#! /bin/sh -e

case $# in 1) ;; *) echo >&2 "usage: $1 ZOOM"; exit 2 ;; esac
zoom=$1

ok=nil
case $zoom in
  */*/*) ;;
  *[!0-9/]*) ;;
  */*) ok=t mul=${zoom%/*} div=${zoom#*/} ;;
  *) ok=t mul=1 div=$zoom ;;
esac
case $ok in nil) echo >&2 "$0: bad zoom $zoom"; exit 2 ;; esac
case $(( $mul > $div )) in 1) echo >&2 "$0: zoom too high"; exit 2 ;; esac

ok=nil
case ${DISPLAY-nil} in
  *:*[!0-9.]*) ;;
  *:*.*.*) ;;
  *:*.*) ok=t dpybase=${DISPLAY%.*} ;;
  *:*) ok=t dpybase=$DISPLAY ;;
esac
case $ok in nil) echo >&2 "$0: bad DISPLAY"; exit 2 ;; esac

set -- $(xqueryptr); scr=$1 x=$2 y=$3
DISPLAY=$dpybase.$scr; export DISPLAY

eval $(xscsize -b)

case $(( $XWIDTH%$div || $XHEIGHT%$div )) in
  0) ;;
  *) echo >&2 "$0: zoom divisor doesn't divide screen size"; exit 2 ;;
esac

{ read _
  found=nil
  while read _ _ respos name; do
    res=${respos%%+*} pos=${respos#*+}
    ww=${res%x*} hh=${res#*x}
    w=${ww%/*} h=${hh%/*}
    x0=${pos%+*} y0=${pos#*+}
    x1=$(( $x0 + $w )) y1=$(( $y0 + $h ))
    case $(( $x0 <= $x && $x < $x1 && $y0 <= $y && $y < $y1 )) in
      1) found=t; break ;;
    esac
  done
} <<EOF
$(xrandr --listmonitors)
EOF

case $found in nil) echo >&2 "$0: pointer not on any screen?"; exit 2 ;; esac

case $(( $mul == $div )) in
  1) pan= ;;
  *) pan="--panning ${XWIDTH}x${XHEIGHT}" ;;
esac

xrandr --fb ${XWIDTH}x${XHEIGHT} \
	--output $name \
	--mode $(( $mul*$XWIDTH/$div ))x$(( $mul*$XHEIGHT/$div )) \
	$pan