LOGO-L> an 8 tube

[MHELHEFNY@FRCU.EUN.EG]

;Hello everybody
;here is a code to draw a tube whose shape is an 8 
;best regards
;Mhelhefny
;-------------
to go
   cs ht
   make "c 1 make "a .2
   perspective
   grid
   shade 200 50 10 
end

to grid 
for [t 0 360 10][for [u 0 360 10][
polystart pd 
              s 
make "t :t+10 s 
make "u :u+10 s 
make "t :t-10 s 
polyend]pu]
end

to len
op sqrt (sin :t)*(sin :t) + (cos 2* :t)*(cos 2* :t)
end

to shade :f :g :h
ask -3[setxyz :f :g :h]
polyview
End

to s
setxyz x*150 y*150 z*150
end

to x
op (:c* cos :t)*(sin :t) + ((:a* sin :u)*(sin :t))/ len
end

to y
op :a* :c* cos :u
end

to z
op cos :t + (:a* :c* (sin :u)*cos(2* :t))/ len
end
;----------
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