create_icon_each_density.rb

require 'fileutils'
require 'rmagick'

# file name
img_file_path = ARGV[0]

if (/\// =~ img_file_path) then
    /^.*\/([^\/]+).png$/ =~ img_file_path
else
    /^(.+).png$/ =~ img_file_path
end

img_file_name = $1 + '.png'

# directory
root_dir = 'res'

if ($DEBUG) then
    root_dir = $1
end

# get xxhdpi image data
img_data = Magick::ImageList.new(img_file_path)

xxhdpi_width = img_data.columns
xxhdpi_height = img_data.rows

RESIZE_IMAGES = [
    {
        'dir' => 'mdpi',
        'scale' => 1.0
    },
    {
        'dir' => 'hdpi',
        'scale' => 1.5
    },
    {
        'dir' => 'xhdpi',
        'scale' => 2.0
    },
    {
        'dir' => 'xxhdpi',
        'scale' => 3.0
    }
]

# resize image
mdpi_width = xxhdpi_width / 3
mdpi_height = xxhdpi_height / 3

img = Magick::Image.read(img_file_path).first

RESIZE_IMAGES.each do |resize_images|
    dir = root_dir + '/drawable-' + resize_images['dir']
    FileUtils.mkdir_p dir, :mode => 0755

    width = mdpi_width * resize_images['scale']
    height = mdpi_height * resize_images['scale']

    img.resize(width, height).write(dir + '/' + img_file_name)
end