#include <stdio.h>
#include <iostream>
#include <cstdio>
#include <GL/glut.h>

using namespace std;

int x1,x2,y1,y2 = 0;

void drawLine ( int x1 , int y1 , int x2 , int y2 )
{
  int dx = x2 - x1 ;
  int dy = y2 - y1 ;
  float m = dy / dx;
  if ( m>=0 && m <= 1 )
    {
      int y = y1;
      int p = 2*dx - dy ;
      glBegin ( GL_POINTS );
      for (int x = x1 ; x <= x2 ; x++  )
	{
	  glVertex2f ( (GLint) x , (GLint) y );

	  if ( p < 0 )
	    {
	      p = p + 2*dy;
	    }else
	    {
	      p = p + 2 * (dy - dx);
	      y = y + 1;
	    }

	}
      glEnd ();
    }else
    {
      int x = x1;
      int p = 2*dy - dx ;
      glBegin ( GL_POINTS );
      for (int y = y1 ; y <= y2 ; y++  )
	{
	  glVertex2f ( (GLint) x , (GLint) y );

	  if ( p < 0 )
	    {
	      p = p + 2*dx;
	    }else
	    {
	      p = p + 2 * (dx - dy);
	      x = x + 1;
	    }

	}
      glEnd ();
    }

}

void Display( void )
{
  glClear ( GL_COLOR_BUFFER_BIT);
  drawLine ( x1, y1, x2 ,y2);
  glFlush ();
}

void reshape ( int w , int h )
{
  glViewport (0,0,(GLsizei) w, (GLsizei) h) ;
  glMatrixMode (GL_PROJECTION);
  glLoadIdentity ();
  gluOrtho2D ( 0.0 , 160.0 , 0.0 , 120.0 );

}

void init ( void )
{
  glClearColor ( 0.0 , 0.8 , 0.0 , 1.0 );
  glPointSize ( 5.0 );
}

int main (int argc, char *argv[] )
{

  x1 = 0 ;
  y1 = 0;
  x2 = 1 ;
  y2 =  100;
  glutInit (&argc , argv );
  glutInitDisplayMode ( GLUT_SINGLE | GLUT_RGB );
  glutInitWindowSize ( 320 , 240 ) ;
  glutCreateWindow ( " Bresenham's Algorithm " ) ;
  init ();
  glutDisplayFunc ( Display );
  glutReshapeFunc ( reshape ) ;
  glutMainLoop ();

  return 0;
}