BYTE *pascal SetWindowPtr(HWND hWnd, int iPtr, BYTE *ptr)

  Sets the value of the single pointer residing at the 'iPtr' position
in the window extra area.

Parameters
  hWnd is the window handle of the window to query.
  iPtr is the 0-based long offset from the start of the window extra area.
  ptr is the single pointer value. It is 2 bytes long in medium model and 4 bytes long in large model.

Returns
  The pointer at pWinExtra[iPtr].