address PR comments

com.unity.render-pipelines.high-definition/HDRP/Editor/Material/Decal/DecalUI.cs

             CoreUtils.SetKeyword(material, "_ALBEDOCONTRIBUTION", material.GetFloat(kAlbedoMode) == 1.0f);
             CoreUtils.SetKeyword(material, "_COLORMAP", material.GetTexture(kBaseColorMap));
             CoreUtils.SetKeyword(material, "_NORMALMAP", material.GetTexture(kNormalMap));
-            CoreUtils.SetKeyword(material, "_MASKMAP", material.GetTexture(kMaskMap)); 
+            CoreUtils.SetKeyword(material, "_MASKMAP", material.GetTexture(kMaskMap));
+            material.SetInt(HDShaderIDs._StencilRef, (int)HDRenderPipeline.StencilBitMask.Decals);
+            material.SetInt(HDShaderIDs._StencilMask, (int)HDRenderPipeline.StencilBitMask.Decals);
             material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, false);
             material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, false);
             material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMAOStr, false);

com.unity.render-pipelines.high-definition/HDRP/Material/Decal/Decal.shader

 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			// back faces with zfail, for cases when camera is inside the decal volume
 													  // back faces with zfail, for cases when camera is inside the decal volume
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			Cull Front
 													   // back faces with zfail, for cases when camera is inside the decal volume
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			Cull Front
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			// back faces with zfail, for cases when camera is inside the decal volume
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			// back faces with zfail, for cases when camera is inside the decal volume
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			// back faces with zfail, for cases when camera is inside the decal volume
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
             // back faces with zfail, for cases when camera is inside the decal volume
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off
 
             Stencil
             {
+                WriteMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass IncrSat
+                Pass Replace
             }
 
 			ZWrite Off

com.unity.render-pipelines.high-definition/HDRP/Material/Decal/DecalNormalBuffer.shader

             normalData.normalWS.xyz = normalize(normalData.normalWS.xyz * DBufferNormal.w + DBufferNormal.xyz);
             EncodeIntoNormalBuffer(normalData, uint2(0, 0), GBufferNormal);
             _NormalBuffer[input.texcoord * _ScreenSize.xy] = GBufferNormal;
-            return GBufferNormal;
+            return float4(0, 0, 0, 0); // normal buffer is written into as a RWTexture
         }
 
     ENDHLSL
             Blend Off
             Cull Off
 
-            // depth prepass increments stencil to 1
-            // dbuffer increments it to 2
-            // not optimal because we also process pixels that might not have any normals
-                Ref 2
+                ReadMask[_StencilMask]
+                Ref[_StencilRef]
-                Pass Zero
+                Pass Zero   // doesn't really matter, but clear to 0 for debugging 
             }
 
             HLSLPROGRAM

com.unity.render-pipelines.high-definition/HDRP/Material/Lit/Lit.shader

 
             ZWrite On
 
-            // decals rely on this to mask out the pixels that need to be updated in the normal buffer (forward)
-            Stencil
-            {
-                Comp Always
-                Pass IncrSat
-            }
-
             HLSLPROGRAM
 
             // In deferred, depth only pass don't output anything.

com.unity.render-pipelines.high-definition/HDRP/RenderPipeline/HDRenderPipeline.cs

         {
             Clear           = 0,             // 0x0
             LightingMask    = 7,             // 0x7  - 3 bit
+            Decals          = 8,             // 0x8  - 1 bit
             ObjectVelocity  = 128,           // 0x80 - 1 bit
             All             = 255            // 0xFF - 8 bit
         }
             m_CopyStencilForNoLighting.SetInt(HDShaderIDs._StencilMask, (int)StencilBitMask.LightingMask);
             m_CameraMotionVectorsMaterial = CoreUtils.CreateEngineMaterial(asset.renderPipelineResources.cameraMotionVectors);
             m_DecalNormalBufferMaterial = CoreUtils.CreateEngineMaterial(asset.renderPipelineResources.decalNormalBuffer);
+            m_DecalNormalBufferMaterial.SetInt(HDShaderIDs._StencilRef, (int)StencilBitMask.Decals);
+            m_DecalNormalBufferMaterial.SetInt(HDShaderIDs._StencilMask, (int)StencilBitMask.Decals);
 
             m_CopyDepth = CoreUtils.CreateEngineMaterial(asset.renderPipelineResources.copyDepthBuffer);