Stop NaN propagation within volumetric lighting shader (v2)

com.unity.render-pipelines.high-definition/HDRP/Lighting/Volumetrics/VolumeVoxelization.compute

 
 // TODO: avoid creating another Constant Buffer...
 CBUFFER_START(UnityVolumetricLighting)
-    float4x4 _VBufferCoordToViewDirWS; // Actually just 3x3, but Unity can only set 4x4
-    float4   _VBufferSampleOffset;     // Not used by this shader
-    float    _CornetteShanksConstant;  // Not used by this shader
+    float4x4 _VBufferCoordToViewDirWS;          // Actually just 3x3, but Unity can only set 4x4
+    float4   _VBufferSampleOffset;              // Not used by this shader
+    float4   _VolumeMaskDimensions;             // x = 1/numTextures , y = width, z = depth = width * numTextures, w = maxLod
-    float4   _VolumeMaskDimensions;    //x = 1/numTextures , y = width, z = depth = width * numTextures, w = maxLod
+    float    _CornetteShanksConstant;           // Not used by this shader
+    uint     _VBufferLightingHistoryIsValid;    // Not used by this shader
 CBUFFER_END
 
 //--------------------------------------------------------------------------------------------------

com.unity.render-pipelines.high-definition/HDRP/Lighting/Volumetrics/VolumetricLighting.compute

 // TODO: avoid creating another Constant Buffer...
 CBUFFER_START(UnityVolumetricLighting)
     float4x4 _VBufferCoordToViewDirWS;          // Actually just 3x3, but Unity can only set 4x4
-    float4   _VBufferSampleOffset;              // Not used by this shader
-    float    _CornetteShanksConstant;           // Not used by this shader
-    uint     _NumVisibleDensityVolumes;
+    float4   _VBufferSampleOffset;
+    float4   _VolumeMaskDimensions;             // Not used by this shader
+    uint     _NumVisibleDensityVolumes;         // Not used by this shader
+    float    _CornetteShanksConstant;
+    uint     _VBufferLightingHistoryIsValid;
 CBUFFER_END
 
 //--------------------------------------------------------------------------------------------------
 
         float3 blendedRadiance = lighting.radianceNoPhase;
 
-        // Uninitialized history texture may contain NaNs.
-        // TODO: clear the texture after creating it. Clearing 3D textures is broken in Unity. :-(
-        bool reprojSuccess = (reprojValue.a != 0) && !isnan(reprojValue.a);
+        bool reprojSuccess = (_VBufferLightingHistoryIsValid != 0) && (reprojValue.a != 0);
 
         if (reprojSuccess)
         {

com.unity.render-pipelines.high-definition/HDRP/Lighting/Volumetrics/VolumetricLighting.cs

         RTHandleSystem.RTHandle       m_LightingBufferHandle;
 
         // Is the feature globally disabled?
-        bool m_supportVolumetrics = false;
+        bool m_SupportVolumetrics = false;
+
+        // The history buffer starts in the uninitialized state after being created or resized,
+        // and contains arbitrary data. Therefore, we must initialize it before use.
+        Vector3Int m_PreviousResolutionOfHistoryBuffer = Vector3Int.zero;
-            m_supportVolumetrics = asset.renderPipelineSettings.supportVolumetrics;
+            m_SupportVolumetrics = asset.renderPipelineSettings.supportVolumetrics;
-            if (!m_supportVolumetrics)
+            if (!m_SupportVolumetrics)
                 return;
 
             preset = asset.renderPipelineSettings.increaseResolutionOfVolumetrics ? VolumetricLightingPreset.High :
         {
             // Note: Here we can't test framesettings as they are not initialize yet
             // TODO: Here we allocate history even for camera that may not use volumetric
-            if (!m_supportVolumetrics)
+            if (!m_SupportVolumetrics)
                 return;
 
             // Start with the same parameters for both frames. Then update them one by one every frame.
                 cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingIntegral, m_LightingBufferHandle); // Write
                 if (enableReprojection)
                 {
-                    cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingHistory,  hdCamera.GetPreviousFrameRT((int)HDCameraFrameHistoryType.VolumetricLighting));// Read
-                    cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingFeedback, hdCamera.GetCurrentFrameRT((int)HDCameraFrameHistoryType.VolumetricLighting)); // Write
+                    var historyRT  = hdCamera.GetPreviousFrameRT((int)HDCameraFrameHistoryType.VolumetricLighting);
+                    var feedbackRT = hdCamera.GetCurrentFrameRT((int)HDCameraFrameHistoryType.VolumetricLighting);
+
+                    // Detect if the history buffer has been recreated or resized.
+                    Vector3Int currentResolutionOfHistoryBuffer = new Vector3Int();
+                    currentResolutionOfHistoryBuffer.x = historyRT.rt.width;
+                    currentResolutionOfHistoryBuffer.y = historyRT.rt.height;
+                    currentResolutionOfHistoryBuffer.z = historyRT.rt.volumeDepth;
+
+                    // We allow downsizing, as this does not cause a reallocation.
+                    bool validHistory = (currentResolutionOfHistoryBuffer.x <= m_PreviousResolutionOfHistoryBuffer.x &&
+                                         currentResolutionOfHistoryBuffer.y <= m_PreviousResolutionOfHistoryBuffer.y &&
+                                         currentResolutionOfHistoryBuffer.z <= m_PreviousResolutionOfHistoryBuffer.z);
+
+                    cmd.SetComputeIntParam(    m_VolumetricLightingCS,         HDShaderIDs._VBufferLightingHistoryIsValid, validHistory ? 1 : 0);
+                    cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingHistory,        historyRT);  // Read
+                    cmd.SetComputeTextureParam(m_VolumetricLightingCS, kernel, HDShaderIDs._VBufferLightingFeedback,       feedbackRT); // Write
+
+                    m_PreviousResolutionOfHistoryBuffer = currentResolutionOfHistoryBuffer;
                 }
 
                 int w = (int)resolution.x;

com.unity.render-pipelines.high-definition/HDRP/RenderPipeline/HDStringConstants.cs

         public static readonly string s_MeshDecalsAOSStr = "DBufferMesh_AOS";
         public static readonly string s_MeshDecalsMAOSStr = "DBufferMesh_MAOS";
         public static readonly string s_MeshDecals3RTStr = "DBufferMesh_3RT";
-       
+
         // ShaderPass name
         public static readonly ShaderPassName s_EmptyName = new ShaderPassName(s_EmptyStr);
         public static readonly ShaderPassName s_ForwardName = new ShaderPassName(s_ForwardStr);
         public static readonly int _NumTileFtplY = Shader.PropertyToID("_NumTileFtplY");
         public static readonly int _NumTileClusteredX = Shader.PropertyToID("_NumTileClusteredX");
         public static readonly int _NumTileClusteredY = Shader.PropertyToID("_NumTileClusteredY");
-        
+
         public static readonly int _IndirectLightingMultiplier = Shader.PropertyToID("_IndirectLightingMultiplier");
 
         public static readonly int g_isLogBaseBufferEnabled = Shader.PropertyToID("g_isLogBaseBufferEnabled");
         public static readonly int _VBufferLighting                = Shader.PropertyToID("_VBufferLighting");
         public static readonly int _VBufferLightingIntegral        = Shader.PropertyToID("_VBufferLightingIntegral");
         public static readonly int _VBufferLightingHistory         = Shader.PropertyToID("_VBufferLightingHistory");
+        public static readonly int _VBufferLightingHistoryIsValid  = Shader.PropertyToID("_VBufferLightingHistoryIsValid");
         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 _VolumeMaskDimensions           = Shader.PropertyToID("_VolumeMaskDimensions");
-        
+
         public static readonly int _EnableLightLayers                = Shader.PropertyToID("_EnableLightLayers");
 
         // Preintegrated texture name