/* Auteur: Nicolas JANEY                           */
/* nicolas.janey@univ-fcomte.fr                    */
/* Octobre 2006                                    */
/* Animation par deplacement sur un carre virtuel  */
/* en C + OpenGL + GLUT                            */

#include <stdlib.h>
#include <stdio.h>
#include <math.h>

#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/glu.h>

static float distanceParcourue = 0.0F;
static float delta = 0.022F;
static float c = 6.0F;
static int animation = 1;

static int l = 1;

void idle(void) {
  distanceParcourue += delta ;
  glutPostRedisplay();
}

void key(unsigned char key,int x,int y) {
  switch ( key ) {
    case 's'  : delta = -delta;
                break;
    case 'a'  : delta /= 1.01F;
                break;
    case 'A'  : delta *= 1.01F;
                break;
    case ' '  : animation = !animation ;
                glutIdleFunc((animation) ? idle : NULL);
                break;
    case 0x0D : l = !l ;
                glutPostRedisplay();
                break;
    case 0x1B : exit(0); }
}

void reshape(int tx,int ty) {
  glViewport(0,0,tx,ty);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(4.5*(double) -tx/ty,4.5*(double) tx/ty,-4.5,4.5,-4.5,4.5) ;
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

float modulo(float a,float b) {
  float r = a - floor(a/b)*b;
  return(r);
}

void display(void) {
  if ( l )
    glEnable(GL_LIGHTING);
    else
    glDisable(GL_LIGHTING);
  glClearColor(0.8F,0.8F,0.8F,1.0F) ;
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT) ;
  float distance = modulo(distanceParcourue,4*c);
  glPushMatrix();
  if ( distance < c )
    glTranslatef(c/2,c/2-distance,0.0F);
    else
    if ( distance < 2*c )
      glTranslatef(c/2-(distance-c),-c/2,0.0F);
      else
      if ( distance < 3*c )
        glTranslatef(-c/2,-c/2+(distance-2*c),0.0F);
        else
        glTranslatef(-c/2+(distance-3*c),c/2,0.0F);
  glutSolidSphere(1.0,72,72);
  glPopMatrix();
  glFlush();
  glutSwapBuffers();
  printf("*");
  int error = glGetError();
  if ( error != GL_NO_ERROR )
    printf("Attention, erreur OpenGL %d\n",error);
}

void init(void) {
  GLfloat l_pos[] = { 0.0F,0.0F,1.0F,0.0F };
  GLfloat c[4] = { 0.5F,0.2F,0.6F,1.0F };
  glMaterialfv(GL_FRONT,GL_DIFFUSE,c);
  glLightfv(GL_LIGHT0,GL_POSITION,l_pos);
  glEnable(GL_LIGHT0);
  glColor4fv(c) ;
  glEnable(GL_DEPTH_TEST);
  glEnable(GL_NORMALIZE);
}

int main(int argc,char **argv) {
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGBA|GLUT_DOUBLE);
  glutInitWindowSize(250,250); 
  glutInitWindowPosition(50,50); 
  glutCreateWindow("Animation par deplacement");
  init(); 
  glutReshapeFunc(reshape);
  glutKeyboardFunc(key);
  glutIdleFunc(idle);
  glutDisplayFunc(display);
  glutMainLoop();
  return(0);
}