structure Ndc = 
struct
  (* ndc = normalised device coordinates *)
  fun ltrbToVertex (left, top, right, bottom) =
    #[ left, bottom
     , right, bottom
     , left, top

     , left, top
     , right, bottom
     , right, top
     ]

  fun ltrbToVertexRgb (left, top, right, bottom, r, g, b) =
    #[ left, bottom, r, g, b
     , right, bottom, r, g, b
     , left, top, r, g, b

     , left, top, r, g, b
     , right, bottom, r, g, b
     , right, top, r, g, b
     ]
end