libm3/src/geometry/PolyRegion.i3

 Copyright (C) 1992, Digital Equipment Corporation                         
 All rights reserved.                                                      
 See the file COPYRIGHT for a full description.                            
                                                                           
 by Steve Glassman, Mark Manasse and Greg Nelson           
 Last modified on Tue Feb 11 16:23:21 PST 1992 by muller   
      modified on Wed Sep 11 15:32:52 PDT 1991 by msm      

<*PRAGMA LL*>

INTERFACE PolyRegion;

IMPORT Rect, Region, Point;

 A PolyRegion.T represents a set of points as a list of Region.T's. 
   If n rectangles are joined together into a PolyRegion.T with the
   JoinRect procedure below, the PolyRegion will contain about lg n
   Regions, and the total cost of the join is likely to be
   about n (lg n)^2 instead of n^2, assuming the rectangles don't
   overlap too badly. 
   

   The procedures modify the data structure pointed to by the private
   field of a PolyRegion; therefore, you must not assign PolyRegions.  


TYPE
  T = RECORD r: Rect.T; p: Private END;
  (* pr.r is the bounding rectangle of the PolyRegion pr. *)
  Private <: REFANY;

PROCEDURE JoinRect(VAR pr: T; READONLY rect: Rect.T);

 pr := Union(pr, rect). 

PROCEDURE JoinRgn(VAR pr: T; READONLY rgn: Region.T);

 pr := Union(pr, rgn). 

PROCEDURE ToRegion(READONLY pr: T): Region.T;

 Return pr as a region. 

PROCEDURE OverlapRect(READONLY pr: T; READONLY rect: Rect.T): BOOLEAN;

 Return whether pr and rect have a non-empty intersection. 

PROCEDURE Complement(READONLY pr: T; READONLY rgn: Region.T): Region.T;

 Return rgn-pr as a region. 

PROCEDURE Meet(READONLY pr: T; READONLY rgn: Region.T): Region.T;

 Return the intersection of pr and rgn as a region. 

CONST Empty = T{Rect.Empty, NIL};

 The following procedure belongs in Region 


PROCEDURE Factor(READONLY t: Region.T; READONLY r: Rect.T;
  READONLY delta: Point.T; VAR rl: REF ARRAY OF Rect.T): CARDINAL;

 Set rl to a list of disjoint rectangles which partition t meetrect
   r, modifying rl^ if possible.  Return the number of rectangles, n,
   in the partition; only the first n rectangles in rl^ are meaningful.
   The order of rl^ is such that if i<j then rl[i] translated by delta
   doesn't intersect rl[j].  If the intersection is empty, 0 is returned. 

END PolyRegion.