in dom0, qt doesn't respect scaling configuration set by xfce

[xyhhx]

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Qubes OS release

R4.2.2

Brief summary

when using qubes os on a computer with a hidpi monitor, and configure xfce in dom0 to scale accordingly (2x), qt is unaffected. this affects qubes manager (among others) resulting in it still being tiny even when the rest of the desktop environment is properly scaled.

a workaround is documented in the arch wiki¹: a user can set QT_SCALE_FACTOR² in /etc/environment to resolve this; but perhaps dom0 could do this by default if a hidpi screen is detected

Steps to reproduce

1. buy a computer with a hidpi monitor
2. install qubes
3. configure scaling in xfce in dom0
4. launch a qt application (for example qubes manager)
5. behold, it is tiny

Expected behavior

qt applications should respect scaling settings set by the desktop environment (xfce appearance settings)

Actual behavior

qt does not respect the desktop environment's scaling configuration, and requires setting environment variables to work properly

Footnotes

1. https://wiki.archlinux.org/title/HiDPI#Qt_5 ↩

2. QT_SCREEN_SCALE_FACTORS might be a better workaround if a user has numerous monitors ↩