require 'opengl'
require 'glut'


module GL

  def StackMatrix
    PushMatrix()
      yield
    PopMatrix()
  end

  def StackAttrib(mask)
    PushAttrib(mask)
      yield
    PopAttrib()
  end

end


class Spheres
  
  include GL
  
  LIGHT_COLORS = 
    [[ 0.8, 0.9, 1.0, 1.0 ],
    [ 1.0, 0.5, 0.0, 1.0 ],
    [ 1.0, 0.9, 0.6, 1.0 ],
    [ 0.4, 0.6, 1.0, 1.0 ]]
  BLACK = [ 0.0, 0.0, 0.0, 1.0 ]
  
  
  def init_window
    GLUT.Init
    GLUT.InitDisplayMode(GLUT::DOUBLE | GLUT::RGB | GLUT::DEPTH)
    GLUT.InitWindowSize(500, 500)
    GLUT.InitWindowPosition(100,100)
    GLUT.CreateWindow
  end
  
  def set_funcs
    GLUT.DisplayFunc(method(:display).to_proc)
    GLUT.ReshapeFunc(method(:reshape).to_proc)
    GLUT.IdleFunc(method(:display).to_proc)
  end
  
  def init
    LIGHT_COLORS.each_with_index{|color, i|
      init_light(lights[i], color)
    }
    ClearColor(0.0, 0.0, 0.0, 0.0)
    ShadeModel(SMOOTH)
    Enable(LIGHTING)
    Enable(DEPTH_TEST)
    Enable(BLEND)
    BlendFunc(SRC_ALPHA, ONE_MINUS_SRC_ALPHA)
  end
  
  def init_light(light, color)
    light_position = [ 1.0, 1.0, 1.0, 0.0 ]
    Lightfv(light, POSITION, light_position)
    Lightfv(light, DIFFUSE, color)
    Lightfv(light, SPECULAR, color)
    Lightf(light, CONSTANT_ATTENUATION, 0.8)
    Lightf(light, LINEAR_ATTENUATION, 0.1)
    Lightf(light, QUADRATIC_ATTENUATION, 0.1)
    Enable(light)
  end
  
  def display
    Clear(COLOR_BUFFER_BIT | DEPTH_BUFFER_BIT)
    MatrixMode(MODELVIEW)
    GL.LoadIdentity
    set_camera
    draw_spheres
    draw_lights
    GL.Flush
    GLUT.SwapBuffers
  end
  
  def set_camera
    time = Time.now.to_f
    puts time
    GLU.LookAt(
      3.0*(Math.sin(0.5*time)), 2.0, 3.0*(Math.cos(0.5*time)), 
      0.0, 0.0, 0.0, 
      0.0, 1.0, 0.0)
  end
  
  def draw_spheres
    StackAttrib(LIGHTING_BIT) do 
      mat_diffuse = [ 1.0, 1.0, 1.0, 1.0]
      mat_specular = [ 1.0, 1.0, 1.0, 1.0 ]
      mat_shininess = [ 150.0 ]
      Material(FRONT, AMBIENT, BLACK)
      Material(FRONT, DIFFUSE, mat_diffuse)
      Material(FRONT, SPECULAR, mat_specular)
      Material(FRONT, SHININESS, mat_shininess)
      big_sphere_detail = 180
      small_sphere_detail = 80
      StackMatrix{
        GLUT.SolidSphere(1.0, big_sphere_detail, big_sphere_detail)
        Translate(1.2, 1.2, 0.0)
        GLUT.SolidSphere(0.25, small_sphere_detail, small_sphere_detail)
        Translate(-2.4, 0.0, 0.0)
        GLUT.SolidSphere(0.25, small_sphere_detail, small_sphere_detail)
        Translate(0.0, -2.4, 0.0)
        GLUT.SolidSphere(0.25, small_sphere_detail, small_sphere_detail)
        Translate(2.4, 0.0, 0.0)
        GLUT.SolidSphere(0.25, small_sphere_detail, small_sphere_detail)
      }
    end
  end
  
  def draw_lights
    time = Time.now.to_f
    light_positions = []
    light_positions[0] = [
      -1.5*Math.sin(2*time), 
      1.2*Math.sin(time),
      1.5*Math.cos(2*time), 
      1.0 ]
    light_positions[1] = [
      -light_positions[0][0],
      -light_positions[0][1],
      -light_positions[0][2],
      light_positions[0][3] ]
    light_positions[2] = [
      1.5*Math.cos(time), 
      -2.0*Math.sin(3*time),
      1.5*Math.sin(2*time), 
      1.0 ]
    light_positions[3] = [
      -light_positions[2][0],
      -light_positions[2][1],
      -light_positions[2][2],
      light_positions[2][3] ]
    (0..3).each{|i|
      update_light(i, lights[i], light_positions[i])
    }
  end
  
  def lights
    @lights ||= (0..7).map{|i| GL.const_get("LIGHT#{i}")}
  end
  
  def update_light(index, light, position)
    StackMatrix{
      Translate(position[0], position[1], position[2])
      StackAttrib(LIGHTING_BIT){
        Material(FRONT, SPECULAR, BLACK)
        Material(FRONT, SHININESS, BLACK)
        lc = LIGHT_COLORS[index]
        Material(FRONT, EMISSION, lc)
        GLUT.SolidSphere(0.1, 30, 30)
      }
    }
    Lightfv(light, POSITION, position)
  end
  
  def reshape(w, h)
    Viewport(0,0, w, h)
    MatrixMode(PROJECTION)
    GL.LoadIdentity
    GLU.Perspective(60.0,  w.to_f/h, 0.5, 200.0)
  end
  
  def run
    init_window
    init
    set_funcs
    GLUT.MainLoop
  end

end

if __FILE__ == $0
  Spheres.new.run
end