Span an X window across all screens

span.sh

#!/bin/bash

# USAGE
# span.sh command [arguments]
#
# DESCRIPTION
# Executes command, waits for a new window to appear, then stretches that window across the entire screen area.
#
# REQUIREMENTS
# wmctrl - for finding and controlling X windows
# xrandr - for detecting the size of the screens
# bc - for timing how long it takes a new window to appear
#
# EXAMPLES
# span.sh chromium-browser --kiosk http://lorempixel.com/1280/720
# span.sh chromium-browser --start-fullscreen http://lorempixel.com/1280/720

# Check to make sure we have a command to execute
if [ $# -lt 1 ]; then
    echo "Usage: $0 command [arguments]"
    echo "Executes command, waits for a new window to appear, then stretches that window across the entire screen area."
    exit 1
fi

# Allocate some temporary files
WF1=`tempfile`
WF2=`tempfile`
WF3=`tempfile`

# Obtain initial list of windows, and execute command
wmctrl -l >$WF1
echo "$@"
"$@" &

# Wait for a new window (time out after 10 seconds)
echo "Waiting for a new window..."
i=0
while [ $i -le 40 ]
do
    wmctrl -l >$WF2
    grep -Fxvf "$WF1" "$WF2" >$WF3
    if [ $? -eq 0 ]; then break; fi
    sleep 0.25
    i=$(( $i + 1 ))
done
rm "$WF1"
rm "$WF2"
if [ $i -gt 40 ]; then
    rm "$WF3"
    echo "New window took longer than 10 seconds, aborting."
    exit 2
fi

# Extract the Window ID of the new window
WID=`cut -d' ' -f 1 "$WF3"`
TIME=$(bc <<<"scale=2; $i / 4")
echo "Found new window ID $WID after $TIME seconds"
rm "$WF3"

# Obtain dimensions of the screen
echo "Detecting screen dimensions..."
SIZE=`xrandr | head -1 | grep -Eo 'current [0-9]+ x [0-9]+'`
EC=$?
if [ $EC -ne 0 ]; then
    echo "Problem detecting screen dimensions (exit code $EC)"
    exit 3
fi
WIDTH=`echo $SIZE | cut -d' ' -f 2 -`
HEIGHT=`echo $SIZE | cut -d' ' -f 4 -`
echo "Detected screen dimensions ${WIDTH}x${HEIGHT}"

# Reposition the window
echo "Repositioning window..."
wmctrl -ir $WID -b remove,fullscreen
wmctrl -ir $WID -b remove,maximized_vert,maximized_horz
wmctrl -ir $WID -e 0,0,0,$WIDTH,$HEIGHT

My "research" has let me to think it might be a problem that the when running the script in Autostart there cannot run two foreground processes at the same time. Do you know if it is possible to run the script another way after the Desktop has loaded?

I'm not sure why, but I ended up not using this script when trying to accomplish the window spanning. Instead, I used an .xinitrc with the following content:

#!/usr/bin/env sh
xrandr --output HDMI-1 --rotate left
xrandr --output HDMI-2 --rotate left --right-of HDMI-1

xset -dpms
xset s off
xset s noblank

unclutter &

chromium-browser http://localhost:3000 \
  --window-size=1600,1280 \
  --window-position=0,0 \
  --start-fullscreen \
  --kiosk \
  --incognito \
  --noerrdialogs \
  --disable-translate \
  --no-first-run \
  --fast \
  --fast-start \
  --disable-infobars \
  --disable-features=TranslateUI \
  --disk-cache-dir=/dev/null \
  --overscroll-history-navigation=0 \
  --disable-pinch

and then including startx in my .bash_profile. You'll probably need to install unclutter.