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import graph;
import animation;
size(0,200);
defaultpen(3);
dotfactor=4;
pair wheelpoint(real t)
{
return (t+cos(t),-sin(t));
}
guide wheel(guide g=nullpath, real a, real b, int n)
{
real width=(b-a)/n;
for(int i=0; i <= n; ++i) {
real t=a+width*i;
g=g--wheelpoint(t);
}
return g;
}
real t1=0;
real t2=t1+2*pi;
draw(circle((0,0),1));
draw(wheel(t1,t2,100),linetype("0 2"));
yequals(Label("$y=-1$",1.0),-1,extend=true,linetype("4 4"));
xaxis(Label("$x$",align=3SW),0);
yaxis("$y$",0,1.2);
pair z1=wheelpoint(t1);
pair z2=wheelpoint(t2);
dot(z1);
dot(z2);
animation a;
int n=10;
real dt=(t2-t1)/n;
for(int i=0; i <= n; ++i) {
save();
real t=t1+dt*i;
draw(circle((t,0),1),red);
dot(wheelpoint(t));
a.add(); // Add currentpicture to animation.
restore();
}
// Produce the final merged gif.
a.movie(BBox(0.25cm),loops=10,delay=250);
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