/* -*-ePiX-*- */
#include "epix.h"
using namespace ePiX;

// Style parameters
const int MESH(12); // number of coordinate grid squares
const int MAX(3); // maximum coordinate

// camera location (in spherical coordinates); must be in first orthant
const P VIEWPT(sph(4*MAX, M_PI/6, M_PI/6));

const double sqrt3(sqrt(3));

// function to be graphed
P f(double x, double y)
{
  //  return P(x, y, 0.75*y*(y-sqrt3*x)*(y+sqrt3*x));
  return P(x,y, 0.9*MAX*exp(-0.5*(x*x+y*y))*x*y);
  //  return P(x, y, 0.25*(x-y*y)*(x-3*y*y));
}

P color(double u, double v, double w)
{
  return P(-0.5*w, 0.25*w, 0.5*w);
}

Color Bk(Green(0.7));

int main()
{
  // picture(P(-2*MAX,-2*MAX), P(2*MAX,2*MAX), "6 x 6in");
  picture(P(-MAX,-MAX), P(MAX,MAX), "6 x 6in");

  begin();
  backing(Bk);

  camera.at(0,-10,4);

  border(Green(0.6), "1pt");

  clip_box(P(MAX,MAX,MAX));

  domain R(P(-MAX,-MAX), P(MAX, MAX), (6*MESH, 6*MESH), mesh(6*MESH, 6*MESH));

  legend L1, L2, L3;
  L1.backing(Bk);
  L2.backing(Bk);
  L3.backing(Bk);

  //  pen(RGB(1, 0.8, 0.2), 0.1);
  for (int i=-10; i <=10; ++i)
    {
      clip_slice(P(0,0,0.1*i), P(0,0,1), 0.1);
      // fill(RGB(0.25+0.1*i, 0, -0.1*i));
      rgb(0.25+0.1*i, 0, -0.1*i);

      std::stringstream buf;
      buf << "$" << 0.1*i - 0.05
	  << "\\leq z \\leq " << 0.1*i + 0.05 << "$";

      if (i <-3)
	L1.fill_item(buf.str());

      else if(i<4)
	L2.fill_item(buf.str());

      else
	L3.fill_item(buf.str());

      nofill();
      surface(f, R);
      clip_restore();
    }

  camera.at(0,0,1000);
  font_size("scriptsize");
  label_color(Black());
  L1.border(0);
  L2.border(0);
  L3.border(0);

  L1.draw(canvas().bl(), P(2,2), tr);
  L2.draw(canvas().bl()+P(2,0), P(2,2), tr);
  L3.draw(canvas().bl()+P(4,0), P(2,2), tr);

  pst_format();
  end();
}