Current state of DPI settings under X

[Pekka Paalanen]

On Tue, 25 Jul 2017 21:15:31 +0300
Vladimir Kudrya <vladimir-csp at yandex.ru> 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?

Hi,

rather than asking "how to set the DPI", why do you want to set the
DPI, what do you hope to accomplish?

Are you looking for making fonts physically the same size on different
monitors?

Are you trying to cope with HiDPI monitors?

Are you trying to make physical measurement units in applications
correspond to real physical dimensions on the screen?

Even these are fairly low-level questions and would need an explanation
on what you are really trying to make to work. Some goals are false to
begin with, some are reasonable but technically hard, and some have
existing solutions depending on software.

In general, DPI is a mess, and very often the actual DPI number is
not even what one should be concerned with.


Thanks,
pq
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