATIO=2 and QT_AUTO_SCREEN_SCALE_FACTOR=2 were still set automatically during the boot/login process. Instead of commenting them out, I then set them to 1 in ~/.bashrc but they still were overriden.
QT_DEVICE_PIXEL_RATIO=1
QT_AUTO_SCREEN_SCALE_FACTOR=1
GRID_UNIT_PX=20

Then I set them in ~/.profile and they were not overriden. Moreover, the unity8 session (8.14+16.10.20160922-0ubuntu2) renders in the correct scale and digikam (5.4.0, Qt 5.7.0) as well. It seems like a Qt API break so that not only these variables are not needed anymore for new programs, but their presence now has the inverse effect.

I'm not sure if this is the right bug to mention it in, but I find the opposite problem on 3200x1800 displays more recently... Unity8 is unscaled and tiny.

Related: bug #1510968