Circle

#include<windows.h>

#include<gl.h>

#include<glu.h>

#include<glut.h>

#include <math.h>

#include<stdio.h>

#define PI 3.1415926535898

GLint circle_points =100;

// This is the draw function.

void draw()

{

    glClear(GL_COLOR_BUFFER_BIT);

    double angle = 2*  PI/circle_points ;

    glBegin(GL_LINE_LOOP);

        double angle1=0.0;

        glVertex2d( cos(0.0) , sin(0.0));

        int i;

        for ( i=0 ; i< circle_points ;i++)

        {

            printf( "angle = %f \n" , angle1);

            glVertex2d(cos(angle1),sin(angle1));

            angle1 += angle ;

        }

    glEnd();

    glFlush();

}

void init()

{

    glClearColor(0.0,0.0,0.0,0.0);

    glMatrixMode(GL_PROJECTION);

    glLoadIdentity();

    glOrtho(-1.0,1.0,-1.0,1.0,-1.0,1.0);

}

void keyboard (unsigned char key , int x, int y)

{

    exit(0);

}

void main( int argc,char **argv)

{

    glutInit(&argc,argv);

    glutInitDisplayMode(GLUT_SINGLE |GLUT_RGB);

    glutInitWindowSize(250,250);

    glutInitWindowPosition(100,100);

    glutCreateWindow("ch06");

    init();

    glutKeyboardFunc(keyboard);

    glutDisplayFunc(draw);

    glutMainLoop();

}