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

typedef struct Direction {
  float x;
  float y;
  float z;
  float w; } Direction ;

float produitScalaire(Direction *d1,Direction *d2) {
  return(d1->x*d2->x+d1->y*d2->y+d1->z*d2->z);
}

int rayonReflechi(Direction *i,Direction *n,Direction *r) {
  float ps = produitScalaire(n,i);
  if ( ps < 0 )
    return(0);
  r->x = 2.0F*ps*n->x - i->x;
  r->y = 2.0F*ps*n->y - i->y;
  r->z = 2.0F*ps*n->z - i->z;
  return(1);
}

int main(void) {
  Direction n = { 0.0F,0.6F,0.8F,0.0F };
  Direction i = { 0.6F,0.8F,0.0F,0.0F };
  Direction r;
  int b = rayonReflechi(&i,&n,&r);
  printf("Rayon incident  : %10f %10f %10f\n",i.x,i.y,i.z);
  printf("Normale         : %10f %10f %10f\n",n.x,n.y,n.z);
  if ( b )
    printf("Rayon reflechi  : %10f %10f %10f\n",r.x,r.y,r.z);
    else
    printf("Pas de rayon reflechi\n");
  return(0);
}