Fix APV not working with subtractive and shadowmask mode

Jira: https://jira.unity3d.com/browse/UUM-44229
This is a continuation of https://github.cds.internal.unity3d.com/unity/unity/pull/43294

Adaptive Probe Volumes (APV) do currently work correctly with mixed lighting modes (Subtractive, Distance shadowmask, Shadowmask) - APV does not store per-probe occlusion like the old light probe system did. This results in missing shadows when use the aforementioned mode. This has resulted in a long standing bug (due to scale of the fix) which has been reported several times by our users. Mixed Lighting is enabled by default and used particularly heavily on mobile.

This PR changes APV to store the missing occlusion data, allowing for proper shadowing when using mixed lighting. The changes include:
- Adding the new occlusion data to APV. It has its own data-file and texture. It is stored in 4 bytes representing [0;1] values for 4 lights per probe.
- Implementing streaming, scenario blending and dilation for the new occlusion data.
- Adding a mode to the debug visualization tool which allows viewing the occlusion data.
- Adding an API function that allows getting shadowmask indices of baked lights. This was missing and required to calculate the occlusion data.
- Updating shader code of the SRP's to allow sampling occlusion.
    - I've added a new define, `USE_APV_PROBE_OCCLUSION`, which is defined when probe occlusion should be sampled from APV. This is _not_ a new keyword, it's simply an alias for some existing keywords. This define is used to strip all the added code related to occlusion sampling when it isn't needed (in particular, when we aren't using mixed lighting).
    - For HDRP, I just sample the occlusion in the GBuffer pass. There's already a slot in the GBuffer for it, it was just not being set before.
    - For URP, the scale of changes is greater. APV supports being sampled both in vertex and fragment shader. For fragment shader sampling, the changes are simple enough, I've changed the code of relevant shaders to read occlusion and feed it to the existing designated outputs. For vertex shader sampling, I had to add a new (conditionally-defined) variable to each relevant `Varyings` struct.

To a user, the change is seamless: If they were using mixed lighting before, their project was missing shadows. If they re-bake after this change, the missing shadows will appear.

Before:
![Unity_EAyMvR5nGB](https://media.github.cds.internal.unity3d.com/user/2392/files/8923ec63-4677-4058-8360-ff4e0ddc6573)

After:
![Unity_FTa9q6bm6h](https://media.github.cds.internal.unity3d.com/user/2392/files/0216cbe5-da2a-4ed5-b195-2d8b86142dc5)

Debug view mode (mimics shadowmask view mode):
![Unity_DW4PdGQfNb](https://media.github.cds.internal.unity3d.com/user/2392/files/56179498-cc3f-4f0a-9bae-af2d245283c7)

Author: pema99

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.Dilate.cs

@@ -44,6 +44,8 @@ struct DilatedProbe
             public Vector4 SO_L0L1;
             public Vector3 SO_Direction;
 
+            public Vector4 ProbeOcclusion;
+
             void ToSphericalHarmonicsL2(ref SphericalHarmonicsL2 sh)
             {
                 SphericalHarmonicsL2Utils.SetCoefficient(ref sh, 0, L0);
@@ -90,6 +92,9 @@ internal void FromSphericalHarmonicsShaderConstants(ProbeReferenceVolume.Cell ce
                     var directions = ProbeVolumeConstantRuntimeResources.GetSkySamplingDirections();
                     SO_Direction = id == 255 ? Vector3.zero : directions[id];
                 }
+
+                if (cellChunkData.probeOcclusion.Length != 0)
+                    ReadFromShaderCoeffsProbeOcclusion(ref ProbeOcclusion, cellChunkData.probeOcclusion, index);
             }
 
             internal void ToSphericalHarmonicsShaderConstants(ProbeReferenceVolume.Cell cell, int probeIdx)
@@ -108,6 +113,9 @@ internal void ToSphericalHarmonicsShaderConstants(ProbeReferenceVolume.Cell cell
                     WriteToShaderSkyOcclusion(SO_L0L1, cellChunkData.skyOcclusionDataL0L1, index * 4);
                 if (cellChunkData.skyShadingDirectionIndices.Length != 0)
                     cellChunkData.skyShadingDirectionIndices[index] = (byte)SkyOcclusionBaker.EncodeSkyShadingDirection(SO_Direction);
+
+                if (cellChunkData.probeOcclusion.Length != 0)
+                    WriteToShaderProbeOcclusion(ProbeOcclusion, cellChunkData.probeOcclusion, index * 4);
             }
         }
 
@@ -328,6 +336,8 @@ static void PerformDilation(ProbeReferenceVolume.Cell cell, ProbeVolumeBakingSet
                 cmd.SetGlobalTexture(ProbeReferenceVolume.ShaderIDs._APVResL2_2, rr.L2_2);
                 cmd.SetGlobalTexture(ProbeReferenceVolume.ShaderIDs._APVResL2_3, rr.L2_3);
 
+                cmd.SetGlobalTexture(ProbeReferenceVolume.ShaderIDs._APVProbeOcclusion, rr.ProbeOcclusion ?? (RenderTargetIdentifier)CoreUtils.whiteVolumeTexture);
+
                 cmd.SetComputeTextureParam(dilationShader, dilationKernel, ProbeReferenceVolume.ShaderIDs._SkyOcclusionTexL0L1, rr.SkyOcclusionL0L1 ?? (RenderTargetIdentifier)CoreUtils.blackVolumeTexture);
                 cmd.SetComputeTextureParam(dilationShader, dilationKernel, ProbeReferenceVolume.ShaderIDs._SkyShadingDirectionIndicesTex, rr.SkyShadingDirectionIndices ?? (RenderTargetIdentifier)CoreUtils.blackVolumeTexture);
                 cmd.SetComputeBufferParam(dilationShader, dilationKernel, ProbeReferenceVolume.ShaderIDs._SkyPrecomputedDirections, rr.SkyPrecomputedDirections);

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.Dilate.cs.hlsl

@@ -19,6 +19,7 @@ struct DilatedProbe
     float3 L2_4;
     float4 SO_L0L1;
     float3 SO_Direction;
+    float4 ProbeOcclusion;
 };
 
 

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.LightTransport.cs

@@ -26,6 +26,7 @@ struct BakingCell
         public Vector4[] skyOcclusionDataL0L1;
         public byte[] skyShadingDirectionIndices;
         public float[] validity;
+        public Vector4[] probeOcclusion;
         public byte[] layerValidity;
         public Vector3[] offsetVectors;
         public float[] touchupVolumeInteraction;
@@ -220,7 +221,7 @@ void ReadAdjustmentVolumes(ProbeVolumeBakingSet bakingSet, BakingBatch bakingBat
         }
 
         internal void SetBakedData(ProbeVolumeBakingSet bakingSet, BakingBatch bakingBatch, TouchupVolumeWithBoundsList localTouchupVolumes, int i, int probeIndex,
-            in SphericalHarmonicsL2 sh, float validity, NativeArray<uint> renderingLayerMasks, NativeArray<Vector3> virtualOffsets, NativeArray<Vector4> skyOcclusion, NativeArray<uint> skyDirection)
+            in SphericalHarmonicsL2 sh, float validity, NativeArray<uint> renderingLayerMasks, NativeArray<Vector3> virtualOffsets, NativeArray<Vector4> skyOcclusion, NativeArray<uint> skyDirection, NativeArray<Vector4> probeOcclusion)
         {
             byte layerValidityMask = (byte)(renderingLayerMasks.IsCreated ? renderingLayerMasks[probeIndex] : 0);
 
@@ -246,6 +247,9 @@ internal void SetBakedData(ProbeVolumeBakingSet bakingSet, BakingBatch bakingBat
             this.validity[i] = currValidity;
             for (int l = 0; l < APVDefinitions.probeMaxRegionCount; l++)
                 validityNeighbourMask[l, i] = currValidityNeighbourMask;
+
+            if (probeOcclusion.IsCreated)
+                this.probeOcclusion[i] = probeOcclusion[probeIndex];
         }
 
         internal int GetBakingHashCode()
@@ -473,7 +477,7 @@ public void Init(ProbeVolumeBakingSet bakingSet, NativeList<Vector3> probePositi
                     defaultSOJob.jobs = jobs;
 
                 lightingJob = lightingOverride ?? new DefaultLightTransport();
-                lightingJob.Initialize(sortedPositions);
+                lightingJob.Initialize(ProbeVolumeLightingTab.GetLightingSettings().mixedBakeMode != MixedLightingMode.IndirectOnly, sortedPositions);
                 if (lightingJob is DefaultLightTransport defaultLightingJob)
                     defaultLightingJob.jobs = jobs;
 
@@ -1059,7 +1063,8 @@ static void BakeDelegate(ref float progress, ref bool done)
                     s_BakeData.lightingJob.irradiance, s_BakeData.lightingJob.validity,
                     s_BakeData.layerMaskJob.renderingLayerMasks,
                     s_BakeData.virtualOffsetJob.offsets,
-                    s_BakeData.skyOcclusionJob.occlusion, s_BakeData.skyOcclusionJob.encodedDirections);
+                    s_BakeData.skyOcclusionJob.occlusion, s_BakeData.skyOcclusionJob.encodedDirections,
+                    s_BakeData.lightingJob.occlusion);
 
                 if (s_BakeData.cellIndex >= m_BakingBatch.cells.Count)
                     s_BakeData.step++;

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.Serialization.cs

@@ -112,6 +112,7 @@ public override void PrepareForBuild(BuildPlayerContext buildPlayerContext)
                         PrepareStreamableAsset(scenario.Value.cellDataAsset, basePath, useStreamingAsset);
                         if (maxSHBands == ProbeVolumeSHBands.SphericalHarmonicsL2)
                             PrepareStreamableAsset(scenario.Value.cellOptionalDataAsset, basePath, useStreamingAsset);
+                        PrepareStreamableAsset(scenario.Value.cellProbeOcclusionDataAsset, basePath, useStreamingAsset);
                     }
 
                     processedBakingSets.Add(bakingSet);

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeGIBaking.cs

@@ -27,7 +27,7 @@ RWStructuredBuffer<DilatedProbe> _OutputProbes;
 
 
 // Sampling is copied from SampleAPV()
-void AddProbeSample(APVResources apvRes, float3 uvw, inout DilatedProbe probe, float weight, inout float shWeight, inout float soWeight)
+void AddProbeSample(APVResources apvRes, float3 uvw, inout DilatedProbe probe, float weight, inout float shWeight, inout float soWeight, inout float poWeight)
 {
     // SH data
     float4 L0_L1Rx = SAMPLE_TEXTURE3D_LOD(apvRes.L0_L1Rx, s_point_clamp_sampler, uvw, 0).rgba;
@@ -55,6 +55,13 @@ void AddProbeSample(APVResources apvRes, float3 uvw, inout DilatedProbe probe, f
         shWeight += weight;
     }
 
+    float4 probeOcclusion = SAMPLE_TEXTURE3D_LOD(apvRes.ProbeOcclusion, s_linear_clamp_sampler, uvw, 0).rgba;
+    if (!all(probeOcclusion < 0.0001f))
+    {
+        probe.ProbeOcclusion = probeOcclusion * weight;
+        poWeight += weight;
+    }
+
     // Sky occlusion data
     if (_APVSkyOcclusionWeight > 0)
     {
@@ -104,7 +111,7 @@ void DilateCell(uint3 id : SV_DispatchThreadID)
 
             float3 uvw;
             uint subdiv;
-            float shWeight = 0, soWeight = 0;
+            float shWeight = 0, soWeight = 0, poWeight = 0;
             float3 uvwDelta = rcp(_APVPoolDim);
 
             float3 biasedPosWS;
@@ -137,7 +144,7 @@ void DilateCell(uint3 id : SV_DispatchThreadID)
                                         {
                                             d *= d;
                                         }
-                                        AddProbeSample(FillAPVResources(), sampleUVW, probe, rcp(d), shWeight, soWeight);
+                                        AddProbeSample(FillAPVResources(), sampleUVW, probe, rcp(d), shWeight, soWeight, poWeight);
                                     }
                                 }
                             }
@@ -153,6 +160,12 @@ void DilateCell(uint3 id : SV_DispatchThreadID)
                 probe.SO_L0L1 *= rcp(soWeight);
             probe.SO_Direction = SafeNormalize(probe.SO_Direction);
 
+            if (poWeight > 0)
+            {
+                probe.ProbeOcclusion *= rcp(poWeight);
+                probe.ProbeOcclusion = saturate(probe.ProbeOcclusion);
+            }
+
             _OutputProbes[probeIdx] = probe;
         }
     }

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeVolumeBuildProcessor.cs

@@ -301,7 +301,12 @@ float3 CalculateDiffuseLighting(v2f i)
     float3 normal = normalize(i.normal);
 
     float3 skyShadingDirection = normal;
-    if (_ShadingMode == DEBUGPROBESHADINGMODE_SKY_DIRECTION)
+    if (_ShadingMode == DEBUGPROBESHADINGMODE_PROBE_OCCLUSION)
+    {
+        float4 shadowmask = apvRes.ProbeOcclusion[texLoc];
+        return float4(shadowmask.rgb * 0.5 + (shadowmask.a * 0.5), 1);
+    }
+    else if (_ShadingMode == DEBUGPROBESHADINGMODE_SKY_DIRECTION)
     {
         if (_APVSkyDirectionWeight > 0)
         {

Packages/com.unity.render-pipelines.core/Editor/Lighting/ProbeVolume/ProbeVolumeCellDilation.compute

@@ -73,7 +73,7 @@
         UNITY_SETUP_INSTANCE_ID(i);
 
         if (_ShadingMode >= DEBUGPROBESHADINGMODE_SH && _ShadingMode <= DEBUGPROBESHADINGMODE_SHL0L1
-            || _ShadingMode == DEBUGPROBESHADINGMODE_SKY_OCCLUSION_SH || _ShadingMode == DEBUGPROBESHADINGMODE_SKY_DIRECTION)
+            || _ShadingMode == DEBUGPROBESHADINGMODE_SKY_OCCLUSION_SH || _ShadingMode == DEBUGPROBESHADINGMODE_SKY_DIRECTION || _ShadingMode == DEBUGPROBESHADINGMODE_PROBE_OCCLUSION)
         {
             return float4(CalculateDiffuseLighting(i) * exp2(_ExposureCompensation) * GetCurrentExposureMultiplier(), 1);
         }