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

Author: sebastienlagarde

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

@@ -33,6 +33,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed compatibility message not displayed correctly when switching platforms.
 - Fixed support for interleaved tiling in path tracing.
 - Fixed robustness issues with the stacklit material in path tracing (case 1373971).
+- Fixed and optimize distance shadowmask fade.
 
 ### Changed
 - Use RayTracingAccelerationStructure.CullInstances to filter Renderers and populate the acceleration structure with ray tracing instances for improved CPU performance on the main thread.

com.unity.render-pipelines.high-definition/Runtime/Lighting/Light/HDGpuLightsBuilder.Jobs.cs

@@ -76,6 +76,12 @@ internal struct CreateGpuLightDataJob : IJobParallelFor
             public Vector3 airExtinctionCoefficient;
             [ReadOnly]
             public float aerosolExtinctionCoefficient;
+            [ReadOnly]
+            public float maxShadowDistance;
+            [ReadOnly]
+            public float shadowOutBorderDistance;
+            
+
             #endregion
 
             #region input light entity data
@@ -321,6 +327,21 @@ public static void ConvertLightToGPUFormat(
                 {
                     lightData.shadowMaskSelector[visibleLightBakingOutput.occlusionMaskChannel] = 1.0f;
                     lightData.nonLightMappedOnly = visibleLightShadowCasterMode == LightShadowCasterMode.NonLightmappedOnly ? 1 : 0;
+                    // Get shadow info from the volume stack.
+                    float maxDistanceSq = maxShadowDistance * maxShadowDistance;
+                    float outBorderDistance = shadowOutBorderDistance;
+                    if (outBorderDistance < 1e-4f)
+                    {
+                        lightData.cascadesBorderFadeScaleBias = new Vector2(1e6f, -maxDistanceSq * 1e6f);
+                    }
+                    else
+                    {
+                        outBorderDistance = 1.0f - outBorderDistance;
+                        outBorderDistance *= outBorderDistance;
+                        float distanceFadeNear = outBorderDistance * maxDistanceSq;
+                        lightData.cascadesBorderFadeScaleBias.x = 1.0f / (maxDistanceSq - distanceFadeNear);
+                        lightData.cascadesBorderFadeScaleBias.y = -distanceFadeNear / (maxDistanceSq - distanceFadeNear);
+                    }
                 }
                 else
                 {
@@ -692,6 +713,7 @@ public void StartCreateGpuLightDataJob(
         {
             var visualEnvironment = hdCamera.volumeStack.GetComponent<VisualEnvironment>();
             var skySettings = hdCamera.volumeStack.GetComponent<PhysicallyBasedSky>();
+            var shadowSettings = hdCamera.volumeStack.GetComponent<HDShadowSettings>();
             Debug.Assert(visualEnvironment != null);
             bool isPbrSkyActive = visualEnvironment.skyType.value == (int)SkyType.PhysicallyBased;
 
@@ -718,6 +740,9 @@ public void StartCreateGpuLightDataJob(
                 airExtinctionCoefficient = skySettings.GetAirExtinctionCoefficient(),
                 aerosolExtinctionCoefficient = skySettings.GetAerosolExtinctionCoefficient(),
 
+                maxShadowDistance = shadowSettings.maxShadowDistance.value,
+                shadowOutBorderDistance = shadowSettings.cascadeShadowBorders[shadowSettings.cascadeShadowSplitCount.value - 1],
+
                 // light entity data
                 lightRenderDataArray = lightEntities.lightData,
 

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

@@ -95,6 +95,8 @@ 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

@@ -72,6 +72,7 @@ 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

@@ -269,19 +269,9 @@ SHADOW_TYPE EvaluateShadow_Directional( LightLoopContext lightLoopContext, Posit
         shadow = lightLoopContext.shadowValue;
 
     #ifdef SHADOWS_SHADOWMASK
-        // 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);
+        float3 camToPixel = posInput.positionWS - GetPrimaryCameraPosition();
+        float distanceCamToPixel2 = dot(camToPixel, camToPixel);
+        float fade = saturate(distanceCamToPixel2 * light.cascadesBorderFadeScaleBias.x + light.cascadesBorderFadeScaleBias.y);
 
         // 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