%@DATE: 14 février 2008
prologues := 3;
outputtemplate := "ber-var/%j-%c.svg";
outputformat := "svg";

verbatimtex
%&latex
\documentclass{minimal}
\usepackage[utf8]{inputenc}
\usepackage[charter]{mathdesign}
\usepackage{amsmath}
\begin{document}
etex

color jaune;
jaune = red+green;

% === Pointer les points avec une couleur cerclée de noir.
def pointe(expr p,c) =
     fill fullcircle scaled 3 shifted p withcolor black;
     fill fullcircle scaled 2 shifted p withcolor c;
enddef;
   
u:=.7cm;
pair O;
%Point fixe
O:=(0,0);
path ber[], cercle;
%diamètre du cercle
r:=2;
cercle=fullcircle scaled (2*r*u);
%quart de la longueur du segment
l:=4;

for j:=0 upto 200: 
 beginfig(j);
%boucle de tracé de la courbe pour un point du segment
  for i:=0 upto 360:
  pair P,M[],N;
  path segment;
  x:=cosd(i)*r*u;
  y:=sind(i)*r*u;
  P:=(x,y);
  k:=sqrt(l*l-(y/u)*(y/u))*u;
  N:=(x+k,0);
  segment:=2[N,P]--2[P,N];
  M3:=point (j/200) of segment;
  if i=0:
    ber3:=M3;
  else:
    ber3:=ber3--M3;
  fi;
  endfor;
%le cercle et la glissière
  pickup pencircle scaled 0.8pt;
  draw O--(1.5*l*u,0);
  draw cercle dashed evenly withcolor blue;
%un petit arrière plan rappelant la construction
  x:=cosd(20)*r*u;
  y:=sind(20)*r*u;
  P:=(x,y);
  k:=sqrt(l*l-(y/u)*(y/u))*u;
  N:=(x+k,0);
  M1:=2[P,N];
  M2:=2[N,P];
  drawoptions(withpen pencircle scaled 1.6pt withcolor 0.8white);
  draw O--P;
  draw M1--M2;
  fill fullcircle scaled 3 shifted O;
  fill fullcircle scaled 3 shifted P;
  fill fullcircle scaled 3 shifted N;
  drawoptions();
%Le point du segment
  M4:= point (j/200) of (M2--M1);
%on trace la courbe
  drawoptions(withpen pencircle scaled 1pt withcolor red);
  draw ber3;
  drawoptions();
%et on met le point auquel se réfère la courbe
  pointe(M4, jaune);
  label.top(btex \textit{Courbes de la bielle de} \textsc{Bérard} \textit{(variations)} etex, (3*r*u,2*r*u));
  draw (-1.8l*u,3*r*u)--(-1.8l*u,-3*r*u)--(2.7l*u,-3*r*u)--(2.7l*u,3*r*u)--cycle withcolor white;
 endfig;
endfor;
end.