"Multiseat" gaming with multi-pointer X

Question

Hello Arch gaming community,
recently I've discovered a decent way to play multiplayer games in multiseat (or pseudo split-screen) manner. It really works - I use it to play Myth II: Soulblighter (on Wine) with my brother
Short explanation:
In recent versions of Xorg (>= 1.7), there's a nice feature - it lets you plug another mouse and make it control a second pointer on the screen. Plug another keyboard, assign it to this pointer, and you can independently work with two windows at a time (each pointer getting it's own focus). Now, if you connect a second physical display and configure it to be a separate X screen belonging to the same X server, you can send your second pointer to that screen, virtually allowing both sets to be used independently. Now, run some game on first screen, then another instance on another, and you can play it multiplayer with your friend
What makes this approach better than a "true" multiseat:
Configuring a proper multiseat system (where each "seat" get's it's own login screen) is not easy, to start with. Often it won't let you use hardware acceleration on both displays unless they're connected to two separate video cards. Mutli-pointer approach lets you use both screens with hardware acceleration with just one dual-head graphics card (like most laptops have). Besides, it's much less painful to set up.
The downsides:
The multi-pointer feature of Xorg is still fairly new, and is not supported by any window manager that I know. Thankfully, it doesn't have to be explicitly supported by a WM in order to be used with it, but most WMs tend to get confused by it. Also, sometimes keyboard focus is not automatically assigned for the second pointer, and you have to explicitly assign it via command-line for the keyobard input to work.
So, how to do it?
The basic steps are:
Prepare an alternative xorg configuration file for both displays (if you don't use both already)
Start another X server with "xinit /usr/bin/xterm -- :1 vt8 -config [your dual screen xorg config file]" (so that when something goes bad, your main desktop won't suffer)
Set up a secondary pointer with xinput utility
Launch two instances of some game, one on each screen
Use xinput with "set-cp" option to assign a second pointer to the window that will be operated by it
Play!
You'll have to repeat all steps (except the first one) each time you want to play in this configuration. As you can see, it requires some tedious typing each time, so right now I'm writing scripts that automate the setup.
Here's one that lets you choose a mouse and keyobard and assign a second pointer to them (uses zenity, but can be adapted to use CLI only):
#/bin/bash
# vim: si ts=4 sw=4
shopt -s extglob
IFS=$'\n' DEVICE_LIST=( $(xinput list --short) )
for (( I=0; I<${#DEVICE_LIST[@]}; I++ )); do
IFS=$'\t' INFO=( ${DEVICE_LIST[$I]} )
[ "${INFO[2]:1:1}" = "s" ] || continue
NAME="${INFO[0]:6}"
NAME="${NAME%%*([[:blank:]])}"
ID="${INFO[1]#id=}"
[[ "$NAME" != *XTEST* ]] || continue
case "${INFO[2]:8:1}" in
"p" )
POINTERS+=( "$ID"$'\t'"$NAME" )
"k" )
KEYBOARDS+=( "$ID"$'\t'"$NAME" )
esac
done
POINTER="$( IFS=$'\t' zenity --title="Select device" --list --text="Choose a pointer" --column="Id" --column="Name" ${POINTERS[@]} )"
KEYBOARD="$( IFS=$'\t' zenity --title="Select device" --list --text="Choose a keyboard" --column="Id" --column="Name" ${KEYBOARDS[@]} )"
[ -n "$POINTER" ] && [ -n "$KEYBOARD" ] || exit 1
MASTER_NAME="second"
xinput create-master "$MASTER_NAME"
xinput reattach "$POINTER" "$MASTER_NAME pointer"
xinput reattach "$KEYBOARD" "$MASTER_NAME keyboard"
Don't ask me for more detailed instructions - I'll provide them when I have time.
Now I'm looking for suggestions where I could place them. Maybe a wiki page would be a good idea? I think it would also be easier to join efforts there. What do you think?

Answer 1

Yes, most of WMs get confused by multiple pointers, because they don't recognize mutliple focuses. That's one of the reasons why I run games in a dedicated X server with a bare-bones TWM setup. I launch it with:
xinit ./xinitrc.dual -- :1 vt8 -config xorg.conf.dual
xinitrc.dual:
twm -f twmrc &
DISPLAY=:1.1 xterm &
xterm
twmrc (compacted):
NoDefaults
NoIconManagers
NoTitleFocus
NoTitleHighlight
NoHighlight
RandomPlacement
UsePPosition "on"
OpaqueMove
DontMoveOff
NoTitle
BorderWidth 0
NoMenuShadows
# Bindings
Button1 = m4 : window|icon : f.move
Button3 = m4 : window : f.resize
Button1 = : icon : f.deiconify
"1" = m4 : all : f.warptoscreen "0"
"2" = m4 : all : f.warptoscreen "1"
"f" = m4 : all : f.focus
"Tab" = m4 : all : f.circleup
"Tab" = m4|s : all : f.circledown
"n" = m4 : window : f.iconify
In this config there are no window decorations, and "Super" (the windows-logo key) is the general window-handling modifier.
Bindings explained:
Super+LMB - drag windows around
Super+RMB - resize windows
Super+1/2 - warp pointer to screen 0 or 1
Super+f - lock/unlock focus
Super[+Shift]+Tab - cycle between windows (more precisely, cycle their stacking order)
Super+n - iconify (minimize) window; iconified windows are restored by clicking on icons.
Why do I see two entries for the USB keyboard ? (ID8 / ID9)
It seems that some devices report themselves that way. Maybe they have some functions that should be logically separated, or something like that. Then, I think it's best to keep them under the same master device to avoid confusion. I've updated my zenity script to allow selecting more than one device:
#/bin/bash
# vim: si ts=4 sw=4
shopt -s extglob
IFS=$'\n' DEVICE_LIST=( $(xinput list --short) )
for (( I=0; I<${#DEVICE_LIST[@]}; I++ )); do
IFS=$'\t' INFO=( ${DEVICE_LIST[$I]} )
[ "${INFO[2]:1:1}" = "s" ] || continue
NAME="${INFO[0]:6}"
NAME="${NAME%%*([[:blank:]])}"
ID="${INFO[1]#id=}"
[[ "$NAME" != *XTEST* ]] || continue
case "${INFO[2]:8:1}" in
"p" )
POINTERS+=( "$ID"$'\t'"$NAME" )
"k" )
KEYBOARDS+=( "$ID"$'\t'"$NAME" )
esac
done
MASTER_NAME="$( zenity --title="Enter name" --entry --text="Enter name for new master" )"
[ -n "$MASTER_NAME" ] || exit 1
POINTER="$( IFS=$'\t' zenity --title="Select device" --list --multiple --text="Choose a pointer" --column="Id" --column="Name" ${POINTERS[@]} )"
[ -n "$POINTER" ] || exit 1
KEYBOARD="$( IFS=$'\t' zenity --title="Select device" --list --multiple --text="Choose a keyboard" --column="Id" --column="Name" ${KEYBOARDS[@]} )"
[ -n "$KEYBOARD" ] || exit 1
xinput create-master "$MASTER_NAME"
IFS="|"
for ID in $POINTER; do
xinput reattach "$ID" "$MASTER_NAME pointer"
done
for ID in $KEYBOARD; do
xinput reattach "$ID" "$MASTER_NAME keyboard"
done
@Darksoul71
This should be all you need. You can adapt my xorg.conf.dual (it's in one of my previous posts), but the way of configuring multiple screens can differ between display drivers, so you'll have to find out how to do it in your case.
EDIT: Forgot to mention:
@Darksoul71
As to you keyboard problem - do you set the client pointer for the second instance's window?
Last edited by Rad3k (2010-09-29 22:06:08)