A game as Space Invaders using Gosu and Ruby. (under construction...)

space_invaders.rb

#
# space_invaders.rb:
#   A game as Space Invaders using Gosu and Ruby.
#
# Authors:
#   (c) 2014 Masafumi Yokoyama
#
# License:
#   This program is licensed under the MIT License.
#

require "gosu"

module SpaceInvaders
  module ZOrder
    Background, Object, Message = *0..2
  end

  module Base
    attr_reader :x, :y, :width

    def warp(x, y)
      @x = x
      @y = y
    end

    def draw_square(window,
                    x1, y1,
                    x2, y2,
                    color, z_order=0)
      window.draw_quad(x1, y1, color,
                       x2, y1, color,
                       x1, y2, color,
                       x2, y2, color,
                       z_order)
    end
  end

  class Ball
    include Base

    def initialize(window, angle=0.0)
      @window = window
      @angle = angle
      @x = 0
      @y = 0
      @width = @window.width * 0.03
      @color = Gosu::Color::WHITE
    end

    def move
      @y += Gosu.offset_y(@angle, @width * 0.2)
    end

    def draw
      x1 = @x - @width * 0.5
      y1 = @y - @width * 0.5
      x2 = @x + @width * 0.5
      y2 = @y + @width * 0.5
      draw_square(@window,
                  x1, y1,
                  x2, y2,
                  @color, ZOrder::Object)
    end
  end

  class Invader
    include Base

    def initialize(window)
      @window = window
      @x = 0
      @y = 0
      @width = @window.width * 0.05
      @color = Gosu::Color::WHITE
    end

    def shot(balls)
      ball = Ball.new(@window, 180.0)
      ball.warp(@x, @y)
      balls << ball
    end

    def move_left
      @x -= @width * 0.1
    end

    def move_right
      @x += @width * 0.1
    end

    def draw
      x1 = @x - @width * 0.3
      y1 = @y - @width * 0.5
      x2 = @x + @width * 0.3
      y2 = @y - @width * 0.5
      x3 = @x - @width * 0.7
      y3 = @y + @width * 0.5
      x4 = @x + @width * 0.7
      y4 = @y + @width * 0.5
      @window.draw_quad(x1, y1, @color,
                        x2, y2, @color,
                        x3, y3, @color,
                        x4, y4, @color,
                        ZOrder::Object)
    end
  end

  class Player
    include Base

    def initialize(window)
      @window = window
      @x = 0
      @y = 0
      @width = @window.width * 0.08
      @color = Gosu::Color::WHITE
    end

    def move_left
      @x -= @width * 0.1 if @x > 0
    end

    def move_right
      @x += @width * 0.1 if @x < @window.width
    end

    def draw
      x1 = @x
      y1 = @y - @width * 0.5
      x2 = @x - @width * 0.5
      y2 = @y + @width * 0.5
      x3 = @x + @width * 0.5
      y3 = @y + @width * 0.5
      @window.draw_triangle(x1, y1, @color,
                            x2, y2, @color,
                            x3, y3, @color,
                            ZOrder::Object)
    end
  end

  class Message
    def initialize(window, text)
      @window = window
      @text = Gosu::Image.from_text(@window,
                                    text,
                                    Gosu.default_font_name,
                                    @window.height / max_length_each_lines(text),
                                    @window.height / 100,
                                    @window.width,
                                    :center)
    end
  
    def draw
      @text.draw(0, @window.height / 3,
                 ZOrder::Message,
                 1, 1,
                 Gosu::Color::WHITE)
    end
  
    def max_length_each_lines(text)
      max_length = 0
      text.each_line do |line|
        if max_length < line.length
          max_length = line.length
        end
      end
      max_length
    end
  end

  class GameWindow < Gosu::Window
    def initialize(width=200, height=200)
      super(width, height, false)
      init
    end

    def update
      @player.move_left if button_down?(Gosu::KbLeft)
      @player.move_right if button_down?(Gosu::KbRight)
      @player_balls.each {|ball| ball.move }
      @invader_balls.each {|ball| ball.move }
      @invaders.each do |invader|
        @player_balls.each do |ball|
          if Gosu.distance(ball.x, ball.y, invader.x, invader.y) < (invader.width * 0.5)
            @invaders.delete(invader)
            @player_balls.delete(ball)
          end
        end
        invader.shot(@invader_balls) if Random.rand(1000) == 0
      end
      @invader_balls.each do |ball|
        if Gosu.distance(ball.x, ball.y, @player.x, @player.y) < (@player.width * 0.5)
          game_over
        end
      end
      @player_balls.reject! {|ball| ball.y < 0 }
      @invader_balls.reject! {|ball| ball.y > self.height }
      game_clear if @invaders.empty? && @message.nil?
    end

    def draw
      @player.draw
      @player_balls.each {|ball| ball.draw }
      @invader_balls.each {|ball| ball.draw }
      @invaders.each {|invader| invader.draw }
      @message.draw if @message
    end

    def button_down(id)
      case id
      when Gosu::KbUp
        return if @player_balls.size > 2
        ball = Ball.new(self)
        ball.warp(@player.x, @player.y)
        @player_balls << ball
      when Gosu::KbEscape
        close
      end
    end

    private
    def init
      @player = Player.new(self)
      @player.warp(width * 0.5, height * 0.9)
      @player_balls = []
      @invader_balls = []
      @invaders = []
      create_invaders
      @message = nil
    end

    def create_invaders
      1.upto(10) do |i|
        invader = Invader.new(self)
        invader.warp(self.width * (0.09 * i), self.height * 0.2)
        @invaders << invader
      end
    end

    def game_over
      sleep(3)
      init
    end

    def game_clear
      @message = Message.new(self, "Clear!")
    end
  end
end

SpaceInvaders::GameWindow.new.show