retina-scale

#!/usr/bin/ruby -w

SCALES = [1, 2, 3]

def usage
  name = File.basename(__FILE__)
  puts "Usage: #{name} <input-image> <output-directory> <output-filename-prefix> <width> <height>"
end

def scale_retina(width, height, scale, in_file, out_dir, prefix)
  file_scale = scale > 1 ? "@#{scale}x" : ''
  filename = "#{prefix}#{file_scale}.png"
  out_file = File.join(out_dir, filename)
  puts "> convert '#{in_file}' -scale #{width * scale}x#{height * scale} '#{out_file}'"
  output = `gm convert '#{in_file}' -scale #{width * scale}x#{height * scale} '#{out_file}'`.strip
  puts output if output.length > 0
end

def image_dimensions(path)
  `gm identify '#{path}'`.split[2].split('x').map(&:to_i)
end

in_file, out_dir, prefix, raw_width, raw_height = ARGV
unless File.exist?(in_file)
  puts "Input image not found: #{in_file}"
  usage
  exit 1
end
unless File.directory?(out_dir)
  puts "Output directory not found: #{out_dir}"
  usage
  exit 2
end
unless prefix && prefix.strip.length > 0
  puts "Missing output filename prefix"
  usage
  exit 3
end
if raw_width && raw_height
  width = raw_width.to_f
  height = raw_height.to_f
else
  width, height = image_dimensions(in_file).map { |x| x / 3 }
end
unless width > 0 && height > 0
  puts "Invalid dimensions: #{raw_width.inspect} #{raw_height.inspect}"
  usage
  exit 4
end

SCALES.each do |scale|
  scale_retina(width, height, scale, in_file, out_dir, prefix)
end