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Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors?

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On 2026-01-22, John-Paul Stewart <jpstewart@personalprojects.net> wrote:
> On 2026-01-22 5:09 a.m., Nuno Silva wrote:
>> On 2026-01-21, Robert Riches wrote:
>> 
>>> On 2025-12-26, John-Paul Stewart <jpstewart@personalprojects.net> wrote:
>>>> On 2025-12-24 11:15 p.m., Robert Riches wrote:
>>>>>
>>>>> Does anyone have favorite tutorials or other helps for dealing
>>>>> with a high-DPI transition?
>>>>>
>>>>> I'm Running Devuan (currently Daedalus, hopefully soon Excalibur)
>>>>> using plain X and fvwm2, no DE as such with 1920x1200 monitors.
>>>>> Just purchased a round of 4k monitors, so I'll be needing to
>>>>> adjust xterm fonts, web browser issues, other GUI application
>>>>> issues, etc.
>>>>
>>>> It's been a couple years since made a similar switch.  But as far as I
>>>> recall, there's not much to do other than configuring X.  I had to
>>>> manually specify the monitors' physical size (in millimetres) in my
>>>> xorg.conf so that X could calculate the correct DPI.  Then everything
>>>> that's measured in points just kind of fell into place.  (E.g., there
>>>> was nothing to be done for LibreOffice, etc.)
>>>>
>>>> You'll need to switch your window manager to a high-DPI theme (easy with
>>>> my choice, xfwm4) since that's all laid out in pixels and you'll have
>>>> tiny icons and title bars if you don't change.
>>>>
>>>> There were very few apps that required any tweaking once X and the
>>>> window manager were correctly configured.  The venerable 'gv' is the
>>>> only one I can think of that required its own DPI setting (in
>>>> ~/.Xresources) rather than using X's own.
>>>>
>>>>> For web browser issues, I anticipate a lot of fun with websites
>>>>> and web apps that use (n)px directives for some of their margins
>>>>> and spacing.  If the browser interprets those at face value,
>>>>> mixed with other directives in units of text elements and such,
>>>>> things could end up looking somewhat different from how the
>>>>> developers intended.
>>>> That's actually not an issue.  HTML/CSS "px" are NOT device pixels but
>>>> units of 1/96 inches.[1]  In other words, HTML/CSS "px" are standardized
>>>> at 96 DPI regardless of actual screen resolution.  So if something
>>>> specifies 24px it actually means 1/4 inch.  On my 4K displays that ends
>>>> up being more like 40 device pixels.  So websites will still work more
>>>> or less as expected.
>>>>
>>>> [1] https://www.w3schools.com/css/css_units.asp
>>>
>>> For anyone finding this thread in the future, there's another
>>> trick for Firefox.  In about:config, set
>>>
>>>         layout.css.devPixelsPerPx
>>>
>>> to a value greater than 1.  For a 27" 4K monitor, the monitor's
>>> device DPI is 163, and a value of 1.6 makes the Firefox UI
>>> elements (menu bar, dialogs, etc.) a reasonable size.  YMMV on
>>> the value for your situation.
>> 
>> IIRC there was a value that would make it get the resolution from the
>> platform. 
> Yes.  On my system layout.css.devPixelsPerPx is set to -1.0 which means
> Firefox will get the value from the system and everything works as
> expected. (I'm also using a 27" 4K monitor at 163 DPI like the previous
> poster.)

-1.0 is what mine had layout.css.devPixelsPerPx set to, as well.
 It was not getting the DPI/resolution from the system.  xdpyinfo
 reports a resolution of 163dpi.

Setting layout.css.devPixelsPerPx to 1.7 shows web page content
at (as far as I could see) the same as zooming to 170%.  Setting
the variable made the menubar, dialogs, etc. reasonably sized,
too.

-- 
Robert Riches
spamtrap42@jacob21819.net
(Yes, that is one of my email addresses.)

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[On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-25 04:15 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? The Natural Philosopher <tnp@invalid.invalid> - 2025-12-25 11:45 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-26 02:03 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2025-12-25 21:38 -0500
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-26 03:55 +0000
      Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2025-12-26 11:10 -0500
        Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2025-12-31 05:00 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? c186282 <c186282@nnada.net> - 2025-12-26 00:03 -0500
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-15 05:09 +0000
      Xorg drivers overriding display resolution (was: Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors?) Nuno Silva <nunojsilva@invalid.invalid> - 2026-01-15 11:20 +0000
    Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-21 22:54 +0000
      Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Nuno Silva <nunojsilva@invalid.invalid> - 2026-01-22 10:09 +0000
        Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? John-Paul Stewart <jpstewart@personalprojects.net> - 2026-01-22 09:34 -0500
          Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? Robert Riches <spamtrap42@jacob21819.net> - 2026-01-23 04:23 +0000
  Re: [On-Topic] any favorite tutorials or other helps for high-DPI monitors? c186282 <c186282@nnada.net> - 2025-12-26 00:00 -0500

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