Centering mouse in the Active Window

This is just a quick post on how to centre your mouse in the currently selected window on Linux.

This is behaviour that can be patched into dwm but for window managers like i3 you will need to call this script whenever you perform an action that you want to shift your mouse’s focus.

#!/bin/sh

ACTIVE_WINDOW_ID=$(xdotool getactivewindow)
DIMS=$(xdotool getwindowgeometry -shell $ACTIVE_WINDOW_ID | awk -F "="  'NR==4,NR==5 {print $2/2}' | tr '\n' ' ')

xdotool mousemove -w $ACTIVE_WINDOW_ID $DIMS

A quick explanation of this:

1. xdotool getactivewindow will return the active window’s ID
2. xdotool getwindowgeometry -shell $ACTIVE_WINDOW_ID will then get that window’s geometry.
3. awk -F "=" 'NR==4,NR==5 {print $2/2}' will run on the geometry command’s output, splitting each line on the = symbol.
   The NR==4, NR==5 will match the 4th and 5th line (width and height).
   And finally the print command will output the second match on each line (the value after the =) divided by 2.
4. The tr command will take each line of the output and replace the new line characters with a space.
5. Finally xdotool mousemove -w $ACTIVE_WINDOW_ID $DIMS will move the mouse to the active window at the given positions (the middle).

With i3 I altered my config so that after every change focus command I execute the above little script. E.g.

# Set script to centre mouse
set $centre_mouse ~/.config/i3/centre-mouse

bindsym $mod+Left focus left; exec --no-startup-id $centre_mouse
bindsym $mod+Down focus down; exec --no-startup-id $centre_mouse
bindsym $mod+Up focus up; exec --no-startup-id $centre_mouse
bindsym $mod+Right focus right; exec --no-startup-id $centre_mouse

I thought I’d share this for anyone else wanting something similar as I saw a thread on Reddit from a few years ago where someone was asking for such.