#!/usr/bin/env ruby

require 'sfml/all'
require 'opengl'
require 'glutil'

include GLUtil

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_shader = GLShader.new(GL_VERTEX_SHADER, <<-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.x * screen_size.y / screen_size.x + scaled_pos.x,
                     pos.y + scaled_pos.y, 0, 1);
        gl_Position = pos_i;
      }
    EOS

    f_shader = GLShader.new(GL_FRAGMENT_SHADER, <<-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

    program = GLProgram.new([v_shader, f_shader])
    $offset_loc = program.get_uniform_location("offset")
    $screen_size_loc = program.get_uniform_location("screen_size")
    program.use
  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*")
    buffer = GLBuffer.new(GL_ARRAY_BUFFER, GL_STATIC_DRAW, quad_attrs, 2 * 4 * 4)

    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