From 65952214fe289636f3357b9f2a68c3ab2f265673 Mon Sep 17 00:00:00 2001
From: Wentao Liu <wentao.liu.zero@outlook.com>
Date: Thu, 9 Jan 2025 14:32:02 +0800
Subject: [PATCH] Fix NAN bug when MLT propose a path with 0 radiance
---
src/pbrt/cpu/integrators.cpp | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)
diff --git a/src/pbrt/cpu/integrators.cpp b/src/pbrt/cpu/integrators.cpp
index a8c541f85..2913d49aa 100644
--- a/src/pbrt/cpu/integrators.cpp
+++ b/src/pbrt/cpu/integrators.cpp
@@ -2679,12 +2679,33 @@ void MLTIntegrator::Render() {
// Compute acceptance probability for proposed sample
Float cProposed = c(LProposed, lambdaProposed);
Float cCurrent = c(LCurrent, lambdaCurrent);
- Float accept = std::min<Float>(1, cProposed / cCurrent);
- // Splat both current and proposed samples to _film_
- if (accept > 0)
- film.AddSplat(pProposed, LProposed * accept / cProposed, lambdaProposed);
- film.AddSplat(pCurrent, LCurrent * (1 - accept) / cCurrent, lambdaCurrent);
+ Float accept = NAN;
+ if (cProposed == 0 && cCurrent == 0) {
+ // neither current path or the proposed found a light source
+ accept = 0.5;
+
+ } else if (cProposed == 0) {
+ // current path found a light source but the proposed didn't
+ accept = 0;
+ film.AddSplat(pCurrent, LCurrent / cCurrent, lambdaCurrent);
+
+ } else if (cCurrent == 0) {
+ // current path didn't find a light source but the proposed did
+ accept = 1;
+ film.AddSplat(pProposed, LProposed / cProposed, lambdaProposed);
+
+ } else {
+ // both paths found a light source
+ accept = std::min<Float>(1, cProposed / cCurrent);
+ // Splat both current and proposed samples to _film_
+ if (accept > 0) {
+ film.AddSplat(pProposed, LProposed * accept / cProposed, lambdaProposed);
+ }
+ if (accept < 1) {
+ film.AddSplat(pCurrent, LCurrent * (1 - accept) / cCurrent, lambdaCurrent);
+ }
+ }
// Accept or reject the proposal
if (rng.Uniform<Float>() < accept) {