指定したPNG画像の外周に透明の1ピクセルを追加するスクリプト。Androidの9patch用。

convert9patch.rb

#!/usr/bin/env ruby

require 'pathname'
require 'rmagick'

if ARGV.empty?
  puts 'Usage: convert9patch.rb [png]'
  exit
end
if !File.exist?(ARGV[0])
  puts "No such file #{ARGV[0]}."
  exit
end

path_name = Pathname.new(ARGV[0])
dir_name = path_name.dirname
ext_name = path_name.extname
file_name = path_name.basename(ext_name)

img = Magick::ImageList.new(ARGV[0])
new_img = Magick::ImageList.new.new_image(img.columns + 4, img.rows + 4) {
  self.background_color = 'none'
}
new_img.composite!(img, Magick::CenterGravity, Magick::OverCompositeOp)
new_img.write([dir_name, "#{file_name}.9#{ext_name}"].join(File::SEPARATOR))