module Animative

animative.rb

require 'fiber'
require 'forwardable'

class Animation

  extend Forwardable

  def_delegators :@fiber, :alive?

  def initialize(init_motion=Motion.new, init_offset=nil)
    @fiber = Fiber.new do |motion, offset=nil|
      reset, restart = nil, nil
      loop do
        catch :reset do
          motion, reset = reset, nil if reset
          motion.step do |count|
            catch :restart do
              offset, restart = restart, nil if restart
              offset = 0 if offset and offset >= motion.length
              if offset then next unless offset == count
              else offset = nil
              end
              params = Fiber.yield(motion.key(count), count)
              if params
                reset, restart = params
              end
              throw :reset if reset
              throw :restart if restart
            end
          end
        end
        break if motion.forward
      end
      Fiber.yield(motion.forward, nil)
    end
    @motion = init_motion
    @offset = init_offset
    @key = @motion.first
    @count = 0
  end

  def start(motion)
    @offset = nil
    @motion = motion
  end

  def change(motion)
    @offset = @count.succ
    @motion = motion
  end

  def update
    unless pause?
      if @motion or @offset
        @key, @count = @fiber.resume(@motion, @offset)
        @motion, @offset = nil, nil
      else
        @key, @count = @fiber.resume
      end
    end
    @key
  end

  def pause
    @pause = true
  end

  def resume
    @pause = false
  end

  def pause?
    @pause
  end

  class Motion

    extend Forwardable

    attr_accessor :wait, :pattern, :forward

    def_delegators :@pattern, :first

    def initialize(wait=0, pattern=[0], forward=nil)
      @wait, @pattern, @forward = wait, pattern, forward
    end

    def step
      length.times {|count| yield count }
    end

    def length
      (1 + @wait) * @pattern.size
    end

    def key(count)
      @pattern[count / (1 + @wait)]
    end

  end

end

class Animator

  extend Forwardable

  attr_accessor :animation_image

  def_delegator :@animation, :pause, :pause_animation
  def_delegator :@animation, :resume, :resume_animation

  def initialize
    @motions = {}
    @animation = Animation.new
    @animation_image = []
  end

  def add_animation(key, wait, pattern, forward=nil)
    @motions[key] = Animation::Motion.new(wait, pattern, forward)
  end

  def start_animation(key, pattern=nil, forward=nil)
    if @motions[key]
      @animation.start(@motions[key])
    else
      @animation.start(Animation::Motion.new(key, pattern, forward))
    end
  end

  def change_animation(key, pattern=nil, forward=nil)
    if @motions[key]
      @animation.change(@motions[key])
    else
      @animation.change(Animation::Motion.new(key, pattern, forward))
    end
  end

  def update
    @animation_image[@animation.update]
  end

end

module Animative

  extend Forwardable

  def_delegators :@__animative_animator,
    :animation_image, :animation_image=,
    :add_animation,
    :start_animation, :change_animation,
    :pause_animation, :resume_animation

  def initialize(*arg)
    super
    @__animative_animator = Animator.new
  end

  def update
    self.image = @__animative_animator.update
  end

end

main.rb

require 'dxruby'
require_relative 'animative'

class Player < Sprite

  include Animative

  attr_accessor :direction

  def turn_left
    @direction = 0
  end

  def turn_right
    @direction = 1
  end

end

player = Player.new(0, 0)
player.turn_right
player.animation_image = Image.load_tiles("player.png", 4, 2)

player.add_animation(:wait_left, 0, [4])
player.add_animation(:wait_right, 0, [0])
player.add_animation(:walk_left, 6, [5,6,7,6])
player.add_animation(:walk_right, 6, [1,2,3,2])
player.start_animation(:wait_right)

Window.loop do
  player.x += Input.x
  player.y += Input.y
  if Input.x < 0
    player.change_animation(:walk_left)
    player.turn_left
  elsif Input.x > 0
    player.change_animation(:walk_right)
    player.turn_right
  else
    player.change_animation([:wait_left, :wait_right][player.direction])
  end
  if Input.y != 0
    player.pause_animation
  else
    player.resume_animation
  end
  player.update
  player.draw
end