gistfile1.txt

#!/usr/bin/env ruby

path = "/tmp/images"
files = Dir["#{path}/*.png"]
base_files = []
for file in files do
  if !file.include? "x.png"
    base_files << file
  end
end

output_path = "/tmp/converted-images"
`rm -rf #{output_path}` # DANGER
`mkdir -p #{output_path}/drawable-xxxhdpi`
`mkdir -p #{output_path}/drawable-xxhdpi`
`mkdir -p #{output_path}/drawable-xhdpi`
`mkdir -p #{output_path}/drawable-hdpi`
`mkdir -p #{output_path}/drawable-mdpi`

# Make sure we have all the variants in the directory
for file in base_files do
  file_name = File.basename(file, ".*") # /tmp/images/foo.png -> foo
  file_name_android = file_name.gsub('-', '_')
  file1x = "#{path}/#{file_name}.png"
  raise "Missing #{file1x}" unless File.exists?(file1x)
  file2x = "#{path}/#{file_name}@2x.png"
  raise "Missing #{file2x}@2x variant" unless File.exists?(file2x)
  file3x = "#{path}/#{file_name}@3x.png"
  raise "Missing #{file3x}@3x variant" unless File.exists?(file3x)

  height=`sips --getProperty pixelHeight #{file1x} | sed -E "s/.*pixelHeight: ([0-9]+)/\\1/g" | tail -1`
  width=`sips --getProperty pixelWidth #{file1x} | sed -E "s/.*pixelWidth: ([0-9]+)/\\1/g" | tail -1`

  `cp #{file1x} #{output_path}/drawable-mdpi/#{file_name_android}.png`
  `cp #{file2x} #{output_path}/drawable-xhdpi/#{file_name_android}.png`
  `cp #{file3x} #{output_path}/drawable-xxhdpi/#{file_name_android}.png`

  `sips --resampleHeightWidth #{(height.to_i * 1.5).round} #{(width.to_i * 1.5).round} #{file2x} --out #{output_path}/drawable-hdpi/#{file_name_android}.png`

  `sips --resampleHeightWidth #{(height.to_i * 4).round} #{(width.to_i * 4).round} #{file3x} --out #{output_path}/drawable-xxxhdpi/#{file_name_android}.png`
end