Merge pull request #1225 from EvgeniiG/master

Port global density volumes to the interpolation volume framework (+ misc improvements)

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/GeometricTools.hlsl

 // Intersection functions
 //-----------------------------------------------------------------------------
 
-// This implementation does not attempt to explicitly handle NaNs.
-// Ref: https://tavianator.com/fast-branchless-raybounding-box-intersections-part-2-nans/
-    float3 rayDirInv = rcp(rayDirection); // Could be precomputed
+    // Could be precomputed. Clamp to avoid INF. clamp() is a single ALU on GCN.
+    // rcp(FLT_EPS) = 16,777,216, which is large enough for our purposes,
+    // yet doesn't cause a lot of numerical issues associated with FLT_MAX.
+    float3 rayDirInv = clamp(rcp(rayDirection), -rcp(FLT_EPS), rcp(FLT_EPS));
 
     // Perform ray-slab intersection (component-wise).
     float3 t0 = boxMin * rayDirInv - (rayOrigin * rayDirInv);

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/ImageBasedLighting.hlsl

                          out real    NdotL,
                          out real    weightOverPdf)
 {
+#if 0
+#else
+    real3 N = localToWorld[2];
+
+    L     = SampleHemisphereCosine(u.x, u.y, N);
+    NdotL = saturate(dot(N, L));
+#endif
 
     // Importance sampling weight for each sample
     // pdf = N.L / PI

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Sampling/Sampling.hlsl

     return r * real2(cosPhi, sinPhi);
 }
 
+real3 SampleSphereUniform(real u1, real u2)
+{
+    real phi      = TWO_PI * u2;
+    real cosTheta = 1.0 - 2.0 * u1;
+
+    return SphericalToCartesian(phi, cosTheta);
+}
+
 // Performs cosine-weighted sampling of the hemisphere.
 // Ref: PBRT v3, p. 780.
 real3 SampleHemisphereCosine(real u1, real u2)
     return localL;
 }
 
-real3 SampleHemisphereUniform(real u1, real u2)
+// Cosine-weighted sampling without the tangent frame.
+// Ref: http://www.amietia.com/lambertnotangent.html
+real3 SampleHemisphereCosine(real u1, real u2, real3 normal)
-    real phi      = TWO_PI * u2;
-    real cosTheta = 1.0 - u1;
-
-    return SphericalToCartesian(phi, cosTheta);
+    real3 pointOnSphere = SampleSphereUniform(u1, u2);
+    return normalize(normal + pointOnSphere);
-real3 SampleSphereUniform(real u1, real u2)
+real3 SampleHemisphereUniform(real u1, real u2)
-    real cosTheta = 1.0 - 2.0 * u1;
+    real cosTheta = 1.0 - u1;
 
     return SphericalToCartesian(phi, cosTheta);
 }

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/SpaceFillingCurves.hlsl

     return x;
 }
 
-// "Insert" two 0 bits after each of the 10 low bits of x/
+// "Insert" two 0 bits after each of the 10 low bits of x.
 // Ref: https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/
 uint Part1By2(uint x)
 {
     return x;
 }
 
-// Inverse of Part1By1 - "delete" all odd-indexed bits/
+// Inverse of Part1By1 - "delete" all odd-indexed bits.
 // Ref: https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/
 uint Compact1By1(uint x)
 {
     return x;
 }
 
-// Inverse of Part1By2 - "delete" all bits not at positions divisible by 3/
+// Inverse of Part1By2 - "delete" all bits not at positions divisible by 3.
 // Ref: https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/
 uint Compact1By2(uint x)
 {

ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/VolumeRendering.hlsl

 // Samples the interval of homogeneous participating medium using the closed-form tracking approach
 // (proportionally to the transmittance).
 // Returns the offset from the start of the interval and the weight = (transmittance / pdf).
-// Ref: Production Volume Rendering, 3.6.1.
+// Ref: Monte Carlo Methods for Volumetric Light Transport Simulation, p. 5.
-    // pdf    = extinction * exp(-extinction * t) / (1 - exp(-intervalLength * extinction))
+    // pdf    = extinction * exp(extinction * (intervalLength - t)) / (exp(intervalLength * extinction - 1)
-    // weight = (1 - exp(-extinction * intervalLength)) / extinction;
+    // weight = (1 - exp(-extinction * intervalLength)) / extinction
+    real c = rcp(extinction);
-    weight = x * rcp(extinction);
-    offset = -log(1 - rndVal * x) * rcp(extinction);
+    weight = x * c;
+    offset = -log(1 - rndVal * x) * c;
 }
 
 // Implements equiangular light sampling.

ScriptableRenderPipeline/Core/CoreRP/Volume/VolumeComponent.cs

                 parameter.OnDisable();
         }
 
+        // You can override this to do your own blending. Either loop through the `parameters` list
+        // or reference direct fields (you'll need to cast `state` to your custom type and don't
+        // forget to use `SetValue` on parameters, do not assign directly to the state object - and
+        // of course you'll need to check for the `overrideState` manually).
+        public virtual void Override(VolumeComponent state, float interpFactor)
+        {
+            int count = parameters.Count;
+
+            for (int i = 0; i < count; i++)
+            {
+                var stateParam = state.parameters[i];
+                var toParam = parameters[i];
+
+                // Keep track of the override state for debugging purpose
+                stateParam.overrideState = toParam.overrideState;
+
+                if (toParam.overrideState)
+                    stateParam.Interp(stateParam, toParam, interpFactor);
+            }
+        }
+
         public void SetAllOverridesTo(bool state)
         {
             SetAllOverridesTo(parameters, state);

ScriptableRenderPipeline/Core/CoreRP/Volume/VolumeManager.cs

                 if (!component.active)
                     continue;
 
-                var target = stack.GetComponent(component.GetType());
-                int count = component.parameters.Count;
-
-                for (int i = 0; i < count; i++)
-                {
-                    var fromParam = target.parameters[i];
-                    var toParam = component.parameters[i];
-
-                    // Keep track of the override state for debugging purpose
-                    fromParam.overrideState = toParam.overrideState;
-
-                    if (toParam.overrideState)
-                        fromParam.Interp(fromParam, toParam, interpFactor);
-                }
+                var state = stack.GetComponent(component.GetType());
+                component.Override(state, interpFactor);
             }
         }
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Sky/AtmosphericScattering/ExponentialFogEditor.cs

-using System.Collections;
+using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEditor;
             PropertyField(m_FogHeightAttenuation);
         }
     }
-}
+}

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDStringConstants.cs

         public static readonly int _Source4 = Shader.PropertyToID("_Source4");
         public static readonly int _Result1 = Shader.PropertyToID("_Result1");
 
+        public static readonly int _AtmosphericScatteringType  = Shader.PropertyToID("_AtmosphericScatteringType");
         public static readonly int _AmbientProbeCoeffs         = Shader.PropertyToID("_AmbientProbeCoeffs");
         public static readonly int _GlobalExtinction           = Shader.PropertyToID("_GlobalExtinction");
         public static readonly int _GlobalScattering           = Shader.PropertyToID("_GlobalScattering");
         public static readonly int _VBufferLightingFeedback    = Shader.PropertyToID("_VBufferLightingFeedback");
         public static readonly int _VBufferSampleOffset        = Shader.PropertyToID("_VBufferSampleOffset");
         public static readonly int _VolumeBounds               = Shader.PropertyToID("_VolumeBounds");
-        public static readonly int _VolumeProperties           = Shader.PropertyToID("_VolumeProperties");
+        public static readonly int _VolumeData                 = Shader.PropertyToID("_VolumeData");
         public static readonly int _NumVisibleDensityVolumes   = Shader.PropertyToID("_NumVisibleDensityVolumes");
     }
 }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/HomogeneousDensityVolume.cs

     [AddComponentMenu("Rendering/Homogeneous Density Volume", 1100)]
     public class HomogeneousDensityVolume : MonoBehaviour
     {
-        public DensityVolumeParameters parameters = new DensityVolumeParameters();
+        public DensityVolumeParameters parameters;
+
+        public HomogeneousDensityVolume()
+        {
+            parameters.albedo       = new Color(0.5f, 0.5f, 0.5f);
+            parameters.meanFreePath = 10.0f;
+            parameters.asymmetry    = 0.0f;
+        }
 
         private void Awake()
         {
 
         void OnDrawGizmos()
         {
-            if (parameters.IsLocalVolume())
-            {
-                Gizmos.color  = parameters.albedo;
-                Gizmos.matrix = transform.localToWorldMatrix;
-                Gizmos.DrawWireCube(Vector3.zero, Vector3.one);
-            }
-        }
-
-        // Returns NULL if a global fog component does not exist, or is not enabled.
-        public static HomogeneousDensityVolume GetGlobalHomogeneousDensityVolume()
-        {
-            HomogeneousDensityVolume globalVolume = null;
-
-            HomogeneousDensityVolume[] volumes = FindObjectsOfType(typeof(HomogeneousDensityVolume)) as HomogeneousDensityVolume[];
-
-            foreach (HomogeneousDensityVolume volume in volumes)
-            {
-                if (volume.enabled && !volume.parameters.IsLocalVolume())
-                {
-                    globalVolume = volume;
-                    break;
-                }
-            }
-
-            return globalVolume;
+            Gizmos.color  = parameters.albedo;
+            Gizmos.matrix = transform.localToWorldMatrix;
+            Gizmos.DrawWireCube(Vector3.zero, Vector3.one);
         }
     }
 } // UnityEngine.Experimental.Rendering.HDPipeline

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VBuffer.hlsl

 // Interpolation in the log space is non-linear.
 // Therefore, given 'logEncodedDepth', we compute a new depth value
 // which allows us to perform HW interpolation which is linear in the view space.
-float ComputeLerpPositionForLogEncoding(float linearDepth, float logEncodedDepth,
+float ComputeLerpPositionForLogEncoding(float  linearDepth,
+                                        float  logEncodedDepth,
                                         float2 VBufferSliceCount,
                                         float4 VBufferDepthDecodingParams)
 {
     float numSlices    = VBufferSliceCount.x;
     float rcpNumSlices = VBufferSliceCount.y;
 
-    float s0 = floor(d * numSlices - 0.5);
-    float s1 = ceil(d * numSlices - 0.5);
+    float s  = d * numSlices - 0.5;
+    float s0 = floor(s);
+    float s1 = ceil(s);
     float d0 = saturate(s0 * rcpNumSlices + (0.5 * rcpNumSlices));
     float d1 = saturate(s1 * rcpNumSlices + (0.5 * rcpNumSlices));
     float z0 = DecodeLogarithmicDepthGeneralized(d0, VBufferDepthDecodingParams);
     return d0 + t * rcpNumSlices;
 }
 
-// Performs trilinear reconstruction of the V-Buffer.
-// If (clampToEdge == false), out-of-bounds loads return 0.
-float4 SampleVBuffer(TEXTURE3D_ARGS(VBufferLighting, trilinearSampler), bool clampToEdge,
-                     float2 positionNDC, float linearDepth,
+// if (correctLinearInterpolation), we use ComputeLerpPositionForLogEncoding() to correct weighting
+// of both slices at the cost of extra ALUs.
+//
+// if (quadraticFilterXY), we perform biquadratic (3x3) reconstruction for each slice to reduce
+// aliasing at the cost of extra ALUs and bandwidth.
+// Warning: you MUST pass a linear sampler in order for the quadratic filter to work.
+//
+// Note: for correct filtering, the data has to be stored in the perceptual space.
+// This means storing tone mapped radiance and transmittance instead of optical depth.
+// See "A Fresh Look at Generalized Sampling", p. 51.
+//
+// if (clampToBorder), samples outside of the buffer return 0 (we perform a smooth fade).
+// Otherwise, the sampler simply clamps the texture coordinate to the edge of the texture.
+// Warning: clamping to border may not work as expected with the quadratic filter due to its extent.
+float4 SampleVBuffer(TEXTURE3D_ARGS(VBuffer, clampSampler),
+                     float2 positionNDC,
+                     float  linearDepth,
+                     float4 VBufferResolution,
-                     float4 VBufferDepthDecodingParams)
+                     float4 VBufferDepthDecodingParams,
+                     bool   correctLinearInterpolation,
+                     bool   quadraticFilterXY,
+                     bool   clampToBorder)
-    float numSlices    = VBufferSliceCount.x;
-    float rcpNumSlices = VBufferSliceCount.y;
-
+    float  w;
-    // Unity doesn't support samplers clamping to border, so we have to do it ourselves.
-    // TODO: add the proper sampler support.
-    bool isInBounds = Min3(uv.x, uv.y, d) > 0 && Max3(uv.x, uv.y, d) < 1;
-
-    UNITY_BRANCH if (clampToEdge || isInBounds)
+    if (correctLinearInterpolation)
-    #if 1
+        // Adjust the texture coordinate for HW linear filtering.
+        w = ComputeLerpPositionForLogEncoding(z, d, VBufferSliceCount, VBufferDepthDecodingParams);
+    }
+    else
+    {
-        float w = d;
-    #else
-        // Adjust the texture coordinate for HW trilinear sampling.
-        float w = ComputeLerpPositionForLogEncoding(z, d, VBufferSliceCount, VBufferDepthDecodingParams);
-    #endif
+        w = d;
+    }
-        return SAMPLE_TEXTURE3D_LOD(VBufferLighting, trilinearSampler, float3(uv, w), 0);
+    float fadeWeight = 1;
+
+    if (clampToBorder)
+    {
+        // Compute the distance to the edge, and remap it to the [0, 1] range.
+        // TODO: add support for the HW border clamp sampler.
+        float weightU = saturate((1 - 2 * abs(uv.x - 0.5)) * VBufferResolution.x);
+        float weightV = saturate((1 - 2 * abs(uv.y - 0.5)) * VBufferResolution.y);
+        float weightW = saturate((1 - 2 * abs(w    - 0.5)) * VBufferSliceCount.x);
+
+        fadeWeight = weightU * weightV * weightW;
-    else
+
+    float4 result = 0;
+
+    if (fadeWeight > 0)
-        return 0;
-    }
-}
+        if (quadraticFilterXY)
+        {
+            float2 xy = uv * VBufferResolution.xy;
+            float2 ic = floor(xy);
+            float2 fc = frac(xy);
-// Returns interpolated {volumetric radiance, transmittance}. The sampler clamps to edge.
-float4 SampleInScatteredRadianceAndTransmittance(TEXTURE3D_ARGS(VBufferLighting, trilinearSampler),
-                                                 float2 positionNDC, float linearDepth,
-                                                 float4 VBufferResolution,
-                                                 float2 VBufferSliceCount,
-                                                 float4 VBufferDepthEncodingParams,
-                                                 float4 VBufferDepthDecodingParams)
-{
-#ifdef RECONSTRUCTION_FILTER_TRILINEAR
-    float4 L = SampleVBuffer(TEXTURE3D_PARAM(VBufferLighting, trilinearSampler), true,
-                             positionNDC, linearDepth,
-                             VBufferSliceCount,
-                             VBufferDepthEncodingParams,
-                             VBufferDepthDecodingParams);
-#else // Perform biquadratic reconstruction in XY, linear in Z, using 4x trilinear taps.
-    float2 uv = positionNDC;
-    float2 xy = uv * VBufferResolution.xy;
-    float2 ic = floor(xy);
-    float2 fc = frac(xy);
+            float2 weights[2], offsets[2];
+            BiquadraticFilter(1 - fc, weights, offsets); // Inverse-translate the filter centered around 0.5
-    // The distance between slices is log-encoded.
-    float z = linearDepth;
-    float d = EncodeLogarithmicDepthGeneralized(z, VBufferDepthEncodingParams);
+            result = (weights[0].x * weights[0].y) * SAMPLE_TEXTURE3D_LOD(VBuffer, clampSampler, float3((ic + float2(offsets[0].x, offsets[0].y)) * VBufferResolution.zw, w), 0)  // Top left
+                   + (weights[1].x * weights[0].y) * SAMPLE_TEXTURE3D_LOD(VBuffer, clampSampler, float3((ic + float2(offsets[1].x, offsets[0].y)) * VBufferResolution.zw, w), 0)  // Top right
+                   + (weights[0].x * weights[1].y) * SAMPLE_TEXTURE3D_LOD(VBuffer, clampSampler, float3((ic + float2(offsets[0].x, offsets[1].y)) * VBufferResolution.zw, w), 0)  // Bottom left
+                   + (weights[1].x * weights[1].y) * SAMPLE_TEXTURE3D_LOD(VBuffer, clampSampler, float3((ic + float2(offsets[1].x, offsets[1].y)) * VBufferResolution.zw, w), 0); // Bottom right
+        }
+        else
+        {
+            result = SAMPLE_TEXTURE3D_LOD(VBuffer, clampSampler, float3(uv, w), 0);
+        }
-#if 0
-    // Ignore non-linearity (for performance reasons) at the cost of accuracy.
-    // The results are exact for a stationary camera, but can potentially cause some judder in motion.
-    float w = d;
-#else
-    // Adjust the texture coordinate for HW trilinear sampling.
-    float w = ComputeLerpPositionForLogEncoding(z, d, VBufferSliceCount, VBufferDepthDecodingParams);
-#endif
+        result *= fadeWeight;
+    }
-    float2 weights[2], offsets[2];
-    BiquadraticFilter(1 - fc, weights, offsets); // Inverse-translate the filter centered around 0.5
+    return result;
+}
-    float2 rcpRes = VBufferResolution.zw;
+float4 SampleVBuffer(TEXTURE3D_ARGS(VBuffer, clampSampler),
+                     float3   positionWS,
+                     float4x4 viewProjMatrix,
+                     float4   VBufferResolution,
+                     float2   VBufferSliceCount,
+                     float4   VBufferDepthEncodingParams,
+                     float4   VBufferDepthDecodingParams,
+                     bool     correctLinearInterpolation,
+                     bool     quadraticFilterXY,
+                     bool     clampToBorder)
+{
+    float2 positionNDC = ComputeNormalizedDeviceCoordinates(positionWS, viewProjMatrix);
+    float  linearDepth = mul(viewProjMatrix, float4(positionWS, 1)).w;
-    // TODO: reconstruction should be performed in the perceptual space (e.i., after tone mapping).
-    // But our VBuffer is linear. How to achieve that?
-    // See "A Fresh Look at Generalized Sampling", p. 51.
-    float4 L = (weights[0].x * weights[0].y) * SAMPLE_TEXTURE3D_LOD(VBufferLighting, trilinearSampler, float3((ic + float2(offsets[0].x, offsets[0].y)) * rcpRes, w), 0)  // Top left
-             + (weights[1].x * weights[0].y) * SAMPLE_TEXTURE3D_LOD(VBufferLighting, trilinearSampler, float3((ic + float2(offsets[1].x, offsets[0].y)) * rcpRes, w), 0)  // Top right
-             + (weights[0].x * weights[1].y) * SAMPLE_TEXTURE3D_LOD(VBufferLighting, trilinearSampler, float3((ic + float2(offsets[0].x, offsets[1].y)) * rcpRes, w), 0)  // Bottom left
-             + (weights[1].x * weights[1].y) * SAMPLE_TEXTURE3D_LOD(VBufferLighting, trilinearSampler, float3((ic + float2(offsets[1].x, offsets[1].y)) * rcpRes, w), 0); // Bottom right
-#endif
+    return SampleVBuffer(TEXTURE3D_PARAM(VBuffer, clampSampler),
+                         positionNDC,
+                         linearDepth,
+                         VBufferResolution,
+                         VBufferSliceCount,
+                         VBufferDepthEncodingParams,
+                         VBufferDepthDecodingParams,
+                         correctLinearInterpolation,
+                         quadraticFilterXY,
+                         clampToBorder);
+}
-    // TODO: add some animated noise to the reconstructed radiance.
-    return float4(L.rgb, Transmittance(L.a));
+// Returns interpolated {volumetric radiance, transmittance}.
+float4 SampleVolumetricLighting(TEXTURE3D_ARGS(VBufferLighting, clampSampler),
+                                float2 positionNDC,
+                                float  linearDepth,
+                                float4 VBufferResolution,
+                                float2 VBufferSliceCount,
+                                float4 VBufferDepthEncodingParams,
+                                float4 VBufferDepthDecodingParams,
+                                bool   correctLinearInterpolation,
+                                bool   quadraticFilterXY)
+{
+    // TODO: add some slowly animated noise to the reconstructed value.
+    return FastTonemapInvert(SampleVBuffer(TEXTURE3D_PARAM(VBufferLighting, clampSampler),
+                                           positionNDC,
+                                           linearDepth,
+                                           VBufferResolution,
+                                           VBufferSliceCount,
+                                           VBufferDepthEncodingParams,
+                                           VBufferDepthDecodingParams,
+                                           correctLinearInterpolation,
+                                           quadraticFilterXY,
+                                           false));
 }
 
 #endif // UNITY_VBUFFER_INCLUDED

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumeVoxelization.compute

 //--------------------------------------------------------------------------------------------------
 
 StructuredBuffer<OrientedBBox>            _VolumeBounds;
-StructuredBuffer<DensityVolumeProperties> _VolumeProperties;
+StructuredBuffer<DensityVolumeProperties> _VolumeData;
 
 RW_TEXTURE3D(float4, _VBufferDensity); // RGB = sqrt(scattering), A = sqrt(extinction)
 
                 if (overlapFraction > 0)
                 {
                     // There is an overlap. Sample the 3D texture, or load the constant value.
-                    voxelScattering += overlapFraction * _VolumeProperties[volumeIndex].scattering;
-                    voxelExtinction += overlapFraction * _VolumeProperties[volumeIndex].extinction;
+                    voxelScattering += overlapFraction * _VolumeData[volumeIndex].scattering;
+                    voxelExtinction += overlapFraction * _VolumeData[volumeIndex].extinction;
                 }
 
     #ifndef USE_CLUSTERED_LIGHTLIST

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumetricLighting.compute

     #define VBUFFER_SLICE_COUNT 128
 #endif
 
-#define SUPPORT_ASYMMETRY       1 // Support asymmetric phase functions
 #define SUPPORT_PUNCTUAL_LIGHTS 1 // Punctual lights contribute to fog lighting
 
 #define GROUP_SIZE_1D 8
 //--------------------------------------------------------------------------------------------------
 
 #include "CoreRP/ShaderLibrary/Common.hlsl"
+#include "CoreRP/ShaderLibrary/Color.hlsl"
 #include "CoreRP/ShaderLibrary/Filtering.hlsl"
 #include "CoreRP/ShaderLibrary/VolumeRendering.hlsl"
 
 // Implementation
 //--------------------------------------------------------------------------------------------------
 
+// A ray with a single origin and two directions:
+// one pointing at the center of the voxel, and one jittered in screen space.
-    float3 strataDirWS;       // Normalized, tile-stratified
-    float3 centerDirWS;       // Normalized, tile-centered
-    float  strataDirInvViewZ; // 1 / ViewSpace(strataDirWS).z
-    float  twoDirRatioViewZ;  // ViewSpace(strataDirWS).z / ViewSpace(centerDirWS).z
+    float3 jitterDirWS;       // Normalized, voxel-jittered in the screen space
+    float3 centerDirWS;       // Normalized, voxel-centered in the screen space
+    float  jitterDirInvViewZ; // 1 / ViewSpace(jitterDirWS).z
+    float  twoDirRatioViewZ;  // ViewSpace(jitterDirWS).z / ViewSpace(centerDirWS).z
-// Returns a point along the stratified direction.
+float ConvertLinearDepthToJitterRayDist(DualRay ray, float z)
+{
+    return z * ray.jitterDirInvViewZ;
+}
+
+float ConvertJitterDistToCenterRayDist(DualRay ray, float t)
+{
+    return t * ray.twoDirRatioViewZ;
+}
+
+// Returns a point along the jittered direction.
-    return ray.originWS + t * ray.strataDirWS;
+    return ray.originWS + t * ray.jitterDirWS;
-// Returns a point along the centered direction. It has a special property:
-// ViewSpace(GetPointAtDistance(ray, t)).z = ViewSpace(GetCenterAtDistance(ray, t)).z,
-// e.i. both points computed from the same value of 't' reside on the same Z-plane in the view space.
-float3 GetCenterAtDistance(DualRay ray, float t)
+// Returns a point along the centered direction.
+float3 GetCenterAtDistance(DualRay ray, float s)
-    t *= ray.twoDirRatioViewZ; // Perform the Z-coordinate conversion
-    return ray.originWS + t * ray.centerDirWS;
+    return ray.originWS + s * ray.centerDirWS;
 }
 
 struct VoxelLighting
                                       color, attenuation);
 
             // Important:
-            // Ideally, all scattering calculations should use the stratified versions
+            // Ideally, all scattering calculations should use the jittered versions
             // of the sample position and the ray direction. However, correct reprojection
             // of asymmetrically scattered lighting (affected by an anisotropic phase
             // function) is not possible. We work around this issue by reprojecting
                     float3 coneAxisX = lenMul * light.right;
                     float3 coneAxisY = lenMul * light.up;
 
-                    sampleLight = IntersectRayCone(ray.originWS, ray.strataDirWS,
+                    sampleLight = IntersectRayCone(ray.originWS, ray.jitterDirWS,
                                                    light.positionWS, light.forward,
                                                    coneAxisX, coneAxisY,
                                                    t0, t1, tEntr, tExit);
 
                     float t, distSq, rcpPdf;
                     ImportanceSamplePunctualLight(rndVal, light.positionWS,
-                                                  ray.originWS, ray.strataDirWS,
+                                                  ray.originWS, ray.jitterDirWS,
                                                   tEntr, tExit, t, distSq, rcpPdf,
                                                   hackMinDistSq);
 
                     float3 L             = -lightToSample * distRcp;
 
                     float3 color; float attenuation;
-                    EvaluateLight_Punctual(context, posInput, light, unused, 0, L, lightToSample,
-                                           distances, color, attenuation);
+                    EvaluateLight_Punctual(context, posInput, light, unused,
+                                           0, L, lightToSample, distances, color, attenuation);
-                    // Ideally, all scattering calculations should use the stratified versions
+                    // Ideally, all scattering calculations should use the jittered versions
                     // of the sample position and the ray direction. However, correct reprojection
                     // of asymmetrically scattered lighting (affected by an anisotropic phase
                     // function) is not possible. We work around this issue by reprojecting
                 float3x3 rotMat = float3x3(light.right, light.up, light.forward);
 
                 float3 o = mul(rotMat, ray.originWS - light.positionWS);
-                float3 d = mul(rotMat, ray.strataDirWS);
+                float3 d = mul(rotMat, ray.jitterDirWS);
 
                 float  range  = light.size.x;
                 float3 boxPt0 = float3(-1, -1, 0);
                     float4 distances     = float4(1, 1, 1, distProj);
 
                     float3 color; float attenuation;
-                    EvaluateLight_Punctual(context, posInput, light, unused, 0, L, lightToSample,
-                                           distances, color, attenuation);
+                    EvaluateLight_Punctual(context, posInput, light, unused,
+                                           0, L, lightToSample, distances, color, attenuation);
-                    // Ideally, all scattering calculations should use the stratified versions
+                    // Ideally, all scattering calculations should use the jittered versions
                     // of the sample position and the ray direction. However, correct reprojection
                     // of asymmetrically scattered lighting (affected by an anisotropic phase
                     // function) is not possible. We work around this issue by reprojecting
 void FillVolumetricLightingBuffer(LightLoopContext context, uint featureFlags,
                                   PositionInputs posInput, DualRay ray)
 {
-    float n  = _VBufferDepthDecodingParams.x + _VBufferDepthDecodingParams.z;
-    float z0 = n;                          // Start integration from the near plane
-    float t0 = ray.strataDirInvViewZ * z0; // Convert view space Z to distance along the stratified ray
-    float de = rcp(VBUFFER_SLICE_COUNT);   // Log-encoded distance between slices
+    const float n  = _VBufferDepthDecodingParams.x + _VBufferDepthDecodingParams.z;
+    const float z0 = n;                        // Start integration from the near plane
+    const float de = rcp(VBUFFER_SLICE_COUNT); // Log-encoded distance between slices
+
+    float t0 = ConvertLinearDepthToJitterRayDist(ray, z0);
 
     // The contribution of the ambient probe does not depend on the position,
     // only on the direction and the length of the interval.
         uint3 voxelCoord = uint3(posInput.positionSS, slice);
 
         float e1 = slice * de + de; // (slice + 1) / sliceCount
-#if defined(SHADER_API_METAL)
-        // Warning: this compiles, but it's nonsense. Use DecodeLogarithmicDepthGeneralized().
-        float z1 = DecodeLogarithmicDepth(e1, _VBufferDepthDecodingParams);
-#else
-#endif
-        float t1 = ray.strataDirInvViewZ * z1; // Convert view space Z to distance along the stratified ray
+        float t1 = ConvertLinearDepthToJitterRayDist(ray, z1);
         float dt = t1 - t0;
 
     #ifdef USE_CLUSTERED_LIGHTLIST
         // Compute the -exact- position of the center of the voxel.
         // It's important since the accumulated value of the integral is stored at the center.
         // We will use it for participating media sampling, asymmetric scattering and reprojection.
-        float  tc       = t0 + 0.5 * dt;
-        float3 centerWS = GetCenterAtDistance(ray, tc);
+        float  s        = ConvertJitterDistToCenterRayDist(ray, t0 + 0.5 * dt);
+        float3 centerWS = GetCenterAtDistance(ray, s);
-        // Sample the participating medium at 'tc' (or 'centerWS').
+        // Sample the participating medium at the center of the voxel.
         // We consider it to be constant along the interval [t0, t1] (within the voxel).
         // TODO: piecewise linear.
         float3 scattering = LOAD_TEXTURE3D(_VBufferDensity, voxelCoord).rgb;
                                                        );
                                                    #endif
     #if ENABLE_REPROJECTION
+
-        float2 reprojPosNDC = ComputeNormalizedDeviceCoordinates(centerWS, _PrevViewProjMatrix);
-        float  reprojZ      = mul(_PrevViewProjMatrix, float4(centerWS, 1)).w;
-        float4 reprojValue  = SampleVBuffer(TEXTURE3D_PARAM(_VBufferLightingHistory, s_trilinear_clamp_sampler),
-                                            false, reprojPosNDC, reprojZ,
-                                            _VBufferSliceCount.xy,
-                                            _VBufferDepthEncodingParams,
-                                            _VBufferDepthDecodingParams);
+        float4 reprojValue = SampleVBuffer(TEXTURE3D_PARAM(_VBufferLightingHistory, s_linear_clamp_sampler),
+                                           centerWS,
+                                           _PrevViewProjMatrix,
+                                           _VBufferResolution,
+                                           _VBufferSliceCount.xy,
+                                           _VBufferDepthEncodingParams,
+                                           _VBufferDepthDecodingParams,
+                                           false, false, true);
 
         // Compute the exponential moving average over 'n' frames:
         // X = (1 - a) * ValueAtFrame[n] + a * AverageOverPreviousFrames.
         // TODO: doesn't seem to be worth it, removed for now.
 
         // Perform temporal blending.
-        // Both radiance values are obtained by integrating over line segments of different length.
-        // Blending only makes sense if the length of both intervals is the same.
-        // Therefore, the reprojected radiance needs to be rescaled by (frame_dt / reproj_dt).
+        // Both radiance values are obtained by integrating over line segments of different length,
+        // with potentially different participating media coverage.
+        // Blending only makes sense if the voxels are virtually identical.
+        // Therefore, we need to rescale the history to make it match the current configuration.
+        // In order to do that, we integrate transmittance over the length of the ray interval
+        // passing through the center of the voxel. The integral can be interpreted as the amount of
+        // isotropically in-scattered radiance from a directional light with unit intensity.
+        // We ignore jittering, as we want values from the same voxel to be reporojected without
+        // any rescaling.
+        float  ds              = ConvertJitterDistToCenterRayDist(ray, dt);
+        float  centerTransmInt = TransmittanceIntegralHomogeneousMedium(extinction, ds);
+
-        float  reprojRcpLen    = reprojSuccess ? rcp(reprojValue.a) : 0;
-        float  lengthScale     = dt * reprojRcpLen;
+        float  reprojScale     = reprojSuccess ? (centerTransmInt * rcp(reprojValue.a)) : 0;
-        float3 blendedRadiance = (1 - blendFactor) * lighting.radianceNoPhase + blendFactor * lengthScale * reprojRadiance;
+        float3 blendedRadiance = (1 - blendFactor) * lighting.radianceNoPhase + blendFactor * reprojScale * reprojRadiance;
 
         // Store the feedback for the voxel.
         // TODO: dynamic lights (which update their position, rotation, cookie or shadow at runtime)
 
-        _VBufferLightingFeedback[voxelCoord] = float4(blendedRadiance, dt);
+        _VBufferLightingFeedback[voxelCoord] = float4(blendedRadiance, centerTransmInt);
-    #if SUPPORT_ASYMMETRY
-    #endif
-
-    #if SUPPORT_ASYMMETRY
-    #else
-        float3 blendedRadiance = lighting.radianceNoPhase;
-    #endif
-
-
-    #if SUPPORT_ASYMMETRY
-        float phase = _CornetteShanksConstant;
-    #else
-        float phase = IsotropicPhaseFunction();
-    #endif
-
-        float4 integral = float4(totalRadiance, opticalDepth);
+        float phase         = _CornetteShanksConstant;
 
         // Integrate the contribution of the probe over the interval.
         // Integral{a, b}{Transmittance(0, t) * L_s(t) dt} = Transmittance(0, a) * Integral{a, b}{Transmittance(0, t - a) * L_s(t) dt}.
         opticalDepth += 0.5 * extinction * dt;
 
         // Store the voxel data.
-        _VBufferLightingIntegral[voxelCoord] = float4(totalRadiance, opticalDepth);
+        // Note: for correct filtering, the data has to be stored in the perceptual space.
+        // This means storing the tone mapped radiance and transmittance instead of optical depth.
+        // See "A Fresh Look at Generalized Sampling", p. 51.
+        _VBufferLightingIntegral[voxelCoord] = float4(FastTonemap(totalRadiance), Transmittance(opticalDepth));
-        z0 = z1;
         t0 = t1;
 
     #ifdef USE_CLUSTERED_LIGHTLIST
 
     float2 centerCoord = voxelCoord + float2(0.5, 0.5);
 #if ENABLE_REPROJECTION
-    float2 strataCoord = centerCoord + _VBufferSampleOffset.xy;
+    float2 jitterCoord = centerCoord + _VBufferSampleOffset.xy;
-    float2 strataCoord = centerCoord;
+    float2 jitterCoord = centerCoord;
-    // Compute the (tile-centered) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
+    // Compute the (voxel-centered in the screen space) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
-    // Compute the (tile-stratified) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
-    float3 strataDirWS     = mul(-float3(strataCoord, 1), (float3x3)_VBufferCoordToViewDirWS);
-    float  strataDirLenSq  = dot(strataDirWS, strataDirWS);
-    float  strataDirLenRcp = rsqrt(strataDirLenSq);
-    float  strataDirLen    = strataDirLenSq * strataDirLenRcp;
+    // Compute the (voxel-jittered in the screen space) ray direction s.t. its ViewSpace(rayDirWS).z = 1.
+    float3 jitterDirWS     = mul(-float3(jitterCoord, 1), (float3x3)_VBufferCoordToViewDirWS);
+    float  jitterDirLenSq  = dot(jitterDirWS, jitterDirWS);
+    float  jitterDirLenRcp = rsqrt(jitterDirLenSq);
+    float  jitterDirLen    = jitterDirLenSq * jitterDirLenRcp;
-    ray.strataDirWS       = strataDirWS * strataDirLenRcp;  // Normalize
+    ray.jitterDirWS       = jitterDirWS * jitterDirLenRcp;  // Normalize
-    ray.strataDirInvViewZ = strataDirLen;                   // View space Z
-    ray.twoDirRatioViewZ  = centerDirLen * strataDirLenRcp; // View space Z ratio
+    ray.jitterDirInvViewZ = jitterDirLen;                   // View space Z
+    ray.twoDirRatioViewZ  = centerDirLen * jitterDirLenRcp; // View space Z ratio
 
     // TODO
     LightLoopContext context;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/Volumetrics/VolumetricLighting.cs

 namespace UnityEngine.Experimental.Rendering.HDPipeline
 {
 [GenerateHLSL]
-public struct DensityVolumeProperties
+public struct DensityVolumeData
-    public static DensityVolumeProperties GetNeutralProperties()
+    public static DensityVolumeData GetNeutralValues()
-        DensityVolumeProperties properties = new DensityVolumeProperties();
+        DensityVolumeData data;
-        properties.scattering = Vector3.zero;
-        properties.extinction = 0;
+        data.scattering = Vector3.zero;
+        data.extinction = 0;
-        return properties;
+        return data;
-[Serializable]
-public class DensityVolumeParameters
+public class VolumeRenderingUtils
-    public bool  isLocal;      // Enables voxelization
-    public Color albedo;       // Single scattering albedo [0, 1]
-    public float meanFreePath; // In meters [1, inf]. Should be chromatic - this is an optimization!
-    public float asymmetry;    // Only used if (isLocal == false)
-
-    public DensityVolumeParameters()
+    public static float MeanFreePathFromExtinction(float extinction)
-        isLocal      = true;
-        albedo       = new Color(0.5f, 0.5f, 0.5f);
-        meanFreePath = 10.0f;
-        asymmetry    = 0.0f;
+        return 1.0f / extinction;
-    public bool IsLocalVolume()
+    public static float ExtinctionFromMeanFreePath(float meanFreePath)
-        return isLocal;
+        return 1.0f / meanFreePath;
-    public Vector3 GetAbsorptionCoefficient()
+    public static Vector3 AbsorptionFromExtinctionAndScattering(float extinction, Vector3 scattering)
-        float   extinction = GetExtinctionCoefficient();
-        Vector3 scattering = GetScatteringCoefficient();
-
-        return Vector3.Max(new Vector3(extinction, extinction, extinction) - scattering, Vector3.zero);
+        return new Vector3(extinction, extinction, extinction) - scattering;
-    public Vector3 GetScatteringCoefficient()
+    public static Vector3 ScatteringFromExtinctionAndAlbedo(float extinction, Vector3 albedo)
-        float extinction = GetExtinctionCoefficient();
-
-        return new Vector3(albedo.r * extinction, albedo.g * extinction, albedo.b * extinction);
+        return extinction * albedo;
-    public float GetExtinctionCoefficient()
+    public static Vector3 AlbedoFromMeanFreePathAndScattering(float meanFreePath, Vector3 scattering)
-        return 1.0f / meanFreePath;
+        return meanFreePath * scattering;
+}
+
+[Serializable]
+public struct DensityVolumeParameters
+{
+    public Color albedo;       // Single scattering albedo [0, 1]. Alpha is ignored
+    public float meanFreePath; // In meters [1, inf]. Should be chromatic - this is an optimization!
+    public float asymmetry;    // Only used if (isLocal == false)
 
     public void Constrain()
     {
+        albedo.a = 1.0f;
-        meanFreePath = Mathf.Max(meanFreePath, 1.0f);
+        meanFreePath = Mathf.Clamp(meanFreePath, 1.0f, float.MaxValue);
-    public DensityVolumeProperties GetProperties()
+    public DensityVolumeData GetData()
-        DensityVolumeProperties properties = new DensityVolumeProperties();
+        DensityVolumeData data = new DensityVolumeData();
-        properties.scattering = GetScatteringCoefficient();
-        properties.extinction = GetExtinctionCoefficient();
+        data.extinction = VolumeRenderingUtils.ExtinctionFromMeanFreePath(meanFreePath);
+        data.scattering = VolumeRenderingUtils.ScatteringFromExtinctionAndAlbedo(data.extinction, (Vector3)(Vector4)albedo);
-        return properties;
+        return data;
-    public List<OrientedBBox>            bounds;
-    public List<DensityVolumeProperties> properties;
+    public List<OrientedBBox>      bounds;
+    public List<DensityVolumeData> density;
 }
 
 public class VolumetricLightingSystem
     ComputeShader m_VolumeVoxelizationCS = null;
     ComputeShader m_VolumetricLightingCS = null;
 
-    List<VBuffer>                 m_VBuffers                = null;
-    List<OrientedBBox>            m_VisibleVolumeBounds     = null;
-    List<DensityVolumeProperties> m_VisibleVolumeProperties = null;
-    public const int              k_MaxVisibleVolumeCount   = 512;
+    List<VBuffer>           m_VBuffers              = null;
+    List<OrientedBBox>      m_VisibleVolumeBounds   = null;
+    List<DensityVolumeData> m_VisibleVolumeData     = null;
+    public const int        k_MaxVisibleVolumeCount = 512;
-    static ComputeBuffer s_VisibleVolumePropertiesBuffer = null;
+    static ComputeBuffer s_VisibleVolumeDataBuffer = null;
 
     float       m_VBufferNearPlane = 0.5f;  // Distance in meters; dynamic modifications not handled by reprojection
     float       m_VBufferFarPlane  = 64.0f; // Distance in meters; dynamic modifications not handled by reprojection
     {
         if (preset == VolumetricLightingPreset.Off) return;
 
-        m_VolumeVoxelizationCS          = asset.renderPipelineResources.volumeVoxelizationCS;
-        m_VolumetricLightingCS          = asset.renderPipelineResources.volumetricLightingCS;
-        m_VBuffers                      = new List<VBuffer>();
-        m_VisibleVolumeBounds           = new List<OrientedBBox>();
-        m_VisibleVolumeProperties       = new List<DensityVolumeProperties>();
-        s_VisibleVolumeBoundsBuffer     = new ComputeBuffer(k_MaxVisibleVolumeCount, System.Runtime.InteropServices.Marshal.SizeOf(typeof(OrientedBBox)));
-        s_VisibleVolumePropertiesBuffer = new ComputeBuffer(k_MaxVisibleVolumeCount, System.Runtime.InteropServices.Marshal.SizeOf(typeof(DensityVolumeProperties)));
+        m_VolumeVoxelizationCS      = asset.renderPipelineResources.volumeVoxelizationCS;
+        m_VolumetricLightingCS      = asset.renderPipelineResources.volumetricLightingCS;
+        m_VBuffers                  = new List<VBuffer>();
+        m_VisibleVolumeBounds       = new List<OrientedBBox>();
+        m_VisibleVolumeData         = new List<DensityVolumeData>();
+        s_VisibleVolumeBoundsBuffer = new ComputeBuffer(k_MaxVisibleVolumeCount, System.Runtime.InteropServices.Marshal.SizeOf(typeof(OrientedBBox)));
+        s_VisibleVolumeDataBuffer   = new ComputeBuffer(k_MaxVisibleVolumeCount, System.Runtime.InteropServices.Marshal.SizeOf(typeof(DensityVolumeData)));
     }
 
     public void Cleanup()
             m_VBuffers[i].Destroy();
         }
 
-        m_VBuffers                = null;
-        m_VisibleVolumeBounds     = null;
-        m_VisibleVolumeProperties = null;
+        m_VBuffers            = null;
+        m_VisibleVolumeBounds = null;
+        m_VisibleVolumeData   = null;
-        CoreUtils.SafeRelease(s_VisibleVolumePropertiesBuffer);
+        CoreUtils.SafeRelease(s_VisibleVolumeDataBuffer);
     }
 
     public void ResizeVBuffer(HDCamera camera, int screenWidth, int screenHeight)
     {
         if (preset == VolumetricLightingPreset.Off) return;
 
-        HomogeneousDensityVolume globalVolume = HomogeneousDensityVolume.GetGlobalHomogeneousDensityVolume();
-
-        // TODO: may want to cache these results somewhere.
-        DensityVolumeProperties globalVolumeProperties = (globalVolume != null) ? globalVolume.parameters.GetProperties()
-                                                                                : DensityVolumeProperties.GetNeutralProperties();
-
-        float asymmetry = globalVolume != null ? globalVolume.parameters.asymmetry : 0;
-        cmd.SetGlobalVector(HDShaderIDs._GlobalScattering, globalVolumeProperties.scattering);
-        cmd.SetGlobalFloat( HDShaderIDs._GlobalExtinction, globalVolumeProperties.extinction);
-        cmd.SetGlobalFloat( HDShaderIDs._GlobalAsymmetry,  asymmetry);
+        // Modify the near plane.
+        // Warning: it can screw up the reprojection. However, we have to do it in order for clustered lighting to work correctly.
+        m_VBufferNearPlane = camera.camera.nearClipPlane;
 
         VBuffer vBuffer = FindVBuffer(camera.GetViewID());
         Debug.Assert(vBuffer != null);
 
-        SetPreconvolvedAmbientLightProbe(cmd, asymmetry);
+        // Get the interpolated asymmetry value.
+        var fog = VolumeManager.instance.stack.GetComponent<VolumetricFog>();
+
+        SetPreconvolvedAmbientLightProbe(cmd, fog.asymmetry);
+
         cmd.SetGlobalVector( HDShaderIDs._VBufferResolution,          new Vector4(w, h, 1.0f / w, 1.0f / h));
         cmd.SetGlobalVector( HDShaderIDs._VBufferSliceCount,          new Vector4(d, 1.0f / d));
         cmd.SetGlobalVector( HDShaderIDs._VBufferDepthEncodingParams, ComputeLogarithmicDepthEncodingParams(m_VBufferNearPlane, m_VBufferFarPlane, k_LogScale));
 
         if (preset == VolumetricLightingPreset.Off) return densityVolumes;
 
+        var visualEnvironment = VolumeManager.instance.stack.GetComponent<VisualEnvironment>();
+
+        if (visualEnvironment.fogType != FogType.Volumetric) return densityVolumes;
+
         using (new ProfilingSample(cmd, "Prepare Visible Density Volume List"))
         {
             Vector3 camPosition = camera.camera.transform.position;
             }
 
             m_VisibleVolumeBounds.Clear();
-            m_VisibleVolumeProperties.Clear();
+            m_VisibleVolumeData.Clear();
 
             // Collect all visible finite volume data, and upload it to the GPU.
             HomogeneousDensityVolume[] volumes = Object.FindObjectsOfType(typeof(HomogeneousDensityVolume)) as HomogeneousDensityVolume[];
                 HomogeneousDensityVolume volume = volumes[i];
 
                 // Only test active finite volumes.
-                if (volume.enabled && volume.parameters.IsLocalVolume())
+                if (volume.enabled)
                 {
                     // TODO: cache these?
                     var obb = OrientedBBox.Create(volume.transform);
                     if (GeometryUtils.Overlap(obb, camera.frustum, 6, 8))
                     {
                         // TODO: cache these?
-                        var properties = volume.parameters.GetProperties();
+                        var data = volume.parameters.GetData();
-                        m_VisibleVolumeProperties.Add(properties);
+                        m_VisibleVolumeData.Add(data);
-            s_VisibleVolumePropertiesBuffer.SetData(m_VisibleVolumeProperties);
+            s_VisibleVolumeDataBuffer.SetData(m_VisibleVolumeData);
-            densityVolumes.properties = m_VisibleVolumeProperties;
+            densityVolumes.density = m_VisibleVolumeData;
 
             return densityVolumes;
         }
             float     vFoV       = camera.camera.fieldOfView * Mathf.Deg2Rad;
             Vector4   resolution = new Vector4(w, h, 1.0f / w, 1.0f / h);
             Matrix4x4 transform  = HDUtils.ComputePixelCoordToWorldSpaceViewDirectionMatrix(vFoV, resolution, camera.viewMatrix, false);
-                                   
-            cmd.SetComputeTextureParam(m_VolumeVoxelizationCS, kernel, HDShaderIDs._VBufferDensity,   vBuffer.GetDensityBuffer());
-            cmd.SetComputeBufferParam( m_VolumeVoxelizationCS, kernel, HDShaderIDs._VolumeBounds,     s_VisibleVolumeBoundsBuffer);
-            cmd.SetComputeBufferParam( m_VolumeVoxelizationCS, kernel, HDShaderIDs._VolumeProperties, s_VisibleVolumePropertiesBuffer);
+
+            cmd.SetComputeTextureParam(m_VolumeVoxelizationCS, kernel, HDShaderIDs._VBufferDensity, vBuffer.GetDensityBuffer());
+            cmd.SetComputeBufferParam( m_VolumeVoxelizationCS, kernel, HDShaderIDs._VolumeBounds,   s_VisibleVolumeBoundsBuffer);
+            cmd.SetComputeBufferParam( m_VolumeVoxelizationCS, kernel, HDShaderIDs._VolumeData,     s_VisibleVolumeDataBuffer);
 
             // TODO: set the constant buffer data only once.
             cmd.SetComputeMatrixParam( m_VolumeVoxelizationCS, HDShaderIDs._VBufferCoordToViewDirWS,  transform);
 
         using (new ProfilingSample(cmd, "Volumetric Lighting"))
         {
-            VBuffer vBuffer = FindVBuffer(camera.GetViewID());
-            Debug.Assert(vBuffer != null);
+            var visualEnvironment = VolumeManager.instance.stack.GetComponent<VisualEnvironment>();
-            HomogeneousDensityVolume globalVolume = HomogeneousDensityVolume.GetGlobalHomogeneousDensityVolume();
-            float asymmetry = globalVolume != null ? globalVolume.parameters.asymmetry : 0;
-
-            if (globalVolume == null)
+            if (visualEnvironment.fogType != FogType.Volumetric)
-                // CoreUtils.SetRenderTarget(cmd, vBuffer.GetLightingIntegralBuffer(), ClearFlag.Color, CoreUtils.clearColorAllBlack);
-                // CoreUtils.SetRenderTarget(cmd, vBuffer.GetLightingFeedbackBuffer(), ClearFlag.Color, CoreUtils.clearColorAllBlack);
+                // CoreUtils.SetRenderTarget(cmd, vBuffer.GetDensityBuffer(), ClearFlag.Color, CoreUtils.clearColorAllBlack);
+
+            VBuffer vBuffer = FindVBuffer(camera.GetViewID());
+            Debug.Assert(vBuffer != null);
 
             // Only available in the Play Mode because all the frame counters in the Edit Mode are broken.
             bool enableClustered    = settings.lightLoopSettings.enableTileAndCluster;
             int sampleIndex = rfc % 7;
             Vector4 offset = new Vector4(xySeq[sampleIndex].x, xySeq[sampleIndex].y, zSeq[sampleIndex], rfc);
 
+            // Get the interpolated asymmetry value.
+            var fog = VolumeManager.instance.stack.GetComponent<VolumetricFog>();
+
-            cmd.SetComputeFloatParam(  m_VolumetricLightingCS,         HDShaderIDs._CornetteShanksConstant,  CornetteShanksPhasePartConstant(asymmetry));
+            cmd.SetComputeFloatParam(  m_VolumetricLightingCS,         HDShaderIDs._CornetteShanksConstant,  CornetteShanksPhasePartConstant(fog.asymmetry));
             cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferDensity,          vBuffer.GetDensityBuffer());          // Read
             cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingIntegral, vBuffer.GetLightingIntegralBuffer()); // Write
             if (enableReprojection)

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScattering.compute

 void SubsurfaceScattering(uint2 groupId       : SV_GroupID,
                           uint  groupThreadId : SV_GroupThreadID)
 {
+    groupThreadId &= GROUP_SIZE_2D - 1; // Help the compiler
+
     // Note: any factor of 64 is a suitable wave size for our algorithm.
     uint waveIndex = WaveReadFirstLane(groupThreadId / 64);
     uint laneIndex = groupThreadId % 64;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/AtmosphericScattering/AtmosphericScattering.cs

-using System;
+using System;
 using System.Diagnostics;
 using UnityEngine.Rendering;
 
     public abstract class AtmosphericScattering : VolumeComponent
     {
-        static readonly int m_TypeParam = Shader.PropertyToID("_AtmosphericScatteringType");
         // Fog Color
         static readonly int m_ColorModeParam = Shader.PropertyToID("_FogColorMode");
         static readonly int m_FogColorDensityParam = Shader.PropertyToID("_FogColorDensity");
 
         public static void PushNeutralShaderParameters(CommandBuffer cmd)
         {
-            cmd.SetGlobalFloat(m_TypeParam, (float)FogType.None);
+            cmd.SetGlobalInt(HDShaderIDs._AtmosphericScatteringType, (int)FogType.None);
+
+            // In case volumetric lighting is enabled, we need to make sure that all rendering passes
+            // (not just the atmospheric scattering one) receive neutral parameters.
+            if (ShaderConfig.s_VolumetricLightingPreset != 0)
+            {
+                var data = DensityVolumeData.GetNeutralValues();
+
+                cmd.SetGlobalVector(HDShaderIDs._GlobalScattering, data.scattering);
+                cmd.SetGlobalFloat( HDShaderIDs._GlobalExtinction, data.extinction);
+                cmd.SetGlobalFloat( HDShaderIDs._GlobalAsymmetry,  0.0f);
+            }
+        // Not used by the volumetric fog.
-            if (frameSettings.enableAtmosphericScattering)
-                cmd.SetGlobalFloat(m_TypeParam, (float)type);
-            else
-                cmd.SetGlobalFloat(m_TypeParam, (float)FogType.None);
+            Debug.Assert(frameSettings.enableAtmosphericScattering);
+
+            cmd.SetGlobalInt(HDShaderIDs._AtmosphericScatteringType, (int)type);
 
             // Fog Color
             cmd.SetGlobalFloat(m_ColorModeParam, (float)colorMode.value);
     {
         None,
         Linear,
-        Exponential
+        Exponential,
+        Volumetric
     }
 
     [GenerateHLSL]

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/AtmosphericScattering/AtmosphericScattering.cs.hlsl

 #define FOGTYPE_NONE (0)
 #define FOGTYPE_LINEAR (1)
 #define FOGTYPE_EXPONENTIAL (2)
+#define FOGTYPE_VOLUMETRIC (3)
 
 //
 // UnityEngine.Experimental.Rendering.HDPipeline.FogColorMode:  static fields

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/AtmosphericScattering/AtmosphericScattering.hlsl

 #endif
 
 CBUFFER_START(AtmosphericScattering)
-float   _AtmosphericScatteringType;
+int     _AtmosphericScatteringType;
 // Common
 float   _FogColorMode;
 float4  _FogColorDensity; // color in rgb, density in alpha
 	float3 fogColor = 0;
 	float  fogFactor = 0;
 
-#if (SHADEROPTIONS_VOLUMETRIC_LIGHTING_PRESET != 0)
-	float4 volFog = SampleInScatteredRadianceAndTransmittance(TEXTURE3D_PARAM(_VBufferLighting, s_trilinear_clamp_sampler),
-															  posInput.positionNDC, posInput.linearDepth,
-															  _VBufferResolution,
-															  _VBufferSliceCount.xy,
-															  _VBufferDepthEncodingParams,
-															  _VBufferDepthDecodingParams);
-	fogColor = volFog.rgb;
-	fogFactor = 1 - volFog.a;
-#else
+	switch (_AtmosphericScatteringType)
+	{
+		case FOGTYPE_LINEAR:
+		{
+			fogColor = GetFogColor(posInput);
+			fogFactor = _FogDensity * saturate((posInput.linearDepth - _LinearFogStart) * _LinearFogOneOverRange) * saturate((_LinearFogHeightEnd - GetAbsolutePositionWS(posInput.positionWS).y) * _LinearFogHeightOneOverRange);
+			break;
+		}
+		case FOGTYPE_EXPONENTIAL:
+		{
+			fogColor = GetFogColor(posInput);
+			float distance = length(GetWorldSpaceViewDir(posInput.positionWS));
+			float fogHeight = max(0.0, GetAbsolutePositionWS(posInput.positionWS).y - _ExpFogBaseHeight);
+			fogFactor = _FogDensity * TransmittanceHomogeneousMedium(_ExpFogHeightAttenuation, fogHeight) * (1.0f - TransmittanceHomogeneousMedium(1.0f / _ExpFogDistance, distance));
+			break;
+		}
+		case FOGTYPE_VOLUMETRIC:
+		{
+		#if (SHADEROPTIONS_VOLUMETRIC_LIGHTING_PRESET != 0)
+			float4 volFog = SampleVolumetricLighting(TEXTURE3D_PARAM(_VBufferLighting, s_linear_clamp_sampler),
+													 posInput.positionNDC,
+													 posInput.linearDepth,
+													 _VBufferResolution,
+													 _VBufferSliceCount.xy,
+													 _VBufferDepthEncodingParams,
+													 _VBufferDepthDecodingParams,
+													 true, true);
-	if (_AtmosphericScatteringType == FOGTYPE_EXPONENTIAL)
-	{
-		fogColor = GetFogColor(posInput);
-		float distance = length(GetWorldSpaceViewDir(posInput.positionWS));
-		float fogHeight = max(0.0, GetAbsolutePositionWS(posInput.positionWS).y - _ExpFogBaseHeight);
-		fogFactor = _FogDensity * TransmittanceHomogeneousMedium(_ExpFogHeightAttenuation, fogHeight) * (1.0f - TransmittanceHomogeneousMedium(1.0f / _ExpFogDistance, distance));
-	}
-	else if (_AtmosphericScatteringType == FOGTYPE_LINEAR)
-	{
-		fogColor = GetFogColor(posInput);
-		fogFactor = _FogDensity * saturate((posInput.linearDepth - _LinearFogStart) * _LinearFogOneOverRange) * saturate((_LinearFogHeightEnd - GetAbsolutePositionWS(posInput.positionWS).y) * _LinearFogHeightOneOverRange);
-	}
-	else // NONE
-	{
+			fogFactor = 1 - volFog.a;                              // Opacity from transmittance
+			fogColor  = volFog.rgb * min(rcp(fogFactor), FLT_MAX); // Un-premultiply, clamp to avoid (0 * INF = NaN)
+		#endif
+			break;
+		}
-#endif
 
 	return float4(fogColor, fogFactor);
 }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/OpaqueAtmosphericScattering.shader

             // #pragma enable_d3d11_debug_symbols
 
             #include "CoreRP/ShaderLibrary/Common.hlsl"
+            #include "CoreRP/ShaderLibrary/Color.hlsl"
             #include "../ShaderVariables.hlsl"
             #include "AtmosphericScattering/AtmosphericScattering.hlsl"
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/VisualEnvironment.cs

-using System;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
         public void PushFogShaderParameters(CommandBuffer cmd, FrameSettings frameSettings)
         {
+            if (!frameSettings.enableAtmosphericScattering)
+            {
+                AtmosphericScattering.PushNeutralShaderParameters(cmd);
+                return;
+            }
+
             switch (fogType.value)
             {
                 case FogType.None:
                 case FogType.Exponential:
                     {
                         var fogSettings = VolumeManager.instance.stack.GetComponent<ExponentialFog>();
+                        fogSettings.PushShaderParameters(cmd, frameSettings);
+                        break;
+                    }
+                case FogType.Volumetric:
+                    {
+                        var fogSettings = VolumeManager.instance.stack.GetComponent<VolumetricFog>();
                         fogSettings.PushShaderParameters(cmd, frameSettings);
                         break;
                     }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Sky/AtmosphericScattering/VolumetricFogEditor.cs

+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEditor;
+using UnityEngine.Experimental.Rendering.HDPipeline;
+using UnityEditor.Experimental.Rendering;
+
+namespace UnityEditor.Experimental.Rendering.HDPipeline
+{
+    [VolumeComponentEditor(typeof(VolumetricFog))]
+    public class VolumetricFogEditor : AtmosphericScatteringEditor
+    {
+        private SerializedDataParameter m_Albedo;
+        private SerializedDataParameter m_MeanFreePath;
+        private SerializedDataParameter m_Asymmetry;
+
+        public override void OnEnable()
+        {
+            base.OnEnable();
+            var o = new PropertyFetcher<VolumetricFog>(serializedObject);
+
+            m_Albedo       = Unpack(o.Find(x => x.albedo));
+            m_MeanFreePath = Unpack(o.Find(x => x.meanFreePath));
+            m_Asymmetry    = Unpack(o.Find(x => x.asymmetry));
+        }
+
+        public override void OnInspectorGUI()
+        {
+            PropertyField(m_Albedo);
+            PropertyField(m_MeanFreePath);
+            PropertyField(m_Asymmetry);
+        }
+    }
+}

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Sky/AtmosphericScattering/VolumetricFogEditor.cs.meta

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+guid: a530ef8d0c07494409d34294d8e04a89
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+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
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ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/AtmosphericScattering/VolumetricFog.cs

+using System;
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Rendering;
+
+namespace UnityEngine.Experimental.Rendering.HDPipeline
+{
+    public class VolumetricFog : AtmosphericScattering
+    {
+        public ColorParameter        albedo       = new ColorParameter(new Color(0.5f, 0.5f, 0.5f));
+        public MinFloatParameter     meanFreePath = new MinFloatParameter(float.MaxValue, 1.0f);
+        public ClampedFloatParameter asymmetry    = new ClampedFloatParameter(0.0f, -1.0f, 1.0f);
+
+        // Override the volume blending function.
+        public override void Override(VolumeComponent state, float interpFactor)
+        {
+            VolumetricFog other = state as VolumetricFog;
+
+            float   thisExtinction  = VolumeRenderingUtils.ExtinctionFromMeanFreePath(meanFreePath);
+            Vector3 thisScattering  = VolumeRenderingUtils.ScatteringFromExtinctionAndAlbedo(thisExtinction, (Vector3)(Vector4)albedo.value);
+
+            float   otherExtinction = VolumeRenderingUtils.ExtinctionFromMeanFreePath(other.meanFreePath);
+            Vector3 otherScattering = VolumeRenderingUtils.ScatteringFromExtinctionAndAlbedo(otherExtinction, (Vector3)(Vector4)other.albedo.value);
+
+            float   blendExtinction =   Mathf.Lerp(otherExtinction, thisExtinction, interpFactor);
+            Vector3 blendScattering = Vector3.Lerp(otherScattering, thisScattering, interpFactor);
+            float   blendAsymmetry  =   Mathf.Lerp(other.asymmetry, asymmetry,      interpFactor);
+
+            float   blendMeanFreePath = VolumeRenderingUtils.MeanFreePathFromExtinction(blendExtinction);
+            Color   blendAlbedo       = (Color)(Vector4)VolumeRenderingUtils.AlbedoFromMeanFreePathAndScattering(blendMeanFreePath, blendScattering);
+                    blendAlbedo.a     = 1.0f;
+
+            if (meanFreePath.overrideState)
+            {
+                other.meanFreePath.value = blendMeanFreePath;
+            }
+
+            if (albedo.overrideState)
+            {
+                other.albedo.value = blendAlbedo;
+            }
+
+            if (asymmetry.overrideState)
+            {
+                other.asymmetry.value = blendAsymmetry;
+            }
+        }
+
+        public override void PushShaderParameters(CommandBuffer cmd, FrameSettings frameSettings)
+        {
+            DensityVolumeParameters param;
+
+            param.albedo       = albedo;
+            param.meanFreePath = meanFreePath;
+            param.asymmetry    = asymmetry;
+
+            DensityVolumeData data = param.GetData();
+
+            cmd.SetGlobalInt(HDShaderIDs._AtmosphericScatteringType, (int)FogType.Volumetric);
+
+            cmd.SetGlobalVector(HDShaderIDs._GlobalScattering, data.scattering);
+            cmd.SetGlobalFloat( HDShaderIDs._GlobalExtinction, data.extinction);
+            cmd.SetGlobalFloat( HDShaderIDs._GlobalAsymmetry,  asymmetry);
+        }
+    }
+}

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Sky/AtmosphericScattering/VolumetricFog.cs.meta

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