main_scene.rb

class MainScene < MG::Scene
  BIRD =  1 << 0
  WORLD = 1 << 1

  def initialize
    self.gravity = [0, -900]

    @backgrounds = []

    add_skyline
    add_ground
    start_game
    @pipe_update = 0
    @random = Random.new

    # On touch, the bird jumps.
    on_touch_begin do
      MG::Audio.play('sfx_wing')
      @bird.velocity = [0, 200]
    end

    # On collision contact, it's game over.
    on_contact_begin do
      MG::Audio.play('sfx_hit')
      puts "game over!"
      @bird.blink 3, 1
      true
    end

  end

  def start_game
    button_start = MG::Button.new()
    button_start.text = "Start Game"
    button_start.font_size = 30
    button_start.position = [MG::Director.shared.size.width / 2.0, MG::Director.shared.size.height / 2.0]
    button_start.on_touch do |type|
      if type == :end
        add_bird
        start_update
        button_start.visible = false
      end
    end
    add button_start
  end

  def add_skyline
    @x = 0
    @backgrounds << []
    2.times do
      skyline = MG::Sprite.new('skyline.png')
      skyline.position = [@x, MG::Director.shared.size.height / 2.0]
      add skyline, 0
      @x += skyline.size.width - 5
      @backgrounds.last << skyline
    end
  end

  def add_ground
    @x = 0
    @backgrounds << []
    2.times do
      ground = MG::Sprite.new('ground.png')
      ground.attach_physics_box
      ground.dynamic = false
      ground.category_mask = WORLD
      ground.contact_mask = BIRD
      ground.position = [@x, 30]
      add ground, 2
      @x += ground.size.width - 5
      @backgrounds.last << ground 
    end
  end

  def add_bird
    @bird = MG::Sprite.new('bird_one.png')
    @bird.attach_physics_box
    @bird.category_mask = BIRD
    @bird.contact_mask = WORLD
    @bird.position = [100, MG::Director.shared.size.height / 2]
    @bird.animate(['bird_one.png', 'bird_two.png', 'bird_three.png'], 0.5, :forever)
    add @bird
  end

  def add_pipe
    @pipe_y = @random.rand(150.0..450.0)
    [['pipe_up.png', 0], ['pipe_down.png', 850]].each do |sprite_name, y_offset|
      pipe = MG::Sprite.new(sprite_name)
      pipe.attach_physics_box
      pipe.category_mask = WORLD
      pipe.contact_mask = BIRD
      pipe.dynamic = false
      pipe.position = [800, @pipe_y + y_offset]
      add pipe, 1
      pipe.move_by([-900, 0], 4.0) { pipe.delete_from_parent }
    end
  end

  def update(delta)
    # Move background pieces.
    @backgrounds.each do |sprite1, sprite2|
      width = sprite1.size.width
      pos1 = sprite1.position
      pos2 = sprite2.position
      movement = 5.0
      pos1.x -= movement
      pos2.x -= movement
      if pos1.x <= -(width / 2.0)
        pos1.x = pos2.x + width - 5
      elsif pos2.x <= -(width / 2.0)
        pos2.x = pos1.x + width - 5
      end
      sprite1.position = pos1
      sprite2.position = pos2
    end

    # Rotate bird.
    @bird.rotation = 360 - [[-90, @bird.velocity.y * 0.2 + 60].max, 30].min if @bird

    # Make a pipe appear every 2 seconds.
    @pipe_update += delta
    if @pipe_update >= 2.0
      add_pipe
      @pipe_update = 0
    end
  end
end