requires wmctrl, xrandr. I bind these to super-left / super-right to make windows cover 50% or fullscreen; and DTRT with multiple monitors

window-left

#!/bin/bash

set -e -u

declare -ir slack=6

declare cur_winid
if [[ $# -eq 1 ]]; then
    cur_winid=$1
else
    cur_winid="$(current-winid)"
fi

# Important: sorted s.t. largest width is first!
declare -a dims=($(xrandr |gawk '/ connected /{print gensub(/.* ([0-9]+x[0-9]+\+[0-9]+\+[0-9]+) \(.*/,"\\1","1")}' | sort -nr))

declare -a widths=(${dims[*]%x*})
declare -a x_offsets=(${dims[*]%+*}); x_offsets=(${x_offsets[*]#*+})

declare -i cur_x cur_w
cur_x=$(wmctrl -l -G |awk -v id="${cur_winid}" '$1==id{print $3}')
cur_w=$(wmctrl -l -G |awk -v id="${cur_winid}" '$1==id{print $5}')

declare -i w x half
for i in "${!widths[@]}"; do
    w=${widths[$i]}
    x=${x_offsets[$i]}
    half=$(( w/2 ))
    if [[ ${cur_w} -eq $w ]]; then
        break
    fi
    if [[ ${cur_x} -gt $(( x + slack )) ]]; then
        break
    fi
done

declare -i half_offset
half_offset=$(( x + half - cur_x )); half_offset=${half_offset#-} # abs

if [[ ${half_offset} -le ${slack} || ${cur_x} -gt $(( x + w )) ]]; then
    wmctrl -ir "${cur_winid}" -b add,maximized_horz
    wmctrl -ir "${cur_winid}" -e "0,$x,0,$w,-1"
    wmctrl -ir "${cur_winid}" -b add,maximized_vert
else
    wmctrl -ir "${cur_winid}" -b remove,maximized_horz
    wmctrl -ir "${cur_winid}" -e "0,$x,0,${half},-1"
    wmctrl -ir "${cur_winid}" -b add,maximized_vert
fi

window-right

#!/bin/bash

set -e -u

declare -ir slack=6

declare cur_winid
if [[ $# -eq 1 ]]; then
    cur_winid=$1
else
    cur_winid="$(current-winid)"
fi

# Important: sorted s.t. largest width is last!
declare -a dims=($(xrandr |gawk '/ connected /{print gensub(/.* ([0-9]+x[0-9]+\+[0-9]+\+[0-9]+) \(.*/,"\\1","1")}' | sort -n))

declare -a widths=(${dims[*]%x*})
declare -a x_offsets=(${dims[*]%+*}); x_offsets=(${x_offsets[*]#*+})

declare -i cur_x cur_w
cur_x=$(wmctrl -l -G |awk -v id="${cur_winid}" '$1==id{print $3}')
cur_w=$(wmctrl -l -G |awk -v id="${cur_winid}" '$1==id{print $5}')

declare -i w x half
for i in "${!widths[@]}"; do
    w=${widths[$i]}
    x=${x_offsets[$i]}
    half=$(( w/2 ))
    if [[ ${cur_w} -eq $w ]]; then
        break
    fi
    if [[ ${cur_x} -lt $(( half - slack )) ]]; then
        break
    fi
done

declare -i half_offset
half_offset=$(( w - half - cur_w )); half_offset=${half_offset#-} # abs

if [[ ${half_offset} -le ${slack} || ${cur_x} -lt $x ]]; then
    wmctrl -ir "${cur_winid}" -b add,maximized_horz
    wmctrl -ir "${cur_winid}" -e "0,$x,0,$w,-1"
    wmctrl -ir "${cur_winid}" -b add,maximized_vert
else
    wmctrl -ir "${cur_winid}" -b remove,maximized_horz
    wmctrl -ir "${cur_winid}" -e "0,$(( x + half )),0,${half},-1"
    wmctrl -ir "${cur_winid}" -b add,maximized_vert
fi