prologues := 3;
outputtemplate := "%j/%j-%c.svg";
outputformat := "svg";

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

% l'unité graphique
u:=.7cm;

% paramètres
a:=-2u;
b:=-4u;
c:=abs(a-b); % rayon du cercle
largeurDroite:=12u;

% fonction(s)
def droite(expr a,b)=
  10[a,b]--10[b,a]
enddef;

def demiedroite(expr a,b)=
  0.01[a,b]--10[a,b]
enddef;

% les ensembles de construction
pair O;
O:=(0,0);
path supportCercle,  supportSegment, cercle,kieroide;

supportCercle:=(-largeurDroite,a)--(+largeurDroite,a);
supportSegment:=(-largeurDroite,b)--(+largeurDroite,b);
cercle:=fullcircle scaled (2*c);

% les constructions mouventes

pair P,N,M;
path  demieNO, cercleP;

for t:=0 step 0.005 until 1:
  i:=round(t*200);
  beginfig(i);
    % le point P parcours la droite supportCercle
    P:=point t of supportCercle;
    % cercle centré en P
    cercleP:=cercle shifted P;
    % M comme intersection
    N:=(xpart P,b);
    demieNO:=demiedroite(N,O);

    M:=demieNO intersectionpoint cercleP;

    %on définie la courbe
    if i=0:
      kieroide:=M;
    else:
      kieroide:=kieroide--M;
    fi;
    % on dessine
    draw supportCercle withcolor green dashed evenly withpen pencircle scaled 1pt;
    draw cercleP dashed evenly  withcolor (0.7,0.7,0.7)  withpen pencircle scaled 1pt;
    draw supportSegment dashed evenly  withcolor (0.7,0.7,0.7)  withpen pencircle scaled 1pt;
    draw N--O withcolor blue withpen pencircle scaled 1pt;
    draw N--P withcolor blue withpen pencircle scaled 1pt;
    draw M--P withcolor blue withpen pencircle scaled 1pt;
    draw kieroide withcolor red withpen pencircle scaled 1pt;
    % les labels
    dotlabel.bot(btex $P$ etex, P);
    dotlabel.bot(btex $M$ etex, M);
    dotlabel.bot(btex $N$ etex, N);
    dotlabel.bot(btex $O$ etex, O);
    label.ulft(btex $\mathcal C$ etex, P+(cosd(125)*c,sind(125)*c));
    label.bot(btex $\Delta$ etex, (8u,a));
    label(btex \itshape La Kiéroïde etex, (5u, u));
    clip currentpicture to (10u,-5u)--(-10u,-5u)--(-10u,2u)--(10u,2u)--cycle;
  endfig;
endfor;
end.