path: root/Master/texmf-dist/metafont/roex/roex.mf

%%%%
%%%% This file belongs to the ROEX package.
%%%%
%%%% ---------------------------------------------------------------------
%%%% MFT formatting commands
%%%% ---------------------------------------------------------------------
%%% length quicksort
%%% length cycle zang pos_turn neg_turn
%%% good enc
%%% labels makelabel
%%% length make_cycle make_join make_cyclic_join make_end make_edge
%%% point predir postdir upredir upostdir udir
%%% dotprod det
%%% subpath pos_subpath neg_subpath
%%% message info_ro info_es
%%% draw roex_default
%%% -- &&
%%%% ---------------------------------------------------------------------
%%%% \TeX formatting commands
%%%% ---------------------------------------------------------------------
%%\vsize245mm
%%\font\titfnt cmtt10 at 48 pt
%%{\let\makefootline\empty \let\makeheadline\empty
%%\vglue0ptplus1fill
%%\centerline{\titfnt ROEX.MF}
%%\bigskip
%%\centerline{ver. 0.56 (Wednesday, October 25th, 1995)}
%%\vfill\vfill\eject}
%% % ---
%% \vsize 245mm
%% % an innocent formatting trick: the underscore character ending a name
%% % will be typeset as an superscript asterisk
%% \let\oriunderscore\_
%% \newif\ifbgroupopen\bgroupopenfalse
%% \def\altdblbackslash#1{\bgroup\bgroupopentrue\it#1}
%% \def\optegroup{\ifbgroupopen\egroup\fi}
%% \def\underscoreasasterisk#1{%
%%   \ifx#1\relax\optegroup^*\else\oriunderscore#1\fi}
%% \def\\#1{%
%%   \let\_\underscoreasasterisk
%%   \altdblbackslash{#1\relax}\optegroup
%%   \let\_\oriunderscore}
%% % ---
%% \def\dblhyph{--}
%% \def\8#1{\def\eightparm{#1}\mathrel{\mathcode`\.="8000 \mathcode`\-="8000
%% \ifx\eightparm\dblhyph\setbox\shorthyf\hbox{\bf -\kern-.05em}\fi%
%%  #1\unkern}} % `..' and `--'
%% % ---
%% \def\MP{{\tenlogo META}\-{\tenlogo POST}}
% ------------------------------------------------------------------------
% This is ROEX.MF file containing \MF definitions implementing
% operations known as `remove overlap' and `expand stroke'.
% ------------------------------------------------------------------------
% Authors: \bf{}B. Jackowski, P. Pianowski, M. Ry\'cko \& S. Soko\l{}owski
% ------------------------------------------------------------------------
%                            H I S T O R Y
% ver. 0.1 (1 / 9 VI 1994):
%   * incunabula version
% ver. 0.5 (15 VIII / 1 IX 1995):
%   * pioneer version, released during the 9th Euro\TeX conference in Arnhem
% ver. 0.55 (26 IX 1995):
%   * if a single path is an argument to |remove_overlap|, removing
%     of self-overlaps is performed, hence several adjustments, most
%     significant changes were introduced in |is_far_enough| and
%     |intersect_two_segments|; this ismprovement is, in fact, a prelude
%     towards a more general approach
%   * a bug trap added in |clean_path|
%   * positioning of labels not forced in |mark_nodes|
%   * |quicksort| more flexible
%   * more statistics available (optionally) in |find_minimal_secant|
%   * displaying information changed
%   * \TeX formatting comments collected at the beginning of the file
%   * a result of mental laps corrected in |build_node_structure|
%     (minimal secant has nothing to do with minimal distance between nodes)
%   * a silly bug removed in |prepare_input_data| (|W| instead of |W_|)
%   This version was released during the CyrTUG-95 meeting in Moscow
% ver. 0.56 (27 X 1995):
%   * comments adjusted to a new distribution
%   * the name |miter_limit| changed to |miter_size| in order to avoid
%     misunderstanding, as in this implementation it is a dimen, while
%     in PostScript it is a dimensionless quantity
% ------------------------------------------------------------------------
%                           S Y N O P S I S
% ------------------------------------------------------------------------
%
% Such operations as `remove overlap' and `expand stroke' are perhaps
% particularly useful in the contex of exporting data from \MF to other
% languages, e.g., to PostScript or HP-GL. Therefore the file ROEX.MF has
% been included into the MFTOEPS package (which accomplishes export from \MF
% to Encapsulated PostScript), although it can be used by ``normal'' \MF
% users, too. Therefore our favourite macros (e.g., |pos_turn|, |neg_turn|,
% |make_list|), are defined identically in both ROEX and MFTOEPS.
%
% We hope that tiny adjustments, if any, should be sufficient for transforming
% the macros to the form accepted by both \MF and \MP.
%
% Sample \MF programs (i.e., simple examples) illustrating the use of the
% ``interface'' macros, i.e., |remove_overlap|, |expand_stroke| and
% |change_weight|, can be found in a subdirectory ROEXSAMP. It is instructive
% to generate EPS files and then to play around with the results using
% CorelDRAW! or Adobe Illustrator.
%
%
% REMOVING OVERLAPS
%
% The command |remove_overlap_| requires three parameters. The first
% parameter is a list of paths to be processed; the paths are assumed to
% have a non-zero |turningnumber| and no self intersecting points (no
% checking is performed, except that non-cyclic paths are ignored).
% The second parameter is a list (possibly empty) of weights assigned
% to paths; more exactly, it is a list of pairs |(i,w.i)|, where |i| is
% the order number of a path and |w.i| is the respective weight.
% If the weight is not specified it is assumed to be equal to |1|.
% The last parameter is a suffix, i.e., the name of the resulting data
% structure; given a suffix is |R|, |R.num| is the number of the resulting
% paths, and |R1|, |R2|, ..., |R[R.num]| are the paths. If the suffix
% contains an index, e.g., |P[x]q|, the user is responsible for providing
% appropriate declarations prior to calling |remove_overlap|,
% in this case: |numeric P[\\]q.num; path P[\\]q[\\]|. If a variable
% |append_results| is assigned a definite value (by default it is undefined),
% |R.num| is not zeroed at the stage of initialisation, thus the results
% are accumulated (see example ROES-02.MF in the subdirectory ROEXSAMP).
%
% The algorithm assumes that a path |p| fills its interior with the colour
% |w*turningnumber(p)|, where |w| is the weight assigned to |p|. If an
% area is coloured by several paths, the colors are summed up. The user
% decides which areas are the resulting ones. By default, these are areas
% which have the interior painted with a colour $\ge1$ and the exterior
% painted with a colour $\le0$. There is a two-parameter function
% (parameters are numbers) that can be redefined by a user, |good_colors|,
% which governs the decision. The user is responsible for a proper definition
% of this function (the formula |good_colors(m,n) and good_colors(n,m)| must
% be false; cf. the default definition of |good_colors| at the end of this
% file). There is also a variable |background_color|, by default equal to |0|,
% which determines the colour of the Euclidian plane. One more function that
% is meant to be redefined by the user, if needed, is one-parameter function
% |touch_path|; the function is applied to every input path at the stage of
% initialisation, and can be used, e.g., for adjusting the direction of paths
% (cf. example RO-04.MF in the subdirectory ROEXSAMP).
%
% The orientation of paths generated by the |remove_overlap| macro is defined
% in such a way that in order to fill the resulting figure the internal
% variable |turningcheck| should be set to zero prior to using the |fill|
% command.
%
% Examples:
%  Assume that paths |A|, |B| and |C| are defined as follow (say, |w=h=1cm|):
%    |A=unitsquare xscaled 1/5w yscaled h shifted (2/5w,0);|
%    |B=A rotatedaround((1/2w,1/2h), 60);|
%    |C=B rotatedaround((1/2w,1/2h), 60);|
%  Calling
%    |remove_overlap (A,B,C) () R;|
%  will result in generating a single path |R1| (|R.num=1|) of a six-arm
%  propeller shape. Adding one more path:
%    |D=reverse fullcircle scaled 3/4w shifted (1/2w,1/2h);|
%  and calling
%    |remove_overlap (A,B,C,D) ((4,2)) R;|
%  (|D| has weight |=2|) will result in generating seven objects: six
%  ``tips'' of a propeler and a regular hexagon in the center. Try to guess
%  what would be the result of
%  |remove_overlap (A,B,C,D) () R;|
%  Not all paths need to intersect. For example, the following set of paths
%    |A=fullcircle scaled w shifted (1/2w,1/2h);|
%    |B=reverse unitsquare xscaled 1/5w yscaled 3/5w shifted (2/5w,1/5w);|
%    |C=B rotatedaround((1/2w,1/2h), 90);|
%  after calling
%    |remove_overlap (A,B,C) () R;|
%  will yield a circle surrounding a white cross. Since the orientation
%  of the resulting paths is important here, the |fill| commands should be
%  preceded by
%    |interim turningcheck:=0;|
%  assignment.
%
%
% EXPANDING STROKES
%
% Expanding stroke means finding the trace of the outline of an imaginary pen
% moving along a path. There are two commands accomplishing expanding stroke:
% |expand_stroke| and |change_weight|. Both make use of the essentially the
% same algorithm, except that the latter finds only one edge and ignores
% non-cyclic paths. Both commands require three parameters: first and third
% are analogous to the parameters of the |expand_stroke| macro (see above),
% the second denotes the radius (not diameter) of the circular pen.
% The algorithm works in such a way that the result of the |expand_stroke|
% does not depend on the direction of a path for cyclic paths, namely,
% the outer edge is always positively directed and the inner is negatively
% directed, provided the radius is positive; if the radius is negative,
% the outer edge is negatively directed and the inner one---positively.
% For non-cyclic paths positive radius yields positively directed resulting
% paths, negative radius---negatively oriented paths. Although the macro
% |change_weight| is subdued to the same rules, the result depends both
% on the direction of a path and on the sign of a radius. Let |t| and |r|
% denote the turning number and the radius, respectively; there are
% four cases:
%   1) |t>0| and |r>0|: the resulting path is an outer edge positively
%      directed,
%   2) |t>0| and |r<0|: the resulting path is an inner edge positively
%      directed,
%   3) |t<0| and |r>0|: the resulting path is an inner edge negatively
%      directed,
%   4) |t<0| and |r<0|: the resulting path is an outer edge negatively
%      directed.
% Following PostScript, we introduced three variables which govern the shape
% of joins and ends: |join_kind| (corresponds to |setlinejoin|), |end_kind|
% (corresponds to |setlinecap|) and |miter_size| (corresponds, as the name
% suggest, to |setmiterlimit|; however, here |miter_size| is a dimen,
% while in PostScript miter limit is a dimensionless quantity).
% Currently both |join_kind| and |end_kind| can receive value |0| or |1|,
% while in PostScript value |2| is also admissible. (The latter option
% will perhaps be included also into the ROEX package some day, but more
% tempting is the implementation of extrapolated non-linear joins.)
% Since the interpretation of |miter_size| (dimen) is slightly different than
% the interpretation of |miter_limit| (a number), |miter_size| must merely
% be non-negative, while |miter_limit| must be greater than or equal to $1$.
% Roughly speaking, value |0| for |join_kind| and |end_kind| denotes cusp
% joins, cut if necessary at miter limit; value |1| denotes rounded rounded
% joins (for details see, e.g., ``PostScript Language Reference Manual,''
% second ed., Addison-Wesley Publishing Company, Ltd.).
%
% Example:
%  Assume that a path |A| is simply a square (say, |w=h=1cm|):
%    |A=unitsquare scaled w;|
%  After calling
%    |expand_stroke(A)(1mm)R;|
%  |R1| is a positively directed square of side |12mm|, and |R2| is
%  negatively directed square of side |8mm|.
% ------------------------------------------------------------------------
%        C A V E A T S ,    H I N T S    A N D    C O M M E N T S
% * The employed algorithms expect that the results are well defined;
%   if the data are weird (e.g., self-loooping path are supplied)
%   the results, if any, may be weird as well.
% * The case of curves partially overlapping is not handled and, frankly
%   speaking, we have no idea how to implement it efficiently and robustly;
%   if there are such pairs of paths in the input data, the algorithm almost
%   certainly will not produce good results.
% * Only circular pens are implemented so far.
% * Be aware of rounding errors, they may cause unpredictable results;
%   in some cases increasing accuracy by using a higher resolution may
%   help, but more adequate seems to be preparing better data (cf. the
%   program RO-07.MF in the subdirectory ROEXSAMP).
% * Comments in the code are meant primarily for the authors; the user
%   is kindly requested not to complain fiercely if they are of a little
%   use to her/him.
% * Unfortunately, \MF has no error-handling facility, hence a lot of
%   ``bug traps'' can be found in the code; messages issued in the case
%   of falling into such a trap are rather useless if you don't know the
%   details of the algorithm; this part of the program is certainly to be
%   improved; usually the error help says ``Better stop now! Algorithm
%   failed'' and this advice should be followed; in practice this means that
%   \MF is not able to recognize the details of the picture because of
%   very close nodes (intersection points).
% * Usually, the first stage of removing overlaps (finding all intersection
%   points) is the longest one, the more segments paths have the longer it
%   lasts; a pity that \MF has no built-in function informing about all
%   intersection points/times of two B\'ezier curves.
% * Improper definition of |good_colors| may result in erroneous behaviour of
%   the algorithm.
% * One peculiar case is considered by the expanding stroke algorithm,
%   namely cyclic path of length 2; some more cases might have been taken
%   into account...
% * There remain a lot of unsolved problems with numerical instability
%   connected with detecting tangent and close points.
% * In The \MF{}book, p. 229, D. E. Knuth writes:
%     ``...tiny little loops won't hurt anything if you are filling cycles
%       in the correct direction.''
%   Cf. also preceding dangerous band paragraph and exercise on pp. 228--229.
%   ROEX does much more complex things with paths than merely filling them,
%   hence tiny loops may cause some mess, the more so as the built-in
%   function |turningnumber| is very sensitive to such loops, e.g., it may
%   happen that |turningnumber(p)=1| while |turningnumber(reverse p)=0|
%   (cf. example RO-6.MF in the subdirectory ROEXSAMP); hence a hopefully
%   more robust (from the point of view of this application) function
%   is used, |check_turn|, which makes use of \MF's |fill| operation.
% * There remain several suboptimal algorithms employed, partially on
%   purpose: less efficient algorithms are usually (although not necessarily)
%   more comprehensible and flexible (easier to modify), which is important
%   at the stage of developing a program.
% * Parameters that may have influence on the process of removing
%   overlaps are |epsil.time|, |epsil.ang| (in degrees), |epsil.dist| (in
%   resolution-dependent units), and |max_idx|; the choice of good default
%   values will need some practice.
% * Incompatible modifications may come, although we shall do our best
%   to avoid them.
% ------------------------------------------------------------------------
% We follow the naming convention of The \MF{}book:
% ``Private tokens always end with the underscore character.''
% Since the underscore is a rather illegible character, in a ``neat''
% printing (using MFT utility) it will appear as an superscript asterisk.
% ------------------------------------------------------------------------
%                          D E F I N I T I O N S
% ------------------------------------------------------------------------
% UNIVERSAL MACROS:
% ---
% Without the following redefinition:
def -- = {curl 1} .. tension (1+eps) .. {curl 1} enddef;
% the result of |p intersectiontimes reverse p|, where |p=(a,b)--(a+3c,b+3d)|,
% |a|, |b|, |c|, |d| are arbitrary (sic!) \MF's numbers, yields the result
% |(1/2,1/2)|, which contradicts the statement preceding the exercise 14.17
% on the page 137 of The \MF{}book. Since it is no longer a ``standard''
% macro, its formatting is slightly modified.
% ---
%%% length ]]] ]]]]
%%% ; ]
def ]]] = ] ] ] enddef;
def ]]]] = ] ] ] ] enddef; % right brackets should be loners, indeed
%%% ) ] ]] ]]] ]]]]
% ---
vardef distance(expr za,zb) = length(za-zb) enddef; % in fact, an alias
% ---
vardef interval(expr ta,tb,p) =
 save ta_,tb_;
 if cycle p:
  ta_:=ta mod length(p); tb_:=tb mod length(p);
  min(length(p)-abs(ta_-tb_), abs(ta_-tb_))
 else:
  ta_:=min(max(0,ta),length(p)); tb_:=min(max(0,tb),length(p));
  abs(ta_-tb_)
 fi
enddef;
% ---
def make_list(expr k,l) suffix s =
 for i_:=k upto l: if i_>k: , fi \\ s[i_] endfor
enddef;
% ---
vardef dec_pair(expr z) =
 "(" & decimal(xpart z) & "," & decimal(ypart z) & ")"
enddef;
% ---
primarydef u det v = % dual operation to |dotprod|
 (xpart u * ypart v - xpart v * ypart u)
enddef;
% ---
vardef zang(expr u,v) = % useful during testing
% computes the angle form |u| to |v| (useful for testing)
 angle(u dotprod v,u det v) mod 360 % CAVEAT! rounding errors
enddef;
% ---
vardef turn_ang(expr za,zb) = % more robust version of |zang|
% The idea of computing the turn angle is based on the following observation:
% |z reflectedabout (origin,right)=1/z| for a complex number |z| such that
% |abs(z)=1|; recall also that multiplication of complex numbers
% (|zscaled| operation) implies addition of their angle arguments.
 if (abs(za)>=epsil.len) and (abs(zb)>=epsil.len): % |eps| may be not enough
  angle(unitvector(za) zscaled (unitvector(zb) reflectedabout (origin,right)))
 else: whatever fi
enddef;
% ---
def predir expr t of p = ((point t of p)-(precontrol t of p)) enddef;
def postdir expr t of p = ((postcontrol t of p)-(point t of p)) enddef;
def udir expr t of p = unitvector(direction t of p) enddef;
def upredir expr t of p = unitvector(predir t of p) enddef;
def upostdir expr t of p = unitvector(postdir t of p) enddef;
% ---
vardef pos_turn primary p =
 interim autorounding:=0;
 if check_turn(p)=0: show p;
  errhelp "I will leave the path intact, continue with crossed fingers.";
  errmessage "Cannot make positive turn (check_turn=0)";
 elseif check_turn(p)<0: reverse fi \\ p
enddef;
% ---
vardef neg_turn primary p =
 interim autorounding:=0;
 if check_turn(p)=0: show p;
  errhelp "I will leave the path intact, continue with crossed fingers.";
  errmessage "Cannot make negative turn (check_turn=0)";
 elseif check_turn(p)>0: reverse fi \\ p
enddef;
% ---
vardef check_turn primary p = % seems more adequate than |turningnumber|
% |epsilon|=|totalweight currentpicture| after |fill unitsquare|,
% |eps/epsilon=32|, i.e., we admit accuracy of 32 pixels (isn't it too many?)
 save r_,currentpicture; picture currentpicture;
 interim turningcheck:=0; interim autorounding:=0;
 currentpicture:=nullpicture; fill p; r_:=totalweight(currentpicture);
 if r_>eps: 1 elseif r_<-eps: -1 else: turningnumber(p) fi
enddef;
% ---
def check_embedding(expr a,b)(suffix res) =
begingroup
% see comment in |check_turn|
 save napb_,panb_,currentpicture; picture currentpicture;
 interim turningcheck:=0; interim autorounding:=0;
 currentpicture:=nullpicture; fill pos_turn a; fill neg_turn b; cullit;
 panb_:=totalweight currentpicture;
 currentpicture:=nullpicture; fill neg_turn a; fill pos_turn b; cullit;
 napb_:=totalweight currentpicture;
 if (panb_<eps) and (napb_<>0): res:=1; % $a \subset b$
 elseif (panb_<>0) and (napb_<eps): res:=2; % $b \subset a$
 else: res:=0; fi % undefined result
endgroup
enddef;
% ---
vardef pos_subpath expr z of p =
 if not cycle p: subpath z of p
 else:
  if xpart(z)<=ypart(z): subpath z of p
  else: subpath (xpart(z),ypart(z)+length(p)) of p
  fi
 fi
enddef;
% ---
vardef neg_subpath expr z of p =
 if not cycle p: subpath z of p
 else: reverse(pos_subpath (ypart z,xpart z) of p) fi
enddef;
% ---
tertiarydef p && q = % |length(p)>0|
  (subpath(0,length(p)-1) of p) ..
   controls (postcontrol length(p)-1 of p) and (precontrol length(p) of p)
   .. q
enddef;
% ---
def make_cycle expr p = % |length(p)>0|
  (subpath(0,length(p)-1) of p) ..
   controls (postcontrol length(p)-1 of p) and (precontrol length(p) of p)
   .. cycle
enddef;
% ---
vardef is_line(expr B) =
% checks if a B\'ezier segment |B| is an almost straight line;
% recall that |z reflectedabout (origin,right)=1/z| for a complex
% number |z| such that |length(z)=1|; recall also that the multiplication
% of complex numbers (|zscale| operation) implies the addition of
% their angle arguments
 save pa_,pb_,pc_,pd_,ba_,da_,dc_; pair pa_,pb_,pc_,pd_,ba_,da_,dc_;
 pa_:=point 0 of B; pd_:=point 1 of B;
 if distance(pa_,pd_)<epsil.dist:
  false % either really not a line or an uncertain situation (rounding errors)
 else:
  da_=unitvector(pd_-pa_) reflectedabout (origin,right);
  pb_:=postcontrol 0 of B; if distance(pa_,pb_)<epsil.dist: pb_:=pa_; fi
  pc_:=precontrol 1 of B; if distance(pd_,pc_)<epsil.dist: pc_:=pd_; fi
  if (pa_=pb_) and (pc_=pd_): true
  elseif (pa_=pb_):
   dc_=unitvector(pd_-pc_); abs(angle(dc_ zscaled da_))<epsil.ang
  elseif (pc_=pd_):
   ba_=unitvector(pb_-pa_); abs(angle(ba_ zscaled da_))<epsil.ang
  else:
   ba_=unitvector(pb_-pa_); dc_=unitvector(pd_-pc_);
   (abs(angle(ba_ zscaled da_))<epsil.ang)
    and (abs(angle(dc_ zscaled da_))<epsil.ang)
  fi
 fi
enddef;
% ---
vardef is_tiny_bez(expr B) =
% checks if B\'ezier segment |B| is negligibly small
 (distance((postcontrol 0 of B),(point 0 of B))<epsil.dist)
 and (distance((precontrol 1 of B),(point 0 of B))<epsil.dist)
 and (distance((point 1 of B),(point 0 of B))<epsil.dist)
enddef;
% ---
vardef are_parallel(expr B,C) =
% checks if B\'ezier segments |B| and |C| are linear and parallel
save a_;
 if is_line(B) and is_line(C):
  a_:=turn_ang((point 0 of B)-(point 1 of B),(point 0 of C)-(point 1 of C));
  (if known a_: abs(a_)<epsil.ang else: false fi)
 else: false fi
enddef;
% ---
vardef tidy_lines(expr P) =
% converts almost linear segments of a path |P| into a ``tidy'' lines (|--|)
 save B_; path B_;
 for i_:=1 upto length(P): if i_>1: & fi
  hide(B_:=subpath (i_-1,i_) of P)
  if is_line(B_): ((point 0 of B_)--(point 1 of B_)) else: B_ fi
 endfor if cycle P: & cycle fi
enddef;
% ---
def add_bez(expr ta,tb, p) =
 .. controls (postcontrol ta of p) and (precontrol tb of p) .. (point tb of p)
enddef;
% ---
vardef clean_path(expr P) =
% this routine joins together colinear neighbouring segments and removes
% ``tiny'' edges of a cyclic path |P| (performed at the end of removing
% overlaps and expanding stroke); since some nodes may become ``midline''
% ones after cleaning, the operation is performed twice
 if cycle P:
  save P_,for_del_,not_del_,i_,j_; path P_;
% mark all deletable nodes and one non-deletable node:
  for i_:=0 upto length(P)-1:
   if are_parallel(subpath (i_-1,i_) of P,subpath (i_,i_+1) of P)
     or is_tiny_bez(subpath(i_-1,i_) of P):
    for_del_[i_]:=1;
   else:
    not_del_:=i_;
   fi
  endfor;
% BUG TRAP:
  if unknown not_del_:
   err_helpless;
   errmessage "ROEX ERROR: all nodes deleted during path cleaning";
  fi
% delete nodes:
  i_:=j_:=not_del_; % we start with |not_del_|: one of not deleted points
  P_:=(point j_ of P)
   forever:
% invariant: |i_| recent not deleted point, |j_| current point
    hide(j_:=(j_+1) mod length(P))
    if unknown for_del_[j_]: add_bez(i_,j_,P) \\ hide(i_:=j_) fi
   exitif j_=not_del_;
   endfor & cycle;
  tidy_lines(P_)
 else: P fi
enddef;
% ---
vardef is_less(expr a,b) = (a<b) enddef;
vardef quicksort@#(expr ii,jj)(suffix s)(text t) =
% sorts |@#.s[ii..jj]| along with |@#.$[ii..jj]| for |$| in |t|,
% using Tony Hoare's ``quick sort'' method; suffix |s| must must not occur
% in the |t| list (no checking is performed); if both |s| and |t| are empty,
% |t| is ignored.
% REMARK 1: the algorithm has no explicit recursion, because of \MF's limits
%           on recursion level.
% REMARK 2: the algorithm, of course, is not stable, i.e., it does not
%           preserve the order of equal items, but it does not matter here
 save i_,j_,k_,l_,cell_,stack_,incl_t_; boolean incl_t_;
 pair stack_[\\]; stack_.lev:=0; stack_[incr stack_.lev]:=(ii,jj);
 i_:=0; for $:=t: i_:=i_+1; endfor % ``measure'' |t|-list
 incl_t_:=(str s <> "") or ((str s = "") and (i_<>0));
 forsuffixes $:= s if incl_t_: , t fi:
  if numeric @#.$[ii]: numeric cell_.$;
  elseif string @#.$[ii]: string cell_.$;
  elseif boolean @#.$[ii]: boolean cell_.$;
  fi
 endfor
 forever:
 exitif stack_.lev<=0;
  numeric i_,j_; (i_,j_)=stack_[stack_.lev]; stack_.lev:=stack_.lev-1;
  if i_<j_:
   forsuffixes $:= s if incl_t_: , t fi: cell_.$:=@#.$[i_]; endfor
   l_:=i_;
   for k_:=i_+1 upto j_:
    if is_less(@#.s[k_],cell_.s):
     forsuffixes $:=s if incl_t_: , t fi:
      @#.$[l_]:=@#.$[k_]; @#.$[k_]:=@#.$[l_+1];
     endfor
     l_:=l_+1;
    fi
   endfor
   forsuffixes $:= s if incl_t_: , t fi: @#.$[l_]:=cell_.$; endfor
   stack_[incr stack_.lev]:=(i_,l_-1); stack_[incr stack_.lev]:=(l_+1,j_);
  fi
 endfor
enddef;
% ---
% R-O MACROS:
% ---
% visualising macros (useful for testing):
% ---
def mark_nodes =
 if proofing>0:
  for i_:=1 upto NODE_.num:
   makelabel(decimal(i_) & ":" & decimal(NODE_.pth[i_]),
    point TIME_[NODE_.pth[i_]]tim[NODE_.tim[i_]] of PATH_[NODE_.pth[i_]]);
  endfor
 fi
enddef;
% ---
def mark_area(expr i) =
begingroup
 save j_,v_; j_:=i; mark_edge(j_); v_[j_]:=0;
 forever: j_:=EDGE_.out[j_]; exitif (j_=i) or (known v_.emerg);
  if known v_[j_]: v_.emerg:=0; else: mark_edge(j_); v_[j_]:=0; fi
 endfor
endgroup
enddef;
% ---
def mark_edge(expr i) =
begingroup
 if proofing>0:
  save currentpen, currentpen_path; pen currentpen; path currentpen_path;
  makelabel(decimal(i),
   (point .5length(the_edge(i)) of the_edge(i))+
   1pt*(udir .5length(the_edge(i)) of the_edge(i)) rotated 90);
  pickup pencircle scaled 1;
  draw (point .5length(the_edge(i)) of the_edge(i))--
   ((point .5length(the_edge(i)) of the_edge(i))+
   (1pt*(udir .5length(the_edge(i)) of the_edge(i)) rotated 90));
  makelabel("", point 0 of the_edge(i));
 fi
endgroup
enddef;
% ---
def mark_edges =
 for i_:=-EDGE_.num upto EDGE_.num: if i_<>0: mark_edge(i_); fi endfor
enddef;
% ---
def show_area(expr i) =
begingroup
 save j_,v_; j_:=i;
 message "EDGE " & decimal(j_) & "/" & decimal(EDGE_.pth[j_]) & ":";
 message "color " &
  if known EDGE_.col[j_]: decimal(EDGE_.col[j_]) else: "???" fi;
 v_[j_]:=0;
 forever: j_:=EDGE_.out[j_]; exitif (j_=i) or (known v_.emerg);
  if known v_[j_]: v_.emerg:=0; fi
  v_[j_]:=0; message "  " & decimal(j_) & "/" & decimal(EDGE_.pth[j_]);
 endfor
endgroup
enddef;
% ---
def show_areas =
 for i_:=-EDGE_.num upto EDGE_.num: if i_<>0: show_area(i_); fi endfor
enddef;
% ---
def err_helpless =
 errhelp "Better stop now! Algorithm failed.";
enddef;
% ---
def err_extra_info(expr i,j) =
 message
"========================== BEGIN OF ERROR INFO: ==========================";
 for k_:=i,j:
  if known k_:
   message "Edge " & decimal(k_) &
    " (a subpath of the path " & decimal(EDGE_.pth[k_]) & "):";
   message "Color:"; show EDGE_.col[k_]; show the_edge(k_);
  fi
 endfor;
enddef;
% ---
% principal macros:
% ---
vardef edge_path(expr i) = PATH_[EDGE_.pth[i]] enddef;
vardef first_time(expr i) =
 TIME_[NODE_.pth[EDGE_.fnd[i]]]tim[NODE_.tim[EDGE_.fnd[i]]]
enddef;
vardef last_time(expr i) =
 TIME_[NODE_.pth[EDGE_.lnd[i]]]tim[NODE_.tim[EDGE_.lnd[i]]]
enddef;
% ---
vardef the_edge(expr i) =
 if i>0: pos_subpath else: neg_subpath fi
  (first_time(i), last_time(i)) of edge_path(i)
enddef;
% ---
vardef make_area(expr i) =
 save j_,q_,v_; path q_; j_:=i; v_[j_]:=0; q_:=the_edge(j_);
 forever: j_:=EDGE_.out[j_]; exitif (j_=i) or (known v_.emerg);
  if known v_[j_]:
   show_area(i); err_helpless;
   errmessage "RO ERROR: Edge " & decimal(j_) & " revisited";
   v_.emerg:=0;
  fi
  v_[j_]:=0; q_:=q_ && the_edge(j_);
 endfor
 make_cycle(q_)
enddef;
% ---
vardef is_tangent(expr i,j,k,l) =
 save e_,d_,pi_,pj_,ti_,tj_; path e_,pi_,pj_;
 if (TIME_[i]num=0) or (TIME_[j]num=0): true
 else:
  ti_.loc:=TIME_[i]tim[k];
  ti_.prv:=TIME_[i]tim[(k-1) mod (TIME_[i]num+1)];
  ti_.nxt:=TIME_[i]tim[(k+1) mod (TIME_[i]num+1)];
  tj_.loc:=TIME_[j]tim[l];
  tj_.prv:=TIME_[j]tim[(l-1) mod (TIME_[j]num+1)];
  tj_.nxt:=TIME_[j]tim[(l+1) mod (TIME_[j]num+1)];
  pi_:=PATH_[i] shifted (-point ti_.loc of PATH_[i]);
  pj_:=PATH_[j] shifted (-point tj_.loc of PATH_[j]);
  d_:=min(
   distance(point ti_.loc of pi_, point ti_.prv of pi_),
   distance(point ti_.loc of pi_, point ti_.nxt of pi_),
   distance(point tj_.loc of pj_, point tj_.prv of pj_),
   distance(point tj_.loc of pj_, point tj_.nxt of pj_));
% BUG TRAP 1:
  if d_<epsil.dist:
   err_helpless;
   errmessage "RO ERROR: Cannot check tangency (too short secants)";
  fi
  e_:=enc.pth scaled (1/2[epsil.dist,d_]);
  save ta_,tb_,tc_,td_;
  save tt_;
  (tt_,ta_)=(pos_subpath (ti_.prv,ti_.loc) of pi_) intersectiontimes e_;
  save tt_;
  (tt_,tb_)=(pos_subpath (ti_.loc,ti_.nxt) of pi_) intersectiontimes e_;
  save tt_;
  (tt_,tc_)=(pos_subpath (tj_.prv,tj_.loc) of pj_) intersectiontimes e_;
  save tt_;
  (tt_,td_)=(pos_subpath (tj_.loc,tj_.nxt) of pj_) intersectiontimes e_;
% BUG TRAP 2:
  if (ta_<0) or (tb_<0) or (tc_<0) or (td_<0):
   err_helpless; errmessage "RO ERROR: Cannot check tangency";
  fi
  forsuffixes tt_:=tb_,tc_,td_: tt_:=(tt_-ta_) mod enc.len; endfor
  ((tc_>=tb_) and (td_>=tb_)) or ((tc_<=tb_) and (td_<=tb_))
 fi
enddef;
% ---
vardef multi_path_case = PATH_.num>1 enddef;
def prepare_input_data(text P)(text W) =
% |P|: list of paths to be processed (non-cyclic paths are ignored);
% |W|: list of weights given as pairs: (index, value)
 PATH_.num:=0;
 for P_:=P: if cycle P_: PATH_[incr PATH_.num]:=touch_path(P_); fi endfor
 for W_:=W: PATH_.wei[xpart W_]:=ypart W_; endfor
 for i_:=1 upto PATH_.num:
  if unknown PATH_.wei[i_]: PATH_.wei[i_]:=1; fi
 endfor
enddef;
% ---
def initialise_removing_overlaps =
% Given paths are |PATH_1|, |PATH_2|, ..., |PATH_[P.num]|;
% if |PATH_[i][j]| is known, paths |PATH_[i]| and |PATH_[j]| at least touch
% each other; |PATH_.wei[i]| is a weight of a path (corresponds to
% multiplying a turning number by this value or, in other words, to
% applying |PATH_.wei[i]| times a fill operation to the path |PATH_[i]|).
numeric PATH_.num, PATH_[\\][\\], PATH_.wei[\\]; path PATH_[\\];
%
% Lone paths are stored in variable |LONE_|; |LONE_.col[i]| determines
% the color (being an integer number) of the plane surrounding the path
% |LONE_[i]|; |LONE_.wei| is a weight inherited from |PATH_.wei| (see above).
numeric LONE_.num, LONE_.col[\\], LONE_.wei[\\]; path LONE_[\\];
%
% |TIME_[i]num| is the number of intersection points for paths |PATH_[i]|,
% |TIME_[i]tim[j]| is the time of intersection of the |j|-th point of path
% |PATH_[i]| (points are sorted with respect to time), |TIME_[i]ntp[j]|
% marks non-tangent points (if known), |TIME_[i]nod[j]| is the node number
% of |j|-th point of path |PATH_[i]| (only non-tangent points are considered
% to be nodes, points on a path are numbered from |0|).
numeric TIME_[\\]num, TIME_[\\]tim[\\], TIME_[\\]ntp[\\], TIME_[\\]nod[\\];
%
% Variables with prefix |EDGE_| describe the edge structure that results from
% intersecting process; the data structure is similar to Dijkstra's data
% structure for the algorithm finding the convex hull of for a given
% set of points (E. W. Dijkstra, ``A Discipline of programming'',
% Prentice-Hall, Inc., 1976): the edges (edsges?) are numbered
% |-EDGE_.num|, |-EDGE_.num+1|, ..., |-1|, |1|, ... |EDGE_.num-1|,
% |EDGE_.num|; edges |i| and |-i| are in fact the same edge but
% differently oriented, the positive value denotes the edge which
% direction is consistent with the direction of the original path;
% |EDGE_.out[i]| is the number of the leftmost edge outcoming from
% the last node, i.e., |EDGE_.lnd[i]|; the number of the first node
% of |i|-th edge is |EDGE_.fnd[i]|; color of |i|-th edge, i.e., the color
% of the area surrounded by the edge and its leftmost successors is stored
% in |EDGE_.col[i]|; |i|-th edge belongs to the path of |PATH_[EDGE_.pth[i]]|;
% |EDGE_.aux[\\]| is an auxiliary variable; all intersecting paths
% can be grouped into |SPOT_.num| of disjoint ``spots''; for |i=1|, |2|, ...,
% |SPOT_.num|, |EDGE_.bed[i]| is the number of the edge which leftmost
% successors form the area being a boundary of the intersecting paths
% for a given spot and |EDGE_.bpa[i]| is the boundary (since there is
% one-to-one correspondence between boundaries and spots, boundaries are
% pairwise disjoint, too).
numeric EDGE_.num, EDGE_.pth[\\], EDGE_.out[\\], EDGE_.aux[\\], EDGE_.col[\\],
 EDGE_.fnd[\\], EDGE_.lnd[\\], EDGE_.are[\\], EDGE_.bed[\\];
path EDGE_.bpa[\\];
%
% Variables with prefix |NODE_| describe the node structure and are related
% to the edge structure; the node is not a point on a plane but a point on a
% path, hence several nodes may correspond to one Euclidian point;
% |NODE_.num| is the number of nodes, |NODE_.pth[i]| is the number of a path
% to which the node |i| belongs, |NODE_.tim[i]| is the corresponding time on
% path |PATH_[NODE_.pth[i]]|, |NODE_.ped[i]| is the ordering number of a
% positively-numbered edge leaving the node |i|, |NODE_.ned[i]| is the
% ordering number of negatitively-numbered edge leaving node |i|,
% |NODE_.nod[i]num| is the number of nodes coinciding with node |i| and
% these are nodes |NODE_.nod[i]1|, |NODE_.nod[i]2|, ...,
% |NODE_.nod[i][NODE_.nod[i]num]|.
numeric NODE_.num, NODE_.pth[\\], NODE_.tim[\\], NODE_.ned[\\],
 NODE_.ped[\\], NODE_.nod[\\]num, NODE_.nod[\\][\\];
%
% It often happens that intersecting paths form disjoint areas or that
% there are paths that do not intersect; it is crucial for the colouring
% algorithm to know the embedding ``hierarchy''; the hierarchy is stored in
% a tree structure: the links (suffix |emb|) point upward (from leaves to
% the root), moreover, with each leaf (node) is associated a ``level,''
% i.e., the number of leaves beneath this leaf; the information stored in
% a leaf is either the number of a lone path or the number of an area being
% the result of the intersecting process (negative value marks the former
% case); the tree is built by adding at first lone paths and next boundary
% paths, i.e., negatively oriented paths surrounding groups of paths (areas,
% see below) resulting from the intersecting process; if there is a lone path
% or a boundary path |q| embedded in a boundary path |p|, there must be also
% an area which belongs to the group of areas surrounded by |p|, which apears
% in the tree between |q| and |p|; such a structure is convenient at the
% stage of finding colors of areas and lone paths.
numeric TREE_.num,TREE_.pth[\\],TREE_.emb[\\],TREE_.lev[\\];
%
% Finally there are areas which arise during intersecting process;
% |AREA_1|, |AREA_2|, ..., |AREA_[AREA_.num]| are the ordering numbers
% of edges which leftmost successors form areas such that areas arising
% from |AREA_[i]| and |AREA_[j]| are either disjoint or have at most a common
% edge, and, moreover, areas arising from |AREA_1|, |AREA_2|, ...,
% |AREA_[AREA_.num]| exhaust the list of all possible areas in question
% (plus lone paths, i.e., with no intersecting points); |AREA_.spt[i]| is
% a spot number (areas of the same spot number are subsets of the same
% boundary, different boundaries are disjoint); areas are sorted wrt spot
% numbers, moreover, |AREA_[SPOT_[s-1]+1]| thru |AREA_[SPOT_[s]]| are areas
% belonging to a spot |s|, |s=1|, |2|, ..., |SPOT_.num|.
numeric AREA_.num, AREA_[\\], AREA_.spt[\\]; numeric SPOT_.num, SPOT_[\\];
enddef;
% ---
vardef is_far_enough(expr i,k,dk) =
 if act_idx_>=max_idx: were_more_:=1; false
 else:
  save z_; pair z_; z_:=point k+dk of PATH_[i];
  true
   for j_:=0 upto TIME_[i]num:
    and
    if multi_path_case:
     (distance(point TIME_[i]tim[j_] of PATH_[i],z_)>=epsil.dist)
    else:
     (interval(TIME_[i]tim[j_],(k+dk),PATH_[i])>=epsil.time)
    fi
   endfor
   for j_:=0 upto ignored_.num:
    and
    if multi_path_case:
     (distance(point ignored_[j_] of PATH_[i],z_)>=epsil.dist)
    else:
     (interval(ignored_[j_],(k+dk),PATH_[i])>=epsil.time)
    fi
   endfor
 fi
enddef;
% ---
def intersect_two_segments(expr i,j,k,l) =
begingroup
 save pi_,pj_,stack_; path pi_,pj_,stack_[\\]; numeric stack_.lev;
 pi_:=subpath (k,k+1) of PATH_[i]; pj_:=subpath (l,l+1) of PATH_[j];
 stack_.lev:=1; stack_[stack_.lev]:=pj_;
 forever:
 exitif stack_.lev<=0;
  pj_:=stack_[stack_.lev]; stack_.lev:=stack_.lev-1;
  save dk_,dl_; (dk_,dl_)=pi_ intersectiontimes pj_;
  if dk_>=0:
   if is_far_enough(i,k,dk_):
    act_idx_:=act_idx_+1; TIME_[i].tim[incr TIME_[i].num]:=k+dk_;
   else: ignored_[incr ignored_.num]:=k+dk_;
   fi
   if (dl_+epsil.time)<length(pj_):
    stack_[incr stack_.lev]:=subpath (dl_+epsil.time,length pj_) of pj_;
   fi
   if (dl_-epsil.time)>0:
    stack_[incr stack_.lev]:=subpath (0,dl_-epsil.time) of pj_;
   fi
  fi
 endfor
endgroup
enddef;
% ---
def intersect_two_paths(expr i,j) =
begingroup
 save ignored_,were_more_,act_idx_;
 act_idx_:=0; ignored_.num:=-1;
 for k_:=0 upto length(PATH_[i])-1:
  for l_:=0 upto length(PATH_[j])-1:
   if (i<>j) or (k_<>l_):
    intersect_two_segments(i,j,k_,l_);
   fi
  endfor
 endfor
 if known were_more_:
  errhelp "Dangerous situation: rounding errors may screw up results.";
  errmessage "RO ERROR: there were more than "
   & decimal(max_idx) & " intersections (thus some were ignored)";
 fi
 quicksort TIME_[i](0,TIME_[i].num)(tim)();
endgroup
enddef;
% ---
def intersect_all_paths =
 for i_:=1 upto PATH_.num: TIME_[i_]num:=-1; endfor
 for i_:=1 upto PATH_.num:
  for j_:=i_+1 upto PATH_.num:
    if xpart(PATH_[i_] intersectiontimes PATH_[j_])>-1:
     PATH_[i_][j_]:=0;
% the process is repeated twice (for both paths in turn) because we haven't
% invented an efficient soultion to the following problem:
% given a subpath |S| of a path |P| and a time |t.S|; find a time |t.P| such
% that |point t.S of S=point t.P of P|
     intersect_two_paths(i_,j_); intersect_two_paths(j_,i_);
    fi
  endfor
 endfor
 if not multi_path_case:
  for i_:=1 upto PATH_.num:
   PATH_[i_][i_]:=0; intersect_two_paths(i_,i_);
  endfor
 fi
enddef;
% ---
vardef find_minimal_secant =
 save secants_, intervals_;
 secants_.num:=0; intervals_.num:=0;
 minimal_secant:=minimal_interval:=infinity;
 for i_:=1 upto PATH_.num:
  for j_:=0 upto TIME_[i_].num:
   if TIME_[i_].num>0:
    secants_[if tracingremoving>1: incr fi \\ secants_.num]:=
     distance(point TIME_[i_]tim[j_] of PATH_[i_],
      point TIME_[i_]tim[(j_+1) mod (TIME_[i_].num+1)] of PATH_[i_]);
    if tracingremoving>1:
     secants_.pth[secants_.num]:=i_; secants_.tim[secants_.num]:=j_;
    fi
    minimal_secant:=min(minimal_secant,secants_[secants_.num]);
    intervals_[if tracingremoving>1: incr fi \\ intervals_.num]:=
     interval(TIME_[i_]tim[j_],
       TIME_[i_]tim[(j_+1) mod (TIME_[i_].num+1)], PATH_[i_]);
    if tracingremoving>1:
     intervals_.pth[intervals_.num]:=i_; intervals_.tim[intervals_.num]:=j_;
    fi
    minimal_interval:=min(minimal_interval,intervals_[intervals_.num]);
   fi
  endfor;
 endfor;
 if minimal_secant<>infinity:
  info_ro "Minimal secant = " & decimal(minimal_secant/pt)
   & "pt, i.e., " & decimal(minimal_secant) & "pxl, " &
   if minimal_secant<4/3epsil.dist: "CAVEAT!" else: "seems OK" fi
   & " (bound=" & decimal(epsil.dist) & "pxl)";
 fi
 if minimal_interval<>infinity:
  info_ro "Minimal interval = " & decimal(minimal_interval) & ", " &
   if minimal_interval<4/3epsil.time: "CAVEAT!" else: "seems OK" fi
   & " (bound=" & decimal(epsil.time) & ")";
 fi
 if tracingremoving>1:
  quicksort secants_(1,secants_.num)()(tim,pth);
  quicksort intervals_(1,intervals_.num)()(tim,pth);
  for i_:=1 upto secants_.num:
   info_ro "secant=" & decimal(secants_[i_])
    & " path=" & decimal(secants_.pth[i_])
    & " time=" & decimal(secants_.tim[i_]);
  endfor
  for i_:=1 upto intervals_.num:
   info_ro "interval=" & decimal(intervals_[i_])
    & " path=" & decimal(intervals_.pth[i_])
    & " time=" & decimal(intervals_.tim[i_]);
  endfor
 fi
enddef;
% ---
def build_node_structure =
begingroup
 save n_,Tik_,Tjl_;
 NODE_.num:=0;
 for i_:=1 upto PATH_.num:
  for j_:=i_ if multi_path_case: +1 fi upto PATH_.num:
   if known PATH_[i_][j_]:
    for k_:=0 upto TIME_[i_]num:
     for l_:=if i_=j_: k_ else: 0 fi upto TIME_[j_]num:
      if distance(point TIME_[i_]tim[k_] of PATH_[i_],
        point TIME_[j_]tim[l_] of PATH_[j_])<epsil.dist:
       if if multi_path_case: not is_tangent(i_,j_,k_,l_) else: true fi:
        TIME_[i_]ntp[k_]:=1; TIME_[j_]ntp[l_]:=1;
        if unknown TIME_[i_]nod[k_]:
         NODE_.num:=NODE_.num+1; TIME_[i_]nod[k_]:=NODE_.num;
         NODE_.pth[NODE_.num]:=i_; NODE_.tim[NODE_.num]:=k_;
         NODE_.nod[NODE_.num]num:=0;
        fi
        if unknown TIME_[j_]nod[l_]:
         NODE_.num:=NODE_.num+1; TIME_[j_]nod[l_]:=NODE_.num;
         NODE_.pth[NODE_.num]:=j_; NODE_.tim[NODE_.num]:=l_;
         NODE_.nod[NODE_.num]num:=0;
        fi
        Tik_:=TIME_[i_]nod[k_]; Tjl_:=TIME_[j_]nod[l_];
        NODE_.nod[Tik_][incr NODE_.nod[Tik_]num]:=Tjl_;
        if (i_<>j_) or (k_<>l_):
         NODE_.nod[Tjl_][incr NODE_.nod[Tjl_]num]:=Tik_;
        fi
       fi
      fi
     endfor
    endfor
   fi
  endfor
 endfor
% BUG TRAP:
 for i_:=1 upto PATH_.num:
  n_:=0;
  for j_:=0 upto TIME_[i_]num: if known TIME_[i_]ntp[j_]: n_:=n_+1; fi endfor
  if n_=1:
   err_helpless;
   errmessage "RO ERROR: Number of non-tangent points must not be 1 (path "
    & decimal(i_) & ")";
  fi
 endfor
endgroup
enddef;
% ---
def identify_close_nodes =
begingroup
% It is assumed that `close points' and `coinciding points' means the same,
% hence we make a transitive closure of the relation of `being close'
% (in ``normal'' cases the relation is transitive, although from
% a mathematical point of view it is obviously not):
 forever:
  % Is this loop really needed? I (BJ) could not devise a case where
  % more than two turns would be necessary and where the algorithm
  % would still work properly
  save changed_;
  for i_:=1 upto NODE_.num:
   save v_;
   for j_:=1 upto NODE_.nod[i_]num: v_[NODE_.nod[i_][j_]]:=0; endfor
   for j_:=1 upto NODE_.nod[i_]num:
    k_:=NODE_.nod[i_][j_];
    for l_:=1 upto NODE_.nod[k_]num:
     if NODE_.nod[k_][l_]<>i_:
      if unknown v_[NODE_.nod[k_][l_]]:
       NODE_.nod[i_][incr NODE_.nod[i_]num]:=NODE_.nod[k_][l_];
       changed_:=v_[NODE_.nod[k_][l_]]:=0;
      fi
     fi
    endfor
   endfor
  endfor
 exitif unknown changed_;
 endfor
endgroup
enddef;
% ---
def build_edge_structure =
begingroup
 numeric min_sec_[\\],min_sec_.tmp;
% |min_sec_[i]| is a minimal secant for |i|-th path, |i=1|, |2|, ..., |PATH_.num|
 save i_,j_,k_;
 EDGE_.num:=0;
 if NODE_.num>0:
  for i_:=1 upto PATH_.num:
   for j_:=0 upto TIME_[i_]num:
    if known TIME_[i_]ntp[j_]:
     EDGE_.num:=EDGE_.num+1; EDGE_.pth[EDGE_.num]=i_;
     EDGE_.pth[-EDGE_.num]=i_; EDGE_.fnd[EDGE_.num]:=TIME_[i_]nod[j_];
% each path should contain at least two non-tangent nodes
     k_:=j_+1;
     forever: exitif known TIME_[i_]ntp[k_ mod (TIME_[i_]num+1)];
      k_:=k_+1;
     endfor;
     EDGE_.lnd[EDGE_.num]:=TIME_[i_]nod[k_ mod (TIME_[i_]num+1)];
     min_sec_.tmp:=
      distance(point first_time(EDGE_.num) of edge_path(EDGE_.num),
       point last_time(EDGE_.num) of edge_path(EDGE_.num));
     if if unknown min_sec_[i_]: true else: min_sec_[i_]>min_sec_.tmp fi:
      min_sec_[i_]:=min_sec_.tmp;
     fi
     EDGE_.fnd[-EDGE_.num]:=EDGE_.lnd[EDGE_.num];
     EDGE_.lnd[-EDGE_.num]:=EDGE_.fnd[EDGE_.num];
    fi
   endfor
  endfor
  for i_:=-EDGE_.num upto EDGE_.num:
   if i_>0: NODE_.ped[EDGE_.fnd[i_]]:=i_;
   elseif i_<0: NODE_.ned[EDGE_.fnd[i_]]:=i_;
   fi
  endfor
 else:
  info_ro "RO WARNING: no intersections detected.";
 fi
endgroup
enddef;
% ---
def find_leftmost_edges =
% a simple method is used: a tiny circle is drawn in a node and its
% intersection points with all edges leaving the node are examined
begingroup
 save ei_,ej_,i_,j_,k_,leftmost_; path ei_,ej_; numeric min_sec_.loc;
 for i_:=-EDGE_.num upto EDGE_.num: if i_<>0:
  if tracingleftmost>0:
   message "@@@ " & decimal(i_) & "/" & decimal(EDGE_.pth[i_])
    & " (" & decimal(EDGE_.fnd[i_]) & "," & decimal(EDGE_.lnd[i_]) & "):";
  fi
  numeric leftmost_.edg,leftmost_.tim,leftmost_.tmp;
  min_sec_.loc:=min_sec_[EDGE_.pth[i_]];
  for k_:=1 upto NODE_.nod[EDGE_.lnd[i_]]num:
   forsuffixes $:=ped,ned:
    j_:=NODE_$[NODE_.nod[EDGE_.lnd[i_]][k_]];
    min_sec_.loc:=min(min_sec_.loc,min_sec_[EDGE_.pth[j_]]);
   endfor
  endfor
% BUG TRAP 1: (should not happen, see |find_minimal_secant|);
  if min_sec_.loc<epsil.dist:
   err_extra_info(i_,whatever); showvariable min_sec_; err_helpless;
   errmessage "RO ERROR: Cannot continue searching for the leftmost edge";
  fi
  ei_:=enc.pth scaled (1/2[epsil.dist,min_sec_.loc])
   shifted point infinity of the_edge(i_);
  save tei_,tt_; (tei_,tt_)=ei_ intersectiontimes the_edge(i_);
  for k_:=1 upto NODE_.nod[EDGE_.lnd[i_]]num:
   forsuffixes $:=ped,ned:
    j_:=NODE_$[NODE_.nod[EDGE_.lnd[i_]][k_]];
    ej_:=enc.pth scaled (1/2[epsil.dist,min_sec_.loc])
     shifted point 0 of the_edge(j_);
    if tracingleftmost>0:
     message "    " & decimal(j_) & "/" & decimal(EDGE_.pth[j_])
     & " (" & decimal(EDGE_.fnd[j_]) & "," & decimal(EDGE_.lnd[j_]) & "):";
    fi
    save tej_,tt_; (tej_,tt_)=ej_ intersectiontimes the_edge(j_);
% BUG TRAP 2:
    if (tei_<0) or (tej_<0):
     err_extra_info(i_,j_); showvariable min_sec_;
     message "Times: " & decimal(tei_) & " " & decimal(tej_);
     err_helpless;
     errmessage "RO ERROR: Unsuccesful search for the leftmost edge";
    fi
% it happens that |i_=j_| if |multi_path_case=false|
    leftmost_.tmp:=if (i_=-j_): 0 else: (tej_-tei_) mod enc.len fi;
    if tracingleftmost>0:
     message "    " & decimal(leftmost_.tmp) & " " & dec_pair((tei_,tej_));
    fi
    if if unknown leftmost_.tim: true else: leftmost_.tmp>leftmost_.tim fi:
     leftmost_.edg:=j_; leftmost_.tim:=leftmost_.tmp;
    fi
   endfor
  endfor
  EDGE_.out[i_]:=leftmost_.edg;
  if tracingleftmost>0: j_:=EDGE_.out[i_];
   message ">>> " & decimal(j_) & "/" & decimal(EDGE_.pth[j_])
   & " (" & decimal(EDGE_.fnd[j_]) & "," & decimal(EDGE_.lnd[j_]) & "):";
  fi
 fi endfor
endgroup
enddef;
% ---
def build_area_structure =
begingroup
 save i_,j_,v_;
 AREA_.num:=0;
 for i_:=1 upto EDGE_.num: % \MF's linear equation solver employed
  EDGE_.col[i_]-PATH_.wei[EDGE_.pth[i_]]=EDGE_.col[-i_];
 endfor
% split to areas (edges surrounding the same area are assigned the same colour):
 for i_:=-EDGE_.num upto EDGE_.num:
  if (i_<>0) and (unknown EDGE_.are[i_]):
   AREA_[incr AREA_.num]:=i_;
   save v_; j_:=i_; v_[j_]:=0; EDGE_.are[j_]:=AREA_.num;
   forever: j_:=EDGE_.out[j_]; exitif (j_=i_) or (known v_.emerg);
% BUG TRAP 1:
    if j_=-i_:
     err_extra_info(i_,whatever); show_area(i_); err_helpless;
     errmessage "RO ERROR: strange area";
    fi
% BUG TRAP 2:
    if known v_[j_]:
     err_extra_info(i_,j_); show_area(i_); err_helpless;
     errmessage "RO ERROR: Edge " & decimal(j_) & " revisited";
     v_.emerg:=0;
    fi
    v_[j_]:=0; EDGE_.are[j_]:=AREA_.num;
    if known (EDGE_.col[i_]-EDGE_.col[j_]):
% BUG TRAP 3:
     if (EDGE_.col[i_]-EDGE_.col[j_])<>0:
      err_extra_info(i_,j_); show_area(i_); err_helpless;
      errmessage "RO ERROR: Edges " & decimal(i_) & " and " & decimal(j_)
      & " have inconsistent colors";
     fi
    else: EDGE_.col[i_]=EDGE_.col[j_]; fi
   endfor
  fi
 endfor
endgroup
enddef;
% ---
def build_spot_structure =
begingroup
 save i_,j_;
% areas having a common edge belong to the same spot (\MF's linear
% equation solver employed):
 for i_:=1 upto EDGE_.num: if (i_<>0):
  if unknown (AREA_.spt[EDGE_.are[i_]]-AREA_.spt[EDGE_.are[-i_]]):
   AREA_.spt[EDGE_.are[i_]]=AREA_.spt[EDGE_.are[-i_]];
  fi
 fi endfor
% count different spots:
 SPOT_.num:=0;
 for i_:=1 upto AREA_.num:
  if unknown AREA_.spt[i_]: AREA_.spt[i_]=incr SPOT_.num; fi
 endfor;
% sort areas wrt spot numbers:
 quicksort AREA_(1,AREA_.num)(spt)();
% define |SPOT_[s]|, |s=1|, |2|, ..., |SPOT_.num|, such that
% |AREA_[SPOT_[s-1]+1]| thru |AREA_[SPOT_[s]]| are areas having the
% same spot number |s|:
 SPOT_0=0; for i_:=1 upto AREA_.num: SPOT_[AREA_.spt[i_]]:=i_; endfor
% identify paths for which |check_turn=-1| (such areas are boundaries and
% should be unique for each spot):
 i_:=0;
 for j_:=1 upto AREA_.num:
  if check_turn(make_area(AREA_[j_]))<=0:
   i_:=i_+1;
   EDGE_.bar[i_]:=j_; EDGE_.bed[i_]:=AREA_[j_];
   EDGE_.bpa[i_]:=make_area(AREA_[j_]);
  fi
 endfor
% BUG TRAP 4:
 if i_<>SPOT_.num:
  message "Number of spots=" & decimal(SPOT_.num) &
   ", number of boundaries=" & decimal(i_);
  err_helpless;
  errmessage "RO ERROR: Inconsistent number of spots and boundaries";
 fi
endgroup
enddef;
% ---
def update_tree_levels(expr n) =
% update levels above the inserted leaf (|n|):
begingroup
 save i_,j_;
 i_:=TREE_.emb[n]; j_:=TREE_.lev[n];
 forever:
 exitif i_=0;
  j_:=TREE_.lev[i_]:=max(j_+1,TREE_.lev[i_]); i_:=TREE_.emb[i_];
 endfor
endgroup
enddef;
% ---
vardef embedding_pair(expr p,n) =
% returns a pair of numbers, |(out_,in_)|, such that |out_| is either a tree
% address of an area surrounded |p| or zero if not found, and |in_| is a
% tree address of an area surrounding |p| or zero if not found; one branch
% is searched, starting from a zero level leaf, |n|.
 save in_,out_,q_; path q_; in_:=out_:=0; n_:=n;
 forever:
  q_:=if TREE_.pth[n_]<0: LONE_[-TREE_.pth[n_]]
   else: make_area(AREA_[TREE_.pth[n_]]) fi;
  check_embedding(p_,q_,r_);
  if r_=1: % |p_| $\subset$ |q_|
   if in_=0: in_:=n_; fi % ``minimal'' surrounding path is to be found
  elseif r_=2: % |q_| $\subset$ |p_|
   out_:=n_; % ``maximal'' surrounded path is to be found
  fi
  exitif TREE_.emb[n_]=0;
  n_:=TREE_.emb[n_];
 endfor
 (out_,in_)
enddef;
% ---
def add_to_queue (expr p,q) =
% updates a queue, i.e., adds to a queue an area belonging to the spot
% of a boundary area, i.e., |AREA_[q]|, surrounding a path described by
% a tree address |p|.
begingroup
 save p_,r_,s_,found_; path p_; boolean found_;
% |AREA_[q]| is a boundary, i.e., it is negatively oriented,
 p_:=if TREE_.pth[p]<0: LONE_[-TREE_.pth[p]]
  else: make_area(AREA_[TREE_.pth[p]]) fi;
% there must be a unique positively oriented area containing |p_|, belonging
% to the ``spot'' of the boundary |AREA_[q]|.
 found_:=false; s_:=SPOT_[AREA_.spt[q]-1];
% |s_| is the last area from a previous spot, |s_+1| will be the first
% area of the current spot
 forever: s_:=s_+1;
  if s_<>q:
   check_embedding(make_area(AREA_[s_]),p_,r_);
   found_:=(r_=2); % |r_=2| implies |p_| $\subset$ |make_area(AREA_[s_])|
  fi
  if found_:
   if unknown LVQ_.inq[s_]: LVQ_[incr LVQ_.num]:=s_; LVQ_.inq[s_]:=1; fi
  elseif s_=SPOT_[AREA_.spt[q]]:
% the list of candidates has been exhausted without a success, hence
% BUG TRAP:
   err_helpless;
   errmessage "RO ERROR: cannot build embedding tree (boundary " &
    decimal(q) & ")";
   found_:=true;
  fi
  exitif found_;
 endfor;
endgroup
enddef;
% ---
def add_to_tree (expr leaf) =
begingroup
 save boundary_,found_,N_,p_; path p_;
 TREE_.num:=TREE_.num+1;
 N_:=TREE_.num; % abbreviation
 TREE_.pth[N_]:=leaf; TREE_.emb[N_]:=0; TREE_.lev[N_]:=0;
 p_:=if leaf<0: LONE_[-leaf] else: make_area(AREA_[leaf]) fi;
 if (leaf>0) and (check_turn(p_)<0): boundary_:=1; fi
 if N_>1:
  for l_:=1 upto LVZ_.num: % climbing up from level zero
   save out_,in_; (out_,in_)=embedding_pair(p_,LVZ_[l_]);
   if (out_<>0) or (in_<>0): % a feasible branch found
    if (out_=0) and (in_<>0): % to be added at the bottom, certain
     TREE_.emb[N_]:=in_;
     if in_=LVZ_[l_]: LVZ_[l_]:=N_; % replace bottom leaf
     else: LVZ_[incr LVZ_.num]:=N_; fi % add new bottom leaf
    elseif (out_<>0) and (in_=0): % to be added at the top, optional
     if TREE_.emb[out_]<>N_: % we weren't here, add
% invariant: |TREE_.emb[out_]=0|
      TREE_.emb[out_]:=N_;
      TREE_.lev[N_]:=max(TREE_.lev[N_],TREE_.lev[out_]+1);
      if known boundary_: add_to_queue(out_,leaf); fi
     fi
    else: % to be added in the midst, optional
     if TREE_.emb[out_]<>N_: % we weren't here, add
% invariant: |TREE_.emb[out_]=in_|
      TREE_.emb[out_]:=N_; TREE_.emb[N_]:=in_;
      TREE_.lev[N_]:=max(TREE_.lev[N_],TREE_.lev[out_]+1);
      if known boundary_: add_to_queue(out_,leaf); fi
     fi
    fi
    found_:=1; update_tree_levels(N_);
   fi
  endfor;
 fi
 if unknown found_: LVZ_[incr LVZ_.num]:=N_; fi % a ``separate'' leaf appeared
endgroup
enddef;
% ---
def build_embedding_tree =
begingroup
 save LVZ_,QUE_;
% |LVZ_1|, |LVZ_2|, ..., |LVZ_[LVZ_.num]| is the list of zero-level leaves,
% (a temporary data structure, used during building a tree), |LVQ_1|, |LVQ_2|,
% ..., |LVQ_[LVQ_.num]| is the list of leaves waiting in a queue (also
% a temporary data structure); if |LVQ_.inq[i]| is known, |i=1|, |2|, ...,
% |AREA_.num|, area |i| is already in a queue.
 TREE_.num:=0; LONE_.num:=0; LVZ_.num:=0; LVQ_.num:=0;
% identify lone paths:
 for i_:=1 upto PATH_.num:
  if true for j_:=0 upto TIME_[i_]num: and (unknown TIME_[i_]ntp[j_]) endfor:
   LONE_[incr LONE_.num]:=PATH_[i_]; LONE_.wei[LONE_.num]:=PATH_.wei[i_];
  fi
 endfor
% build the tree:
 for i_:=1 upto LONE_.num: add_to_tree(-i_); endfor
 for i_:=1 upto SPOT_.num: add_to_tree(EDGE_.bar[i_]); endfor
 for i_:=1 upto LVQ_.num: add_to_tree(LVQ_[i_]); endfor
endgroup
enddef;
% ---
def color_paths = % \MF's linear equation solver heavily exploited
begingroup
 save i_,j_;
 for i_:=1 upto TREE_.num:
  if TREE_.emb[i_]=0: % outer path
   if TREE_.pth[i_]<0: LONE_.col[-TREE_.pth[i_]]=background_color;
   else: EDGE_.col[AREA_[TREE_.pth[i_]]]=background_color; fi
  else: % inner path, inherits color from the surrounding path
   j_:=TREE_.emb[i_];
   if TREE_.pth[i_]<0:
    if TREE_.pth[j_]<0:
     LONE_.col[-TREE_.pth[i_]]=LONE_.col[-TREE_.pth[j_]]
      +LONE_.wei[-TREE_.pth[j_]]*check_turn(LONE_[-TREE_.pth[j_]]);
    else:
     LONE_.col[-TREE_.pth[i_]]=EDGE_.col[AREA_[TREE_.pth[j_]]];
    fi
   else:
    if TREE_.pth[j_]<0:
     EDGE_.col[AREA_[TREE_.pth[i_]]]=LONE_.col[-TREE_.pth[j_]]
      +LONE_.wei[-TREE_.pth[j_]]*check_turn(LONE_[-TREE_.pth[j_]]);
    else:
     if AREA_.spt[TREE_.pth[i_]]<>AREA_.spt[TREE_.pth[j_]]:
      EDGE_.col[AREA_[TREE_.pth[i_]]]=EDGE_.col[AREA_[TREE_.pth[j_]]];
     fi
    fi
   fi
  fi
 endfor;
endgroup
enddef;
% ---
def recombine_edges(suffix R) =
% this routine can be used several times (after completing the process
% of finding the structure of paths after intersecting) with various
% definitions of |good_color| function in order to select various
% sets of areas
 if not path R0: numeric R.num; path R[\\]; fi
 if (unknown R.num) or (unknown append_results): R.num:=0; fi
% |R|: resulting data structure, namely, |R.num| is the number of output
% paths, |R1|, |R2|, ..., |R[R.num]| are the resulting paths
begingroup
 save i_,j_,out_,in_;
 for i_:=1 upto LONE_.num:
  out_:=LONE_.col[i_]; in_:=out_+LONE_.wei[i_]*check_turn(LONE_[i_]);
  if good_colors(in_,out_) or good_colors(out_,in_):
   R[incr R.num]:=LONE_[i_];
   R[R.num]:=if good_colors(in_,out_): pos_turn else: neg_turn fi \\ R[R.num];
  fi
 endfor
 for i_:=-EDGE_.num upto EDGE_.num: if i_<>0:
  EDGE_.aux[i_]:=whatever;
 fi endfor
 for i_:=-EDGE_.num upto EDGE_.num: if i_<>0:
% BUG TRAP 1:
  if unknown EDGE_.col[i_]:
   err_extra_info(i_,whatever); err_helpless;
   errmessage "RO ERROR: Edge " & decimal(j_) & " not colored";
  fi
  if good_colors(EDGE_.col[i_],EDGE_.col[-i_]) and (unknown EDGE_.aux[i_]):
   save v_;
   R.num:=R.num+1; j_:=i_; v_[j_]:=0;
   EDGE_.aux[j_]:=0; R[R.num]:=the_edge(j_);
   forever: j_:=EDGE_.out[j_]; exitif (j_=i_) or (known v_.emerg);
% BUG TRAP 2:
    if known v_[j_]:
     err_extra_info(i_,j_); err_helpless;
     errmessage "RO ERROR: Edge " & decimal(j_) & " revisited";
     v_.emerg:=0;
    fi
    v_[j_]:=0;
    if good_colors(EDGE_.col[j_],EDGE_.col[-j_]):
     EDGE_.aux[j_]:=0; R[R.num]:=R[R.num] && the_edge(j_);
    else: j_:=-j_;
    fi
   endfor
   R[R.num]:=clean_path(clean_path(make_cycle(R[R.num])));
  fi
 fi endfor
endgroup
enddef;
% ---
def remove_overlap (text P)(text W) suffix R =
begingroup interim autorounding:=0;
% |P|: list of paths to be processed (non-cyclic paths are ignored);
% |W|: list of weights given as pairs: (index, value)
% |R|: resulting data structure, i.e., |R.num| is the number of output paths,
% |R1|, |R2|, ..., |R[R.num]| are the resulting paths
 info_ro "initialise_removing_overlaps"; initialise_removing_overlaps;
 info_ro "prepare_input_data"; prepare_input_data(P)(W);
 info_ro "intersect_all_paths"; intersect_all_paths;
 info_ro "find_minimal_secant"; find_minimal_secant;
 info_ro "build_node_structure"; build_node_structure;
 info_ro "identify_close_nodes"; identify_close_nodes;
 info_ro "build_edge_structure"; build_edge_structure;
 info_ro "find_leftmost_edges"; find_leftmost_edges;
 info_ro "build_area_structure"; build_area_structure;
 info_ro "build_spot_structure"; build_spot_structure;
 info_ro "build_embedding_tree"; build_embedding_tree;
 info_ro "color_paths"; color_paths;
 info_ro "recombine_edges"; recombine_edges(R);
endgroup
enddef;
% ---
% E-S MACROS:
% ---
vardef make_join@#(expr pa,pb)=
 save kind_; string kind_; kind_:=str @#; if kind_="": kind_:="0" fi;
 if (kind_<>"0") and (kind_<>"1"):
  errhelp "Will use default.";
  errmessage "ES ERROR: don't know how to join";
  kind_:="0";
 fi
 if distance(point length(pa) of pa,point 0 of pb)<epsil.dist:
  if (point length(pa) of pa)<>(point 0 of pb):
   info_es "Points " & dec_pair(point length(pa) of pa) &
    " and " & dec_pair(point 0 of pb) & " joined";
   if (tracingexpanding>0) and (proofing>0):
    makelabel.lft.nodot("joined",point length(pa) of pa);
   fi
  fi
  pa && pb
 elseif kind_="0":
  if miter_size<=0: % a special case, isn't it?
   pa--pb
  else:
   save ta_,tb_,za_,da_,zb_,db_,zc_,zd_,ze_,zf_;
   pair za_,da_,zb_,db_,zc_,zd_,ze_,zf_;
   za_=point length(pa) of pa;
   da_=direction length(pa) of pa;
   zb_=point 0 of pb;
   db_=direction 0 of pb;
   zc_=whatever[za_,za_+da_]=whatever[ze_,ze_+(zb_-za_)];
   zd_=whatever[zb_,zb_+db_]=whatever[ze_,ze_+(zb_-za_)];
   ze_=.5[za_,zb_]+miter_size*(unitvector(da_-db_));
% we used to check |turningnumber(za_--zc_--zd_--zb_--cycle)|, but it was
% not sufficiently robust
   (ta_,tb_)=(za_--zc_) intersectiontimes (zd_--zb_);
   if ta_<0: % |miter_size| in force:
     pa
      if distance(point length(pa) of pa,zc_)>=epsil.dist: --zc_ fi
      if (distance(zc_,zd_)>=epsil.dist)
        and (distance(point 0 of pb,zd_)>=epsil.dist): --zd_ fi
     --pb
   else:
    zf_:=point ta_ of (za_--zc_);
    if abs(zf_-.5[za_,zb_])>abs(ze_-.5[za_,zb_]): % |miter_size| in force:
     pa
      if distance(point length(pa) of pa,zc_)>=epsil.dist: --zc_ fi
      if (distance(zc_,zd_)>=epsil.dist)
       and (distance(point 0 of pb,zd_)>=epsil.dist): --zd_ fi
     --pb
    else:
     pa
      if (distance(point length(pa) of pa,zf_)>=epsil.dist)
       and (distance(point 0 of pb,zf_)>=epsil.dist): --zf_ fi
     --pb
    fi
   fi
  fi
 elseif kind_="1":
  pa{direction length(pa) of pa}..{direction 0 of pb}pb
 fi
enddef;
% ---
vardef make_cyclic_join@#(expr p)=
 save kind_; string kind_; kind_:=str @#; if kind_="": kind_:="0" fi;
 if (kind_<>"0") and (kind_<>"1"):
  errhelp "Will use default.";
  errmessage "ES ERROR: don't know how to join";
  kind_:="0";
 fi
 if distance(point length(p) of p,point 0 of p)<epsil.dist:
  if (point length(p) of p)<>(point 0 of p):
   info_es "Points " & dec_pair(point length(p) of p) &
    " and " & dec_pair(point 0 of p) & " joined (cycle)";
   if (tracingexpanding>0) and (proofing>0):
    makelabel.lft.nodot("joined (cycle)",point length(p) of p);
   fi
  fi
  make_cycle(p)
 elseif kind_="0":
  if miter_size<=0: % a special case, isn't it?
   p--cycle
  else:
   save ta_,tb_,za_,da_,zb_,db_,zc_,zd_,ze_,zf_; pair za_,da_,zb_,db_,zc_,zd_,ze_,zf_;
   za_=point length(p) of p; da_=direction length(p) of p;
   zb_=point 0 of p; db_=direction 0 of p;
   zc_=whatever[za_,za_+da_]=whatever[ze_,ze_+(zb_-za_)];
   zd_=whatever[zb_,zb_+db_]=whatever[ze_,ze_+(zb_-za_)];
   ze_=.5[za_,zb_]+miter_size*(unitvector(da_-db_));
% we used to check |turningnumber(za_--zc_--zd_--zb_--cycle)|, but it was
% not sufficiently robust
   (ta_,tb_)=(za_--zc_) intersectiontimes (zd_--zb_);
   if ta_<0: % |miter_size| in force:
     p
      if distance(point length(p) of p,zc_)>=epsil.dist: --zc_ fi
      if (distance(zc_,zd_)>=epsil.dist)
       and (length((point 0 of p)-zd_)>=epsil.dist): --zd_ fi
     --cycle
   else:
    zf_:=point ta_ of (za_--zc_);
    if abs(zf_-.5[za_,zb_])>abs(ze_-.5[za_,zb_]): % |miter_size| in force:
     p
      if distance(point length(p) of p,zc_)>=epsil.dist: --zc_ fi
      if (distance(zc_,zd_)>=epsil.dist)
       and (distance(point 0 of p,zd_)>=epsil.dist): --zd_ fi
     --cycle
    else:
     p
      if (distance(point length(p) of p,zf_)>=epsil.dist)
       and (distance(point 0 of p,zf_)>=epsil.dist): --zf_ fi
     --cycle
    fi
   fi
  fi
 elseif kind_="1":
  p{direction length(p) of p}..{direction 0 of p}cycle
 fi
enddef;
% ---
vardef make_end@#(expr pr,pl) =
 save kind_; string kind_; kind_:=str @#; if kind_="": kind_:="0" fi;
 if (kind_<>"0") and (kind_<>"1"):
  errhelp "Will use default.";
  errmessage "ES ERROR: don't know how to end";
  kind_:="0";
 fi
 if kind_="0": pr--pl--cycle
 elseif kind_="1":
  save za_,zb_; pair za_,zb_;
  za_=1/2[point length(pr) of pr,point 0 of pl]
   +(1/2((point length(pr) of pr)-(point 0 of pl)) rotated 90);
  zb_=1/2[point length(pl) of pl,point length 0 of pr]
   +(1/2((point length(pl) of pl)-(point 0 of pr)) rotated 90);
  pr{direction length(pr) of pr}..za_..{direction 0 of pl}pl
   {direction length(pl) of pl}..zb_..{direction 0 of pr}cycle
 fi
enddef;
% ---
vardef opt_tensions(expr p,b) =
% for a given B\'ezier segment |p| and a distance |b|, an optimal pair of
% `tensions' $(\alpha,\beta)$ is found using least square method such that
% |bez_edge|$(p,b,\alpha,\beta)$ (see below) approximates the edge of
% a circular pen of diameter |b| traversing |p| (more on the employed
% method be found in the article of B. Jackowski and M. Ry\'cko:
% ``Labyrinth of \MF paths in outline,'' proceedings of the 8th European
% \TeX Conference, Sept. 26--30, 1994, Gda\'nsk, Poland)
%
 save alpha_,beta_,gx_,gy_,n_,t_,ta_,tb_,tc_,td_,u_,v_,nu_,nv_,x_,y_;
 numeric alpha_,beta_,n_,ta_,tb_,tc_,td_,
   gx_[\\],gy_[\\],gx_.alpha[\\],gy_.alpha[\\],gx_.beta[\\],gy_.beta[\\],
   u_.x,u_.y,v_.x,v_.y,nu_.x,nu_.y,nv_.x,nv_.y,
   x_[\\],y_[\\];
 n_:=5; % perhaps for |n_|$=\infty$ algebraic formulas can be derived, but...
 (u_.x,u_.y)=(postcontrol 0 of p)-(point 0 of p);
 (v_.x,v_.y)=(precontrol 1 of p)-(point 1 of p);
 (nu_.x,nu_.y)=unitvector(u_.x,u_.y); (nv_.x,nv_.y)=unitvector(v_.x,v_.y);
 for t_:=0 upto n_:
  (x_[t_],y_[t_])=(point t_/n_ of p)+b*((udir t_/n_ of p) rotated -90);
 endfor
 for t_:=1 upto n_-1:
  td_:=t_/n_; ta_:=1-td_; tb_:=3ta_*ta_*td_; tc_:=3ta_*td_*td_;
  ta_:=ta_*ta_*ta_; td_:=td_*td_*td_;
  gx_[t_]=ta_*x_0+tb_*(x_0+alpha_*u_.x)+tc_*(x_[n_]+beta_*v_.x)+td_*x_[n_];
  gx_.alpha[t_]=tb_*nu_.x; gx_.beta[t_]=tc_*nv_.x;
  gy_[t_]=ta_*y_0+tb_*(y_0+alpha_*u_.y)+tc_*(y_[n_]+beta_*v_.y)+td_*y_[n_];
  gy_.alpha[t_]=tb_*nu_.y; gy_.beta[t_]=tc_*nv_.y;
 endfor
 0=0 for t_:=1 upto n_-1:
   +((gx_[t_]-x_[t_])*gx_.alpha[t_]+(gy_[t_]-y_[t_])*gy_.alpha[t_])/n_
  endfor;
 0=0 for t_:=1 upto n_-1:
   +((gx_[t_]-x_[t_])*gx_.beta[t_]+(gy_[t_]-y_[t_])*gy_.beta[t_])/n_
  endfor;
%| (u_.x,u_.y)=(postcontrol 0 of p)-(point 0 of p);|
%| (v_.x,v_.y)=(precontrol 1 of p)-(point 1 of p);|
%| ta_:=1/4length((u_.x,u_.y))+1/4length((v_.x,v_.y))|
%|  +1/4length((postcontrol 0 of p)-(precontrol 1 of p))|
%|  +1/4length((point 0 of p)-(point 1 of p));|
%| message "accuracy=" & decimal|
%|   (0+for t_:=1 upto n_-1:+(((gx_[t_]-x_[t_])++(gy_[t_]-y_[t_]))/ta_)/n_|
%|  endfor);|
%| message "   alpha=" & decimal(alpha_) & " beta=" & decimal(beta_);|
%| for t_:=0 upto n_: fill fullcircle scaled 3 shifted (x_[t_],y_[t_]); endfor|
%| for t_:=1 upto n_-1: makelabel("g" & decimal(t_),(gx_[t_],gy_[t_])); endfor|
 (alpha_,beta_)
enddef;
% ---
vardef bez_edge(expr p,b,uv) =
 save za_,zb_,u_,v_; pair za_,zb_; u_:=xpart(uv); v_:=ypart(uv);
 za_=b*((udir 0 of p) rotated -90); zb_=b*((udir 1 of p) rotated -90);
 ((point 0 of p)+za_) .. controls (u_[point 0 of p,postcontrol 0 of p]+za_)
  and (v_[point 1 of p,precontrol 1 of p]+zb_) .. ((point 1 of p)+zb_)
enddef;
% ---
def remove_global_loops(suffix E) =
begingroup
% warning: we don't trust too much in the results of ex. 14.17 from
% The \MF{}book, hence a ``par force'' approach; there still exist
% weird cases (e.g., local loops) which remain unsolved, but in practice
% the following algorithm should suffice:
 save opt_,ta_,tb_; pair opt_;
 opt_:=(0,length(E));
 for i_:=0 upto length(E)-1:
  for j_:=i_+2 upto length(E)-1:
   numeric ta_,tb_;
   (ta_,tb_)=(subpath (i_,i_+1) of E)
    intersectiontimes (subpath (j_,j_+1) of E);
   if (ta_>0) and ((ta_+i_)>xpart(opt_)) and ((tb_+j_)<ypart(opt_)):
    opt_:=(ta_+i_,tb_+j_);
   fi
  endfor
 endfor
 if xpart(opt_)>0:
  E:=make_cycle(subpath(xpart(opt_),ypart(opt_)) of E);
 fi
endgroup
enddef;
% ---
vardef make_edge@#(expr p,b)=
 save E_,e_,ta_,tb_,tc_,td_; path E_,e_[\\];
 for i_:=0 upto length(p)-1:
  E_:=subpath (i_,i_+1) of p; e_[i_]=bez_edge(E_,b,opt_tensions(E_,b));
 endfor
 E_:=e_0;
 for i_:=1 upto length(p)-1:
  if (length(p)=2) and (cycle p): % this is a peculiar case, indeed!
   numeric ta_,tb_,tc_,td_;
   (ta_,tb_)=E_ intersectiontimes e_[i_];
   (1-tc_,1-td_)=reverse(E_) intersectiontimes reverse(e_[i_]);
   if ta_>=0:
    E_:=(subpath(min(ta_,tc_),max(ta_,tc_)) of E_)
     && (subpath(min(tb_,td_),max(tb_,td_)) of e_[i_]);
   else: E_:=make_join@#(E_,e_[i_]);
   fi
  else:
   numeric ta_,tb_;
   (ta_,tb_)=(subpath(length(E_)-1,length(E_)) of E_)
    intersectiontimes e_[i_];
   if ta_>=0:
     E_:=(subpath (0,length(E_)-1+ta_) of E_)
      && (subpath(tb_,1) of e_[i_]);
   else: E_:=make_join@#(E_,e_[i_]); fi
  fi
 endfor
 if cycle p:
  remove_global_loops(E_);
  if not (cycle E_): E_:=make_cyclic_join@#(E_); fi
 fi
 E_
enddef;
% ---
def expand_stroke(text P)(expr b) suffix R =
begingroup interim autorounding:=0;
 numeric PATH_.num; path PATH_[\\];
 PATH_.num:=0; for P_:=P: PATH_[incr PATH_.num]:=touch_path(P_); endfor
 if not path R0: numeric R.num; path R[\\]; fi
 if (unknown R.num) or (unknown append_results): R.num:=0; fi
 if unknown join_kind: save join_kind; join_kind=0; fi
 if unknown end_kind: save end_kind; end_kind=0; fi
 for i_:=1 upto PATH_.num:
  if not cycle PATH_[i_]:
   R[incr R.num]:=make_end[end_kind]
     (make_edge[join_kind](PATH_[i_],b),
      reverse make_edge[join_kind](PATH_[i_],-b));
  else:
   R[incr R.num]:=make_edge[join_kind](PATH_[i_],b);
   R[incr R.num]:=reverse make_edge[join_kind](PATH_[i_],-b);
  fi
 endfor
 for i_:=1 upto R.num: R[i_]:=clean_path(clean_path(R[i_])); endfor
endgroup
enddef;
% ---
def change_weight(text P)(expr b) suffix R =
begingroup interim autorounding:=0;
 numeric PATH_.num; path PATH_[\\];
 PATH_.num:=0; for P_:=P: PATH_[incr PATH_.num]:=touch_path(P_); endfor
 if not path R0: numeric R.num; path R[\\]; fi
 if (unknown R.num) or (unknown append_results): R.num:=0; fi
 if unknown join_kind: save join_kind; join_kind=0; fi
 for i_:=1 upto PATH_.num:
% non-cyclic paths are ignored
  if cycle PATH_[i_]: R[incr R.num]:=make_edge[join_kind](PATH_[i_],b); fi
 endfor
endgroup
enddef;
% ---
def info_ro expr s = if tracingremoving>0: message s; message ""; fi enddef;
def info_es expr s = if tracingexpanding>0: message s; message ""; fi enddef;
% ---
% DEFAULTS:
% ---
def roex_default text t =
 forsuffixes S_:=t:
  if str S_ = "good_colors":
% the formula |good_colors(p,q) and good_colors(q,p)| must be |false|!
   vardef good_colors(expr i,o) = ((i>=1) and (o<=0)) enddef;
  elseif str S_ = "touch_path":
   vardef touch_path(expr p) = p enddef;
  elseif str S_ = "background_color": background_color:=0;
  elseif str S_ = "miter_size":
   miter_size:=10pixels_per_inch/72; % i.e., 10bp
% incidentally, |10bp| would convert to |10.00002| during export at |300dpi|
  elseif str S_ = "epsil.ang": epsil.ang:=1/10; % in degrees
  elseif str S_ = "epsil.dist": epsil.dist:=1/10pt; % ca |2/5|pxl at |300dpi|
  elseif str S_ = "epsil.time": epsil.time:=1/100;
  elseif str S_ = "epsil.len": epsil.len:=1/1000; % used in |turn_ang|
  elseif str S_ = "max_idx": max_idx:=125;
  elseif str S_ = "enc":
% |enc| is a prefix of a data structure used in checking tangent
% points and searching for the leftmost edge; |enc.pth| is in both
% cases scaled differently
   vardef enc.pth = fullcircle enddef; enc.len:=length(enc.pth);
  fi
 endfor
enddef;
%
roex_default good_colors, touch_path, background_color, miter_size,
 epsil.ang, epsil.dist, epsil.time, epsil.len, max_idx, enc;
% ---
numeric append_results; % initially unknown
newinternal tracingleftmost; tracingleftmost:=0;
newinternal tracingremoving; tracingremoving:=0;
newinternal tracingexpanding; tracingexpanding:=0;
% ---
endinput
%%\end