algorithm for creating a circle.

#include <GL/glut.h>#include <cmath>namespace {// display function that renders the scene.void display() {    // clear colour buffer (default colour is black on my machine)    glClear( GL_COLOR_BUFFER_BIT );    // set the circle colour to be white    glColor3f( 1.0f, 1.0f, 1.0f );    // make a smooth circle using 100 steps    int const steps = 100;    // instead of re-computing the angle each iteration,    // I just use the delta value    float const angleDelta = 3.141592654f * 2 / steps;    float angle = 0.0f;    // begin the loop    glBegin(GL_LINE_LOOP);    // iterate over the line segments and update the angle    for ( int i = 0; i < steps; ++i, angle += angleDelta ) {        // use the values as-is - the circle could be made smaller by        // multiplying x and y by some radius r        glVertex2f( cos(angle), sin(angle) );    }    glEnd();    // I use double-bufering, so present the rendered scene by     // swapping the buffers    glutSwapBuffers();}}int main(int argc, char * argv[]) {    // setup the display mode to use double buffering and an RGB colour buffer    glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB );        glutInitWindowSize( 512, 512 );    glutCreateWindow( "circle" );    glutDisplayFunc( display );    // setup complete - start the rendering loop    glutMainLoop();}