void LightArray::sample(LightQuery* query) const
{
// Handle empty light accel
if (light_indices.size() == 0 && assembly_lights.size() == 0) {
query->spec_samp = SpectralSample(query->spec_samp.hero_wavelength, 0.0f);
return;
}
const float local_prob = static_cast<double>(light_indices.size()) / (total_assembly_lights + light_indices.size());
const float child_prob = 1.0f - local_prob;
// If we're sampling a light in this assembly
if (query->n <= local_prob) {
// Update probabilities
query->n /= local_prob;
// Get light instance
const auto index = light_indices[static_cast<uint32_t>(query->n * light_indices.size()) % light_indices.size()];
const Instance& instance = assembly->instances[index]; // Shorthand
// Get light data
Light* light = dynamic_cast<Light*>(assembly->objects[instance.data_index].get());
/// Get transforms if any
if (instance.transform_count > 0) {
auto cbegin = assembly->xforms.cbegin() + instance.transform_index;
auto cend = cbegin + instance.transform_count;
auto instance_xform = lerp_seq(query->time, cbegin, cend);
query->pos = instance_xform.pos_to(query->pos);
query->nor = instance_xform.nor_to(query->nor).normalized();
query->xform *= instance_xform;
}
// Sample the light
float p;
query->spec_samp = light->sample(query->pos, query->u, query->v, query->wavelength, query->time, &(query->to_light), &p);
query->to_light = query->xform.dir_from(query->to_light);
query->light_sample_pdf = p;
// FIll in the light's instance ID
query->id.push_back(index, assembly->element_id_bits());
}
// If we're sampling a light in a child assembly
else {
// Update probabilities
query->n = (query->n - local_prob) / child_prob;
// Select assembly
// TODO: a binary search would be faster
size_t index = 0;
const size_t target_index = static_cast<size_t>(total_assembly_lights * query->n) % total_assembly_lights;
for (const auto& al: assembly_lights) {
if (std::get<0>(al) <= target_index && target_index < (std::get<0>(al) + std::get<1>(al))) {
index = std::get<2>(al);
break;
}
}
// Get assembly instance shorthand
const Instance& instance = assembly->instances[index];
// Get assembly
Assembly* child_assembly = assembly->assemblies[instance.data_index].get();
// Get transforms if any
if (instance.transform_count > 0) {
auto cbegin = assembly->xforms.cbegin() + instance.transform_index;
auto cend = cbegin + instance.transform_count;
auto instance_xform = lerp_seq(query->time, cbegin, cend);
query->pos = instance_xform.pos_to(query->pos);
query->xform *= instance_xform;
}
// Push the assembly's instance ID
query->id.push_back(index, assembly->element_id_bits());
// Traverse into child assembly
child_assembly->light_accel.sample(query);
}
// Selection PDF is just one, since all lights have equal probability of
// being selected.
query->selection_pdf = 1.0f;
}
void LightTree::sample(LightQuery* query) const {
const Node* node = &(nodes[0]);
float tot_prob = 1.0f;
// Traverse down the tree, keeping track of the relative probabilities
while (!node->is_leaf) {
// Calculate the relative probabilities of the two children
float p1 = node_prob(*query, node->index1);
float p2 = node_prob(*query, node->index2);
const float total = p1 + p2;
if (total <= 0.0f) {
p1 = 0.5f;
p2 = 0.5f;
} else {
p1 /= total;
p2 /= total;
}
if (query->n <= p1) {
tot_prob *= p1;
node = &(nodes[node->index1]);
query->n /= p1;
} else {
tot_prob *= p2;
node = &(nodes[node->index2]);
query->n = (query->n - p1) / p2;
}
}
// Instance shorthand
const Instance& instance = assembly->instances[node->instance_index];
// Push the instance index onto the ID
query->id.push_back(node->instance_index, assembly->element_id_bits());
// Get transforms if any
if (instance.transform_count > 0) {
auto cbegin = assembly->xforms.cbegin() + instance.transform_index;
auto cend = cbegin + instance.transform_count;
auto instance_xform = lerp_seq(query->time, cbegin, cend);
query->pos = instance_xform.pos_to(query->pos);
query->nor = instance_xform.nor_to(query->nor).normalized();
query->xform *= instance_xform;
}
// Do light sampling
if (instance.type == Instance::OBJECT) {
const Object* obj = assembly->objects[instance.data_index].get(); // Shorthand
if (obj->get_type() == Object::LIGHT) {
const Light* light = dynamic_cast<const Light*>(obj);
float p = 1.0f;
query->spec_samp = light->sample(query->pos, query->u, query->v, query->wavelength, query->time, &(query->to_light), &p);
query->to_light = query->xform.dir_from(query->to_light);
query->selection_pdf *= (tot_prob * light_count());
query->light_sample_pdf = p;
}
// TODO: handle non-light objects that emit light
} else if (instance.type == Instance::ASSEMBLY) {
const Assembly* asmb = assembly->assemblies[instance.data_index].get(); // Shorthand
query->selection_pdf *= (tot_prob * light_count()) / asmb->light_accel.light_count();
asmb->light_accel.sample(query);
}
}