Merge pull request #284 from EvgeniiG/master

Tweak SSS transmission

Assets/ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipeline.cs

             Shader.SetGlobalInt(     "_TransmissionFlags",  (int)sssParameters.transmissionFlags);
             cmd.SetGlobalFloatArray( "_ThicknessRemaps",         sssParameters.thicknessRemaps);
             cmd.SetGlobalVectorArray("_ShapeParameters",         sssParameters.shapeParameters);
-            cmd.SetGlobalVectorArray("_SurfaceAlbedos",          sssParameters.surfaceAlbedos);
+            cmd.SetGlobalVectorArray("_VolumeAlbedos",           sssParameters.volumeAlbedos);
 
             renderContext.ExecuteCommandBuffer(cmd);
             cmd.Dispose();

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

 #define LTC_LUT_OFFSET (0.5 * rcp(LTC_LUT_SIZE))
 
 #define MIN_N_DOT_V    0.0001               // The minimum value of 'NdotV'
+#define SSS_WRAP_ANGLE (PI/12)              // Used for wrap lighting
+#define SSS_WRAP_LIGHT cos(PI/2 - SSS_WRAP_ANGLE)
 
 uint   _EnableSSS;                          // Globally toggles subsurface scattering on/off
 uint   _TexturingModeFlags;                 // 1 bit/profile; 0 = PreAndPostScatter, 1 = PostScatter
-float4 _SurfaceAlbedos[SSS_N_PROFILES];     // RGB = color, A = unused
+float4 _VolumeAlbedos[SSS_N_PROFILES];      // RGB = color, A = unused
 
 //-----------------------------------------------------------------------------
 // Helper functions/variable specific to this material
     if (bsdfData.enableTransmission)
     {
         bsdfData.transmittance = ComputeTransmittance(_ShapeParameters[subsurfaceProfile].rgb,
-                                                      _SurfaceAlbedos[subsurfaceProfile].rgb,
+                                                      _VolumeAlbedos[subsurfaceProfile].rgb,
                                                       bsdfData.thickness, bsdfData.subsurfaceRadius);
     }
 
     float3 positionWS = posInput.positionWS;
 
     float3 L = -lightData.forward; // Lights are pointing backward in Unity
-    float illuminance = saturate(dot(bsdfData.normalWS, L));
+    float NdotL = dot(bsdfData.normalWS, L);
+    float illuminance = saturate(NdotL);
 
     diffuseLighting  = float3(0.0, 0.0, 0.0);
     specularLighting = float3(0.0, 0.0, 0.0);
 
     [branch] if (bsdfData.enableTransmission)
     {
-        float LdotV = dot(L, V); // Also computed in BSDF()
-        // Compute the normal at the back of the object as R = reflect(N, -V)
-        // float RdotL = NdotL - 2 * preLightData.NdotV * LdotV;
-        float illuminance = saturate(-LdotV);
+        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
+        // Ref: Steve McAuley - Energy-Conserving Wrapped Diffuse
+        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT);
 
         // For low thickness, we can reuse the shadowing status for the back of the object.
         shadow       = bsdfData.useThinObjectMode ? shadow : 1;
     float attenuation = GetDistanceAttenuation(unL, lightData.invSqrAttenuationRadius);
     // Reminder: lights are ortiented backward (-Z)
     attenuation *= GetAngleAttenuation(L, -lightData.forward, lightData.angleScale, lightData.angleOffset);
-    float illuminance = saturate(dot(bsdfData.normalWS, L)) * attenuation;
+    float NdotL = dot(bsdfData.normalWS, L);
+    float illuminance = saturate(NdotL * attenuation);
 
     diffuseLighting  = float3(0.0, 0.0, 0.0);
     specularLighting = float3(0.0, 0.0, 0.0);
 
     [branch] if (bsdfData.enableTransmission)
     {
-        float LdotV = dot(L, V); // Also computed in BSDF()
-        // Compute the normal at the back of the object as R = reflect(N, -V)
-        // float RdotL = NdotL - 2 * preLightData.NdotV * LdotV;
-        float illuminance = saturate(-LdotV * attenuation);
+        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
+        // Ref: Steve McAuley - Energy-Conserving Wrapped Diffuse
+        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT) * attenuation;
 
         // For low thickness, we can reuse the shadowing status for the back of the object.
         shadow       = bsdfData.useThinObjectMode ? shadow : 1;
     float clipFactor = ((positionLS.z >= 0) && (abs(positionNDC.x) <= 1 && abs(positionNDC.y) <= 1)) ? 1 : 0;
 
     float3 L = -lightData.forward; // Lights are pointing backward in Unity
-    float illuminance = saturate(dot(bsdfData.normalWS, L) * clipFactor);
+    float NdotL = dot(bsdfData.normalWS, L);
+    float illuminance = saturate(NdotL * clipFactor);
 
     diffuseLighting  = float3(0.0, 0.0, 0.0);
     specularLighting = float3(0.0, 0.0, 0.0);
 
     [branch] if (bsdfData.enableTransmission)
     {
-        float LdotV = dot(L, V); // Also computed in BSDF()
-        // Compute the normal at the back of the object as R = reflect(N, -V)
-        // float RdotL = NdotL - 2 * preLightData.NdotV * LdotV;
-        float illuminance = saturate(-LdotV * clipFactor);
+        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
+        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT) * clipFactor;
 
         // For low thickness, we can reuse the shadowing status for the back of the object.
         shadow       = bsdfData.useThinObjectMode ? shadow : 1;

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/LitData.hlsl

     // Done one time for all layered - cumulate with spec occ alpha for now
     surfaceData.specularOcclusion *= GetHorizonOcclusion(V, surfaceData.normalWS, interpolatedVertexNormal, _HorizonFade);
 
-    uint transmissionMode = BitFieldExtract(_TransmissionFlags, 2u, 2u * surfaceData.subsurfaceProfile);
-
-    if (transmissionMode != SSS_TRSM_MODE_THIN)
-    {
-        // Convert thickness along the normal to thickness along the viewing direction.
-        // We assume that the thickness along the normal corresponds to the diameter of a sphere.
-        // We then find a position on the sphere which corresponds to the normal, and
-        // compute the length of the chord of the sphere along the viewing direction.
-        // We add a small bias to (hopefully) have non-zero thickness.
-        surfaceData.thickness *= saturate(dot(interpolatedVertexNormal, V) + 0.01);
-    }
-
     // Caution: surfaceData must be fully initialize before calling GetBuiltinData
     GetBuiltinData(input, surfaceData, alpha, depthOffset, builtinData);
 }

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

                 return /* 0.25 * */ S * (expOneThird + expOneThird * expOneThird * expOneThird);
             }
 
-            // Computes F(x)/P(x), s.t. x = sqrt(r^2 + z^2).
-            float3 ComputeBilateralWeight(float3 S, float r, float z, float rcpDistScale, float rcpPdf)
+            // Computes F(x)/P(x), s.t. x = sqrt(r^2 + t^2).
+            float3 ComputeBilateralWeight(float3 S, float r, float t, float rcpDistScale, float rcpPdf)
-                float3 valX = KernelValCircle(sqrt(r * r + z * z) * rcpDistScale, S);
+                float3 valX = KernelValCircle(sqrt(r * r + t * t) * rcpDistScale, S);
-                float rcpPdfX = rcpPdf * (1 + abs(z) / r);
+                float rcpPdfX = rcpPdf * (1 + abs(t) / r);
 
                 return valX * rcpPdfX;
             }
             {                                                                                   \
                 float  r   = kernel[profileID][i][0];                                           \
-                /* The relative sample position is known at the compile time. */                \
+                /* The relative sample position is known at compile time. */                    \
-                float  depth      = LOAD_TEXTURE2D(_MainDepthTexture, position).r;              \
+                /* TODO: see if making this a [branch] improves performance. */                 \
-                if (any(irradiance) == false)                                                   \
+                if (any(irradiance))                                                            \
+                {                                                                               \
+                    /* Apply bilateral weighting. */                                            \
+                    float  z = LOAD_TEXTURE2D(_MainDepthTexture, position).r;                   \
+                    float  d = LinearEyeDepth(z, _ZBufferParams);                               \
+                    float  t = millimPerUnit * d - (millimPerUnit * centerDepthVS);             \
+                    float3 w = ComputeBilateralWeight(shapeParam, r, t, rcpDistScale, rcpPdf);  \
+                                                                                                \
+                    totalIrradiance += w * irradiance;                                          \
+                    totalWeight     += w;                                                       \
+                }                                                                               \
+                else                                                                            \
                 {                                                                               \
                     /*************************************************************************/ \
                     /* The irradiance is 0. This could happen for 3 reasons.                 */ \
                     /* We do not terminate the loop since we want to gather the contribution */ \
                     /* of the remaining samples (e.g. in case of hair covering skin).        */ \
                     /*************************************************************************/ \
-                    continue;                                                                   \
+            }
+
+            #define SSS_LOOP(n, kernel, profileID, shapeParam, centerPosUnSS, centerDepthVS,    \
+                    millimPerUnit, scaledPixPerMm, rcpDistScale, totalIrradiance, totalWeight)  \
+            {                                                                                   \
+                float  centerRcpPdf = kernel[profileID][0][1];                                  \
+                float3 centerWeight = KernelValCircle(0, shapeParam) * centerRcpPdf;            \
-                /* Apply bilateral weighting. */                                                \
-                float  d = LinearEyeDepth(depth, _ZBufferParams);                               \
-                float  z = millimPerUnit * d - (millimPerUnit * centerDepthVS);                 \
-                float3 w = ComputeBilateralWeight(shapeParam, r, z, rcpDistScale, rcpPdf);      \
+                totalIrradiance = centerWeight * centerIrradiance;                              \
+                totalWeight     = centerWeight;                                                 \
-                totalIrradiance += w * irradiance;                                              \
-                totalWeight     += w;                                                           \
+                /* Perform integration over the screen-aligned plane in the view space. */      \
+                /* TODO: it would be more accurate to use the tangent plane instead.    */      \
+                [unroll]                                                                        \
+                for (uint i = 1; i < n; i++)                                                    \
+                {                                                                               \
+                    SSS_ITER(i, n, kernel, profileID, shapeParam, centerPosUnSS, centerDepthVS, \
+                    millimPerUnit, scaledPixPerMm, rcpDistScale, totalIrradiance, totalWeight)  \
+                }                                                                               \
             }
 
             struct Attributes
 
             float4 Frag(Varyings input) : SV_Target
             {
-                PositionInputs posInput = GetPositionInput(input.positionCS.xy, _ScreenSize.zw, uint2(0, 0));
+                PositionInputs posInput = GetPositionInput(input.positionCS.xy, _ScreenSize.zw);
 
                 float3 unused;
 
                 float2 centerPosition   = posInput.unPositionSS;
                 float3 centerIrradiance = LOAD_TEXTURE2D(_IrradianceSource, centerPosition).rgb;
 
-                float maxDistancePixels = maxDistance * max(scaledPixPerMm.x, scaledPixPerMm.y);
+                float  maxDistInPixels  = maxDistance * max(scaledPixPerMm.x, scaledPixPerMm.y);
-                if (maxDistancePixels < 0.5)
+                if (maxDistInPixels < 1)
-                #if SSS_DEBUG
-                    return float4(0, 0, 1, 1);
-                #else
-                    return float4(bsdfData.diffuseColor * centerIrradiance, 1);
-                #endif
+                    #if SSS_DEBUG
+                        return float4(0, 0, 1, 1);
+                    #else
+                        return float4(bsdfData.diffuseColor * centerIrradiance, 1);
+                    #endif
                 }
 
                 // Accumulate filtered irradiance and bilateral weights (for renormalization).
                 [branch]
-                if (maxDistancePixels < 4)
+                if (maxDistInPixels < SSS_LOD_THRESHOLD)
-                    #endif
-
-                    float  centerRcpPdf = _FilterKernelsFarField[profileID][0][1];
-                    float3 centerWeight = KernelValCircle(0, shapeParam) * centerRcpPdf;
-
-                    totalIrradiance = centerWeight * centerIrradiance;
-                    totalWeight     = centerWeight;
-
-                    // Perform integration over the screen-aligned plane in the view space.
-                    // TODO: it would be more accurate to use the tangent plane in the world space.
-                    [unroll]
-                    for (uint i = 1; i < SSS_N_SAMPLES_FAR_FIELD; i++)
-                    {
-                        SSS_ITER(i, SSS_N_SAMPLES_FAR_FIELD, _FilterKernelsFarField,
+                    #else
+                        SSS_LOOP(SSS_N_SAMPLES_FAR_FIELD, _FilterKernelsFarField,
-                    }
+                    #endif
-                    #endif
-
-                    float  centerRcpPdf = _FilterKernelsNearField[profileID][0][1];
-                    float3 centerWeight = KernelValCircle(0, shapeParam) * centerRcpPdf;
-
-                    totalIrradiance = centerWeight * centerIrradiance;
-                    totalWeight     = centerWeight;
-
-                    // Perform integration over the screen-aligned plane in the view space.
-                    // TODO: it would be more accurate to use the tangent plane in the world space.
-                    [unroll]
-                    for (uint i = 1; i < SSS_N_SAMPLES_NEAR_FIELD; i++)
-                    {
-                        SSS_ITER(i, SSS_N_SAMPLES_NEAR_FIELD, _FilterKernelsNearField,
+                    #else
+                        SSS_LOOP(SSS_N_SAMPLES_NEAR_FIELD, _FilterKernelsNearField,
-                    }
+                    #endif
                 }
 
                 return float4(bsdfData.diffuseColor * totalIrradiance / totalWeight, 1);

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/SubsurfaceScatteringProfile.cs

         public const int SSS_NEUTRAL_PROFILE_ID   = SSS_N_PROFILES - 1; // Does not result in blurring
         public const int SSS_N_SAMPLES_NEAR_FIELD = 55; // Used for extreme close ups; must be a Fibonacci number
         public const int SSS_N_SAMPLES_FAR_FIELD  = 21; // Used at a regular distance; must be a Fibonacci number
+        public const int SSS_LOD_THRESHOLD        = 4;  // The LoD threshold of the near-field kernel (in pixels)
         public const int SSS_TRSM_MODE_NONE       = 0;
         public const int SSS_TRSM_MODE_THIN       = 1;
     }
         public enum TransmissionMode : uint { None = SssConstants.SSS_TRSM_MODE_NONE, ThinObject = SssConstants.SSS_TRSM_MODE_THIN, Regular };
 
         public Color            surfaceAlbedo;              // Color, 0 to 1
+        public Color            volumeAlbedo;               // Color, 0 to 1
         public float            lenVolMeanFreePath;         // Length of the volume mean free path (in millimeters)
         public TexturingMode    texturingMode;
         public TransmissionMode transmissionMode;
         public SubsurfaceScatteringProfile()
         {
             surfaceAlbedo      = Color.white;
+            volumeAlbedo       = Color.white;
             lenVolMeanFreePath = 0.5f;
             texturingMode      = TexturingMode.PreAndPostScatter;
             transmissionMode   = TransmissionMode.None;
         [NonSerialized] public uint          transmissionFlags;         // 2 bit/profile; 0 = inf. thick, 1 = thin, 2 = regular
         [NonSerialized] public float[]       thicknessRemaps;           // Remap: 0 = start, 1 = end - start
         [NonSerialized] public Vector4[]     shapeParameters;           // RGB = S = 1 / D, A = filter radius
-        [NonSerialized] public Vector4[]     surfaceAlbedos;            // RGB = color, A = unused
+        [NonSerialized] public Vector4[]     volumeAlbedos;             // RGB = color, A = unused
         [NonSerialized] public float[]       worldScales;               // Size of the world unit in meters
         [NonSerialized] public float[]       filterKernelsNearField;    // 0 = radius, 1 = reciprocal of the PDF
         [NonSerialized] public float[]       filterKernelsFarField;     // 0 = radius, 1 = reciprocal of the PDF
                 shapeParameters = new Vector4[shapeParametersLen];
             }
 
-            const int surfaceAlbedosLen = SssConstants.SSS_N_PROFILES;
-            if (surfaceAlbedos == null || surfaceAlbedos.Length != surfaceAlbedosLen)
+            const int volumeAlbedosLen = SssConstants.SSS_N_PROFILES;
+            if (volumeAlbedos == null || volumeAlbedos.Length != volumeAlbedosLen)
-                surfaceAlbedos = new Vector4[surfaceAlbedosLen];
+                volumeAlbedos = new Vector4[volumeAlbedosLen];
             }
 
             const int filterKernelsNearFieldLen = 2 * SssConstants.SSS_N_PROFILES * SssConstants.SSS_N_SAMPLES_NEAR_FIELD;
                 worldScales[i]             = profiles[i].worldScale;
                 shapeParameters[i]         = profiles[i].shapeParameter;
                 shapeParameters[i].w       = profiles[i].scatteringDistance;
-                surfaceAlbedos[i]          = profiles[i].surfaceAlbedo;
+                volumeAlbedos[i]           = profiles[i].volumeAlbedo;
 
                 for (int j = 0, n = SssConstants.SSS_N_SAMPLES_NEAR_FIELD; j < n; j++)
                 {
                 int i = SssConstants.SSS_NEUTRAL_PROFILE_ID;
 
                 shapeParameters[i] = Vector4.zero;
-                surfaceAlbedos[i]  = Vector4.zero;
+                volumeAlbedos[i]   = Vector4.zero;
                 worldScales[i]     = 1.0f;
 
                 for (int j = 0, n = SssConstants.SSS_N_SAMPLES_NEAR_FIELD; j < n; j++)
             public readonly GUIContent   sssTransmittancePreview0     = new GUIContent("Transmittance Preview");
             public readonly GUIContent   sssTransmittancePreview1     = new GUIContent("Shows the fraction of light passing through the object for thickness values from the remap.");
             public readonly GUIContent   sssTransmittancePreview2     = new GUIContent("Can be viewed as a cross section of a slab of material illuminated by white light from the left.");
-            public readonly GUIContent   sssProfileSurfaceAlbedo      = new GUIContent("Surface Albedo", "Color which determines the shape of the profile. Alpha is ignored.");
+            public readonly GUIContent   sssProfileSurfaceAlbedo      = new GUIContent("Surface Albedo", "Color which determines the shape of the profile. Alpha is ignored. Typically, it is similar to the diffuse color.");
+            public readonly GUIContent   sssProfileVolumeAlbedo       = new GUIContent("Volume Albedo", "Color which tints transmitted light. Alpha is ignored. Typically, it is a more saturated version of the diffuse color.");
             public readonly GUIContent   sssProfileLenVolMeanFreePath = new GUIContent("Volume Mean Free Path", "The length of the volume mean free path (in millimeters) describes the average distance a photon travels within the volume before an extinction event occurs. Determines the effective radius of the filter.");
             public readonly GUIContent   sssProfileScatteringDistance = new GUIContent("Scattering Distance", "Effective radius of the filter (in millimeters). The blur is energy-preserving, so a wide filter results in a large area with small contributions of individual samples. Reducing the distance increases the sharpness of the result.");
             public readonly GUIContent   sssTexturingMode             = new GUIContent("Texturing Mode", "Specifies when the diffuse texture should be applied.");
 
         private RenderTexture      m_ProfileImage, m_TransmittanceImage;
         private Material           m_ProfileMaterial, m_TransmittanceMaterial;
-        private SerializedProperty m_LenVolMeanFreePath, m_ScatteringDistance, m_SurfaceAlbedo, m_S,
+        private SerializedProperty m_LenVolMeanFreePath, m_ScatteringDistance, m_SurfaceAlbedo, m_VolumeAlbedo, m_S,
+            m_VolumeAlbedo          = serializedObject.FindProperty("volumeAlbedo");
             m_LenVolMeanFreePath    = serializedObject.FindProperty("lenVolMeanFreePath");
             m_ScatteringDistance    = serializedObject.FindProperty("m_ScatteringDistance");
             m_S                     = serializedObject.FindProperty("m_S");
 
             EditorGUI.BeginChangeCheck();
             {
-                EditorGUILayout.PropertyField(m_SurfaceAlbedo,      styles.sssProfileSurfaceAlbedo);
+                EditorGUILayout.PropertyField(m_SurfaceAlbedo, styles.sssProfileSurfaceAlbedo);
                 m_LenVolMeanFreePath.floatValue = EditorGUILayout.Slider(styles.sssProfileLenVolMeanFreePath, m_LenVolMeanFreePath.floatValue, 0.01f, 1.0f);
                 
                 GUI.enabled = false;
                 m_TexturingMode.intValue        = EditorGUILayout.Popup(styles.sssTexturingMode,           m_TexturingMode.intValue,    styles.sssTexturingModeOptions);
                 m_TransmissionMode.intValue     = EditorGUILayout.Popup(styles.sssProfileTransmissionMode, m_TransmissionMode.intValue, styles.sssTransmissionModeOptions);
 
+                EditorGUILayout.PropertyField(m_VolumeAlbedo,   styles.sssProfileVolumeAlbedo);
                 EditorGUILayout.PropertyField(m_ThicknessRemap, styles.sssProfileMinMaxThickness);
                 Vector2 thicknessRemap = m_ThicknessRemap.vector2Value;
                 EditorGUILayout.MinMaxSlider(styles.sssProfileThicknessRemap, ref thicknessRemap.x, ref thicknessRemap.y, 0.0f, 50.0f);
 
             float   d = m_ScatteringDistance.floatValue;
             Vector4 A = m_SurfaceAlbedo.colorValue;
+            Vector4 V = m_VolumeAlbedo.colorValue;
+            bool transmissionEnabled = m_TransmissionMode.intValue != (int)SubsurfaceScatteringProfile.TransmissionMode.None;
 
             // Draw the profile.
             m_ProfileMaterial.SetFloat("_ScatteringDistance", d);
             EditorGUILayout.LabelField(styles.sssTransmittancePreview2, EditorStyles.centeredGreyMiniLabel);
             EditorGUILayout.Space();
 
-            bool transmissionEnabled = m_TransmissionMode.intValue != (int)SubsurfaceScatteringProfile.TransmissionMode.None;
-
-            m_TransmittanceMaterial.SetVector("_SurfaceAlbedo",     transmissionEnabled ? A : Vector4.zero);
+            m_TransmittanceMaterial.SetVector("_VolumeAlbedo",      transmissionEnabled ? V : Vector4.zero);
             m_TransmittanceMaterial.SetVector("_ShapeParameter",    S);
             m_TransmittanceMaterial.SetVector("_ThicknessRemap",    R);
             EditorGUI.DrawPreviewTexture(GUILayoutUtility.GetRect(16, 16), m_TransmittanceImage, m_TransmittanceMaterial, ScaleMode.ScaleToFit, 16.0f);

Assets/ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/SubsurfaceScatteringProfile.cs.hlsl

 #define SSS_NEUTRAL_PROFILE_ID (7)
 #define SSS_N_SAMPLES_NEAR_FIELD (55)
 #define SSS_N_SAMPLES_FAR_FIELD (21)
+#define SSS_LOD_THRESHOLD (4)
 #define SSS_TRSM_MODE_NONE (0)
 #define SSS_TRSM_MODE_THIN (1)
 

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/Resources/DrawSssProfile.shader

             //-------------------------------------------------------------------------------------
 
             #include "../../../ShaderLibrary/Common.hlsl"
-            #include "../../../ShaderLibrary/Color.hlsl"
             #include "../../ShaderVariables.hlsl"
 
             //-------------------------------------------------------------------------------------
                 float3 S = _ShapeParameter.rgb;
                 float3 M = S * (exp(-r * S) + exp(-r * S * (1.0 / 3.0))) / (8 * PI * r);
 
-                // Apply gamma for visualization only. It is not present in the actual formula!
-                return float4(pow(M * _SurfaceAlbedo.rgb, 1.0 / 3.0), 1);
+                // Apply gamma for visualization only. Do not apply gamma to the color.
+                return float4(pow(M, 1.0 / 3.0) * _SurfaceAlbedo.rgb, 1);
             }
             ENDHLSL
         }

Assets/ScriptableRenderPipeline/ShaderLibrary/CommonMaterial.hlsl

 // ----------------------------------------------------------------------------
 
 // Computes the fraction of light passing through the object.
-// N.b.: it is not just zero scattering (light traveling in a straight path)!
-// We derive the transmittance function from the SSS profile, by normalizing it s.t. R(0) = 1.
+// Evaluate Int{0, inf}{2 * Pi * r * R(sqrt(r^2 + d^2))}, where R is the diffusion profile.
-float3 ComputeTransmittance(float3 S, float3 surfaceAlbedo, float thickness, float radiusScale)
+float3 ComputeTransmittance(float3 S, float3 volumeAlbedo, float thickness, float radiusScale)
 {
     // Thickness and SSS radius are decoupled for artists.
     // In theory, we should modify the thickness by the inverse of the radius scale of the profile.
 
-    return 0.5 * (expOneThird + expOneThird * expOneThird * expOneThird) * surfaceAlbedo;
+    return 0.25 * (expOneThird + 3 * expOneThird * expOneThird * expOneThird) * volumeAlbedo;
+}
+
+// Ref: Steve McAuley - Energy-Conserving Wrapped Diffuse
+float ComputeWrappedDiffuseLighting(float NdotL, float w)
+{
+    return saturate((-NdotL + w) / ((1 + w) * (1 + w)));
 }
 
 // MACRO from Legacy Untiy

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/Resources/DrawTransmittanceGraph.shader

             // Include
             //-------------------------------------------------------------------------------------
 
-            #include "../../ShaderLibrary/Common.hlsl"
-            #include "../../ShaderLibrary/Color.hlsl"
-            #include "../../ShaderLibrary/CommonMaterial.hlsl"
-            #include "../ShaderVariables.hlsl"
+            #include "../../../ShaderLibrary/CommonMaterial.hlsl"
+            #include "../../../ShaderLibrary/Common.hlsl"
+            #include "../../ShaderVariables.hlsl"
-            float4 _SurfaceAlbedo, _ShapeParameter, _ThicknessRemap;
+            float4 _VolumeAlbedo, _ShapeParameter, _ThicknessRemap;
             float _ScatteringDistance; // See 'SubsurfaceScatteringProfile'
 
             //-------------------------------------------------------------------------------------
             float4 Frag(Varyings input) : SV_Target
             {
                 float  d = (_ThicknessRemap.x + input.texcoord.x * (_ThicknessRemap.y - _ThicknessRemap.x));
-                float3 T = ComputeTransmittance(_ShapeParameter.rgb, _SurfaceAlbedo.rgb, d, 1);
+                float3 T = ComputeTransmittance(_ShapeParameter.rgb, float3(1, 1, 1), d, 1);
-                return float4(T, 1);
+                // Apply gamma for visualization only. Do not apply gamma to the color.
+                return float4(pow(T, 1.0 / 3) * _VolumeAlbedo.rgb, 1);
             }
             ENDHLSL
         }

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/DrawGaussianProfile.shader.meta

-fileFormatVersion: 2
-guid: 2e8a76823cb2af944b4b45169f2649f9
-timeCreated: 1487181006
-licenseType: Pro
-ShaderImporter:
-  defaultTextures: []
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 

Assets/ScriptableRenderPipeline/HDRenderPipeline/SceneSettings/DrawGaussianProfile.shader

-Shader "Hidden/HDRenderPipeline/DrawGaussianProfile"
-{
-    Properties
-    {
-        [HideInInspector] _StdDev1("", Color) = (0, 0, 0)
-        [HideInInspector] _StdDev2("", Color) = (0, 0, 0)
-        [HideInInspector] _LerpWeight("", Float) = 0
-    }
-
-    SubShader
-    {
-        Pass
-        {
-            Cull   Off
-            ZTest  Off
-            ZWrite Off
-            Blend  Off
-
-            HLSLPROGRAM
-            #pragma target 4.5
-            #pragma only_renderers d3d11 ps4 metal // TEMP: until we go further in dev
-
-            #pragma vertex Vert
-            #pragma fragment Frag
-
-            //-------------------------------------------------------------------------------------
-            // Include
-            //-------------------------------------------------------------------------------------
-
-            #include "../../ShaderLibrary/Common.hlsl"
-            #include "../../ShaderLibrary/Color.hlsl"
-            #include "../ShaderVariables.hlsl"
-
-            //-------------------------------------------------------------------------------------
-            // Inputs & outputs
-            //-------------------------------------------------------------------------------------
-
-            float4 _StdDev1, _StdDev2; float _LerpWeight; // See 'SubsurfaceScatteringParameters'
-
-            //-------------------------------------------------------------------------------------
-            // Implementation
-            //-------------------------------------------------------------------------------------
-
-            struct Attributes
-            {
-                float3 vertex   : POSITION;
-                float2 texcoord : TEXCOORD0;
-            };
-
-            struct Varyings
-            {
-                float4 vertex   : SV_POSITION;
-                float2 texcoord : TEXCOORD0;
-            };
-
-            Varyings Vert(Attributes input)
-            {
-                Varyings output;
-                output.vertex   = TransformWorldToHClip(input.vertex);
-                output.texcoord = input.texcoord.xy;
-                return output;
-            }
-
-            float4 Frag(Varyings input) : SV_Target
-            {
-                float  dist = length(input.texcoord - 0.5);
-
-                float3 var1 = _StdDev1.rgb * _StdDev1.rgb;
-                float3 var2 = _StdDev2.rgb * _StdDev2.rgb;
-
-                // Evaluate the linear combination of two 2D Gaussians instead of
-                // product of a linear combination of two normalized 1D Gaussians
-                // since we do not want to bother artists with the lack of radial symmetry.
-
-                float3 magnitude = lerp(exp(-dist * dist / (2 * var1)) / (TWO_PI * var1),
-                                        exp(-dist * dist / (2 * var2)) / (TWO_PI * var2), _LerpWeight);
-
-                return float4(magnitude, 1);
-            }
-            ENDHLSL
-        }
-    }
-    Fallback Off
-}