Flêche le long d’un chemin

Auteur ou autrice : Vincent Zoonekynd.

Mise en ligne le 12 octobre 2024

Code

u:=1cm;
beginfig(160)
  vardef longueur(expr p) =
    save l,i;
    numeric l;
    l:=0;
    for i=0 step .01 until length(p):
      l:=l+abs( (point i of p) - (point(i+.01) of p) );
    endfor;
    l % Pas de point-virgule
  enddef;
  vardef milieu(expr p) =
    save l,i,tot,A,B;
    numeric l,tot,i;
    pair A,B;
    tot := longueur(p);
    l:=0;
    B := point 0 of p;
    for i:=0 step .01 until length(p):
      A := B;
      B := point i of p;
      l := l+abs(B-A);
      exitif l > 1/2 tot;
    endfor;
    1/2[A,B]
  enddef;
  vardef milieu_time(expr p) =
  save l,i,tot,A,B,t;
  numeric l,tot,i,t;
  pair A,B;
  tot := longueur(p);
  l:=0;
  B := point 0 of p;
  for i:=0 step .01 until length(p):
    t:=i;
    A := B;
    B := point i of p;
    l := l+abs(B-A);
    exitif l > 1/2 tot;
  endfor;
  t
  enddef;
  save arrowhead;
  vardef arrowhead expr p =
    save A,u; pair A,u;
    A := milieu(p);
    u := unitvector(direction milieu_time(p) of p);
    A -- (A - ahlength*u rotated 15) --
    (A - ahlength*u rotated -15) -- cycle
  enddef;

  u:=1cm;
  drawarrow (0,0) .. (-u,u) .. (u,u);
endfig;

end.