Merge pull request #820 from Unity-Technologies/Fix-issue-with-SSS

Fix misc issue with sss

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScattering.hlsl

     bool enableSss = _EnableSubsurfaceScattering != 0;
 #endif
 
-    if (enableSss)
+    // We can enter in this function even if SSS is not enabled in case of material classification per tile
+    // (If there is SSS inside the tile we need to enable the feature for the whole tile with neutral value)
+    // thus why we test != DIFFUSION_PROFILE_NEUTRAL_ID here, to be sure neutral profile don't affect the scene
+    if (enableSss && diffusionProfile != DIFFUSION_PROFILE_NEUTRAL_ID)
     {
         bool performPostScatterTexturing = IsBitSet(asuint(_TexturingModeFlags), diffusionProfile);
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScattering.shader

     Properties
     {
         [HideInInspector] _DstBlend("", Float) = 1 // Can be set to 1 for blending with specular
+
+        [HideInInspector] _StencilMask("_StencilMask", Int) = 7
     }
 
     SubShader
             Stencil
             {
+                ReadMask[_StencilMask]
                 Ref  1 // StencilLightingUsage.SplitLighting
                 Comp Equal
                 Pass Keep

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScatteringManager.cs

             m_SssVerticalFilterPass = CoreUtils.CreateEngineMaterial(hdAsset.renderPipelineResources.subsurfaceScattering);
             m_SssVerticalFilterPass.DisableKeyword("SSS_FILTER_HORIZONTAL_AND_COMBINE");
             m_SssVerticalFilterPass.SetFloat(HDShaderIDs._DstBlend, (float)BlendMode.Zero);
+            m_SssVerticalFilterPass.SetInt(HDShaderIDs._StencilMask, (int)HDRenderPipeline.StencilBitMask.LightingMask);
+            m_SssHorizontalFilterAndCombinePass.SetInt(HDShaderIDs._StencilMask, (int)HDRenderPipeline.StencilBitMask.LightingMask);
 
             m_CopyStencilForSplitLighting = CoreUtils.CreateEngineMaterial(hdAsset.renderPipelineResources.copyStencilBuffer);
             m_CopyStencilForSplitLighting.SetInt(HDShaderIDs._StencilRef, (int)StencilLightingUsage.SplitLighting);