Revert: Fix shadow mask fade and optimize it at same time #5911

Author: sebastienlagarde

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

@@ -35,7 +35,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed crossfade not working on the HD ST8 ShaderGraph [case 1369586](https://fogbugz.unity3d.com/f/cases/1369586/)
 - Fixed range compression factor being clamped. (case 1365707)
 - Fixed tooltip not showing on labels in ShaderGraphs (1358483).
-- Fixed and optimize distance shadowmask fade.
 - Fix API warnings in Matcap mode on Metal.
 - Fix D3D validation layer errors w.r.t shadow textures when an atlas is not used.
 

com.unity.render-pipelines.high-definition/Runtime/Lighting/LightDefinition.cs

@@ -95,8 +95,6 @@ struct DirectionalLightData
         [SurfaceDataAttributes(precision = FieldPrecision.Real)]
         public Vector4 shadowMaskSelector;      // Used with ShadowMask feature
 
-        public Vector2 cascadesBorderFadeScaleBias;
-
         public float diffuseDimmer;
         public float specularDimmer;
         public float penumbraTint;

com.unity.render-pipelines.high-definition/Runtime/Lighting/LightDefinition.cs.hlsl

@@ -72,7 +72,6 @@ struct DirectionalLightData
     real minRoughness;
     int screenSpaceShadowIndex;
     real4 shadowMaskSelector;
-    float2 cascadesBorderFadeScaleBias;
     float diffuseDimmer;
     float specularDimmer;
     float penumbraTint;

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

@@ -269,9 +269,19 @@ SHADOW_TYPE EvaluateShadow_Directional( LightLoopContext lightLoopContext, Posit
         shadow = lightLoopContext.shadowValue;
 
     #ifdef SHADOWS_SHADOWMASK
-        float3 camToPixel = posInput.positionWS - GetPrimaryCameraPosition();
-        float distanceCamToPixel2 = dot(camToPixel, camToPixel);
-        float fade = saturate(distanceCamToPixel2 * light.cascadesBorderFadeScaleBias.x + light.cascadesBorderFadeScaleBias.y);
+        // TODO: Optimize this code! Currently it is a bit like brute force to get the last transistion and fade to shadow mask, but there is
+        // certainly more efficient to do
+        // We reuse the transition from the cascade system to fade between shadow mask at max distance
+        uint  payloadOffset;
+        real  fade;
+        int cascadeCount;
+        int shadowSplitIndex = 0;
+
+        shadowSplitIndex = EvalShadow_GetSplitIndex(lightLoopContext.shadowContext, light.shadowIndex, posInput.positionWS, fade, cascadeCount);
+
+        // we have a fade caclulation for each cascade but we must lerp with shadow mask only for the last one
+        // if shadowSplitIndex is -1 it mean we are outside cascade and should return 1.0 to use shadowmask: saturate(-shadowSplitIndex) return 0 for >= 0 and 1 for -1
+        fade = ((shadowSplitIndex + 1) == cascadeCount) ? fade : saturate(-shadowSplitIndex);
 
         // In the transition code (both dithering and blend) we use shadow = lerp( shadow, 1.0, fade ) for last transition
         // mean if we expend the code we have (shadow * (1 - fade) + fade). Here to make transition with shadow mask