function plugin_init()
  register('lua interface test plugin', 'not Versioned', 'Hawkear');

  require('Usdx.Gl', 'Usdx.TextGl', 'Usdx.ScreenSing');

  Usdx.Hook('Display.Draw', 'OnDraw');

  return true
end

function OnDraw()
  -- Calculate FPS
  FPScounter = 1 + (FPScounter or 0) -- increment FPScounter (which is nil, when undefined, therefore "or 0")
  if Usdx.Time() > (LastTime or 0) then
    LastTime = Usdx.Time() + 1000

    print("FPS:    " .. FPScounter - (LastFPScounter or 0)) -- print is only displayed, if compiled with DEBUG
    LastFPSCounted = FPScounter - (LastFPScounter or 0)

    LastFPScounter = FPScounter

    -- Show the first 200 Textures
    TexNum = 1 + (TexNum or 0)
    if TexNum > 200 then TexNum = 1 end
    print("TexNum: " .. (TexNum or 0))
  end

  -- draw fps to top right corner
  TextGl.Style(0)
  TextGl.Pos(650, 36)
  TextGl.Size(30)
  TextGl.Italic(False)
  Gl.Color(0.9, 0.9, 0.9, 0.7)
  TextGl.Print('FPS: ' .. LastFPSCounted)

  TextGl.Pos(650, 50)
  TextGl.Print('Beat: ' .. ScreenSing.GetBeat())

  -- Draw some rectanGles
  Gl.Enable("Gl_BLEND")
  Gl.Color(1, 1, 1, 0.5)
  for i = 1,10 do
    Gl.Begin("Gl_LINE_loop")
    Gl.Vertex(0+4*i, 0+4*i);
    Gl.Vertex(0+4*i, 600-4*i);
    Gl.Vertex(800-4*i, 600-4*i);
    Gl.Vertex(800-4*i, 0+4*i);
    Gl.End()
  end
  Gl.Disable("Gl_BLEND")

  -- Display a Texture
  Gl.Enable("Gl_BLEND")
  Gl.Enable("Gl_TEXTURE_2D")
  Gl.Color(1, 1, 1, 1)
  Gl.BindTexture("Gl_TEXTURE_2D", TexNum or 0)
  Gl.Begin("Gl_QUADS")
    Gl.TexCoord(0, 0); Gl.Vertex(10,  10);
    Gl.TexCoord(0, 1); Gl.Vertex(10,  110);
    Gl.TexCoord(1, 1); Gl.Vertex(110, 110);
    Gl.TexCoord(1, 0); Gl.Vertex(110, 10);
  Gl.End()
  Gl.Disable("Gl_TEXTURE_2D")
  Gl.Disable("Gl_BLEND")
end