partial solution for the initial problem. Remember my goal is to scale a full hd screen to make it display in a hd one (make 1366x768 look as if it was 1920x1080). This works with intel drivers (not any amd, no idea for nvidia). Two monitors setup, the external is full hd. This works in kde/plasma leap 15.1 and xfce leap 15.3, I try to make it work in kde/plasma 15.3 Thanks to felix, I discovered than the guilty was kscreen2. De-activating it was a step. Then start my script (see below the last version). But this didn't work completely, I got two monitors with identical content and the laptop one was blurry. BUT! arandr fixed the thing. With arandr I could set the display and use it. the good thing is that arandr can save the commands in a bash script, I expect to be able to launch this automatically, but it's not yet the case :-( my last script dunno why it don't works!: xrandr --newmode "1920x1080_60.00" 173.00 1920 2048 2248 2576 1080 1083 1088 1120 -hsync +vsync xrandr --addmode VIRTUAL1 1920x1080_60.00 xrandr --fb 1920x1080 --dpi 96 --output eDP1 --primary --mode 1366x768 --pos 0x0 --rotate normal --scale-from 1920x1080 --same-as VIRTUAL1 --output DP1 --mode 1920x1080 --pos 1920x0 --rotate normal --output HDMI1 --off --output HDMI2 --off --output VIRTUAL2 --off arandr script: #!/bin/sh xrandr --output eDP1 --primary --mode 1366x768 --pos 0x0 --rotate normal --output DP1 --mode 1920x1080 --pos 1920x0 --rotate normal --output HDMI1 --off --output HDMI2 --off --output VIRTUAL1 --off --output VIRTUAL2 --off thanks jdd -- http://dodin.org