After seeing the reaction to a possible +30KB increase to round.min.js, I wanted to make image gallery lightweight for both the server and client.

A single webp image with all the thumbnails is lazy fetched by the client when Background -> Picture is clicked. Lila does no processing aside from lazy fetching a directory listing from a json file. And that's all.

Everything is static, so:

• If you want to change the order of images or add/remove some, you set them up in a directory and run lifat/background/make-gallery.js
• Tweak the sizes, borders, gallery layouts, etc by altering the imagemagick montage params in lifat/background/make-gallery.js
• You might want to improve hiliting of the current selection, currently it's a green 1 pixel outline but a superimposed green checkmark or other indicators are also fine.

If/when this pull request is approved, the commit hash in lila/bin/download-lifat must be changed to e06857a9303d05581e13e2c814b3019c4e5beae2 to actually deploy the images.

I deployed it on https://lichess.dev/

server {
  server_name assets.lichess.dev;
  [...]
  charset_types text/html application/javascript application/json text/css;
  location /assets/lifat/ {
    add_header Cache-Control public;
    add_header Access-Control-Allow-Origin "*";
    add_header Cross-Origin-Resource-Policy "cross-origin";
    alias /home/lifat/;
  }
}