gistfile1.nim

type
  Bitmap = ref PBitmap
  PBitmap = ptr object
    w,h: int

proc load_bitmap_pvt (file:cstring): PBitmap {.importc:"bitmap_load".}
proc destroy (bmp:PBitmap) {.importc:"bitmap_destroy".}

proc free (B:Bitmap) =
  destroy B.bmp
proc load_bitmap (file:string): Bitmap =
  var b = load_bitmap_pvt(file)
  if not b.isNil:
    new(result, free)
    result[] = b

let b = load_bitmap("ello.bmp")
echo b.w,"x",b.h

# we can define this so Bitmap converts automatically to PBitmap
converter tobmp (b:Bitmap):PBitmap = b[]