Make SampleInScatteredRadianceAndTransmittance() return transmittance

ScriptableRenderPipeline/HDRenderPipeline/HDRP/HDRenderPipeline.cs

 
             int viewId = hdCamera.camera.GetInstanceID(); // Warning: different views can use the same camera
 
-            // Warning: (resolutionChanged == false) is you open a new Editor tab of the same size!
+            // Warning: (resolutionChanged == false) if you open a new Editor tab of the same size!
             if (m_VolumetricLightingPreset != VolumetricLightingPreset.Off)
                 ResizeVBuffer(viewId, texWidth, texHeight);
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/LightLoop/LightLoop.cs

                     // Set up clustered lighting for volumetrics.
                     cmd.SetGlobalBuffer(HDShaderIDs.g_vLightListGlobal, s_PerVoxelLightLists);
                 }
-
             }
         }
 

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Lighting/VBuffer.hlsl

     }
 }
 
-// Returns interpolated {volumetric radiance, opacity}. The sampler clamps to edge.
+// Returns interpolated {volumetric radiance, transmittance}. The sampler clamps to edge.
 float4 SampleInScatteredRadianceAndTransmittance(TEXTURE3D_ARGS(VBufferLighting, trilinearSampler),
                                                  float2 positionNDC, float linearDepth,
                                                  float4 VBufferResolution,
 #endif
 
     // TODO: add some animated noise to the reconstructed radiance.
-    return float4(L.rgb, 1 - Transmittance(L.a));
+    return float4(L.rgb, Transmittance(L.a));
 }
 
 #endif // UNITY_VBUFFER_INCLUDED

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

 // Returns fog color in rgb and fog factor in alpha.
 float4 EvaluateAtmosphericScattering(PositionInputs posInput)
 {
+    float3 fogColor  = 0;
+    float  fogFactor = 0;
+
-    return SampleInScatteredRadianceAndTransmittance(TEXTURE3D_PARAM(_VBufferLighting, s_trilinear_clamp_sampler),
-                                                     posInput.positionNDC, posInput.linearDepth,
-                                                     _VBufferResolution, _VBufferScaleAndSliceCount,
-                                                     _VBufferDepthEncodingParams);
-#endif
+    float4 volFog = SampleInScatteredRadianceAndTransmittance(TEXTURE3D_PARAM(_VBufferLighting, s_trilinear_clamp_sampler),
+                                                              posInput.positionNDC, posInput.linearDepth,
+                                                              _VBufferResolution, _VBufferScaleAndSliceCount,
+                                                              _VBufferDepthEncodingParams);
+    fogColor  = volFog.rgb;
+    fogFactor = 1 - volFog.a;
-    float3 fogColor; float fogFactor;
+#else
 
     if (_AtmosphericScatteringType == FOGTYPE_EXPONENTIAL)
     {
     }
     else // NONE
     {
-        return float4(0.0, 0.0, 0.0, 0.0);
+#endif
 
     return float4(fogColor, fogFactor);
 }