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I have a touchscreen Dell XPS 9550 and an external 27" Dell screen.

How can I make sure the external monitor doesn't scale everything up as it currently is by 2x?

The XPS is HiDPI whilst the screen is FHD. Output from xrandr -q reveals the following:

eDP1 connected primary 3840x2160+2560+0 (normal left inverted right x axis y axis) 350mm x 190mm ... HDMI1 connected 2560x1440+0+214 (normal left inverted right x axis y axis) 600mm x 340mm

I initially followed the instructions on https://askubuntu.com/questions/393400/is-it-possible-to-have-two-different-dpi-configurations-for-two-different-screen however Pantheon keeps resetting itself, and I'm unable to set the desired dimensions ( adjusted the calculations based upon the output above.

I'm trying to set the XPS to the right of the monitor.

2

This largely works for me:

xrandr --output eDP1 --scale 1x1 --pos 3840x0 ; xrandr --output HDMI1 --scale 2x2 --mode 1920x1080 --fb 7680x2160 --pos 0x0

Only downside is the topbar seems to get in the way on my laptop screen. Obviously you'll need to adjust if you don't have same resolution as I do. Afraid there is no GUI solution yet. I just popped this command into a file so I can quickly switch.

UPDATE Pantheon keeps crashing out on me now, when changing res!

UPDATE 2

Seems to be more successful when you plug in monitor after fully loading up and logging in.

  • Trying to run this on my setup (very similar to the one from Demwunz) and I am getting 'xrandr: cannot find mode 1920x1080' - my screen does have a res of 1920x1080 so not sure why that happens. Any ideas? – Markus Aug 3 '17 at 8:52
1

Unfortunately, the current Linux desktop supports only one scale factor for the entire desktop, so either you scale down your HiDPI monitor, or you get double size on your external.

I have a very similar setup and the simple work-around I use now is to set the laptop display to 1280 x 720 in System Settings > Displays.

For more info check out these blog posts:

https://medium.com/elementaryos/what-is-hidpi-and-why-does-it-matter-b024eabea20d
https://medium.com/elementaryos/top-3-misconceptions-about-hidpi-f5ef493d7bf8

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