Split transmission and SSS

- Move IOR field to both transmission and specular
- Split transmission and SSS
- Still need to add the UI in the Lit/layeredLit interface

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/DiffusionProfile/DiffusionProfileSettingsEditor.cs

                             EditorGUILayout.PropertyField(profile.lerpWeight, s_Styles.profileLerpWeight);
                         }
 
+                        EditorGUILayout.Slider(profile.ior, 1.0f, 2.0f, s_Styles.profileIor);
                         EditorGUILayout.PropertyField(profile.worldScale, s_Styles.profileWorldScale);
 
                         EditorGUILayout.Space();
-                        EditorGUILayout.Slider(profile.ior, 1.0f, 2.0f, s_Styles.profileIor);
 
                         EditorGUILayout.Space();
                         EditorGUILayout.LabelField(s_Styles.TransmissionLabel, EditorStyles.boldLabel);

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/LayeredLitData.hlsl

 #ifdef _MATERIAL_FEATURE_SUBSURFACE_SCATTERING
     surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING;
 #endif
-#ifdef _MATERIAL_FEATURE_TRANSMISSION
-    surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_TRANSMISSION;
+#ifdef _MATERIAL_FEATURE_TRANSMISSION
+    // TEMP: The UI must control if we have transmission or not.
+    // Currently until we update the UI, this is control in the diffusion profile
+    uint transmissionMode = BitFieldExtract(asuint(_TransmissionFlags), 2u * surfaceData.diffusionProfile, 2u);
+    // Caution: Because of this dynamic test we don't know anymore statically if we have transmission, which mess with performance.
+    // in deferred case as we still have both sss and transmission until we update the UI it should be the same perf
+    if (transmissionMode != TRANSMISSION_MODE_NONE)
+    {
+        surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_TRANSMISSION;
+    }
 #endif
 
     // Init other parameters

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

 
 // Enum for materialFeatureId (only use for encode/decode GBuffer)
 #define GBUFFER_LIT_STANDARD         0
-#define GBUFFER_LIT_TRANSMISSION     1 // TODO
-#define GBUFFER_LIT_TRANSMISSION_SSS 2
-#define GBUFFER_LIT_ANISOTROPIC      3
-#define GBUFFER_LIT_IRIDESCENCE      4 // TODO
+// we have not enough space (3bit) to store mat feature to have SSS and Transmission as bitmask, such why we have all variant
+#define GBUFFER_LIT_SSS              1
+#define GBUFFER_LIT_TRANSMISSION     2 
+#define GBUFFER_LIT_TRANSMISSION_SSS 3
+#define GBUFFER_LIT_ANISOTROPIC      4
+#define GBUFFER_LIT_IRIDESCENCE      5 // TODO
 
 #define CLEAR_COAT_IOR 1.5
 #define CLEAR_COAT_IETA (1.0 / CLEAR_COAT_IOR) // IETA is the inverse eta which is the ratio of IOR of two interface
     // RT2 - 8:8:8:8
     uint materialFeatureId;
 
-    // TODO: split SSS and transmission.
-        materialFeatureId = GBUFFER_LIT_TRANSMISSION_SSS;
+        // Reminder that during GBuffer pass we know statically material materialFeatures
+        if ((surfaceData.materialFeatures & (MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING | MATERIALFEATUREFLAGS_LIT_TRANSMISSION)) == (MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING | MATERIALFEATUREFLAGS_LIT_TRANSMISSION))
+            materialFeatureId = GBUFFER_LIT_TRANSMISSION_SSS;
+        else if ((surfaceData.materialFeatures & MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING) == MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING)
+            materialFeatureId = GBUFFER_LIT_SSS;
+        else
+            materialFeatureId = GBUFFER_LIT_TRANSMISSION;
+
+        // We perform the same encoding for SSS and transmission even if not used as it is the same cost
+        // Note that regarding EncodeIntoSSSBuffer, as the lit.shader IS the deferred shader (and the SSS fullscreen pass is based on deferred encoding),
+        // it know the details of the encoding, so it is fine to assume here how SSSBuffer0 is encoded
 
         // For the SSS feature, the alpha channel is overwritten with (diffusionProfile | subsurfaceMask).
         // It is done so that the SSS pass only has to read a single G-Buffer 0.
     UnpackFloatUInt8bit(inGBuffer2.a, 8, coatMask, materialFeatureId);
 
     uint pixelFeatureFlags    = MATERIALFEATUREFLAGS_LIT_STANDARD; // Only sky/background do not have the Standard flag.
-    bool pixelHasSubsurface   = materialFeatureId == GBUFFER_LIT_TRANSMISSION_SSS;
-    bool pixelHasTransmission = materialFeatureId == GBUFFER_LIT_TRANSMISSION || pixelHasSubsurface;
+    bool pixelHasSubsurface   = materialFeatureId == GBUFFER_LIT_TRANSMISSION_SSS || materialFeatureId == GBUFFER_LIT_SSS;
+    bool pixelHasTransmission = materialFeatureId == GBUFFER_LIT_TRANSMISSION_SSS || materialFeatureId == GBUFFER_LIT_TRANSMISSION;
     bool pixelHasAnisotropy   = materialFeatureId == GBUFFER_LIT_ANISOTROPIC;
     bool pixelHasIridescence  = materialFeatureId == GBUFFER_LIT_IRIDESCENCE;
     bool pixelHasClearCoat    = coatMask > 0;

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

     surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_SUBSURFACE_SCATTERING;
 #endif
 #ifdef _MATERIAL_FEATURE_TRANSMISSION
-    surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_TRANSMISSION;
+    // TEMP: The UI must control if we have transmission or not.
+    // Currently until we update the UI, this is control in the diffusion profile
+    uint transmissionMode = BitFieldExtract(asuint(_TransmissionFlags), 2u * surfaceData.diffusionProfile, 2u);
+    // Caution: Because of this dynamic test we don't know anymore statically if we have transmission, which mess with performance.
+    // in deferred case as we still have both sss and transmission until we update the UI it should be the same perf
+    if (transmissionMode != TRANSMISSION_MODE_NONE)
+    {
+        surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_TRANSMISSION;
+    }
 #endif
 #ifdef _MATERIAL_FEATURE_ANISOTROPY
     surfaceData.materialFeatures |= MATERIALFEATUREFLAGS_LIT_ANISOTROPY;