Avoid issues causing faulty transitions in shadows (resulting in no shadows with unconventional aspect ratio) #2776

Author: FrancescoC-unity

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed issue where some ShaderGraph generated shaders were not SRP compatible because of UnityPerMaterial cbuffer layout mismatches (case 1292501)
 - Fixed computation of geometric normal in path tracing (case 1293029).
 - Fixed issues with path-traced volumetric scattering (cases 1295222, 1295234).
+- Fixed issue with faulty shadow transition when view is close to an object under some aspect ratio conditions
 
 ### Changed
 - Now reflection probes cannot have SSAO, SSGI, SSR, ray tracing effects or volumetric reprojection.

com.unity.render-pipelines.high-definition/Runtime/Lighting/Shadow/HDShadowAlgorithms.hlsl

@@ -206,12 +206,15 @@ int EvalShadow_GetSplitIndex(HDShadowContext shadowContext, int index, float3 po
 
     // The above code will generate transitions on the whole cascade sphere boundary.
     // It means that depending on the light and camera direction, sometimes the transition appears on the wrong side of the cascade
-    // To avoid that we attenuate the effect (lerp to 0.0) when view direction and cascade center to pixel vector face opposite directions.
+    // To avoid that we attenuate the effect (lerp very sharply to 0.0) when view direction and cascade center to pixel vector face opposite directions.
     // This way you only get fade out on the right side of the cascade.
     float3 viewDir = GetWorldSpaceViewDir(positionWS);
-    float  cascDot = dot(viewDir, wposDir);
-    alpha = lerp(alpha, 0.0, saturate(cascDot * 4.0));
 
+    float  cascDot = dot(viewDir, wposDir);
+    // At high border sizes the sharp lerp is noticeable, hence we need to lerp how sharpenss factor
+    // if we are below 80% we keep the very sharp transition.
+    float lerpSharpness = 8.0f + 512.0f * smoothstep(1.0f, 0.7f, border);// lerp(1024.0f, 8.0f, saturate(border - 0.8) / 0.2f);
+    alpha = lerp(alpha, 0.0, saturate(cascDot * lerpSharpness));
     return shadowSplitIndex;
 }
 
@@ -298,7 +301,7 @@ float EvalShadow_CascadedDepth_Dither_SplitIndex(HDShadowContext shadowContext,
 
         /* We select what split we need to sample from */
         float nextSplit = min(shadowSplitIndex + 1, cascadeCount - 1);
-        bool evalNextCascade = nextSplit != shadowSplitIndex && step(InterleavedGradientNoise(positionSS.xy, _TaaFrameInfo.z), alpha);
+        bool evalNextCascade = nextSplit != shadowSplitIndex && alpha > 0 && step(InterleavedGradientNoise(positionSS.xy, _TaaFrameInfo.z), alpha);
 
         if (evalNextCascade)
         {