(* Copyright (C) 1992, Digital Equipment Corporation                         *)
(* All rights reserved.                                                      *)
(* See the file COPYRIGHT for a full description.                            *)
(*                                                                           *)
(* Last modified on Thu Dec 31 13:44:28 PST 1992 by mhb                      *)
(*      modified on Tue Jun 16 12:56:44 PDT 1992 by muller                   *)
(*      modified on Fri Apr 17 18:14:06 1992 by steveg                       *)

(* The "Pts" interface contains utilities to convert between
   points and pixels.  VBTkit uses 72 points per inch, 
   following the Postscript convention \cite[page 151]{Postscript}.
   There are 25.4 millimeters to the inch. 

   The locking level is arbitrary for all procedures in this interface. *)

INTERFACE Pts;

IMPORT Axis, VBT;

PROCEDURE ToScreenPixels (v: VBT.T; pts: REAL; ax: Axis.T):
  INTEGER;
(* Return the number of screen pixels that correspond to "pts"
   points on "v"'s screentype in the axis "ax"; or return "0" if
   "v"'s screentype is "NIL".  Equivalent to
| ROUND (ToPixels (v, pts, ax))
  *)

PROCEDURE ToPixels (v: VBT.T; pts: REAL; ax: Axis.T): REAL;
(* Return the number of pixels that correspond to "pts" points on
   "v"'s screentype in the axis "ax"; or return "0" if "v"'s
   screentype is "NIL". *)

CONST
  PtsPerInch = 72.0;
  MMPerInch  = 25.4;

PROCEDURE FromMM (mm: REAL): REAL;
(* Convert from millimeters to points. *)

PROCEDURE ToMM (pts: REAL): REAL;
(* Convert from points to millimeters. *)

END Pts.