Bug#986821: freecad: Garbled menu makes freecad unusable

[jaroslav at thinline.cz]

Hello,

I found this bug report trying to troubleshoot the same issue - for me, 
FreeCAD UI is completely garbled, all menu items, all icons, all other 
UI elements are larger than the space allocated for them, resulting in 
"create new empty document" icon being cut after 90% of its length, 
"open document" after 60% etc. making 4th icon barely visible and rest 
completely invisible. Essentially, the UI element graphics is being 
drawn into different positions compared to where those elements are 
actually placed in the UI.

Since the symptoms were the same for me - no issue for clean slate 
system user - I tried the strace approach. But even after filtering 
things that are the same out, I was unsuccessful. However, using the 
QT_SCALE_FACTOR=1 QT_AUTO_SCREEN_SCALE_FACTOR=0 variables made the thing 
work and eventually I figured out the problem is caused by my monitor 
DPI settings (xfce4-settings-manager -> Appearance -> Fonts -> Custom 
DPI settings)

I have this value set to 80. Tried changing it to "default" 96 and that 
fixed the issue for me.

I would say this is a FreeCAD bug though, according to my x.org log, my 
monitor does have 80DPI:

(++) RADEON(0): DPI set to (80, 80)

(The monitor has 59.6x33.6cm screen dimensions with 1920x1080 
resolution, which also amounts to 80DPI.)

As far as I know (was told once by some develeper), developers tend to 
assume that every monitor has 96DPI and write programs accordingly. 
Might be the case here.