use transmission tint to disable transmittance instead of adding a multiplier

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/DiffusionProfile/DiffusionProfileSettings.cs

         [NonSerialized] public Vector4[] worldScales;               // X = meters per world unit; Y = world units per meter
         [NonSerialized] public Vector4[] shapeParams;               // RGB = S = 1 / D, A = filter radius
         [NonSerialized] public Vector4[] transmissionTintsAndFresnel0; // RGB = color, A = fresnel0
+        [NonSerialized] public Vector4[] disabledTransmissionTintsAndFresnel0; // RGB = black, A = fresnel0 - For debug to remove the transmission
         [NonSerialized] public Vector4[] filterKernels;             // XY = near field, ZW = far field; 0 = radius, 1 = reciprocal of the PDF
 
         // Old SSS Model >>>
             ValidateArray(ref worldScales,       DiffusionProfileConstants.DIFFUSION_N_PROFILES);
             ValidateArray(ref shapeParams,       DiffusionProfileConstants.DIFFUSION_N_PROFILES);
             ValidateArray(ref transmissionTintsAndFresnel0, DiffusionProfileConstants.DIFFUSION_N_PROFILES);
+            ValidateArray(ref disabledTransmissionTintsAndFresnel0, DiffusionProfileConstants.DIFFUSION_N_PROFILES);
             ValidateArray(ref filterKernels,     DiffusionProfileConstants.DIFFUSION_N_PROFILES * DiffusionProfileConstants.SSS_N_SAMPLES_NEAR_FIELD);
 
             // Old SSS Model >>>
             float fresnel0 = (profiles[p].ior - 1.0f) / (profiles[p].ior + 1.0f);
             fresnel0 *= fresnel0; // square
             transmissionTintsAndFresnel0[i] = new Vector4(profiles[p].transmissionTint.r * 0.25f, profiles[p].transmissionTint.g * 0.25f, profiles[p].transmissionTint.b * 0.25f, fresnel0); // Premultiplied
+            disabledTransmissionTintsAndFresnel0[i] = new Vector4(0.0f, 0.0f, 0.0f, fresnel0);
 
             for (int j = 0, n = DiffusionProfileConstants.SSS_N_SAMPLES_NEAR_FIELD; j < n; j++)
             {

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.hlsl

     bsdfData.useThickObjectMode = transmissionMode != TRANSMISSION_MODE_THIN;
 
 #if SHADEROPTIONS_USE_DISNEY_SSS
-    bsdfData.transmittance = _TransmittanceMultiplier * ComputeTransmittanceDisney( _ShapeParams[diffusionProfile].rgb,
-                                                                                    _TransmissionTintsAndFresnel0[diffusionProfile].rgb,
-                                                                                    bsdfData.thickness, 1.0);
+    bsdfData.transmittance = ComputeTransmittanceDisney(    _ShapeParams[diffusionProfile].rgb,
+                                                            _TransmissionTintsAndFresnel0[diffusionProfile].rgb,
+                                                            bsdfData.thickness, 1.0);
-    bsdfData.transmittance = _TransmittanceMultiplier * ComputeTransmittanceJimenez( _HalfRcpVariancesAndWeights[diffusionProfile][0].rgb,
-                                                                                        _HalfRcpVariancesAndWeights[diffusionProfile][0].a,
-                                                                                        _HalfRcpVariancesAndWeights[diffusionProfile][1].rgb,
-                                                                                        _HalfRcpVariancesAndWeights[diffusionProfile][1].a,
-                                                                                        _TransmissionTintsAndFresnel0[diffusionProfile].rgb,
-                                                                                        bsdfData.thickness, 1.0);
+    bsdfData.transmittance = ComputeTransmittanceJimenez(   _HalfRcpVariancesAndWeights[diffusionProfile][0].rgb,
+                                                            _HalfRcpVariancesAndWeights[diffusionProfile][0].a,
+                                                            _HalfRcpVariancesAndWeights[diffusionProfile][1].rgb,
+                                                            _HalfRcpVariancesAndWeights[diffusionProfile][1].a,
+                                                            _TransmissionTintsAndFresnel0[diffusionProfile].rgb,
+                                                            bsdfData.thickness, 1.0);
 #endif
 }
 
         bsdfData.enableAnisotropy = true;
     }
 
-    if (bsdfData.enableAnisotropy)
+    if (bsdfData.enableIridescence)
     {
         FillMaterialIridescence(inGBuffer2.g, bsdfData);
     }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/LitData.hlsl

         // however it will not optimize the lightprobe case due to the proxy volume relying on dynamic if (we rely must get right of this dynamic if), not a problem for SH9, but a problem for proxy volume.
         // TODO: optimize more this code.
         // Add GI transmission contribution by resampling the GI for inverted vertex normal
-        builtinData.bakeDiffuseLighting += SampleBakedGI(input.positionWS, -input.worldToTangent[2], input.texCoord1, input.texCoord2) * bsdfData.transmittance * _TransmittanceMultiplier;
+        builtinData.bakeDiffuseLighting += SampleBakedGI(input.positionWS, -input.worldToTangent[2], input.texCoord1, input.texCoord2) * bsdfData.transmittance;
     }
 
 #ifdef SHADOWS_SHADOWMASK

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScattering.hlsl

 // Warning: Unity is not able to losslessly transfer integers larger than 2^24 to the shader system.
 // Therefore, we bitcast uint to float in C#, and bitcast back to uint in the shader.
 uint   _EnableSubsurfaceScattering; // Globally toggles subsurface and transmission scattering on/off
-float  _TransmittanceMultiplier;    // Allow to switch on/off the transmittance but doesn't save the cost
 float  _TexturingModeFlags;       // 1 bit/profile; 0 = PreAndPostScatter, 1 = PostScatter
 float  _TransmissionFlags;        // 2 bit/profile; 0 = inf. thick, 1 = thin, 2 = regular
 // Old SSS Model >>>

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/SubsurfaceScattering/SubsurfaceScatteringManager.cs

         {
             // Broadcast SSS parameters to all shaders.
             cmd.SetGlobalInt(HDShaderIDs._EnableSubsurfaceScattering, frameSettings.enableSubsurfaceScattering ? 1 : 0);
-            cmd.SetGlobalFloat(HDShaderIDs._TransmittanceMultiplier, frameSettings.enableTransmission ? 1.0f : 0.0f);
             unsafe
             {
                 // Warning: Unity is not able to losslessly transfer integers larger than 2^24 to the shader system.
             cmd.SetGlobalVectorArray(HDShaderIDs._ThicknessRemaps, sssParameters.thicknessRemaps);
             cmd.SetGlobalVectorArray(HDShaderIDs._ShapeParams, sssParameters.shapeParams);
             cmd.SetGlobalVectorArray(HDShaderIDs._HalfRcpVariancesAndWeights, sssParameters.halfRcpVariancesAndWeights);
-            cmd.SetGlobalVectorArray(HDShaderIDs._TransmissionTintsAndFresnel0, sssParameters.transmissionTintsAndFresnel0);
+            // To disable transmission, we simply nullify the transmissionTint
+            cmd.SetGlobalVectorArray(HDShaderIDs._TransmissionTintsAndFresnel0, frameSettings.enableTransmission ? sssParameters.transmissionTintsAndFresnel0 : sssParameters.disabledTransmissionTintsAndFresnel0);
             cmd.SetGlobalVectorArray(HDShaderIDs._WorldScales, sssParameters.worldScales);
         }