Elementary OS 0.4 “Loki” does support HDPi screens by default, but it is limited to double the scaling (1x, 2x, …). xrandr gives the ability to scale down the screen afterwards. This allows scaling support as seen in Windows or MacOS (100%, 125%, 150%, …).

To get started configure Elementary OS to scale the screen up 2x. This can be done by executing the following in a terminal.

gsettings set org.gnome.desktop.interface scaling-factor 2

Now you can use xrandr to scale down the screen, in a multi screen environment this has to be done for each monitor. It is also important to configure the position of the second screen correctly, otherwise there will be an overlap.

List all connected screens:

$ xrandr
DP-0 connected primary 3840x2160+0+0 (normal left inverted right x axis...
   3840x2160     60.00*+
   ...
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected 3840x2160+3840+0 (normal left inverted right x axis y...
   3840x2160     60.00*+
   ...
DP-3 disconnected (normal left inverted right x axis y axis)

Now scale the screen as you would like (in this example 150%) Using “scale” will use a greater resolution for rendering and afterwards scale everything down to the native screen resolution:

$ xrandr --output DP-0 --scale 1.5x1.5
$ xrandr --output DP-2 --pos 5760x0 --scale 1.5x1.5

The --pos ensured that the screens don’t overlap. Use Use Screen-1_Width * Scale-Factor for the first value. In this example 3840*1.5=5760.

xrandr shows now the downscaled configuration:

$ xrandr
DP-0 connected primary 5760x3240+0+0 (normal left inverted right x axis...
   3840x2160     60.00*+
   ...
DP-1 disconnected (normal left inverted right x axis y axis)
DP-2 connected 5760x3240+3840+0 (normal left inverted right x axis y...
   3840x2160     60.00*+
   ...
DP-3 disconnected (normal left inverted right x axis y axis)