#!/usr/bin/env ruby

require 'sfml/all'
require 'opengl'

class Example
  include SFML

  TITLE = "Josh's Ruby SFML/OpenGL Example"

  def initialize
    @fullscreen = false
    @window = Window.new
    create_window
  end

  def load_shaders
    v_id = glCreateShader(GL_VERTEX_SHADER)
    glShaderSource(v_id, <<-EOS)
      uniform vec2 offset;
      uniform vec2 screen_size;
      attribute vec2 pos;
      varying vec4 pos_i;

      void main()
      {
        vec2 scaled_pos = vec2((offset.x - screen_size.x / 2) / screen_size.x * 2,
                               (offset.y - screen_size.y / 2) / screen_size.y * 2);
        pos_i = vec4(pos + scaled_pos, 0, 1);
        gl_Position = pos_i;
      }
    EOS
    glCompileShader(v_id)
    unless glGetShaderiv(v_id, GL_COMPILE_STATUS)
      raise glGetShaderInfoLog(v_id)
    end

    f_id = glCreateShader(GL_FRAGMENT_SHADER)
    glShaderSource(f_id, <<-EOS)
      varying vec4 pos_i;

      void main()
      {
        gl_FragColor = vec4((pos_i.x + 1.0) / 2.0,
                            (pos_i.y + 1.0) / 2.0,
                            0, 1);
      }
    EOS
    glCompileShader(f_id)
    unless glGetShaderiv(f_id, GL_COMPILE_STATUS)
      raise glGetShaderInfoLog(f_id)
    end

    p_id = glCreateProgram()
    glAttachShader(p_id, v_id)
    glAttachShader(p_id, f_id)
    glLinkProgram(p_id)
    unless glGetProgramiv(p_id, GL_LINK_STATUS)
      raise glGetProgramInfoLog(p_id)
    end
    $offset_loc = glGetUniformLocation(p_id, "offset")
    $screen_size_loc = glGetUniformLocation(p_id, "screen_size")

    glUseProgram(p_id)
  end

  def create_window
    if @fullscreen
      @window.create(VideoMode.get_desktop_mode, TITLE, Style::Fullscreen)
    else
      @window.create([1200, 900], TITLE)
    end

    glClearColor(1, 0.5, 0, 0)
    load_shaders
  end

  def run
    quad_attrs = [0.02, 0.02,
                  -0.02, 0.02,
                  -0.02, -0.02,
                  0.02, -0.02].pack("f*")
    b_id = glGenBuffers(1).first
    glBindBuffer(GL_ARRAY_BUFFER, b_id);
    glBufferData(GL_ARRAY_BUFFER, 2 * 4 * 4, quad_attrs, GL_STATIC_DRAW);

    x, y = 0, 0
    while @window.open?
      @window.each_event do |event|
        case event.type
        when Event::Closed
          @window.close
        when Event::KeyPressed
          case event.key.code
          when Keyboard::Escape
            @window.close
          when Keyboard::F
            @fullscreen = !@fullscreen
            create_window
          end
        when Event::MouseMoved
          x = event.mouse_move.x
          y = event.mouse_move.y
        when Event::Resized # Resize event : adjust viewport
          x = event.size.width / 2
          y = event.size.height / 2
          glViewport(0, 0, event.size.width, event.size.height)
        end
      end
      break unless @window.open?

      glClear(GL_COLOR_BUFFER_BIT)

      glUniform2f($offset_loc, x, @window.getSize.y - y)
      glUniform2f($screen_size_loc, @window.getSize.x, @window.getSize.y)
      glEnableVertexAttribArray(0)
      glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * 4, 0);
      glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

      @window.display
    end
  end
end

Example.new.run