[HDRP][Ray Tracing] Meshes added to the accel struct now default to dbl-sided when they mix single and dbl-sided materials

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

@@ -40,6 +40,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Added Area Light support for Hair and Fabric master nodes.
 - Added a fallback for the ray traced directional shadow in case of a transmission (case 1307870).
 - Added support for Fabric material in Path Tracing.
+- Added Global settings check in Wizard
+- Added localization on Wizard window
+- Added an info box for micro shadow editor (case 1322830).
 
 ### Fixed
 - Fixed Intensity Multiplier not affecting realtime global illumination.
@@ -196,9 +199,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Embed the HDRP config package instead of copying locally, the `Packages` folder is versionned by Collaborate. (case 1276518)
 - Improved lighting models for AxF shader area lights.
 - Updated Wizard to better handle RenderPipelineAsset in Quality Settings
-- Added Global settings check in Wizard
-- Added localization on Wizard window
-- Added an info box for micro shadow editor (case 1322830).
+- Changed default sidedness to double, when a mesh with a mix of single and double-sided materials is added to the ray tracing acceleration structure (case 1323451).
 
 ## [11.0.0] - 2020-10-21
 

com.unity.render-pipelines.high-definition/Runtime/RenderPipeline/Raytracing/HDRaytracingManager.cs

@@ -165,7 +165,7 @@ AccelerationStructureStatus AddInstanceToRAS(Renderer currentRenderer,
             // We need to build the instance flag for this renderer
             uint instanceFlag = 0x00;
 
-            bool singleSided = false;
+            bool doubleSided = false;
             bool materialIsOnlyTransparent = true;
             bool hasTransparentSubMaterial = false;
 
@@ -207,9 +207,9 @@ AccelerationStructureStatus AddInstanceToRAS(Renderer currentRenderer,
                         else if (transparentMaterial)
                             subMeshFlagArray[meshIdx] |= RayTracingSubMeshFlags.UniqueAnyHitCalls;
 
-                        // Force it to be non single sided if it has the keyword if there is a reason
-                        bool doubleSided = currentMaterial.doubleSidedGI || currentMaterial.IsKeywordEnabled("_DOUBLESIDED_ON");
-                        singleSided |= !doubleSided;
+                        // Check if we want to enable double-sidedness for the mesh
+                        // (note that a mix of single and double-sided materials will result in a double-sided mesh in the AS)
+                        doubleSided |= currentMaterial.doubleSidedGI || currentMaterial.IsKeywordEnabled("_DOUBLESIDED_ON");
 
                         // Check if the material has changed since last time we were here
                         if (!m_MaterialsDirty)
@@ -229,12 +229,9 @@ AccelerationStructureStatus AddInstanceToRAS(Renderer currentRenderer,
                     }
                 }
 
-                // If the mesh was not valid, exclude it
+                // If the mesh was not valid, exclude it (without affecting sidedness)
                 if (!validMesh)
-                {
                     subMeshFlagArray[meshIdx] = RayTracingSubMeshFlags.Disabled;
-                    singleSided = true;
-                }
             }
 
             // If the material is considered opaque, every sub-mesh has to be enabled and with unique any hit calls
@@ -301,7 +298,7 @@ AccelerationStructureStatus AddInstanceToRAS(Renderer currentRenderer,
             if (instanceFlag == 0) return AccelerationStructureStatus.Added;
 
             // Add it to the acceleration structure
-            m_CurrentRAS.AddInstance(currentRenderer, subMeshFlags: subMeshFlagArray, enableTriangleCulling: singleSided, mask: instanceFlag);
+            m_CurrentRAS.AddInstance(currentRenderer, subMeshFlags: subMeshFlagArray, enableTriangleCulling: !doubleSided, mask: instanceFlag);
 
             // Indicates that a transform has changed in our scene (mesh or light)
             m_TransformDirty |= currentRenderer.transform.hasChanged;