perf(volumetric shadows): optimise data and fix cascades

features/Volumetric Shadows/Shaders/VolumetricShadows/VolumetricShadows.hlsli

@@ -8,34 +8,9 @@ namespace VolumetricShadows
 {
 	Texture2D<float2> SharedShadowMap : register(t18);
 
-	struct ShadowData
-	{
-		float4 VPOSOffset;
-		float4 ShadowSampleParam;    // fPoissonRadiusScale / iShadowMapResolution in z and w
-		float4 EndSplitDistances;    // cascade end distances int xyz, cascade count int z
-		float4 StartSplitDistances;  // cascade start distances int xyz, 4 int z
-		float4 FocusShadowFadeParam;
-		float4 DebugColor;
-		float4 PropertyColor;
-		float4 AlphaTestRef;
-		float4 ShadowLightParam;  // Falloff in x, ShadowDistance squared in z
-		float4x3 FocusShadowMapProj[4];
-		// Since ShadowData is passed between c++ and hlsl, can't have different defines due to strong typing
-		float4x3 ShadowMapProj[2][3];
-		float4x4 CameraViewProjInverse[2];
-	};
-
-	StructuredBuffer<ShadowData> SharedShadowData : register(t19);
-
 	static const float VSM_MIN_VARIANCE = 0.00001;
 	static const float VSM_BLEEDING_REDUCTION = 0.2;
 
-	float GetShadowDepth(float3 positionWS, uint eyeIndex)
-	{
-		float4 positionCS = mul(FrameBuffer::CameraViewProj[eyeIndex], float4(positionWS, 1));
-		return positionCS.z / positionCS.w;
-	}
-
 	// Chebyshev upper bound on P(X >= t)
 	// moments.x = mean(z), moments.y = mean(z^2)
 	float ComputeVSM(float2 moments, float depth)
@@ -84,35 +59,39 @@ namespace VolumetricShadows
 
 	float GetVSMShadow3D(float3 startPosition, float3 endPosition, float noise, uint baseSampleCount, uint eyeIndex, out float surfaceShadow)
 	{
-		ShadowData sD = SharedShadowData[0];
+		DirectionalShadowLightData directionalShadowLightData = DirectionalShadowLights[0];
 
+		// View-space z — matches the linear cascade split distances from BSShadowDirectionalLight.
 		float3 midPosition = (startPosition + endPosition) * 0.5;
-		float shadowMapDepth = GetShadowDepth(midPosition, eyeIndex);
+		float shadowMapDepth = SharedData::GetScreenDepth(FrameBuffer::GetShadowDepth(midPosition, eyeIndex));
+
+		// Cascade projections are world-space; positions come in camera-relative.
+		startPosition += FrameBuffer::CameraPosAdjust[eyeIndex].xyz;
+		endPosition += FrameBuffer::CameraPosAdjust[eyeIndex].xyz;
 
 		// Early out beyond cascade range
-		if (shadowMapDepth >= sD.EndSplitDistances.w) {
+		if (shadowMapDepth >= directionalShadowLightData.EndSplitDistances.y) {
 			surfaceShadow = 1.0;
 			return 1.0;
 		}
 
 		// Reduce over distance
-		float distSq = dot(midPosition, midPosition);
-		float fade = saturate(distSq / sD.ShadowLightParam.z);
+		float fade = saturate(shadowMapDepth / directionalShadowLightData.EndSplitDistances.y);
 
 		uint sampleCount = max(1, ceil(float(baseSampleCount) * (1.0 - fade)));
 		float rcpSampleCount = rcp(sampleCount);
 
 		// Compute cascade blend factor with smoothstep
-		float cascadeSelect = saturate((shadowMapDepth - sD.StartSplitDistances.y) / (sD.EndSplitDistances.x - sD.StartSplitDistances.y));
+		float cascadeSelect = saturate((shadowMapDepth - directionalShadowLightData.StartSplitDistances.y) / (directionalShadowLightData.EndSplitDistances.x - directionalShadowLightData.StartSplitDistances.y));
 
 		// Determine which cascade(s) to sample
 		uint primaryCascade = uint(cascadeSelect);
 		bool needsBlending = (cascadeSelect > 0.0) && (cascadeSelect < 1.0);
 
 		// Transform ray to light space for primary cascade
-		float4x3 shadowProj = sD.ShadowMapProj[eyeIndex][primaryCascade];
-		float3 startLS = mul(transpose(shadowProj), float4(startPosition, 1));
-		float3 endLS = mul(transpose(shadowProj), float4(endPosition, 1));
+		float4x4 shadowProj = directionalShadowLightData.ShadowProj[primaryCascade];
+		float3 startLS = mul(shadowProj, float4(startPosition, 1)).xyz;
+		float3 endLS = mul(shadowProj, float4(endPosition, 1)).xyz;
 		startLS.xy = saturate(startLS.xy);
 		endLS.xy = saturate(endLS.xy);
 
@@ -126,9 +105,9 @@ namespace VolumetricShadows
 		{
 			uint secondaryCascade = 1 - primaryCascade;
 
-			shadowProj = sD.ShadowMapProj[eyeIndex][secondaryCascade];
-			startLS = mul(transpose(shadowProj), float4(startPosition, 1));
-			endLS = mul(transpose(shadowProj), float4(endPosition, 1));
+			shadowProj = directionalShadowLightData.ShadowProj[secondaryCascade];
+			startLS = mul(shadowProj, float4(startPosition, 1)).xyz;
+			endLS = mul(shadowProj, float4(endPosition, 1)).xyz;
 			startLS.xy = saturate(startLS.xy);
 			endLS.xy = saturate(endLS.xy);
 
@@ -139,7 +118,7 @@ namespace VolumetricShadows
 		}
 
 		// Apply distance fade
-		float fadeFactor = 1.0 - pow(fade, 8);
+		float fadeFactor = 1.0 - pow(fade * fade, 8);
 		surfaceShadow = lerp(1.0, surfaceShadow, fadeFactor);
 		return lerp(1.0, shadow, fadeFactor);
 	}
@@ -153,30 +132,31 @@ namespace VolumetricShadows
 
 	float GetVSMShadow2D(float3 position, uint eyeIndex, out float detailedShadow)
 	{
-		ShadowData sD = SharedShadowData[0];
+		DirectionalShadowLightData directionalShadowLightData = DirectionalShadowLights[0];
 
-		float shadowMapDepth = GetShadowDepth(position, eyeIndex);
+		float shadowMapDepth = SharedData::GetScreenDepth(FrameBuffer::GetShadowDepth(position, eyeIndex));
 
 		// Early out beyond cascade range
-		if (shadowMapDepth >= sD.EndSplitDistances.w) {
+		if (shadowMapDepth >= directionalShadowLightData.EndSplitDistances.y) {
 			detailedShadow = 1.0;
 			return 1.0;
 		}
 
 		// Reduce over distance
-		float distSq = dot(position, position);
-		float fade = saturate(distSq / sD.ShadowLightParam.z);
+		float fade = saturate(shadowMapDepth / directionalShadowLightData.EndSplitDistances.y);
+
+		// Cascade projections are world-space; position comes in camera-relative.
+		float3 positionWS = position + FrameBuffer::CameraPosAdjust[eyeIndex].xyz;
 
 		// Compute cascade blend factor with smoothstep
-		float cascadeSelect = saturate((shadowMapDepth - sD.StartSplitDistances.y) / (sD.EndSplitDistances.x - sD.StartSplitDistances.y));
+		float cascadeSelect = saturate((shadowMapDepth - directionalShadowLightData.StartSplitDistances.y) / (directionalShadowLightData.EndSplitDistances.x - directionalShadowLightData.StartSplitDistances.y));
 
 		// Determine which cascade(s) to sample
 		uint primaryCascade = uint(cascadeSelect);
 		bool needsBlending = (cascadeSelect > 0.0) && (cascadeSelect < 1.0);
 
-		// Transform ray to light space for primary cascade
-		float4x3 shadowProj = sD.ShadowMapProj[eyeIndex][primaryCascade];
-		float3 positionLS = mul(transpose(shadowProj), float4(position, 1));
+		// Transform position to light space for primary cascade
+		float3 positionLS = mul(directionalShadowLightData.ShadowProj[primaryCascade], float4(positionWS, 1)).xyz;
 		positionLS.xy = saturate(positionLS.xy);
 
 		// Sample primary cascade
@@ -187,16 +167,15 @@ namespace VolumetricShadows
 		{
 			uint secondaryCascade = 1 - primaryCascade;
 
-			shadowProj = sD.ShadowMapProj[eyeIndex][secondaryCascade];
-			positionLS = mul(transpose(shadowProj), float4(position, 1));
+			positionLS = mul(directionalShadowLightData.ShadowProj[secondaryCascade], float4(positionWS, 1)).xyz;
 			positionLS.xy = saturate(positionLS.xy);
 
 			float shadowBlend = SampleVSMCascade2D(secondaryCascade, positionLS);
 			shadow = lerp(shadow, shadowBlend, cascadeSelect);
 		}
 
 		// Apply distance fade
-		float fadeFactor = 1.0 - pow(fade, 8);
+		float fadeFactor = 1.0 - pow(fade * fade, 8);
 		detailedShadow = lerp(1.0, ReduceBleeding(shadow, VSM_BLEEDING_REDUCTION), fadeFactor);
 		return lerp(1.0, shadow, fadeFactor);
 	}

package/Shaders/Common/FrameBuffer.hlsli

@@ -85,6 +85,15 @@ namespace FrameBuffer
 		return clamp(screenPositionDR, minValue, maxValue);
 	}
 
+	// Projects a world-space (camera-relative) point into NDC using the eye's CameraViewProj
+	// and returns the post-perspective z (NDC depth). Combine with SharedData::GetScreenDepth
+	// to get a linear view-space distance suitable for cascade-split comparisons.
+	float GetShadowDepth(float3 positionWS, uint eyeIndex)
+	{
+		float4 positionCS = mul(FrameBuffer::CameraViewProj[eyeIndex], float4(positionWS, 1));
+		return positionCS.z / positionCS.w;
+	}
+
 	/**
 	 * @brief Converts normalized screen UVs to dynamic-resolution UVs and clamps them.
 	 *

package/Shaders/Common/ShadowSampling.hlsli

@@ -21,6 +21,19 @@
 #	include "Common/Spherical Harmonics/SphericalHarmonics.hlsli"
 #endif
 
+// Populated once per frame by Deferred::CopyShadowLightData from BSShadowDirectionalLight.
+// Column-major float4x4 projections so HLSL `mul(proj, float4(pos, 1))` matches the
+// XMMATRIX layout written by XMStoreFloat4x4 on the C++ side.
+struct DirectionalShadowLightData
+{
+	column_major float4x4 ShadowProj[2];
+	column_major float4x4 InvShadowProj[2];
+	float2 EndSplitDistances;
+	float2 StartSplitDistances;
+};
+
+StructuredBuffer<DirectionalShadowLightData> DirectionalShadowLights : register(t98);
+
 #if defined(VOLUMETRIC_SHADOWS)
 #	include "VolumetricShadows/VolumetricShadows.hlsli"
 #endif