Current state of DPI settings under X

[Allan Sandfeld Jensen]

On Dienstag, 25. Juli 2017 20:15:31 CEST Vladimir Kudrya wrote:
> Hi all!
> 
> I would like to know the current 'proper' way of setting DPI in X (if
> there is any).
> I see conflicting information on the topic, and different applications
> seem to have different source of this setting. I currently counted 3 of
> them:
>    - fontconfig
>    - xrdb
>    - randr
> 
> Different versions of gtk2 seem to either demand or ignore dpi setting
> in xrdb.
> And there is also this recent change that gives xdpyinfo the ability to
> state different DPI for different outputs simultaneously:
> https://lists.x.org/archives/xorg-devel/2017-April/053430.html
> 
> Is there any DE- and toolkit-agnostic approach for letting applications
> know the proper DPI and/or notifying them that DPI has changed?

Yes, the official X11 DPI value you call xrandr in your list. And fixing 
toolkits that ignore, or even worse; override the value. The other values can 
be set or calculated based on the physical data, but only X11 has the physical 
data of the screen.

'Allan