Merge pull request #729 from Unity-Technologies/Fix-issue-with-shadow-and-tessellation-

Fix issue with tessellation and shadow

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/GeometricTools.hlsl

     return edgesOutside;
 }
 
-// Returns 'true' if a triangle defined by 3 vertices is back-facing.
-// 'epsilon' is the (negative) value of dot(N, V) below which we cull the triangle.
-// 'winding' can be used to change the order: pass 1 for (p0 -> p1 -> p2), or -1 for (p0 -> p2 -> p1).
-bool CullTriangleBackFace(float3 p0, float3 p1, float3 p2, float epsilon, float3 viewPos, float winding)
+bool CullTriangleBackFaceView(float3 p0, float3 p1, float3 p2, float epsilon, float3 V, float winding)
-    float3 N     = cross(edge1, edge2);
-    float3 V     = viewPos - p0;
+    float3 N = cross(edge1, edge2);
     float  NdotV = dot(N, V) * winding;
 
     // Optimize:
     // NdotV < Epsilon * sqrt(dot(N, N) * dot(V, V))
     return NdotV < epsilon * sqrt(dot(N, N) * dot(V, V));
+}
+
+// Returns 'true' if a triangle defined by 3 vertices is back-facing.
+// 'epsilon' is the (negative) value of dot(N, V) below which we cull the triangle.
+// 'winding' can be used to change the order: pass 1 for (p0 -> p1 -> p2), or -1 for (p0 -> p2 -> p1).
+bool CullTriangleBackFace(float3 p0, float3 p1, float3 p2, float epsilon, float3 viewPos, float winding)
+{
+    float3 V = viewPos - p0;
+    return CullTriangleBackFaceView(p0, p1, p2, epsilon, V, winding);
 }
 
 #endif // UNITY_GEOMETRICTOOLS_INCLUDED

ScriptableRenderPipeline/Core/CoreRP/Shadow/Shadow.cs

                     }
                     else
                         vp = invvp = Matrix4x4.identity; // should never happen, though
+
                     if (cameraRelativeRendering)
                     {
                         Vector3 camPosWS = camera.transform.position;
                             m_TmpSplits[key.faceIdx].z -= camPosWS.z;
                         }
                     }
+
                     // write :(
                     ce.current.shadowAlgo = shadowAlgo;
                     m_EntryCache[ceIdx] = ce;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/LitDataMeshModification.hlsl

     {
         // Handle transform mirroring (like negative scaling)
         // Note: We don't need to handle handness of view matrix here as the backface is perform in worldspace
+        // note2: When we have an orthogonal matrix (cascade shadow map), we need to use the direction of the light.
+        // Otherwise we use only p0 instead of the mean of P0, p1,p2 to save ALU as with tessellated geomerty it is rarely needed and user can still control _TessellationBackFaceCullEpsilon.
-        faceCull = CullTriangleBackFace(p0, p1, p2, _TessellationBackFaceCullEpsilon, GetCurrentViewPosition(), winding); // Use shadow view
+        faceCull = CullTriangleBackFaceView(p0, p1, p2, _TessellationBackFaceCullEpsilon, GetWorldSpaceNormalizeViewDir(p0), winding); // Use shadow view
     }
 #endif
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Sky/VisualEnvironmentEditor.cs.meta

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