//**********************************************
void Photon_map :: irradiance_estimate(
float irrad[3], // returned irradiance
const float pos[3], // surface position
const float normal[3], // surface normal at pos
const float max_dist, // max distance to look for photons
const int nphotons ) const // number of photons to use
//**********************************************
{
irrad[0] = irrad[1] = irrad[2] = 0.0;
NearestPhotons np;
np.dist2 = (float*)alloca( sizeof(float)*(nphotons+1) );
np.index = (const Photon**)alloca( sizeof(Photon*)*(nphotons+1) );
np.pos[0] = pos[0]; np.pos[1] = pos[1]; np.pos[2] = pos[2];
np.max = nphotons;
np.found = 0;
np.got_heap = 0;
np.dist2[0] = max_dist*max_dist;
// locate the nearest photons
locate_photons( &np, 1 );
// if less than 8 photons return
if (np.found<8)
return;
float pdir[3];
// sum irradiance from all photons
for (int i=1; i<=np.found; i++) {
const Photon *p = np.index[i];
// the photon_dir call and following if can be omitted (for speed)
// if the scene does not have any thin surfaces
photon_dir( pdir, p );
if ( (pdir[0]*normal[0]+pdir[1]*normal[1]+pdir[2]*normal[2]) < 0.0f ) {
irrad[0] += p->power[0];
irrad[1] += p->power[1];
irrad[2] += p->power[2];
}
}
const float tmp=(1.0f/PI)/(np.dist2[0]); // estimate of density
irrad[0] *= tmp;
irrad[1] *= tmp;
irrad[2] *= tmp;
}
//******************************************
void PhotonMap::locate_photons(NearestPhotons *const np, const int index) const
//******************************************
{
const Photon *p = &photons[index];
float dist1;
if (index < half_stored_photons) {
dist1 = np->pos[p->plane] - p->pos[p->plane];
if (dist1 > 0.0) { // if dist1 is positive search right plane
locate_photons(np, 2 * index + 1);
if (dist1 * dist1 < np->dist2[0])
locate_photons(np, 2 * index);
} else { // dist1 is negative search left first
locate_photons(np, 2 * index);
if (dist1 * dist1 < np->dist2[0])
locate_photons(np, 2 * index + 1);
}
}
// compute squared distance between current photon and np->pos
dist1 = p->pos[0] - np->pos[0];
float dist2 = dist1 * dist1;
dist1 = p->pos[1] - np->pos[1];
dist2 += dist1 * dist1;
dist1 = p->pos[2] - np->pos[2];
dist2 += dist1 * dist1;
if (dist2 < np->dist2[0]) {
// we found a photon [:)] Insert it in the candidate list
if (np->found < np->max) {
// heap is not full; use array
np->found++;
np->dist2[np->found] = dist2;
np->index[np->found] = p;
} else {
int j, parent;
if (np->got_heap == 0) { // Do we need to build the heap?
// Build heap
float dst2;
const Photon *phot;
int half_found = np->found >> 1;
for (int k = half_found; k >= 1; k--) {
parent = k;
phot = np->index[k];
dst2 = np->dist2[k];
while (parent <= half_found) {
j = parent + parent;
if (j < np->found && np->dist2[j] < np->dist2[j + 1])
j++;
if (dst2 >= np->dist2[j])
break;
np->dist2[parent] = np->dist2[j];
np->index[parent] = np->index[j];
parent = j;
}
np->dist2[parent] = dst2;
np->index[parent] = phot;
}
np->got_heap = 1;
}
// insert new photon into max heap
// delete largest element, insert new and reorder the heap
parent = 1;
j = 2;
while (j <= np->found) {
if (j < np->found && np->dist2[j] < np->dist2[j + 1])
j++;
if (dist2 > np->dist2[j])
break;
np->dist2[parent] = np->dist2[j];
np->index[parent] = np->index[j];
parent = j;
j += j;
}
np->index[parent] = p;
np->dist2[parent] = dist2;
np->dist2[0] = np->dist2[1];
}
}