Remove other material features from terrain other than StandardLit.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/LayeredLit/TerrainLitUI.cs

                 useDensityModeEnable |= material.GetFloat(kOpacityAsDensity + i) != 0.0f;
             }
             CoreUtils.SetKeyword(material, "_DENSITY_MODE", useDensityModeEnable);
-
-            BaseLitGUI.MaterialId materialId = (BaseLitGUI.MaterialId)material.GetFloat(kMaterialID);
-            CoreUtils.SetKeyword(material, "_MATERIAL_FEATURE_SUBSURFACE_SCATTERING", materialId == BaseLitGUI.MaterialId.LitSSS);
-            CoreUtils.SetKeyword(material, "_MATERIAL_FEATURE_TRANSMISSION", materialId == BaseLitGUI.MaterialId.LitTranslucent || (materialId == BaseLitGUI.MaterialId.LitSSS && material.GetFloat(kTransmissionEnable) > 0.0f));
         }
 
         public override void OnGUI(MaterialEditor materialEditor, MaterialProperty[] props)

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/Lit/BaseLitUI.cs

         protected MaterialProperty supportDBuffer = null;
         protected const string kSupportDBuffer = "_SupportDBuffer";
 
+        protected virtual MaterialId defaultMaterialID { get { return MaterialId.LitStandard; } }
 
         protected override void FindBaseMaterialProperties(MaterialProperty[] props)
         {
             depthOffsetEnable = FindProperty(kDepthOffsetEnable, props, false);
 
             // MaterialID
-            materialID = FindProperty(kMaterialID, props);
-            transmissionEnable = FindProperty(kTransmissionEnable, props);
+            materialID = FindProperty(kMaterialID, props, false);
+            transmissionEnable = FindProperty(kTransmissionEnable, props, false);
 
             displacementMode = FindProperty(kDisplacementMode, props, false);
             displacementLockObjectScale = FindProperty(kDisplacementLockObjectScale, props, false);
                 EditorGUI.indentLevel--;
             }
 
-            m_MaterialEditor.ShaderProperty(materialID, StylesBaseLit.materialIDText);
+            if (materialID != null)
+            {
+                m_MaterialEditor.ShaderProperty(materialID, StylesBaseLit.materialIDText);
-            if ((int)materialID.floatValue == (int)BaseLitGUI.MaterialId.LitSSS)
-            {
-                EditorGUI.indentLevel++;
-                m_MaterialEditor.ShaderProperty(transmissionEnable, StylesBaseLit.transmissionEnableText);
-                EditorGUI.indentLevel--;
+                if ((int)materialID.floatValue == (int)BaseLitGUI.MaterialId.LitSSS)
+                {
+                    EditorGUI.indentLevel++;
+                    m_MaterialEditor.ShaderProperty(transmissionEnable, StylesBaseLit.transmissionEnableText);
+                    EditorGUI.indentLevel--;
+                }
             }
 
             m_MaterialEditor.ShaderProperty(supportDBuffer, StylesBaseLit.supportDBufferText);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/TerrainLit.shader

         [Enum(Flip, 0, Mirror, 1, None, 2)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
         [HideInInspector] _DoubleSidedConstants("_DoubleSidedConstants", Vector) = (1, 1, -1, 0)
 
-        // For layering, due to combinatorial explosion, we only support SSS/Transmission and Standard. We let other case for the shader graph
-        [Enum(Subsurface Scattering, 0, Standard, 1, Translucent, 5)] _MaterialID("MaterialId", Int) = 1 // MaterialId.Standard
-        [ToggleUI] _TransmissionEnable("_TransmissionEnable", Float) = 1.0
-
         _PPDMinSamples("Min sample for POM", Range(1.0, 64.0)) = 5
         _PPDMaxSamples("Max sample for POM", Range(1.0, 64.0)) = 15
         _PPDLodThreshold("Start lod to fade out the POM effect", Range(0.0, 16.0)) = 5
 
     #pragma shader_feature _DISABLE_DBUFFER
 
-    // MaterialFeature are used as shader feature to allow compiler to optimize properly
-    #pragma shader_feature _MATERIAL_FEATURE_SUBSURFACE_SCATTERING
-    #pragma shader_feature _MATERIAL_FEATURE_TRANSMISSION
-
     //enable GPU instancing support
     #pragma multi_compile_instancing
 
     #define SURFACE_GRADIENT
     // This shader support vertex modification
     #define HAVE_VERTEX_MODIFICATION // TODO: Implement ApplyVertexModification for terrain heightmap sampling
-
-    // If we use subsurface scattering, enable output split lighting (for forward pass)
-    #if defined(_MATERIAL_FEATURE_SUBSURFACE_SCATTERING) && !defined(_SURFACE_TYPE_TRANSPARENT)
-    #define OUTPUT_SPLIT_LIGHTING
-    #endif
 
     //-------------------------------------------------------------------------------------
     // Include

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/TerrainLitData.hlsl

     surfaceData.thickness = SURFACEDATA_BLEND_SCALAR(surfaceData, thickness, weights);
     surfaceData.diffusionProfile = SURFACEDATA_BLEND_DIFFUSION_PROFILE(surfaceData, diffusionProfile, weights);
 
-    // Layered shader support SSS and Transmission features
-
-#ifdef _MATERIAL_FEATURE_SUBSURFACE_SCATTERING
-    surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING;
-#endif
-#ifdef _MATERIAL_FEATURE_TRANSMISSION
-    surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_TRANSMISSION;
-#endif
 
     // Init other parameters
     surfaceData.anisotropy = 0.0;