I have a dell xps13 laptop with a whopping 3200 x 1800 resolution. This causes any text to come up tiny... (so tiny it's almost unworkable on first boot to figure out how to change font dpi settings)

I can change the dpi setting of fonts, which was in system settings as an option, this causes most applications to be readable on my 13 inch screen.

When I work, I connect an external screen (a different one, depending on home or office), the screen is a normal HD resolution. Because my screen is 24 inch (versus 13 inch with huge resolution), it comes up gigantic on my external screen.

I have two requests for kde:

- can the dpi settings be automatically detected so I don't need to change dpi settings + reboot each time I want to work on a big screen
- can I have different dpi settings for each screen in a dual setup? If not, I can basically not use both screens at the same time.

Many many thanks for your efforts in creating a great desktop environment. I can imagine that my request wil become more important with upcoming 4k screens on laptops.

Thanks!

1st off, this has nothing to do with KDE.

X11 doesn't support different resolutions on screens unless you run a zaphod setup (where you cannot move windows between screens - you basically have two independent sessions)
It'd also cause quite some trouble, windows would have to resize when moved between screens and if they're on both, things are really weird

As for not working:
Unless you touch any configs, the resolution should be calculated by the X11 server and from there picked by fontconfig (unless you configured a value in the fonts kcm or anywhere else)
This value should then be accounted except when overridden in xrdb.

checks:

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xdpyinfo | grep resolution
xrdb -query | grep -i xft
grep -i dpi ~/.config/fontconfig/fonts.conf


Yes, it's a mess - X11 is 30 years old

Thanks for clarifying! It really is too bad there is no option to have multiple dpi's on different screen. I guess most people have the higher dpi on their biggest screen, so it's not so much of a contrast...

Here is the output of the commands you asked for:

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~$ xdpyinfo | grep resolution
  resolution:    96x96 dots per inch

(currently working mainly on my HD screen, attached, otherwise I set the font dpi to 144 when the screen is not attached)

$ xrdb -query | grep -i xft
Xft.hinting:    -1
Xft.rgba:       none

$ grep -i dpi ~/.config/fontconfig/fonts.conf
$

The X resolution is nuts (at least if this is on your HD screen) - if that's a 16:10 panel, the resolution should be more like 290x260, for a 16:9 it's 280x280 (so assuming square pixels, it will be 16:9)

Run

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xrandr --dpi 280


Any application started afterwards should pick the proper resolution automagically (since there's no other config)

Depending on what configures your screens (on changes, ie. do they auto-add when plugging them in/out?) the kscreen daemon should probably do that, but if there're two screens and one has 280dpi and the other 96, it's oc. hard to decide what value to pick

This thread has been dead for quite some time but I just came across it looking for multi-dpi support in Linux.

I also used to think it is weird until I bought a laptop with 4k display but connected it to my old 30" screen without 4k.
The DPI difference is enormous. Either, text on the laptop is unreadable, or everything on the large screen is so big that it is impossible to use the monitor efficiently.

Windows has support for multiple "scaling" levels as of Windows 10, and besides it needs some time to get used to windows resizing while you move them across a screen border, it works more or less well.
It would be great to have such a feature in KDE as well. Otherwise, it makes multiple screen with significant dpi difference more or less unusable.

Same problem.
It seems

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xrandr --output eDP1 --auto --output DP1 --auto --panning 3840x2160+3200+0 --scale 2x2 --right-of eDP1

partially to solve this problem.
However, plasma 5 seems failed to scale properly and the fcitx location are not correct.

Why is the dpi setting part of the fonts configuration? Since the dpi is a characteristic of the screen(s), it should be part of the display settings instead.

Instead of setting different magnification values for different displays (as Sebastian Kügler seems to plan for Wayland), it would be helpful to be able to set the correct dpi for each display. This should not only affect the fonts, but everything that gets displayed would then have a suitable size.

Same here.
I found at least two related open bugs in KDE bug tracker.
* https://bugs.kde.org/show_bug.cgi?id=222428
* https://bugs.kde.org/show_bug.cgi?id=374687

Until this implemented seems the only possible solution as @luebking mentioned is to use ZaphodHeads option and run separate X instances for different screens. But then the problem is that kwin doesn't support Multi-Screen setup and everyone is waiting for that feature to be implemented in Wayland (https://community.kde.org/Plasma/5.9_Errata#Wayland).