Fix volumetric fog nan #2174

Author: Antoine Lelievre

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

@@ -30,6 +30,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - VFX : Debug material view were rendering pink for albedo. (case 1290752)
 - Fixed NaNs happening when upscaling ray tracing reflections in performance mode (case 1294076).
 - Fixed LayeredLit shader compilation issue with metal shader and raytracing
+- Fixed nan in reflection probe when volumetric fog filtering is enabled, causing the whole probe to be invalid.
 
 ### Changed
 - Removed XRSystemTests. The GC verification is now done during playmode tests (case 1285012).

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

@@ -783,10 +783,15 @@ void FilterVolumetricLighting(uint3 dispatchThreadId : SV_DispatchThreadID,
 
             // If this is outside of the image, force the weight to 0
             #ifdef VERTICAL_PASS
-            if (tapCoord.y < 0.0 || tapCoord.y >= _VBufferViewportSize.y) weight = 0;
+            if (tapCoord.y < 0.0 || tapCoord.y >= _VBufferViewportSize.y)
             #else
-            if (tapCoord.x < 0.0|| tapCoord.x >= _VBufferViewportSize.x) weight = 0;
+            if (tapCoord.x < 0.0 || tapCoord.x >= _VBufferViewportSize.x)
             #endif
+            {
+                // To avoid NaNs, we have to override this value
+                currentValue = 0.0f;
+                weight = 0.0f;
+            }
 
             // Accumulate the value and weight
             value += currentValue * weight;