System: Slackware Linux (version 15.0)
CPUs: Intel(R) Core(TM) i5-3230M CPU @2.60GHz
GPU: Mesa DRI Intel(R) HD Graphics 4000
Xephyr supports extensions like composite, damage and randr.
bash-5.1$ cat ~/.local/share/applications/Xephyr.desktop
[Desktop Entry]
Type=Application
Name=Xephyr
Comment=Nested X Server
Exec=/home/eric/bin/fluxbox.sh
Icon=xorg
Terminal=false
Categories=System;
bash-5.1$ cat ~/bin/fluxbox.sh
#!/bin/sh
Xephyr -screen 1024x680 -terminate :1 2>/dev/null &
sleep 0.5
DISPLAY=:1 fluxbox
bash-5.1$
See the earlier Post on Xnest.
