/* -*-ePiX-*- */
/* torus.xp -- April 02, 2003 */
#include "epix.h"
using namespace ePiX;

P F(double t1, double t2)
{
  return P(Cos(t1)*(2+Sin(t2)), Sin(t1)*(2+Sin(t2)), Cos(t2));
}

const int N = 12; // to control fineness of mesh
domain R(P(0,0), P(1,1), mesh(4*N, 2*N), mesh(6*N, 6*N));
domain R1(P(0,0), P(1,1), mesh(1,1), mesh(60,60));

int main() 
{
  unitlength("1pt");
  bounding_box(P(-3,-2), P(3,2));
  picture(300,200);

  begin();
  viewpoint(1.7,-1, 0.75);
  camera.range(6);
  revolutions();

  // bulk of torus
  rgb(0.2, 0.5, 0.7);
  plot(F, R.resize1(0,0.875));

  // purple patch
  bold();
  rgb(0.5, 0.3, 0.9);
  plot(F, R.resize1(0, 0.125).resize2(-0.375, 0));

  // latitude and longitude
  red();
  dashed();
  plot(F, R1);

  end();
}