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Prevent NEE on constant emitter #1616

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Prevent NEE on constant emitter #1616

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17 changes: 16 additions & 1 deletion src/emitters/constant.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,7 @@ geometry that uses basic (e.g. diffuse) materials.
template <typename Float, typename Spectrum>
class ConstantBackgroundEmitter final : public Emitter<Float, Spectrum> {
public:
MI_IMPORT_BASE(Emitter, m_flags)
MI_IMPORT_BASE(Emitter, m_flags, m_sampling_weight)
MI_IMPORT_TYPES(Scene, Shape, Texture)

ConstantBackgroundEmitter(const Properties &props) : Base(props) {
Expand All @@ -60,10 +60,17 @@ class ConstantBackgroundEmitter final : public Emitter<Float, Spectrum> {

m_radiance = props.texture_d65<Texture>("radiance", 1.f);

// By default NEE is disabled with Constant emitter as BSDF sampling will always perform better
m_enable_nee = props.get<bool>("enable_nee", false);

if (m_radiance->is_spatially_varying())
Throw("Expected a non-spatially varying radiance spectra!");

m_flags = +EmitterFlags::Infinite;

// Disable NEE with constant emitters
if (!m_enable_nee)
m_sampling_weight = 0.f;
}

void traverse(TraversalCallback *callback) override {
Expand Down Expand Up @@ -123,6 +130,9 @@ class ConstantBackgroundEmitter final : public Emitter<Float, Spectrum> {
Mask active) const override {
MI_MASKED_FUNCTION(ProfilerPhase::EndpointSampleDirection, active);

if (!m_enable_nee)
return { dr::zeros<DirectionSample3f>(), 0.f }; // Disable NEE with constant emitters

Vector3f d = warp::square_to_uniform_sphere(sample);

// Automatically enlarge the bounding sphere when it does not contain the reference point
Expand Down Expand Up @@ -153,6 +163,9 @@ class ConstantBackgroundEmitter final : public Emitter<Float, Spectrum> {
Mask active) const override {
MI_MASKED_FUNCTION(ProfilerPhase::EndpointEvaluate, active);

if (!m_enable_nee)
return 0.f; // Disable NEE with constant emitters

return warp::square_to_uniform_sphere_pdf(ds.d);
}

Expand Down Expand Up @@ -204,6 +217,8 @@ class ConstantBackgroundEmitter final : public Emitter<Float, Spectrum> {

/// Surface area of the bounding sphere
Float m_surface_area;

bool m_enable_nee;
};

MI_IMPLEMENT_CLASS_VARIANT(ConstantBackgroundEmitter, Emitter)
Expand Down
11 changes: 7 additions & 4 deletions src/render/scene.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -99,11 +99,14 @@ MI_VARIANT
void Scene<Float, Spectrum>::update_emitter_sampling_distribution() {
// Check if we need to use non-uniform emitter sampling.
bool non_uniform_sampling = false;
for (auto &e : m_emitters) {
if (e->sampling_weight() != ScalarFloat(1.0)) {
non_uniform_sampling = true;
break;

if (m_emitters.size() > 1) {
for (auto &e : m_emitters) {
if (e->sampling_weight() != ScalarFloat(1.0)) {
non_uniform_sampling = true;
break;
}
}
}
size_t n_emitters = m_emitters.size();
if (non_uniform_sampling) {
Expand Down