circles.cpp

// File triangles.cpp
// Hugo Gallée
// Sat Feb 25 13:02:15 CET 2012

#include <GL/glut.h>
#include <math.h>

#define _USE_MATH_DEFINES

void circle(float x, float y, float radius, int n) {
  float teta;
  glBegin (GL_LINE_LOOP);
    glColor3f (1.0, 0.0, 0.0);
    for (int i = 0; i < n; i++) {
      teta = i * 2 * M_PI / n;
      glVertex3f (radius * sin(teta) + x, radius * cos(teta) + y, 0.0);
    }
  glEnd();
}

void init (void) {
  // select clearing color
  glClearColor (1.0, 1.0, 1.0, 0.0);

  // initialize viewing values
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}

void display(void) {
  // clear all pixels
  glClear (GL_COLOR_BUFFER_BIT);

  int nbSegments = 40;
  float teta = 1.0;
  float scale = 1.2;

  float radius = 0.4;
  float x = 0.5;
  float y = 0.5;
  while (radius > 0.02) {
    circle(x, y, radius, nbSegments);
    x += (radius - radius / scale) * sin(teta);
    y += (radius - radius / scale) * cos(teta);
    radius /= scale;
    circle(x, y, radius, nbSegments);
    teta += 0.5;
  }

  // Swap the buffers to show the oneon which we writed
  glutSwapBuffers();
}

/*
 * Declare initial window size, position, and display mode
 * (double buffer and RGB).  Open window with "hello"
 * in its title bar.  Call initialization routines.
 * Register callback function to display graphics.
 * Enter main loop and process events.
 */
int main(int argc, char** argv) {
  glutInit(&argc, argv);
  glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowSize (500, 500);
  glutInitWindowPosition (100, 100);
  glutCreateWindow ("circles");
  init ();
  glutDisplayFunc(display);
  glutMainLoop();
  return 0;
}