Ellipse using OpenGl

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#include<gl/glut.h>
#include<gl/glu.h>
#include<gl/gl.h>
#include<iostream>

using namespace std;
int xc=0,yc=0,rx=40,ry=60;

void display()
{
float rxsq=rx*rx;
float rysq=ry*ry;

float x=0,y=ry,p;
float px=0,py=2*rxsq*y;

glClear(GL_COLOR_BUFFER_BIT);
glPointSize(1);
glBegin(GL_POINTS);
glVertex2i(xc+x,yc+y);
glVertex2i(-(xc+x),-(yc+y));
cout<<xc+x<<" "<<yc+y<<endl;
p=rysq-(rxsq-ry)+(0.25*rxsq);
while(px<py)
{
x++;
px=px+2*rysq;
if(p<0)
p=p+rysq+px;
else
{
y--;
py=py-2*rxsq;
p=p+rysq+px-py;
}
glVertex2i(xc+x,yc+y);
glVertex2i(xc+x,-(yc+y));
glVertex2i(-(xc+x),yc+y);
glVertex2i(-(xc+x),-(yc+y));

cout<<xc+x<<" "<<yc+y<<endl;
}

p=rysq*(x+0.5)*(x+0.5) + rxsq*(y-1)*(y-1) -rxsq*rysq;
while(y>0)
{
y--;
py=py-2*rxsq;
if(p>0)
{
p=p+rxsq-py;
}
else
{
x++;
px=px+2*rysq;
p=p+rxsq-py+px;
}
glVertex2i(xc+x,yc+y);

glVertex2i(xc+x,-(yc+y));
glVertex2i(-(xc+x),yc+y);
glVertex2i(-(xc+x),-(yc+y));

cout<<xc+x<<" "<<yc+y<<endl;
}
glEnd();
glFlush();
}
void init()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-100,100,-100,100);
}

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow ("Mid Point Ellipse Algorithm ");
init ();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}

This program is to draw ellipse using points. You have to enter horizontal and vertical radius to draw ellipse. 

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