Fixed the bad blending between the sun and the clouds (case 1373282).

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

@@ -50,6 +50,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Fixed geometry scale issue with the Eye Shader.
 - Fixed motion vector buffer not accessible from custom passes in the BeforeTransparent, BeforePreRefraction and AfterDepthAndNormal injection points.
 - Fixed the point distribution for the diffuse denoiser sometimes not being properly intialized.
+- Fixed the bad blending between the sun and the clouds (case 1373282).
 
 ### Changed
 - Use RayTracingAccelerationStructure.CullInstances to filter Renderers and populate the acceleration structure with ray tracing instances for improved CPU performance on the main thread.

com.unity.render-pipelines.high-definition/Documentation~/Override-Volumetric-Clouds.md

@@ -157,3 +157,4 @@ When importing these two map Textures, disable **sRGB**. For best results, do no
 * When enabled for [Reflection Probes](Reflection-Probe.md), the volumetric clouds are rendered at low resolution, without any form of temporal accumulation for performance and stability reasons.
 * By default volumetric clouds are enabled on the baked [Reflection Probes](Reflection-Probe.md) if the asset allows it. They are rendered at full resolution without any form of temporal accumulation.
 * Volumetric clouds do not appear in ray-traced effects.
+* Transmittance is not applied linearly on the camera color to provide a better blending with the sun light (or high intensity pixels). If [Multi-sample anti-aliasing (MSAA)](#MSAA) is enabled on the camera, due to internal limitations, a different blending profile is used that may result in darker cloud edges.

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/HDRenderPipeline.VolumetricClouds.cs

@@ -455,7 +455,7 @@ void UpdateShaderVariableslClouds(ref ShaderVariablesClouds cb, HDCamera hdCamer
 
             // If this is a planar reflection, we need to compute the non oblique matrices
             cb._IsPlanarReflection = (cameraData.cameraType == TVolumetricCloudsCameraType.PlanarReflection) ? 1 : 0;
-            if (cameraData.cameraType == TVolumetricCloudsCameraType.PlanarReflection)
+            if (cb._IsPlanarReflection == 1)
             {
                 // Build a non-oblique projection matrix
                 var projectionMatrixNonOblique = Matrix4x4.Perspective(hdCamera.camera.fieldOfView, hdCamera.camera.aspect, hdCamera.camera.nearClipPlane, hdCamera.camera.farClipPlane);

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/HDRenderPipeline.VolumetricCloudsAccumulation.cs

@@ -162,6 +162,10 @@ VolumetricCloudsParameters_Accumulation PrepareVolumetricCloudsParameters_Accumu
             cameraData.enableIntegration = true;
             UpdateShaderVariableslClouds(ref parameters.commonData.cloudsCB, hdCamera, settings, cameraData, cloudModelData, false);
 
+            // If this is a default camera, we want the improved blending, otherwise we don't (in the case of a planar)
+            parameters.commonData.cloudsCB._ImprovedTransmittanceBlend = parameters.commonData.cameraType == TVolumetricCloudsCameraType.Default ? 1 : 0;
+            parameters.commonData.cloudsCB._CubicTransmittance = parameters.commonData.cameraType == TVolumetricCloudsCameraType.Default && hdCamera.msaaEnabled ? 1 : 0;
+
             return parameters;
         }
 
@@ -198,8 +202,8 @@ static void TraceVolumetricClouds_Accumulation(CommandBuffer cmd, VolumetricClou
             parameters.commonData.cloudsCB._HistoryViewportSize = new Vector2(previousViewportSize.x, previousViewportSize.y);
             parameters.commonData.cloudsCB._HistoryBufferSize = new Vector2(previousHistory0Buffer.rt.width, previousHistory0Buffer.rt.height);
 
-            // Bind the constant buffer
-            ConstantBuffer.Push(cmd, parameters.commonData.cloudsCB, parameters.commonData.volumetricCloudsCS, HDShaderIDs._ShaderVariablesClouds);
+            // Bind the constant buffer (global as we need it for the .shader as well)
+            ConstantBuffer.PushGlobal(cmd, parameters.commonData.cloudsCB, HDShaderIDs._ShaderVariablesClouds);
 
             RTHandle currentDepthBuffer = depthPyramid;
 
@@ -293,7 +297,7 @@ static void TraceVolumetricClouds_Accumulation(CommandBuffer cmd, VolumetricClou
                     parameters.cloudCombinePass.SetTexture(HDShaderIDs._VolumetricCloudsUpscaleTextureRW, intermediateUpscaleBuffer);
 
                     // Composite the clouds into the MSAA target via hardware blending.
-                    HDUtils.DrawFullScreen(cmd, parameters.cloudCombinePass, colorBuffer);
+                    HDUtils.DrawFullScreen(cmd, parameters.cloudCombinePass, colorBuffer, null, 0);
 
                     CoreUtils.SetKeyword(cmd, "USE_INTERMEDIATE_BUFFER", false);
                 }

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/VolumetricClouds.compute

@@ -1401,13 +1401,13 @@ void UPSAMPLE_KERNEL(uint3 finalCoord : SV_DispatchThreadID,
     cloudPosInput.positionWS = -viewDir * cloudDistance;
 #endif
 
+#ifdef USE_INTERMEDIATE_BUFFER
     // Compute the fog attenuation of the clouds
     float3 fogColor;
     float3 fogOpacity;
     EvaluateAtmosphericScattering(cloudPosInput, viewDir, fogColor, fogOpacity);
-    currentClouds.xyz = currentClouds.xyz * (1 - fogOpacity) + fogColor * (1.0 - currentClouds.a);
+    currentClouds.xyz = currentClouds.xyz * (1 - fogOpacity) + fogColor * (1.0 - (_CubicTransmittance ? currentClouds.a * currentClouds.a : currentClouds.a));
 
-#ifdef USE_INTERMEDIATE_BUFFER
     // Store the upscaled result only, composite in later pass.
     _VolumetricCloudsUpscaleTextureRW[COORD_TEXTURE2D_X(finalCoord.xy)] = currentClouds;
 #else
@@ -1417,8 +1417,18 @@ void UPSAMPLE_KERNEL(uint3 finalCoord : SV_DispatchThreadID,
 #else
     float4 currentColor = _CameraColorTexture[COORD_TEXTURE2D_X(finalCoord.xy)];
 #endif
-    // If this is a background pixel, we want the cloud value, otherwise we do not.
-    _VolumetricCloudsUpscaleTextureRW[COORD_TEXTURE2D_X(finalCoord.xy)] = float4(currentColor.xyz * currentClouds.a + currentClouds.xyz, currentColor.a);
+
+    // Estimate the transmittance that shall be used
+    float finalTransmittance = EvaluateFinalTransmittance(currentColor, currentClouds.w);
+
+    // Compute the fog attenuation of the clouds
+    float3 fogColor;
+    float3 fogOpacity;
+    EvaluateAtmosphericScattering(cloudPosInput, viewDir, fogColor, fogOpacity);
+    currentClouds.xyz = currentClouds.xyz * (1 - fogOpacity) + fogColor * (1.0 - finalTransmittance);
+
+    // Apply the transmittance
+    _VolumetricCloudsUpscaleTextureRW[COORD_TEXTURE2D_X(finalCoord.xy)] = float4(currentColor.xyz * finalTransmittance + currentClouds.xyz, currentColor.a);
 #endif
 }
 

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/VolumetricCloudsCombine.shader

@@ -62,7 +62,9 @@ Shader "Hidden/HDRP/VolumetricCloudsCombine"
                 UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(input);
 
                 // Composite the result via hardware blending.
-                return LOAD_TEXTURE2D_X(_VolumetricCloudsUpscaleTextureRW, input.positionCS.xy);
+                // If MSAA is enabled on the camera, due to internal limitations, a different blending profile is used that may result in darker cloud edges.
+                float4 cloudData = LOAD_TEXTURE2D_X(_VolumetricCloudsUpscaleTextureRW, input.positionCS.xy);
+                return float4(cloudData.xyz, _CubicTransmittance ? cloudData.w * cloudData.w : cloudData.w);
             }
             ENDHLSL
         }

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

@@ -151,9 +151,11 @@ unsafe struct ShaderVariablesClouds
 
         // Flag that allows us to know if the maxZMask texture is valid
         public int _ValidMaxZMask;
-        // Padding
-        public int _Padding0;
-        public Vector2 _Padding1;
+        // Flag that allows to know if we should be using the improved transmittance blending
+        public int _ImprovedTransmittanceBlend;
+        // Flag that defines if the transmittance should follow a cubic profile (For MSAA)
+        public int _CubicTransmittance;
+        public int _Padding1;
 
         [HLSLArray(3 * 4, typeof(Vector4))]
         public fixed float _DistanceBasedWeights[12 * 4];

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/VolumetricCloudsDef.cs.hlsl

@@ -71,8 +71,9 @@ CBUFFER_START(ShaderVariablesClouds)
     int _EnableFastToneMapping;
     int _IsPlanarReflection;
     int _ValidMaxZMask;
-    int _Padding0;
-    float2 _Padding1;
+    int _ImprovedTransmittanceBlend;
+    int _CubicTransmittance;
+    int _Padding1;
     float4 _DistanceBasedWeights[12];
 CBUFFER_END
 

com.unity.render-pipelines.high-definition/Runtime/Lighting/VolumetricLighting/VolumetricCloudsUtilities.hlsl

@@ -499,6 +499,13 @@ void FillCloudUpscaleNeighborhoodData(int2 groupThreadId, int subRegionIdx, out
     neighborhoodData.lowWeightC = _DistanceBasedWeights[subRegionIdx * 3 + 2].x;
 }
 
+float EvaluateFinalTransmittance(float3 color, float transmittance)
+{
+    // Due to the high intensity of the sun, we often need apply the transmittance in a tonemapped space
+    float3 resultColor = color / (1.0 + color) * transmittance;
+    resultColor = resultColor / (1.0 - resultColor);
+    return _ImprovedTransmittanceBlend ? (resultColor / color) : transmittance;
+}
 #endif // REAL_TIME_VOLUMETRIC_CLOUDS
 
 #endif // VOLUMETRIC_CLOUD_UTILITIES_H