Port the scattering code

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/Resources/AtmosphericScattering.hlsl

 #endif
 }
 
-inline float4 LinearEyeDepth4(float4 z) { return float4(1.0, 1.0, 1.0, 1.0) / (_ZBufferParams.zzzz * z + _ZBufferParams.wwww); }
-
 float VolundSampleScatterOcclusion(float2 pos) {
 #if defined(ATMOSPHERICS_OCCLUSION)
     float2 uv = UVFromPos(pos);
     baseUV.xy = uv + _DepthTextureScaledTexelSize.xw; xDepth.z = SAMPLE_TEXTURE2D_LOD(_CameraDepthTexture, SRL_BilinearSampler, baseUV);
     baseUV.xy = uv + _DepthTextureScaledTexelSize.zw; xDepth.w = SAMPLE_TEXTURE2D_LOD(_CameraDepthTexture, SRL_BilinearSampler, baseUV);
 
-    xDepth = LinearEyeDepth4(xDepth);
+    xDepth.x = LinearEyeDepth4(xDepth.x);
+    xDepth.y = LinearEyeDepth4(xDepth.y);
+    xDepth.z = LinearEyeDepth4(xDepth.z);
+    xDepth.w = LinearEyeDepth4(xDepth.w);
 
     float4 diffDepth = xDepth - cDepth.rrrr;
     float4 maskDepth = abs(diffDepth) < _OcclusionDepthThreshold;

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/Resources/SkyHDRI.shader

 
             TEXTURECUBE(_Cubemap);
             SAMPLERCUBE(sampler_Cubemap);
-            float4 _SkyParam; // x exposure, y multiplier, z rotation
+
+            float4x4 _InvViewProjMatrix;
+            float4   _SkyParam; // x exposure, y multiplier, z rotation
 
             struct Attributes
             {
                 float3 rotDirY = float3(sinPhi, 0, cosPhi);
                 dir = float3(dot(rotDirX, dir), dir.y, dot(rotDirY, dir));
 
-                return ClampToFloat16Max(SAMPLE_TEXTURECUBE_LOD(_Cubemap, sampler_Cubemap, dir, 0) * exp2(_SkyParam.x) * _SkyParam.y);
+                float3 skyDome = ClampToFloat16Max(SAMPLE_TEXTURECUBE_LOD(_Cubemap, sampler_Cubemap, dir, 0).rgb * exp2(_SkyParam.x) * _SkyParam.y);
+
+                Coordinate coord = GetCoordinate(input.positionCS.xy, _ScreenSize.zw);
+
+                // TODO: what sort of depth and world position values do we compute here?
+                float  rawDepth   = LOAD_TEXTURE2D(_CameraDepthTexture, coord.unPositionSS).r;
+                float3 positionWS = UnprojectToWorld(rawDepth, coord.positionSS, _InvViewProjMatrix);
+
+                float4 c1, c2, c3;
+                VolundTransferScatter(positionWS, c1, c2, c3);
+
+                float4 coord1 = float4(c1.rgb + c3.rgb, max(0.f, 1.f - c1.a - c3.a));
+                float3 coord2 = c2.rgb;
+
+                float sunCos = dot(normalize(dir), _SunDirection);
+                float miePh  = MiePhase(sunCos, _MiePhaseAnisotropy);
+
+                float2 occlusion  = float2(1.0, 1.0); // TODO.
+                float  extinction = coord1.a;
+                float3 scatter    = coord1.rgb * occlusion.x + coord2 * miePh * occlusion.y;
+
+                #ifdef ATMOSPHERICS_DEBUG
+                    switch (_AtmosphericsDebugMode)
+                    {
+                        case ATMOSPHERICS_DBG_RAYLEIGH:           return c1;
+                        case ATMOSPHERICS_DBG_MIE:                return c2 * miePh;
+                        case ATMOSPHERICS_DBG_HEIGHT:             return c3;
+                        case ATMOSPHERICS_DBG_SCATTERING:         return float4(scatter, 1.0);
+                        case ATMOSPHERICS_DBG_OCCLUSION:          return float4(occlusion.xy, 0.0, 1.0);
+                        case ATMOSPHERICS_DBG_OCCLUDEDSCATTERING: return float4(scatter, 1.0);
+                    }
+                #endif
+
+                return float4(skyDome * extinction + scatter, 1.0);
             }
 
             ENDHLSL

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/SkyRenderer.cs

 
             m_RenderSkyPropertyBlock.SetTexture("_Cubemap", skyParameters.skyHDRI);
             m_RenderSkyPropertyBlock.SetVector("_SkyParam", new Vector4(skyParameters.exposure, skyParameters.multiplier, skyParameters.rotation, 0.0f));
+            m_RenderSkyPropertyBlock.SetMatrix("_InvViewProjMatrix", Utilities.GetViewProjectionMatrix(camera).inverse);
 
             var cmd = new CommandBuffer { name = "" };
             cmd.DrawMesh(skyMesh, Matrix4x4.identity, m_SkyHDRIMaterial, 0, 0, m_RenderSkyPropertyBlock);