mesh decals work with some per channel masks

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

             Metal_AO_Smoothness,
             Metal_Smoothness,
             Metal,
-            AO,
-            Smoothness
+            Smoothness,
+            AO
         }
         protected string[] blendModeNames = Enum.GetNames(typeof(BlendMode));
 
             CoreUtils.SetKeyword(material, "_COLORMAP", material.GetTexture(kBaseColorMap));
             CoreUtils.SetKeyword(material, "_NORMALMAP", material.GetTexture(kNormalMap));
             CoreUtils.SetKeyword(material, "_MASKMAP", material.GetTexture(kMaskMap));
+            CoreUtils.SetKeyword(material, "_NORMAL_BLEND_MASK_B", material.GetFloat(kNormalBlendSrc) == 1.0f);
+            CoreUtils.SetKeyword(material, "_MAOS_BLEND_MASK_B", material.GetFloat(kMaskBlendSrc) == 1.0f);
+            if (material.GetFloat(kMaskBlendMode) == 0.0f)
+            {
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsStr, true);    
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMSStr, false);    
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, false);
+            }
+            else if (material.GetFloat(kMaskBlendMode) == 1.0f)
+            {
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMSStr, true);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, false);
+            }
+            else if (material.GetFloat(kMaskBlendMode) == 2.0f)
+            {
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, true);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, false);
+            }
+            else if (material.GetFloat(kMaskBlendMode) == 3.0f)
+            {
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsSStr, true);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, false);
+            }
+            else if (material.GetFloat(kMaskBlendMode) == 4.0f)
+            {
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsMStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsSStr, false);
+                material.SetShaderPassEnabled(HDShaderPassNames.s_MeshDecalsAOStr, true);
+            }
         }
 
         protected void SetupMaterialKeywordsAndPassInternal(Material material)
                     m_MaterialEditor.TexturePropertySingleLine(Styles.baseColorText2, baseColorMap, baseColor);                    
                 }
                 m_MaterialEditor.TexturePropertySingleLine(Styles.normalMapText, normalMap);                               
-                normalBlendSrcValue = EditorGUILayout.Popup( "Normal Per Pixel Blend", (int)normalBlendSrcValue, blendSourceNames);               
+                normalBlendSrcValue = EditorGUILayout.Popup( "Normal blend source", (int)normalBlendSrcValue, blendSourceNames);               
                 m_MaterialEditor.TexturePropertySingleLine(Styles.maskMapText, maskMap);
                 maskBlendSrcValue = EditorGUILayout.Popup( "Mask blend source", (int)maskBlendSrcValue, blendSourceNames);                                    
                 maskBlendModeValue = EditorGUILayout.Popup( "Mask blend mode", (int)maskBlendModeValue, blendModeNames);   

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

             [SurfaceDataAttributes("Mask", true)]
             public Vector4 mask;
             [SurfaceDataAttributes("AOSBlend", true)]
-            public Vector2 AOSBlend;
+            public Vector2 MAOSBlend;
             [SurfaceDataAttributes("HTileMask")]
             public uint HTileMask;
         };

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

     float4 baseColor;
     float4 normalWS;
     float4 mask;
-	float2 AOSBlend;
+	float2 MAOSBlend;
     uint HTileMask;
 };
 

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

     outDBuffer0 = surfaceData.baseColor;
     outDBuffer1 = surfaceData.normalWS;
     outDBuffer2 = surfaceData.mask;
-	outDBuffer3 = surfaceData.AOSBlend;
+	outDBuffer3 = surfaceData.MAOSBlend;
 }
 
 void DecodeFromDBuffer(
     surfaceData.normalWS.xyz = inDBuffer1.xyz * 2.0f - 1.0f;
     surfaceData.normalWS.w = inDBuffer1.w;
     surfaceData.mask = inDBuffer2;
-	surfaceData.AOSBlend = inDBuffer3;
+	surfaceData.MAOSBlend = inDBuffer3;
 }

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

     #pragma shader_feature _MASKMAP
 	#pragma shader_feature _ALBEDOCONTRIBUTION
 
-	#pragma shader_feature _NORMAL_BLEND_ALBEDO_A
-
-	#pragma shader_feature _METALNESS_BLEND_ZERO
-	#pragma shader_feature _METALNESS_BLEND_ALBEDO_A
-	#pragma shader_feature _METALNESS_BLEND_MASK_B
-
-	#pragma shader_feature _AO_BLEND_ZERO
-	#pragma shader_feature _AO_BLEND_ALBEDO_A
-	#pragma shader_feature _AO_BLEND_MASK_B
-
-	#pragma shader_feature _SMOOTHNESS_BLEND_ZERO
-	#pragma shader_feature _SMOOTHNESS_BLEND_ALBEDO_A
-	#pragma shader_feature _SMOOTHNESS_BLEND_MASK_B
+	#pragma shader_feature _MAOS_BLEND_MASK_B
 
     #pragma multi_compile_instancing
     //-------------------------------------------------------------------------------------
         Pass
         {
             Name "DBufferProjector"  // Name is not used
-            Tags { "LightMode" = "DBufferProjector" } // This will be only for opaque object based on the RenderQueue index
+            Tags { "LightMode" = "DBufferProjector" } // pass 0 for decal projectors
 
             // back faces with zfail, for cases when camera is inside the decal volume
             Cull Front
 
 		Pass
 		{
-			Name "DBufferMesh"  // Name is not used
-			Tags{"LightMode" = "DBufferMesh"} // This will be only for opaque object based on the RenderQueue index
+			Name "DBufferMesh_MAOS"  // Name is not used
+			Tags{"LightMode" = "DBufferMesh_MAOS"} // Metalness AO and Smoothness
-			Blend SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 0 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 1 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 2 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 3 Zero OneMinusSrcColor
+
+			HLSLPROGRAM
+
+			#define SHADERPASS SHADERPASS_DBUFFER_MESH
+			#include "../../ShaderVariables.hlsl"
+			#include "Decal.hlsl"
+			#include "ShaderPass/DecalSharePass.hlsl"
+			#include "DecalData.hlsl"
+			#include "../../ShaderPass/ShaderPassDBuffer.hlsl"
+
+			ENDHLSL
+		}
+
+		Pass
+		{
+			Name "DBufferMesh_MS"  // Name is not used
+			Tags{"LightMode" = "DBufferMesh_MS"} // Metalness and smoothness
+
+			Cull Back
+			ZWrite Off
+			ZTest LEqual
+			// using alpha compositing https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
+			Blend 0 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 1 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 2 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 3 Zero OneMinusSrcColor
+
+			ColorMask RBA 2	// metal/smoothness/smoothness alpha 
+			ColorMask R 3	// metal alpha
+
+			HLSLPROGRAM
+
+			#define SHADERPASS SHADERPASS_DBUFFER_MESH
+			#include "../../ShaderVariables.hlsl"
+			#include "Decal.hlsl"
+			#include "ShaderPass/DecalSharePass.hlsl"
+			#include "DecalData.hlsl"
+			#include "../../ShaderPass/ShaderPassDBuffer.hlsl"
+
+			ENDHLSL
+		}
+
+		Pass
+		{
+			Name "DBufferMesh_M"  // Name is not used
+			Tags{"LightMode" = "DBufferMesh_M"} // Metalness only
+
+			Cull Back
+			ZWrite Off
+			ZTest LEqual
+			// using alpha compositing https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
+			Blend 0 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 1 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 2 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 3 Zero OneMinusSrcColor
+
+			ColorMask R 2	// metal 
+			ColorMask R 3	// metal alpha
+
+			HLSLPROGRAM
+
+			#define SHADERPASS SHADERPASS_DBUFFER_MESH
+			#include "../../ShaderVariables.hlsl"
+			#include "Decal.hlsl"
+			#include "ShaderPass/DecalSharePass.hlsl"
+			#include "DecalData.hlsl"
+			#include "../../ShaderPass/ShaderPassDBuffer.hlsl"
+
+			ENDHLSL
+		}
+
+		Pass
+		{
+			Name "DBufferMesh_S"  // Name is not used
+			Tags{"LightMode" = "DBufferMesh_S"} // Metalness only
+
+			Cull Back
+			ZWrite Off
+			ZTest LEqual
+			// using alpha compositing https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
+			Blend 0 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 1 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 2 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 3 Zero OneMinusSrcColor
+
+			ColorMask BA 2	// smoothness/smoothness alpha
+			ColorMask 0 3	
+
+			HLSLPROGRAM
+
+			#define SHADERPASS SHADERPASS_DBUFFER_MESH
+			#include "../../ShaderVariables.hlsl"
+			#include "Decal.hlsl"
+			#include "ShaderPass/DecalSharePass.hlsl"
+			#include "DecalData.hlsl"
+			#include "../../ShaderPass/ShaderPassDBuffer.hlsl"
+
+			ENDHLSL
+		}
+
+		Pass
+		{
+			Name "DBufferMesh_AO"  // Name is not used
+			Tags{"LightMode" = "DBufferMesh_AO"} // AO only
+
+			Cull Back
+			ZWrite Off
+			ZTest LEqual
+			// using alpha compositing https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch23.html
+			Blend 0 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 1 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 2 SrcAlpha OneMinusSrcAlpha, Zero OneMinusSrcAlpha
+			Blend 3 Zero OneMinusSrcColor
+
+			ColorMask G 2	// ao
+			ColorMask G 3	// ao alpha
 
 			HLSLPROGRAM
 

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

     surfaceData.baseColor = _BaseColor;
     surfaceData.normalWS = float4(0,0,0,0);
     surfaceData.mask = float4(0,0,0,0);
-	surfaceData.AOSBlend = float2(0, 0);
+	surfaceData.MAOSBlend = float2(0, 0);
-    float totalBlend = clamp(normalToWorld[0][3], 0.0f, 1.0f);
+    float albedoMapBlend = clamp(normalToWorld[0][3], 0.0f, 1.0f);
-	float totalBlend = _DecalBlend;
+	float albedoMapBlend = _DecalBlend;
 	float2 texCoords = input.texCoord0;
 #endif
 
-	surfaceData.baseColor.w *= totalBlend;
-	totalBlend = surfaceData.baseColor.w;   // base alpha affects all other channels;
-
+	surfaceData.baseColor.w *= albedoMapBlend;
+	albedoMapBlend = surfaceData.baseColor.w;   
 // outside _COLORMAP because we still have base color
 #if _ALBEDOCONTRIBUTION
 	surfaceData.HTileMask |= DBUFFERHTILEBIT_DIFFUSE;
 
+	float maskMapBlend;
+#if _MASKMAP
+    surfaceData.mask = SAMPLE_TEXTURE2D(_MaskMap, sampler_MaskMap, texCoords);
+	maskMapBlend = surfaceData.mask.z * _DecalBlend;	// store before overwriting with smoothness
+    surfaceData.mask.z = surfaceData.mask.w;
+	surfaceData.HTileMask |= DBUFFERHTILEBIT_MASK;
+#if _MAOS_BLEND_MASK_B
+	surfaceData.mask.w = maskMapBlend;
+#else
+    surfaceData.mask.w = albedoMapBlend;
+#endif
+#endif
+
+	// needs to be after mask, because blend source could be in the mask map blue
 #if _NORMALMAP
 	float3 normalTS = UnpackNormalmapRGorAG(SAMPLE_TEXTURE2D(_NormalMap, sampler_NormalMap, texCoords));
 #if (SHADERPASS == SHADERPASS_DBUFFER_PROJECTOR)
 	GetNormalWS(input, 0, normalTS, normalWS);
 #endif
-    surfaceData.normalWS.xyz = normalWS * 0.5f + 0.5f;
-    surfaceData.normalWS.w = totalBlend;
-    surfaceData.HTileMask |= DBUFFERHTILEBIT_NORMAL;
+	surfaceData.normalWS.xyz = normalWS * 0.5f + 0.5f;
+	surfaceData.HTileMask |= DBUFFERHTILEBIT_NORMAL;
+#if _NORMAL_BLEND_MASK_B
+	surfaceData.normalWS.w = maskMapBlend;
+#else
+	surfaceData.normalWS.w = albedoMapBlend;
+#endif	
-
-#if _MASKMAP
-    surfaceData.mask = SAMPLE_TEXTURE2D(_MaskMap, sampler_MaskMap, texCoords);
-    surfaceData.mask.z = surfaceData.mask.w;
-    surfaceData.mask.w = totalBlend;
-    surfaceData.HTileMask |= DBUFFERHTILEBIT_MASK;
-#endif
+	surfaceData.MAOSBlend.xy = float2(surfaceData.mask.w, surfaceData.mask.w);
 }

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

         }
         if(mask & DBUFFERHTILEBIT_MASK)
         {
-            surfaceData.metallic = surfaceData.metallic * decalSurfaceData.mask.w + decalSurfaceData.mask.x;
-            surfaceData.ambientOcclusion = surfaceData.ambientOcclusion * decalSurfaceData.mask.w + decalSurfaceData.mask.y;
+            surfaceData.metallic = surfaceData.metallic * decalSurfaceData.MAOSBlend.x + decalSurfaceData.mask.x;
+			surfaceData.ambientOcclusion = surfaceData.ambientOcclusion * decalSurfaceData.MAOSBlend.y + decalSurfaceData.mask.y;
             surfaceData.perceptualSmoothness = surfaceData.perceptualSmoothness * decalSurfaceData.mask.w + decalSurfaceData.mask.z;
         }
     }

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

                     sorting = { flags = SortFlags.CommonOpaque }
                 };
                 drawSettings.SetShaderPassName(0, HDShaderPassNames.s_MeshDecalsName);
+                drawSettings.SetShaderPassName(1, HDShaderPassNames.s_MeshDecalsMSName);
+                drawSettings.SetShaderPassName(2, HDShaderPassNames.s_MeshDecalsMName);
+                drawSettings.SetShaderPassName(3, HDShaderPassNames.s_MeshDecalsSName);
+                drawSettings.SetShaderPassName(4, HDShaderPassNames.s_MeshDecalsAOName);
+                
+                
                 FilterRenderersSettings filterRenderersSettings = new FilterRenderersSettings(true)
                 {
                     renderQueueRange = HDRenderQueue.k_RenderQueue_AllOpaque

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

         public static readonly string s_TransparentDepthPostpassStr = "TransparentDepthPostpass";
         public static readonly string s_MetaStr = "Meta";
         public static readonly string s_ShadowCasterStr = "ShadowCaster";
-        public static readonly string s_MeshDecalsStr = "DBufferMesh";
+        public static readonly string s_MeshDecalsStr = "DBufferMesh_MAOS";
+        public static readonly string s_MeshDecalsMSStr = "DBufferMesh_MS";
+        public static readonly string s_MeshDecalsMStr = "DBufferMesh_M";
+        public static readonly string s_MeshDecalsSStr = "DBufferMesh_S";
+        public static readonly string s_MeshDecalsAOStr = "DBufferMesh_AO";
 
         // ShaderPass name
         public static readonly ShaderPassName s_EmptyName = new ShaderPassName(s_EmptyStr);
         public static readonly ShaderPassName s_TransparentBackfaceName = new ShaderPassName(s_TransparentBackfaceStr);
         public static readonly ShaderPassName s_TransparentDepthPostpassName = new ShaderPassName(s_TransparentDepthPostpassStr);
         public static readonly ShaderPassName s_MeshDecalsName = new ShaderPassName(s_MeshDecalsStr);
+        public static readonly ShaderPassName s_MeshDecalsMSName = new ShaderPassName(s_MeshDecalsMSStr);
+        public static readonly ShaderPassName s_MeshDecalsMName = new ShaderPassName(s_MeshDecalsMStr);
+        public static readonly ShaderPassName s_MeshDecalsSName = new ShaderPassName(s_MeshDecalsSStr);
+        public static readonly ShaderPassName s_MeshDecalsAOName = new ShaderPassName(s_MeshDecalsAOStr);
 
         // Legacy name
         public static readonly ShaderPassName s_AlwaysName = new ShaderPassName("Always");