Factor out ComputeWrappedDiffuseLighting()

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

     {
         // 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 = saturate((-NdotL + SSS_WRAP_LIGHT) / ((1 + SSS_WRAP_LIGHT) * (1 + SSS_WRAP_LIGHT)));
+        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;
     {
         // 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 = saturate((-NdotL + SSS_WRAP_LIGHT) / ((1 + SSS_WRAP_LIGHT) * (1 + SSS_WRAP_LIGHT)));
+        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;
     [branch] if (bsdfData.enableTransmission)
     {
         // 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 = saturate((-NdotL + SSS_WRAP_LIGHT) / ((1 + SSS_WRAP_LIGHT) * (1 + SSS_WRAP_LIGHT)));
+        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/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)