Combine multiple files into an animated gif with ruby-vips

combine_gif.rb

require 'vips'

images = Dir["input-*.png"].map { |file| Vips::Image.new_from_file(file) }

combined = Vips::Image.arrayjoin(images, across: 1)
buffer = combined.gifsave_buffer(page_height: images.first.height)
gif_image = Vips::Image.new_from_buffer(buffer, "", n: images.length)

gif_image = gif_image.mutate do |y|
  y.set!("delay", images.length.times.map { 1000 }) # time is in ms
end

gif_image.gifsave("animation.gif")