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

const P LdY(0, 4);
const P LdX(4, 0);

std::string sfmt(const std::string& msg)
{
#ifdef SANSSERIF
  return "$\\mathsf{"+msg+"}$";
#else
  return "$"+msg+"$";
#endif
}

void ray(const P& tail, const P& head, double s)
{
  line(tail, tail + (1+0.01*s)*(head-tail));
}

const double K(0.5);

const double X0(0.75);
const double dX(-0.1);

P f(double t)
{
  return P(1 + K*(1 + 2.5*t)*t, t);
}

int main()
{
  picture(P(0, 0), P(3,1), "4 x 2in");

  begin();

  P ptO(0,0), ptP(f(X0)), ptQ(f(X0+dX)), ptR(ptP.x1(), ptQ.x2());
  P ptM(ptP.x1(), 0), ptN(ptQ.x1(), 0), ptx(3,0), pty(0,0.75);

  Segment TP(f(X0), f(X0+0.0001));
  P ptT(Segment(ptO, ptx)*TP);

  plot(f, 0, 1, 40);

  line(ptQ, ptR);
  line(ptN, ptQ);
  line(ptM, ptP);

  line(ptO, pty);
  line(ptO, ptx, 20);

  ray(ptT, ptP, 35);

  label(ptO, -LdY, sfmt("O"), b);
  label(ptM, -LdY, sfmt("M"), b);
  label(ptN, -LdY, sfmt("N"), b);
  label(ptx, -LdY, "$x$", b);

  label(ptT, -LdY, sfmt("T"), b);

  label(pty, -LdX, "$y$", bl);

  label(ptR,  LdX, sfmt("R"), r);
  label(ptP,  LdY, sfmt("P"), tl);

  label(ptQ, -1.5*LdY, sfmt("Q"), bl);

  tikz_format();
  end();
}