Fixed Nans happening due to volumetric clouds when the pixel color is perfectly black (case 1379185).

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -41,6 +41,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed exception on DLSS when motion vectors are disabled (case # 1377986).
 - Fixed decal performances when they use different material and the same draw order.
 - Fixed alpha channel display in color picker in Local Volumetric Fog component (the alpha is not used for the fog) (case 1381267).
+- Fixed Nans happening due to volumetric clouds when the pixel color is perfectly black (case 1379185).
 
 ### Changed
 - Optimizations for the physically based depth of field.

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/VolumetricCloudsUtilities.hlsl

@@ -502,9 +502,17 @@ void FillCloudUpscaleNeighborhoodData(int2 groupThreadId, int subRegionIdx, out
 float EvaluateFinalTransmittance(float3 color, float transmittance)
 {
     // Due to the high intensity of the sun, we often need apply the transmittance in a tonemapped space
-    float3 resultColor = color / (1.0 + color) * transmittance;
-    resultColor = resultColor / (1.0 - resultColor);
-    return _ImprovedTransmittanceBlend ? Luminance(resultColor / color) : transmittance;
+    // As we only produce one transmittance, we evaluate the approximation on the luminance of the color
+    float luminance = Luminance(color);
+
+    // Apply the tone mapping and then the transmittance
+    float resultLuminance = luminance / (1.0 + luminance) * transmittance;
+
+    // reverse the tone mapping
+    resultLuminance = resultLuminance / (1.0 - resultLuminance);
+
+    // This approach only makes sense if the color is not black
+    return (luminance > 0.0 && _ImprovedTransmittanceBlend == 1) ? resultLuminance / luminance : transmittance;
 }
 #endif // REAL_TIME_VOLUMETRIC_CLOUDS