#include <GL/glut.h>#include <stdlib.h>#include <stdio.h>int central_orbit_period = 0;int planet_rotation_period = 0;int satellite_rotation_period = 0;void init(void){   glClearColor(0.1, 0.1, 0.1, 0.0);   glEnable(GL_COLOR_MATERIAL);   glShadeModel(GL_SMOOTH);   glEnable(GL_LIGHTING);   glEnable(GL_LIGHT0);   glEnable(GL_CULL_FACE);   glCullFace(GL_BACK);   glEnable(GL_DEPTH_TEST);}void display(void) {  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // push matrix, draw central planet, then pop matrix:  glPushMatrix();  {    glRotatef((GLfloat)planet_rotation_period, 0.0, 1.0, 0.0);    glColor4f(1.0, 0.0, 0.0, 1.0);    glutSolidSphere(1.0, 10, 8);   // Draw the central planet  } glPopMatrix();  // push matrix, draw satellite, then pop matrix:  glPushMatrix();  {    glRotatef((GLfloat)central_orbit_period, 0.0, 1.0, 0.0);    glTranslatef(1.9, 0.0, 0.0);    glRotatef((GLfloat)-satellite_rotation_period, 0.0, 1.0, 0.0);    glColor4f(0.0, 1.0, 0.0, 1.0);    glutSolidSphere(0.2, 5, 4);    // Draw the orbiting satellite  } glPopMatrix();    glutSwapBuffers();  central_orbit_period = (central_orbit_period + 2) % 360;  planet_rotation_period = (planet_rotation_period + 1) % 360;  satellite_rotation_period = (satellite_rotation_period + 6) % 360;  glutPostRedisplay();}void reshape(int w, int h){   glViewport(0, 0, w, h);    glMatrixMode(GL_PROJECTION);   glLoadIdentity();   gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 20.0);   glMatrixMode(GL_MODELVIEW);   glLoadIdentity();   gluLookAt(0.0, 0.0, 4.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);}void cycle_view() {  static int count = 0;  static int shade_flag = 0;  if (++count > 2) {    count = 0;    shade_flag = 1 - shade_flag;  }  glLoadIdentity();  switch (count)    {    case 0:      gluLookAt(0.0, 0.0, 4.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);      break;    case 1:      gluLookAt(0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0);      break;    case 2:      gluLookAt(0.0, 0.5, -3.3, 1.0, 0.0, 0.0, -0.7, 0.2, 0.4);      break;    }   if (shade_flag == 0) glShadeModel(GL_SMOOTH);   else                 glShadeModel(GL_FLAT);}void key_press_callback(unsigned char key, int x, int y) {  switch (key)    {    case 27: /* escape character */    case 'q':    case 'Q':      exit(1);    default:      cycle_view();      break;    }}int main(int argc, char *argv[]){   glutInit(&argc, argv);   glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);   glutInitWindowSize(500, 500);    glutInitWindowPosition(100, 100);   glutCreateWindow(argv[0]);   init();   glutKeyboardFunc(key_press_callback);   glutDisplayFunc(display);    glutReshapeFunc(reshape);   glutMainLoop();   return 0;}