Resize images and move from ./originals to ./

sprites.rake

namespace :sprites do
  originals = Rake::FileList.new('app/assets/images/**/originals/*.png')
  resized = originals.pathmap("%{/originals$,/}d%f")
  task resize: resized
end

from_originals = ->(tn) {
  tn.pathmap("%d/originals/%f")
}

rule(/^((?!originals).)*.png$/ => [from_originals]) do |t|
  original = t.prerequisites[0]
  width = 80
  sh "convert #{original} -resize #{width}x #{t.name}"
end