This is a reimplementation of hybrid-windump with the opposite use-case: doing all rendering using the integrated intel card and using the additional card just to get more outputs (e.g. a triple-head with ThinkPad T420). As such, it uses the DAMAGE extension to avoid unnecessary redraws and the RECORD extension to capture mouse movements, which are translated to mouse movements on the destination X server.
For this to work correctly, an additional virtual Xinerama screen must be available. To get one, see my virtual CRTC for intel patch.
This is not the original version, but a patched version designed so that you can run more one copy of screenclone on the same screen. I've added the ability to specify the x_offset (-t) and the y_offset (-u) where the screen will copied to. I personally use this with a Thinkpad W530 when docked to the Mini dock III plus. The display ports on the dock are wired directly to the nvidia chipset so it's not available to the intel chip I use while undocked.
By using a combination of the virtual crtc patch and screenclone, I can create a dual screen display. Here is the general script I use:
#!/bin/bash
#change values below to your defaults
x=1920
y=1080
if [ -n "$1" ]
then
x=$1
fi
if [ -n "$2" ]
then
y=$2
fi
#generate a modeline from x/y
modeline=`cvt $x $y | sed "1d" | sed 's/Modeline //'`
mode=`echo $modeline | sed 's/ .*//'`
#create the mode and ignore xrandr error if the mode is already there
xrandr --newmode $modeline &> /dev/null 2>&1
#add the mode to the other display
xrandr --addmode VIRTUAL1 $mode
#activate external monitor and set options for it
xrandr --output LVDS1 --auto --output VIRTUAL1 --mode $mode --right-of LVDS1
#run screenclone in optirun. this way the NVIDIA card will automatically start and shut down. kill with ctrl+c
echo $mode
optirun screenclone -s $DISPLAY -d :8 -x 0 &
optirun screenclone -s $DISPLAY -d :8 -x 1 -t 1920
#deactivate monitor after screenclone is killed (kill this script with ctrl+C)
pkill optirun
xrandr --output VIRTUAL1 --off