Add a subsurface scattering manager to allocate RT

ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipeline.cs

-using System.Collections.Generic;
+using System.Collections.Generic;
 using UnityEngine.Rendering;
 using System;
 using System.Diagnostics;
         readonly List<RenderPipelineMaterial> m_MaterialList = new List<RenderPipelineMaterial>();
 
         readonly GBufferManager m_GbufferManager = new GBufferManager();
+        readonly SubsurfaceScatteringManager m_SSSBufferManager = new SubsurfaceScatteringManager();
 
         // Renderer Bake configuration can vary depends on if shadow mask is enabled or no
         RendererConfiguration m_currentRendererConfigurationBakedLighting = HDUtils.k_RendererConfigurationBakedLighting;
 
                     cmd.SetComputeVectorArrayParam(m_SubsurfaceScatteringCS, HDShaderIDs._WorldScales,        sssParameters.worldScales);
                     cmd.SetComputeVectorArrayParam(m_SubsurfaceScatteringCS, HDShaderIDs._FilterKernels,      sssParameters.filterKernels);
-                    cmd.SetComputeVectorArrayParam(m_SubsurfaceScatteringCS, HDShaderIDs._ShapeParams,        sssParameters.shapeParams);
-
-                    // TODO: abstract this in SSS manager
-                    cmd.SetComputeTextureParam(m_SubsurfaceScatteringCS, m_SubsurfaceScatteringKernel, HDShaderIDs._SSSBufferTexture0,  m_GbufferManager.GetGBuffers()[0]);
-
+                    cmd.SetComputeVectorArrayParam(m_SubsurfaceScatteringCS, HDShaderIDs._ShapeParams,        sssParameters.shapeParams);                        
+
+                    for (int i = 0; i < m_SSSBufferManager.sssBufferCount; ++i)
+                    {
+                        cmd.SetComputeTextureParam(m_SubsurfaceScatteringCS, m_SubsurfaceScatteringKernel, HDShaderIDs._SSSBufferTexture[i], m_SSSBufferManager.GetSSSBuffers(i));
+                    }
 
                     if (NeedTemporarySubsurfaceBuffer())
                     {
                 }
                 else
                 {
-                    // TODO: abstract this in SSS manager
-                    cmd.SetGlobalTexture(HDShaderIDs._SSSBufferTexture0, m_GbufferManager.GetGBuffers()[0]);
+                    for (int i = 0; i < m_SSSBufferManager.sssBufferCount; ++i)
+                    {
+                        cmd.SetGlobalTexture(HDShaderIDs._SSSBufferTexture[i], m_SSSBufferManager.GetSSSBuffers(i));
+                    }
 
                     cmd.SetGlobalTexture(HDShaderIDs._IrradianceSource, m_CameraSssDiffuseLightingBufferRT);  // Cannot set a RT on a material
                     m_SssVerticalFilterPass.SetVectorArray(HDShaderIDs._WorldScales,              sssParameters.worldScales);
                     cmd.GetTemporaryRT(m_DepthPyramidBuffer, m_DepthPyramidBufferDesc, FilterMode.Trilinear);
                     // End
 
-                    // TODO: commented just to test forward SSS until we implement correct manager.
-                    // In forward we need to allocate a target for SSSBuffer0
-                    //if (!m_Asset.globalRenderingSettings.ShouldUseForwardRenderingOnly())
+                    if (!m_Asset.globalRenderingSettings.ShouldUseForwardRenderingOnly())
+                    {
+                        m_SSSBufferManager.InitGBuffers(w, h, m_GbufferManager, cmd);
+                    }
+                    else
+                    {
+                        // We need to allocate target for SSS
+                        m_SSSBufferManager.InitGBuffers(w, h, cmd);
+                    }
 
                     CoreUtils.SetRenderTarget(cmd, m_CameraColorBufferRT, m_CameraDepthStencilBufferRT, ClearFlag.Depth);
                 }

ScriptableRenderPipeline/HDRenderPipeline/HDStringConstants.cs

         public static readonly int g_BaseFeatureFlags = Shader.PropertyToID("g_BaseFeatureFlags");
         public static readonly int g_TileFeatureFlags = Shader.PropertyToID("g_TileFeatureFlags");
 
-        public static readonly int _GBufferTexture0 = Shader.PropertyToID("_GBufferTexture0");
-        public static readonly int _GBufferTexture1 = Shader.PropertyToID("_GBufferTexture1");
-        public static readonly int _GBufferTexture2 = Shader.PropertyToID("_GBufferTexture2");
-        public static readonly int _GBufferTexture3 = Shader.PropertyToID("_GBufferTexture3");
-        public static readonly int _GBufferTexture4 = Shader.PropertyToID("_GBufferTexture4");
-        public static readonly int _GBufferTexture5 = Shader.PropertyToID("_GBufferTexture5");
-        public static readonly int _GBufferTexture6 = Shader.PropertyToID("_GBufferTexture6");
-        public static readonly int _GBufferTexture7 = Shader.PropertyToID("_GBufferTexture7");
-
-        public static readonly int _SSSBufferTexture0 = Shader.PropertyToID("_SSSBufferTexture0");
-        public static readonly int _SSSBufferTexture1 = Shader.PropertyToID("_SSSBufferTexture1");
-        public static readonly int _SSSBufferTexture2 = Shader.PropertyToID("_SSSBufferTexture2");
-        public static readonly int _SSSBufferTexture3 = Shader.PropertyToID("_SSSBufferTexture3");
-
         public static readonly int g_DispatchIndirectBuffer = Shader.PropertyToID("g_DispatchIndirectBuffer");
         public static readonly int g_TileList = Shader.PropertyToID("g_TileList");
         public static readonly int g_NumTiles = Shader.PropertyToID("g_NumTiles");
             Shader.PropertyToID("_GBufferTexture5"),
             Shader.PropertyToID("_GBufferTexture6"),
             Shader.PropertyToID("_GBufferTexture7")
+        };
+
+        public static readonly int[] _SSSBufferTexture =
+        {
+            Shader.PropertyToID("_SSSBufferTexture0"),
+            Shader.PropertyToID("_SSSBufferTexture1"),
+            Shader.PropertyToID("_SSSBufferTexture2"),
+            Shader.PropertyToID("_SSSBufferTexture3"),
         };
 
         public static readonly int _VelocityTexture = Shader.PropertyToID("_VelocityTexture");

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

 fileFormatVersion: 2
-guid: 26e79cea58f13e241ba3ecee1a281ebc
+guid: 3cc1ef76b6eee1248b23ec5f6dee0bae
 MonoImporter:
   externalObjects: {}
   serializedVersion: 2

ScriptableRenderPipeline/HDRenderPipeline/Material/SubsurfaceScattering/SubsurfaceScatteringManager.cs

+using UnityEngine.Rendering;
+using System;
+
+namespace UnityEngine.Experimental.Rendering.HDPipeline
+{
+    public class SubsurfaceScatteringManager
+    {
+        // Currently we only support SSSBuffer with one buffer. If the shader code change, it may require to update the shader manager
+        public const int k_MaxSSSBuffer = 1;
+
+        readonly int m_SSSBuffer0;
+        readonly RenderTargetIdentifier m_SSSBuffer0RT;
+
+        public int sssBufferCount { get; set; }
+
+        RenderTargetIdentifier[] m_ColorMRTs;
+        RenderTargetIdentifier[] m_RTIDs = new RenderTargetIdentifier[k_MaxSSSBuffer];
+
+        public SubsurfaceScatteringManager()
+        {
+            m_SSSBuffer0RT = new RenderTargetIdentifier(m_SSSBuffer0);
+        }
+
+        // In case of deferred, we must be in sync with SubsurfaceScattering.hlsl and lit.hlsl files and setup the correct buffers
+        // for SSS
+        public void InitGBuffers(int width, int height, GBufferManager gbufferManager, CommandBuffer cmd)
+        {
+            sssBufferCount = k_MaxSSSBuffer;
+
+            m_RTIDs[0] = gbufferManager.GetGBuffers()[0];
+        }
+
+        // In case of full forward we must allocate the render target for forward SSS (or reuse one already existing)
+        // TODO: Provide a way to reuse a render target
+        public void InitGBuffers(int width, int height, CommandBuffer cmd)
+        {
+            sssBufferCount = k_MaxSSSBuffer;
+     
+            m_RTIDs[0] = m_SSSBuffer0RT;
+
+            cmd.ReleaseTemporaryRT(m_SSSBuffer0);
+            cmd.GetTemporaryRT(m_SSSBuffer0, width, height, 0, FilterMode.Point, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Linear);            
+        }
+
+        public RenderTargetIdentifier GetSSSBuffers(int index)
+        {
+            Debug.Assert(index < sssBufferCount);
+            return m_RTIDs[index];
+        }
+    }
+}

ScriptableRenderPipeline/HDRenderPipeline/Material/SubsurfaceScattering/SubsurfaceScattering.cs

-using UnityEngine.Rendering;
-using System;
-
-namespace UnityEngine.Experimental.Rendering.HDPipeline
-{
-    public class SubsurfaceScatteringManager
-    {
-        public const int k_MaxGbuffer = 2;
-
-        public int sssbufferCount { get; set; }
-
-        RenderTargetIdentifier[] m_ColorMRTs;
-        RenderTargetIdentifier[] m_RTIDs = new RenderTargetIdentifier[k_MaxGbuffer];
-
-
-       // public RenderTargetIdentifier SSSBuffer[2];
-
-       // public SetSSSBuffer();
-    }
-}