gi/hdGatling: add doubleSidedAsThinWalled render setting

src/gi/include/Gi.h

@@ -108,6 +108,7 @@ namespace gtl
     GiAovId            aovId;
     bool               depthOfField;
     bool               domeLightCameraVisible;
+    bool               doubleSidedAsThinWalled;
     bool               filterImportanceSampling;
     uint32_t           materialCount;
     const GiMaterial** materials;

src/gi/shaders/rp_main.chit

@@ -152,7 +152,10 @@ void main()
     uint mediumIdx = shadeRayPayloadGetMediumIdx(rayPayload);
     bool doubleSided = bool(payload.bitfield & BLAS_PAYLOAD_BITFLAG_IS_DOUBLE_SIDED);
 
-    bool thinWalled = doubleSided;
+    bool thinWalled = false;
+#ifdef DOUBLE_SIDED_AS_THIN_WALLED
+    thinWalled = doubleSided;
+#endif
 #ifdef IS_THIN_WALLED
     if (mdl_thin_walled(shading_state))
     {

src/gi/src/Gi.cpp

@@ -1019,6 +1019,7 @@ namespace gtl
             .baseFileName = "rp_main.chit",
             .commonParams = commonParams,
             .directionalBias = material->directionalBias,
+            .doubleSidedAsThinWalled = params.doubleSidedAsThinWalled,
             .enableSceneTransforms = material->requiresSceneTransforms,
             .hasCutoutTransparency = material->hasCutoutTransparency,
             .hasVolumeAbsorptionCoeff = material->hasVolumeAbsorptionCoeff,

src/gi/src/GlslShaderGen.cpp

@@ -269,6 +269,10 @@ namespace gtl
     {
       stitcher.appendDefine("SCENE_TRANSFORMS");
     }
+    if (params.doubleSidedAsThinWalled)
+    {
+      stitcher.appendDefine("DOUBLE_SIDED_AS_THIN_WALLED");
+    }
 
     fs::path filePath = m_shaderPath / params.baseFileName;
     if (!stitcher.appendSourceFile(filePath))

src/gi/src/GlslShaderGen.h

@@ -88,6 +88,7 @@ namespace gtl
       std::string_view baseFileName;
       CommonShaderParams commonParams;
       float directionalBias;
+      bool doubleSidedAsThinWalled;
       bool enableSceneTransforms;
       bool hasCutoutTransparency;
       bool hasVolumeAbsorptionCoeff;

src/hdGatling/renderDelegate.cpp

@@ -79,6 +79,7 @@ HdGatlingRenderDelegate::HdGatlingRenderDelegate(const HdRenderSettingsMap& sett
   _settingDescriptors.push_back(HdRenderSettingDescriptor{ "Clipping planes", HdGatlingSettingsTokens->clippingPlanes, VtValue{false} });
   _settingDescriptors.push_back(HdRenderSettingDescriptor{ "Medium stack size", HdGatlingSettingsTokens->mediumStackSize, VtValue{0} });
   _settingDescriptors.push_back(HdRenderSettingDescriptor{ "Max volume walk length", HdGatlingSettingsTokens->maxVolumeWalkLength, VtValue{7} });
+  _settingDescriptors.push_back(HdRenderSettingDescriptor{ "Double-sided as thin-walled", HdGatlingSettingsTokens->doubleSidedAsThinWalled, VtValue{false} });
 
   _debugSettingDescriptors.push_back(HdRenderSettingDescriptor{ "Progressive accumulation", HdGatlingSettingsTokens->progressiveAccumulation, VtValue{true} });
 

src/hdGatling/renderPass.cpp

@@ -431,6 +431,7 @@ void HdGatlingRenderPass::_Execute(const HdRenderPassStateSharedPtr& renderPassS
         .aovId = aovId,
         .depthOfField = _settings.find(HdGatlingSettingsTokens->depthOfField)->second.Get<bool>(),
         .domeLightCameraVisible = (domeLightCameraVisibilityValueIt == _settings.end()) || domeLightCameraVisibilityValueIt->second.GetWithDefault<bool>(true),
+        .doubleSidedAsThinWalled = _settings.find(HdGatlingSettingsTokens->doubleSidedAsThinWalled)->second.Get<bool>(),
         .filterImportanceSampling = _settings.find(HdGatlingSettingsTokens->filterImportanceSampling)->second.Get<bool>(),
         .materialCount = (uint32_t) materials.size(),
         .materials = materials.data(),

src/hdGatling/tokens.h

@@ -34,6 +34,7 @@ PXR_NAMESPACE_OPEN_SCOPE
   ((lightIntensityMultiplier, "light-intensity-multiplier")) \
   ((mediumStackSize, "medium-stack-size"))                   \
   ((maxVolumeWalkLength, "max-volume-walk-length"))          \
+  ((doubleSidedAsThinWalled, "double-sided-as-thin-walled")) \
   ((clippingPlanes, "clipping-planes"))
 
 // mtlx node identifier is given by UsdMtlx.