Disable blending during the first SSS pass

Assets/ScriptableRenderLoop/HDRenderPipeline/HDRenderPipeline.cs

 
         // Various set of material use in render loop
         readonly Material m_DebugViewMaterialGBuffer;
-        readonly Material m_CombineSubsurfaceScattering;
+        readonly Material m_FilterSubsurfaceScattering;
+        readonly Material m_FilterAndCombineSubsurfaceScattering;
         readonly Material m_DebugDisplayShadowMap;
 
         // Various buffer
 
             m_DebugViewMaterialGBuffer = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/DebugViewMaterialGBuffer");
 
-            m_CombineSubsurfaceScattering = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/CombineSubsurfaceScattering");
+            m_FilterSubsurfaceScattering = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/CombineSubsurfaceScattering");
+            m_FilterSubsurfaceScattering.SetFloat("_DstBlend", (float)BlendMode.Zero);
+            m_FilterSubsurfaceScattering.SetFloat("_FilterHorizontal", 0);
+
+            m_FilterAndCombineSubsurfaceScattering = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/CombineSubsurfaceScattering");
+            m_FilterAndCombineSubsurfaceScattering.SetFloat("_DstBlend", (float)BlendMode.One);
+            m_FilterAndCombineSubsurfaceScattering.SetFloat("_FilterHorizontal", 1);
+
             m_DebugDisplayShadowMap = Utilities.CreateEngineMaterial("Hidden/HDRenderPipeline/DebugDisplayShadowMap");
 
             m_ShadowPass = new ShadowRenderPass(owner.shadowSettings);
 
             // Assume that the height of the projection window is 2 meters.
             float distanceToProjectionWindow = 1.0f / Mathf.Tan(0.5f * Mathf.Deg2Rad * hdCamera.camera.fieldOfView);
-            m_CombineSubsurfaceScattering.SetFloat("_DistToProjWindow", distanceToProjectionWindow);
-            m_CombineSubsurfaceScattering.SetFloat("_BilateralScale", 0.05f * sssParameters.bilateralScale);
 
             // Upload the kernel data.
             Vector4[] kernelData = new Vector4[SubsurfaceScatteringParameters.maxNumProfiles * SubsurfaceScatteringProfile.numSamples];
                     kernelData[n * j + i] = sssParameters.profiles[j].filterKernel[i];
                 }
             }
-            m_CombineSubsurfaceScattering.SetVectorArray("_FilterKernels", kernelData);
 
             MaterialPropertyBlock properties = new MaterialPropertyBlock();
 
-            properties.SetFloat("_DstBlend", (float)BlendMode.Zero); // TODO: this doesn't work for some reason...
-            properties.SetFloat("_FilterHorizontal", 0);
+            m_FilterSubsurfaceScattering.SetFloat("_DistToProjWindow", distanceToProjectionWindow);
+            m_FilterSubsurfaceScattering.SetFloat("_BilateralScale", 0.05f * sssParameters.bilateralScale);
+            m_FilterSubsurfaceScattering.SetVectorArray("_FilterKernels", kernelData);
-            Utilities.DrawFullscreen(cmd, m_CombineSubsurfaceScattering, hdCamera,
+            Utilities.DrawFullscreen(cmd, m_FilterSubsurfaceScattering, hdCamera,
-            properties.SetFloat("_DstBlend", (float)BlendMode.One);  // TODO: this doesn't work for some reason...
-            properties.SetFloat("_FilterHorizontal", 1);
+            m_FilterAndCombineSubsurfaceScattering.SetFloat("_DistToProjWindow", distanceToProjectionWindow);
+            m_FilterAndCombineSubsurfaceScattering.SetFloat("_BilateralScale", 0.05f * sssParameters.bilateralScale);
+            m_FilterAndCombineSubsurfaceScattering.SetVectorArray("_FilterKernels", kernelData);
-            Utilities.DrawFullscreen(cmd, m_CombineSubsurfaceScattering, hdCamera,
+            Utilities.DrawFullscreen(cmd, m_FilterAndCombineSubsurfaceScattering, hdCamera,
                                      m_CameraColorBufferRT, m_CameraStencilBufferRT, properties);
 
             context.ExecuteCommandBuffer(cmd);

Assets/ScriptableRenderLoop/HDRenderPipeline/Material/Lit/Resources/CombineSubsurfaceScattering.shader

 
             ZTest  Always
             ZWrite Off
-            Blend  One [_DstBlend], Zero [_DstBlend]
+            Blend  One [_DstBlend]
 
             HLSLPROGRAM
             #pragma target 4.5
                 return output;
             }
 
-            float4 Frag(Varyings input) : SV_Target
+            float3 Frag(Varyings input) : SV_Target
             {
                 PositionInputs posInput = GetPositionInput(input.positionCS.xy, _ScreenSize.zw);
 
                     filteredIrradiance += lerp(sampleIrradiance, centerIrradiance, t) * sampleWeight;
                 }
 
-                return float4(filteredIrradiance, 1.0);
+                return filteredIrradiance;
             }
             ENDHLSL
         }