atlas_json_builder.rb

require 'json'

class AtlasJsonBuilder
  def build(file_name, dist)
    patterns = %w(up upright right downright down downleft left upleft)
    sprites = []
    patterns.each_with_index do |name, i|
      4.times do |frame|
        sprites << SpriteRule.new(name: name, frame: frame, pattern: i, width: 24, height: 32)
      end
    end

    hashes = sprites.each_with_object({}) do |s, list|
      list.merge! s.template_json
    end
    jsons = {
      frames: hashes,
      meta: {
	      app: "http://www.codeandweb.com/texturepacker",
	      version: "1.0",
	      image: file_name,
	      format: "RGBA8888",
	      size: {w:256,h:256},
	      scale: 1,
	      smartupdate: "$TexturePacker:SmartUpdate:4d39c0a2b05b86b5a26de044242bd6ef:f98eef6920bac6b6005274cd69b5e8ce:eb1c03f86a55fce9b06582a0b985db04$"
      }
    }

    File.write(dist, jsons.to_json)
  end
end

class SpriteRule
  def initialize(name:, frame:, pattern:, width:, height:)
    @name = name
    @frame = frame
    @width = width
    @height = height
    @pattern = pattern
  end

  def template_json
    {
      "#{@name}_#{@frame}": {
        frame: { x: @width * @frame, y: @height * @pattern, w: @width, h: @height },
        rotated: false,
        trimmed: false,
        spriteSourceSize: { x:0,y:0,w: @width, h: @height },
        sourceSize: { w: @width, h: @height }
      }
    }
  end
end