#include "colors.inc"       /* Makes a trefoil knot using a hypotrochoid */      background { color White }  global_settings { assumed_gamma 1.0}  camera   {   location <0, 0, -25>   right <1,0,0> up <0,1,0>   look_at  <0, 0, 0>   angle 5   }   light_source   {   <0, 20, -50>   color White   area_light <5, 0, 0>, <0, 5, 0>, 10, 10  /* very slow, decrease 10 to 2 for experiments */   adaptive 3   }    #declare r_tube = 0.1; #declare num_steps = 36; #declare step_size = 1/num_steps;                 sphere_sweep   {   cubic_spline num_steps+3,   #declare N = -1;   #while(N <= num_steps + 1)     #declare theta = 2 * pi * N * step_size;     <0.3*( 2*sin(2*theta)-sin(theta) ), 0.3*( 2*cos(2*theta)+cos(theta) ), 0.3*sin(3*theta)>, r_tube     /* uses a hypotrochoid */     #declare N = N + 1;   #end   pigment { color rgb <0,0.25,1> }   finish               {     ambient 0.15     diffuse 0.85     brilliance 2     phong 0.25     phong_size 5     }   }   plane   {   <0,0,-1>, -0.4   pigment { color White }   finish     {     ambient 0.35     diffuse 0.65     }   }