i may misunderstand the question, but since @mikus mentioning splitting a wallpaper over three displays, my solution is just a little imagemagick with bash, to simply cut a given image into three same sized parts, and set them on every display individually.
here’s the script, in case it helps somebody:
#!/bin/bash
# Input file
input_file="$1"
# Get image dimensions
width=$(identify -format "%w" "$input_file")
height=$(identify -format "%h" "$input_file")
# Calculate the width of each part (since the height remains unchanged)
part_width=$((width / 3))
# Split the image horizontally into three equal parts
convert "$input_file" -crop ${part_width}x${height}+0+0 +repage part1.jpg
convert "$input_file" -crop ${part_width}x${height}+${part_width}+0 +repage part2.jpg
convert "$input_file" -crop ${part_width}x${height}+$(($part_width * 2))+0 +repage part3.jpg
echo "Image split into 3 horizontally tiled parts: part1.jpg, part2.jpg, part3.jpg"
simply use it by: script.sh yourwidescreenwallpaper.jpg