i3lock-multimonitor

#!/bin/bash

#Constants
DISPLAY_RE="([0-9]+)x([0-9]+)\\+([0-9]+)\\+([0-9]+)" # Regex to find display dimensions
IMAGE_RE="([0-9]+)x([0-9]+)"    # Regex to find image dimensions
FOLDER=`dirname "$BASH_SOURCE"` # Current folder
CACHE_FOLDER="$FOLDER"/img/cache/ # Cache folder

#Image paths
BKG_IMG="$FOLDER/img/background.png" # Path of background image
MD5_BKG_IMG=$(md5sum $BKG_IMG | cut -c 1-10)
MD5_SCREEN_CONFIG=$(xrandr | md5sum - | cut -c 1-32) # Hash of xrandr output
OUTPUT_IMG="$CACHE_FOLDER""$MD5_SCREEN_CONFIG"."$MD5_BKG_IMG".png # Path of final image
OUTPUT_IMG_WIDTH=0 # Decide size to cover all screens
OUTPUT_IMG_HEIGHT=0 # Decide size to cover all screens

if [ -e $OUTPUT_IMG ]
then
    # Lock screen since image already exists
    i3lock --image=$OUTPUT_IMG --tiling --show-failed-attempts
    exit 0
fi

#Execute xrandr to get information about the monitors:
while read LINE
do
  #If we are reading the line that contains the position information:
  if [[ $LINE =~ $DISPLAY_RE ]]; then
    #Extract information and append some parameters to the ones that will be given to ImageMagick:
    SCREEN_WIDTH=${BASH_REMATCH[1]}
    SCREEN_HEIGHT=${BASH_REMATCH[2]}
    SCREEN_X=${BASH_REMATCH[3]}
    SCREEN_Y=${BASH_REMATCH[4]}
    
    CACHE_IMG="$CACHE_FOLDER""$SCREEN_WIDTH"x"$SCREEN_HEIGHT"."$MD5_BKG_IMG".png
    ## if cache for that screensize doesnt exist
    if ! [ -e $CACHE_IMG ]
    then
        eval convert  '$BKG_IMG' '-resize' '${SCREEN_WIDTH}X${SCREEN_HEIGHT}!' \
            '$CACHE_IMG'
    fi

    # Decide size of output image
    if (( $OUTPUT_IMG_WIDTH < $SCREEN_WIDTH+$SCREEN_X )); then OUTPUT_IMG_WIDTH=$(($SCREEN_WIDTH+$SCREEN_X)); fi;
    if (( $OUTPUT_IMG_HEIGHT < $SCREEN_HEIGHT+$SCREEN_Y )); then OUTPUT_IMG_HEIGHT=$(( $SCREEN_HEIGHT+$SCREEN_Y )); fi;

    PARAMS="$PARAMS $CACHE_IMG -geometry +$SCREEN_X+$SCREEN_Y -composite "
  fi
done <<<"`xrandr`"

#Execute ImageMagick:
eval convert -size ${OUTPUT_IMG_WIDTH}x${OUTPUT_IMG_HEIGHT} 'xc:black' $OUTPUT_IMG
eval convert $OUTPUT_IMG $PARAMS $OUTPUT_IMG

#Lock the screen:
i3lock --image=$OUTPUT_IMG --tiling --show-failed-attempts