Ubuntu 15.04 HiDPi to Full HD external screen

Question

I just got a Dell XPS 13 2015 and I installed Ubuntu 15.04. Everything is working fine with the exception of using an external display.

The resolution on my laptop is 3200x1800, my external screen is 1920x1080. When I connect my laptop to my external display everything is twice the size.

I read this article https://wiki.archlinux.org/index.php/HiDPI#External_displays but it didn't help me to find a solution.

Answer 1

One possible solution is to switch your laptop resolution to 1920x1080 (I know.. it's not native). Then make sure you set all HiDPI settings back to use 1920x1080. Now if you connect your external display at 1920x1080 it will show everything at "normal" size.

Depending on how advanced your windows manager is you can also do it the other way around by upscaling external monitor, like this: https://askubuntu.com/questions/393400/is-it-possible-to-have-two-different-dpi-configurations-for-two-different-screen

assuming you run Gnome by default for Ubuntu 15.04.

Answer 2

The best solution I've found here is to effectively scale a 4k resolution onto the HD screen. Note that the positioning in this script assumes your external display is above your laptop:

xrandr --output DP-1 --scale 2x2 --mode 1920x1080 --fb 4160x4320 --pos 0x0
xrandr --output eDP-1 --scale 1x1 --pos 320x2160

Since I use my laptop on the go between the office and home I created a little script for this so you can create a keyboard shortcut to toggle the resolutions. It also supports 1920x1200:

https://github.com/oligray/ubuntu/blob/master/togglemonitors.sh