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% electrospiral.mp
% L. Nobre G.
% 2004
numeric turnstep;
turnstep = 1cm;
def spiral( expr Ang ) =
begingroup
numeric k, r;
k = turnstep/360.0;
r = k*Ang;
( r*dir(Ang) )
endgroup
enddef;
beginfig(1);
numeric i, angstep, actx, ray, corner, sider;
path spir, cutter;
pair thispos, sw, nw, ne, se, actpos;
angstep = 30;
ray = 0.7mm;
corner = 4.2;
sider = 10.5;
spir = origin..
for i=angstep step angstep until 4000-1:
spiral(i)..
endfor
spiral(4000);
draw spir;
actx = 1;
forever:
thispos := (turnstep*actx,0);
for i=1 upto actx:
actpos := thispos+ray*normaldeviate*dir(uniformdeviate(359));
draw actpos withpen pencircle scaled 1.5mm;
endfor;
actx := 2*actx;
exitif actx > 9;
endfor;
sw = turnstep*(-corner,-corner);
nw = turnstep*(-corner,corner);
ne = turnstep*(sider,corner);
se = turnstep*(sider,-corner);
cutter = sw--nw--ne--se--cycle;
clip currentpicture to cutter;
endfig;
end;
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