sig
  type draw_buffer_mode =
      GL_NONE
    | GL_FRONT_LEFT
    | GL_FRONT_RIGHT
    | GL_BACK_LEFT
    | GL_BACK_RIGHT
    | GL_FRONT
    | GL_BACK
    | GL_LEFT
    | GL_RIGHT
    | GL_FRONT_AND_BACK
    | GL_AUX0
    | GL_AUX1
    | GL_AUX2
    | GL_AUX3
end