Current state of DPI settings under X

[Vladimir Kudrya]

Imagine a situation: a laptop that is used by itself, or docked at place 
A, or docked at place B, frequently moving around.

In each case there are different display(s) and each configuration has a 
comfortable DPI setting (not necessarily matched with physical DPI).

I apply xrandr configuration with needed DPI, some set of programs 
conform to this. I publish DPI to xrdb, another set of apps is affected, 
finally I configure fontconfig to affect the rest.

I successfully automated the whole process recently 
(https://github.com/Vladimir-csp/rerandr3), it does the job more or 
less. But I feel the strong urge to choose 2 sets of apps out of these 
3, declare their behavior as buggy and submit some bug reports, no 
matter how futile they may be.


2017-07-26 09:52, Pekka Paalanen пишет:
> 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