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

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

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

typedef struct Couleur {
  float r;
  float v;
  float b;
  float a; } Couleur ;

typedef struct Energie {
  float er;
  float ev;
  float eb; } Energie ;

typedef struct LumierePonctuelle {
  Position p;
  Couleur c;
  float e; } LumierePonctuelle ;

typedef struct Material {
  Couleur kd; } Material ;

float distanceAuCarre(Position *p1,Position *p2) {
  return((float) (pow(p1->x-p2->x,2.0)+
                  pow(p1->y-p2->y,2.0)+
                  pow(p1->z-p2->z,2.0)));
}

void energieRecue(Position *p,LumierePonctuelle *lp,Energie *e) {
  float d2 = distanceAuCarre(p,&lp->p);
  float f = lp->e/d2;
  e->er = f*lp->c.r;
  e->ev = f*lp->c.v;
  e->eb = f*lp->c.b;
}

void calculVecteurNorme(Position *p1,Position *p2,Direction *d) {
  d->x = p2->x-p1->x;
  d->y = p2->y-p1->y;
  d->z = p2->z-p1->z;
  float dist =(float) sqrt(distanceAuCarre(p1,p2));
  if ( dist != 0 ) {
    d->x /= dist;
    d->y /= dist;
    d->z /= dist; }
}

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

void energieDiffusee(Position *p,Direction *n,Material *m,LumierePonctuelle *lp,Energie *e) {
  Direction i;
  calculVecteurNorme(p,&lp->p,&i);
  float ps = produitScalaire(n,&i);
  if ( ps <= 0 ) {
    e->er = e->ev = e->eb = 0.0F; }
    else {
    energieRecue(p,lp,e);
    e->er *= m->kd.r * ps;
    e->ev *= m->kd.v * ps;
    e->eb *= m->kd.b * ps; }
}

int main(void) {
  LumierePonctuelle lp1 = { { 1.0F,1.0F,3.0F,1.0F },
                            { 0.9F,0.6F,0.3F,1.0F },
                            2.5F };
  Position p1 = { -0.5F,0.5F,-1.0F,1.0F };
  Direction n1 = { 0.0F,0.0F,1.0F,0.0F };
  Material m1 = { { 0.2F,0.9F,0.9F,1.0F } };
  Energie e;
  energieRecue(&p1,&lp1,&e);
  printf("Energie recue    : %f %f %f\n",e.er,e.ev,e.eb);
  energieDiffusee(&p1,&n1,&m1,&lp1,&e);
  printf("Energie diffusee : %f %f %f\n",e.er,e.ev,e.eb);
  return(0);
}