Replace wrapped lighting with Fresnel for transmission

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

 
     [branch] if (bsdfData.enableTransmission)
     {
-        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
-        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT);
+        // Use the reversed normal from the front for the back of the object.
+        illuminance = F_Transm_Schlick(bsdfData.fresnel0, saturate(-NdotL));
-        // The difference between the Disney Diffuse and the Lambertian BRDF for transmission is negligible.
-        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale * Lambert());
+        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale);
-        float3 transmittedLight = backLight * bsdfData.diffuseColor * bsdfData.transmittance;
+        float3 transmittedLight = backLight * (bsdfData.diffuseColor * bsdfData.transmittance);
 
         // We use diffuse lighting for accumulation since it is going to be blurred during the SSS pass.
         diffuseLighting += transmittedLight;
 
     [branch] if (bsdfData.enableTransmission)
     {
-        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
-        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT) * attenuation;
+        // Use the reversed normal from the front for the back of the object.
+        illuminance = F_Transm_Schlick(bsdfData.fresnel0, saturate(-NdotL)) * attenuation;
-        // The difference between the Disney Diffuse and the Lambertian BRDF for transmission is negligible.
-        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale * Lambert());
+        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale);
-        float3 transmittedLight = backLight * bsdfData.diffuseColor * bsdfData.transmittance;
+        float3 transmittedLight = backLight * (bsdfData.diffuseColor * bsdfData.transmittance);
 
         // We use diffuse lighting for accumulation since it is going to be blurred during the SSS pass.
         diffuseLighting += transmittedLight;
 
     [branch] if (bsdfData.enableTransmission)
     {
-        // Reverse the normal + do some wrap lighting to have a nicer transition between regular lighting and transmittance
-        illuminance = ComputeWrappedDiffuseLighting(NdotL, SSS_WRAP_LIGHT) * clipFactor;
+        // Use the reversed normal from the front for the back of the object.
+        illuminance = F_Transm_Schlick(bsdfData.fresnel0, saturate(-NdotL)) * clipFactor;
-        // The difference between the Disney Diffuse and the Lambertian BRDF for transmission is negligible.
-        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale * Lambert());
+        float3 backLight = (cookie.rgb * lightData.color) * (illuminance * lightData.diffuseScale);
-        float3 transmittedLight = backLight * bsdfData.diffuseColor * bsdfData.transmittance;
+        float3 transmittedLight = backLight * (bsdfData.diffuseColor * bsdfData.transmittance);
 
         // We use diffuse lighting for accumulation since it is going to be blurred during the SSS pass.
         diffuseLighting += transmittedLight;

Assets/ScriptableRenderPipeline/ShaderLibrary/CommonMaterial.hlsl

     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
 // Transforms 2D UV by scale/bias property
 #define TRANSFORM_TEX(tex, name) ((tex.xy) * name##_ST.xy + name##_ST.zw)