Drawing a circle using OpenGL

 // C program to demonstrate

// drawing a circle using

// OpenGL

#include<stdio.h>

#include<GL/glut.h>

#include<math.h>

#define pi 3.142857

// function to initialize

void myInit (void)

{

// making background color black as first

// 3 arguments all are 0.0

glClearColor(0.0, 0.0, 0.0, 1.0);

// making picture color green (in RGB mode), as middle argument is 1.0

glColor3f(0.0, 1.0, 0.0);

// breadth of picture boundary is 1 pixel

glPointSize(2.0);

glMatrixMode(GL_PROJECTION);

glLoadIdentity();

// setting window dimension in X- and Y- direction

gluOrtho2D(-780, 780, -420, 420);

}

void display (void)

{

glClear(GL_COLOR_BUFFER_BIT);

glBegin(GL_POINTS);

float x, y, i;

// iterate y up to 2*pi, i.e., 360 degree

// with small increment in angle as

// glVertex2i just draws a point on specified co-ordinate

for ( i = 0; i < (2 * pi); i += 0.001)

{

// let 200 is radius of circle and as,

// circle is defined as x=r*cos(i) and y=r*sin(i)

x = 200 * cos(i);

y = 200 * sin(i);

glVertex2i(x, y);

}

glEnd();

glFlush();

}

int main (int argc, char** argv)

{

glutInit(&argc, argv);

glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);

// giving window size in X- and Y- direction

glutInitWindowSize(1366, 768);

glutInitWindowPosition(0, 0);

// Giving name to window

glutCreateWindow("Circle Drawing");

myInit();

glutDisplayFunc(display);

glutMainLoop();

}

Output: