handler geons.

operator(31,xfx,#).      % to describe points

	%:-nodbgcomp.

	option(keep_heads,off).            
	option(check_already_in,off).            

constrained(X) :-
	delayed_goals(X, [_|_]).

delay ground(X) if nonground(X).
ground(X).

geon(S,A,B):- geons(S,[rect(A,B)]).		% upward compatibility

% approximate walls by small rectangles
approx_walls([],[]).
approx_walls([wall(A#B,A#C)|W],[rect(A1#B,A2#C)|R]):- !,
	A1 is A-1, A2 is A+1,
	approx_walls(W,R).
approx_walls([wall(B#A,C#A)|W],[rect(B#A1,C#A2)|R]):- !,
	A1 is A-1, A2 is A+1,
	approx_walls(W,R).
approx_walls([wall(A#B,C#D)|W],[rect(A#B,C#D)|R]):-
	approx_walls(W,R).



constraints geons/2.

/**** geons(Sender, GeonList) ***/

label_with geons(S, L) if true.

geons(X#Y, L1), geons(X#Y, L2) <=> 
	intersect_geons(L1, L2, L3), 
	L3 \== [], 
	geons(X#Y, L3).

geons(X#Y, GeonList):-
	member(rect(A#B, C#D), GeonList), 
	X is (A+C)/2, Y is (B+D)/2.


intersect_geons(L1, L2, L3):-
	bagof(Rect, intersect_geon(L1, L2, Rect), L3).

intersect_geon(L1, L2, rect(A#B, C#D)):-
	member(rect(A1#B1, C1#D1), L1), 
	member(rect(A2#B2, C2#D2), L2), 
	A is max(A1, A2), B is max(B1, B2), 
	C is min(C1, C2), D is min(D1, D2), 
	A=<C, B=<D.