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def OneCurl (expr a,da, b,db, above, pangle) =
begingroup
save dx, dy, p;
pair dx; dx= b-a;
pair dy; dy= dx rotated 90;
pair p; p= (a+.5dx+above*dy);
a{da} .. {dx rotated pangle}p &
p{dx rotated -pangle} .. {db}b
endgroup
enddef;
def CurlIt(expr tp, % the path
n, % how often
above, % the peak above the path
pangle % the direction at the peak
) =
begingroup
save dl; pair dl[];
save dr; pair dr[];
save i,l,r,ll,rr,delta;
numeric i,l,r,delta
i= 0;
l= 0;
r= length(tp);
delta= length(tp)/n;
forever:
if i = n-i:
z0l[i] = z0r[i] = point .5length(tp) of tp;
dl[i] = dr[i] = direction .5length(tp) of tp;
else:
numeric ll;
if i=0: ll = l else: ll = l-(n-i)*.06delta fi;
z0l[i] = good.lft (point ll of tp);
dl[i] = direction ll of tp;
numeric rr;
if i=0: rr = r else: rr = r+(n-i)*.06delta fi;
z0r[i] = good.rt (point rr of tp);
dr[i] = direction rr of tp;
fi
exitif r-l < eps;
i:= incr i;
l:= l+delta;
r:= r-delta;
endfor;
for i:= incr i step 1 until n:
z0l[i] = z0r[n-i];
z0r[i] = z0l[n-i];
dl[i] = dr[n-i];
dr[i] = dl[n-i];
endfor;
OneCurl(z0l0, dl0, z0l1, dl1, above, pangle)
for i:= 2 step 1 until n:
& OneCurl(z0l[i-1], dl[i-1], z0l[i], dl[i], above, pangle)
endfor
endgroup
enddef;
z0l = (10,10);
z0r = (200, 10);
z0 = .5[z0l,z0r] shifted 30up;
draw CurlIt(z0l .. z0 .. z0r, 5, 0.1, 30);
undraw(z0l3);
showit;
:map q :w:!mf
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