Setting 100% zoom shows as 35.8% in reality

[Rudolf_Dovicin (Rudolf Dovičín)]

Hello.

When I open new diagram in Dia Diagram Editor (version 0.97+git, compiled Feb 14 2020), default zoom is 100%.
But it shows 96 cm on full width ruler of my notebook screen, which is exactly 34.4 cm wide.
So, it shows alleged 100% zoom as real 35.8% zoom.

I use Xfce 4.16 on Debian GNU/Linux 11 with custom 142 DPI in appearance setting (screen has width 1920 pixels).
My X.Org X Server 1.20.11 correctly detects size of screen in millimetres and pixels, but it sets DPI to 96 for me for unknown reason (as I can read in my /var/log/Xorg.0.log).
Even if Dia would read this Xorg DPI resolution, 35.8 % ratio cannot be calculated in my opinion (96DPI / 142DPI = 67.6%)

(Another applications like Libre Office Draw show paper size A4 width in 100% zoom as real 21 cm.)

Please, what can be wrong?

[zbrown (Zander Brown)]

Dia is entirely DPI unaware (which clearly isn’t ideal), and for $REASONS, calculates sizes based on 72 DPI (or 28.346457 pixels per centimetre)

Of course how those ‘application pixels’ relate to your screen’s actual pixels is another matter

@Rudolf_Dovicin

Please, what can be wrong?

Well, you’ve got a lovely mix of X11, Gtk2, and Dia being weird. Sadly most likely nothing is wrong with your setup, rather just software showing it’s age…

(I do hope this will change in future though, certainly no reason to believe it can’t be resolved)