ball_invaders.rb

require 'gosu'

# The game skeleton we built on 16.6. - A ball moving right to left and back, slowly invading the bottom of the screen...
class GameWindow < Gosu::Window

  def initialize
    super(640, 480)
    self.caption = "Gosu Tutorial Game (Interval: #{self.update_interval})"

    @ball = Gosu::Image.new('media/ball.png')
    @x = 0
    @y = 0
    @scale = 5
    @velocity_x = 5
  end

  def update
    # move ball
    @x = @x + @velocity_x

    # turn left
    if @x > self.width-@ball.width * @scale or @x < 0
      # go down one
      @y = @y + 1 * @ball.height * @scale

      # change direction
      @velocity_x = @velocity_x * -1
    end
  end

  def draw
    @ball.draw(@x, @y, 0, @scale, @scale)
  end

end

window = GameWindow.new
window.show