Port of donut.c to Ruby. Original: http://www.a1k0n.net/2011/07/20/donut-math.html

donut.rb

            include Math;R1=1.0; R2=2.0;K2=5.0
         SS=40;K1=SS*K2*3/(8*(R1+R2));def rf(a, b)
      cosA=cos(a);sinA=sin(a);cosB=cos(b);sinB=sin(b)
   o=Array.new(SS).fill{Array.new(SS).fill(' ')};b=Array.
  new(SS).fill{ Array.new(SS).fill(0)}; t=0.0;while t<2*PI
cost=cos(t);sint=sin(t);p=0.0;while p<2*PI;cosp=cos(p);sinp=
sin(p);cx=R2+R1*cost;cy=R1*       sint;x=cx*(cosB*cosp+sinA*
sinB*sinp)-cy*cosA*sinB;             y=cx*(sinB*cosp-sinA*##
cosB*sinp)+cy*cosA*cosB               ;z=K2+cosA*cx*sinp+cy*
sinA;ooz=1/z;xp=(SS/2+K1*            ooz*x).to_i ;yp= (SS/2-
K1*ooz*y).to_i;l=cosp*cost*       sinB-cosA*cost* sinp-sinA*
sint+cosB*(cosA*sint-cost*sinA*sinp);if l>0;if ooz>b[xp][yp]
 b[xp][yp]=ooz;o[xp][yp]='.,-~:;=!*#$@'[(l*8.0).to_i]||" ";
  end; end;p+=0.02 ; end;t+=0.07; end;print("\x1b[H");SS.#
     times{|j|SS.times{|i|;print(o[i][j])};print("\n")
        };end;a=b=1.0;loop{rf a,b; a+= 0.07;b+=0.03
           sleep 0.01;}#based on a1k0n's donut.c

increadible!