#include <graphics.h>	
#include <stdlib.h>	
#include <stdio.h>	
#include <conio.h>	
#include <math.h>	
#include <dos.h>	
#define Pi 3.1415926536	
enum Action{move,draw};	
struct Point3D	
{	
  int x;	
  int y;	
  int z;	
  Action action;	
};	
// this function initializes graphics mode	
// it will work only if you're using Borland C++ compiler & BGI drivers	
// if you're using another compiler you should overwrite body of this function	
void init_gr(void)	
{	
   /* request autodetection */	
   int gdriver = DETECT, gmode, errorcode;	
   /* initialize graphics mode */	
   initgraph(&gdriver, &gmode, "");	
   /* read result of initialization */	
   errorcode = graphresult();	
   if (errorcode != grOk)    /* an error occurred */	
   {	
      printf("Graphics error: %s\n", grapherrormsg(errorcode));	
      printf("Press any key to halt:");	
      getch();	
      exit(1);               /* return with error code */	
   }	
}	
// this function shuts graphics mode down	
// it will work only if you're using Borland C++ compiler & BGI drivers	
// if you're using another compiler you should overwrite body of this function	
void end_gr(void)	
{	
  closegraph();	
}	
// this function moves CP to (x,y) position	
// it will work only if you're using Borland C++ compiler & BGI drivers	
// if you're using another compiler you should overwrite body of this function	
void MoveTo(int x, int y)	
{	
  moveto(x,y);	
}	
// this function draws a line to (x,y) position	
// it will work only if you're using Borland C++ compiler & BGI drivers	
// if you're using another compiler you should overwrite body of this function	
void LineTo(int x, int y)	
{	
  lineto(x,y);	
}	
void draw3Dobject(Point3D *object, int N, float rho, float theta,	
                  float phi, float dist_to_screen, int xshift, int yshift)	
{	
  int x,y;	
  float xe,ye,ze,costh,sinph,cosph,sinth,v11,v12,v13,v21,v22,v32,v33,v23,v43;	
  // calculating coefficients	
  costh=cos(theta);	
  sinth=sin(theta);	
  cosph=cos(phi);	
  sinph=sin(phi);	
  v11=-sinth; v12=-cosph*costh; v13=-sinph*costh;	
  v21=costh;  v22=-cosph*sinth; v23=-sinph*sinth;	
              v32=sinph;        v33=-cosph;	
                                v43=rho;	
  for (int i=0;i<N;i++)	
  {	
      // calculating eye coordinates	
      xe=v11*(object+i)->x+v21*(object+i)->y;	
      ye=v12*(object+i)->x+v22*(object+i)->y+v32*(object+i)->z;	
      ze=v13*(object+i)->x+v23*(object+i)->y+v33*(object+i)->z+v43;	
 
      // calculating screen coordinates	
      x=dist_to_screen*xe/ze+xshift;	
      y=dist_to_screen*ye/ze+yshift;	
 
      // drawing	
      if((object+i)->action==move)	
        MoveTo(x,y);	
      else	
        LineTo(x,y);	
  }	
}	
int main(void)	
{	
  const int n=20;  // number of torus' segments	
  Point3D torus[2*n*(n+1)]; // coordinates for torus' points	
  float rho=1800,theta=0,phi=3*Pi/4,dist_to_screen=600; // view point	
  int xshift=300, yshift=250; // picture offset	
  float delta=2.0*Pi/n, r=75, R=300; // torus' parameters	
  float alpha,cosa,sina,beta,x; // auxulary variables	
  // initializing graphics mode	
  init_gr();	
  // generating torus	
  for (int i=0;i<n;i++)	
  {	
     alpha=i*delta;	
     cosa=cos(alpha);	
     sina=sin(alpha);	
     for (int j=0;j<n+1;j++)	
     {	
       beta=j*delta;	
       x=R+r*cos(beta);	
       torus[i*(n+1)+j].x=cosa*x;	
       torus[i*(n+1)+j].y=sina*x;	
       torus[i*(n+1)+j].z=r*sin(beta);	
       torus[i*(n+1)+j].action=((i==0 && j==0)?move:draw);	
     }	
  }	
  int c=n*n+n;	
  for (i=0;i<n;i++)	
  {	
     beta=i*delta;	
     x=R+r*cos(beta);	
     for (int j=0;j<n+1;j++)	
     {	
       alpha=j*delta;	
       cosa=cos(alpha);	
       sina=sin(alpha);	
       torus[c+i*(n+1)+j].x=cosa*x;	
       torus[c+i*(n+1)+j].y=sina*x;	
       torus[c+i*(n+1)+j].z=r*sin(beta);	
       torus[c+i*(n+1)+j].action=draw;	
     }	
  }	
  // drawing	
  draw3Dobject(torus,2*n*(n+1),rho,theta,phi,dist_to_screen,xshift,yshift);	
  /* clean up */	
  getch();	
  end_gr();	
  return 0;	
}