HDrenderPipeline: Add some comment to shadow tessellation fix

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

 {
     float maxDisplacement = GetMaxDisplacement();
 
+
+    // For tessellation we want to process tessellation factor always from the point of view of the camera (to be consistent and avoid Z-fight).
+    // For the culling part however we want to use the current view (shadow view).
+    // Thus the following code play with both.
+
-    bool frustumCulled = WorldViewFrustumCull(p0, p1, p2, maxDisplacement, (float4[4])_FrustumPlanes);
+    bool frustumCulled = WorldViewFrustumCull(p0, p1, p2, maxDisplacement, (float4[4])_FrustumPlanes); // _FrustumPlanes are primary camera planes
-    bool frustumCulled = WorldViewFrustumCull(p0, p1, p2, maxDisplacement, (float4[4])unity_CameraWorldClipPlanes);
+    bool frustumCulled = WorldViewFrustumCull(p0, p1, p2, maxDisplacement, (float4[4])unity_CameraWorldClipPlanes); // unity_CameraWorldClipPlanes is set by legacy Unity in case of shadow and contain shadow view plan
 #endif
 
     bool faceCull = false;
     if (_TessellationBackFaceCullEpsilon > -0.99) // Is backface culling enabled ?
     {
-        faceCull = BackFaceCullTriangle(p0, p1, p2, _TessellationBackFaceCullEpsilon, GetCurrentViewPosition());
+        faceCull = BackFaceCullTriangle(p0, p1, p2, _TessellationBackFaceCullEpsilon, GetCurrentViewPosition()); // Use shadow view
     }
 #endif
 
     if (_TessellationFactorTriangleSize > 0.0)
     {
         // return a value between 0 and 1
-        tessFactor *= GetScreenSpaceTessFactor( p0, p1, p2, _ViewProjMatrix, _ScreenSize, _TessellationFactorTriangleSize);
+        tessFactor *= GetScreenSpaceTessFactor( p0, p1, p2, _ViewProjMatrix, _ScreenSize, _TessellationFactorTriangleSize); // Use primary camera view
-        float3 distFactor = GetDistanceBasedTessFactor(p0, p1, p2, GetPrimaryCameraPosition(), _TessellationFactorMinDistance, _TessellationFactorMaxDistance);
+        float3 distFactor = GetDistanceBasedTessFactor(p0, p1, p2, GetPrimaryCameraPosition(), _TessellationFactorMinDistance, _TessellationFactorMaxDistance);  // Use primary camera view
         // We square the disance factor as it allow a better percptual descrease of vertex density.
         tessFactor *= distFactor * distFactor;
     }

Assets/TestScenes/HDTest/Material/StandardShaderMaterials/Gray.mat

   m_PrefabParentObject: {fileID: 0}
   m_PrefabInternal: {fileID: 0}
   m_Name: Gray
-  m_Shader: {fileID: 0}
+  m_Shader: {fileID: 46, guid: 0000000000000000f000000000000000, type: 0}
+  m_DoubleSidedGI: 0
   m_CustomRenderQueue: -1
   stringTagMap: {}
   disabledShaderPasses: []

Assets/TestScenes/HDTest/Material/StandardShaderMaterials/Green.mat

   m_PrefabParentObject: {fileID: 0}
   m_PrefabInternal: {fileID: 0}
   m_Name: Green
-  m_Shader: {fileID: 0}
+  m_Shader: {fileID: 46, guid: 0000000000000000f000000000000000, type: 0}
+  m_DoubleSidedGI: 0
   m_CustomRenderQueue: -1
   stringTagMap: {}
   disabledShaderPasses: []

Assets/TestScenes/HDTest/Material/StandardShaderMaterials/Red.mat

   m_PrefabParentObject: {fileID: 0}
   m_PrefabInternal: {fileID: 0}
   m_Name: Red
-  m_Shader: {fileID: 0}
+  m_Shader: {fileID: 46, guid: 0000000000000000f000000000000000, type: 0}
+  m_DoubleSidedGI: 0
   m_CustomRenderQueue: -1
   stringTagMap: {}
   disabledShaderPasses: []

Assets/TestScenes/HDTest/Material/StandardShaderMaterials/Std_Blue_Emissive.mat

   m_PrefabParentObject: {fileID: 0}
   m_PrefabInternal: {fileID: 0}
   m_Name: Std_Blue_Emissive
-  m_Shader: {fileID: 0}
+  m_Shader: {fileID: 46, guid: 0000000000000000f000000000000000, type: 0}
+  m_DoubleSidedGI: 0
   m_CustomRenderQueue: -1
   stringTagMap: {}
   disabledShaderPasses: []