Add support for AOColor

- This need few test to found the correct formula compare to
GTAOMultiBounce

ScriptableRenderPipeline/HDRenderPipeline/HDRenderPipeline.cs

                                 enableRandomWrite = true
                             }, FilterMode.Bilinear);
                             postProcessLayer.BakeMSVOMap(cmd, camera, HDShaderIDs._AmbientOcclusionTexture, GetDepthTexture(), true);
-                            cmd.SetGlobalFloat(HDShaderIDs._AmbientOcclusionDirectLightStrenght, settings.directLightingStrength.value);
+                            cmd.SetGlobalVector(HDShaderIDs._AmbientOcclusionParam, new Vector4(settings.color.value.r, settings.color.value.g, settings.color.value.b, settings.directLightingStrength.value));
-
-                            // AO color is available at:
-                            //  settings.color.value
-                            cmd.SetGlobalFloat(HDShaderIDs._AmbientOcclusionDirectLightStrenght, 0.0f);
+                            cmd.SetGlobalVector(HDShaderIDs._AmbientOcclusionParam, Vector4.zero);
                         }
                     }
 

ScriptableRenderPipeline/HDRenderPipeline/HDStringConstants.cs

         public static readonly int _CosTime = Shader.PropertyToID("_CosTime");
         public static readonly int unity_DeltaTime = Shader.PropertyToID("unity_DeltaTime");
         public static readonly int _EnvLightSkyEnabled = Shader.PropertyToID("_EnvLightSkyEnabled");
-        public static readonly int _AmbientOcclusionDirectLightStrenght = Shader.PropertyToID("_AmbientOcclusionDirectLightStrenght");
+        public static readonly int _AmbientOcclusionParam = Shader.PropertyToID("_AmbientOcclusionParam");
         public static readonly int _SkyTexture = Shader.PropertyToID("_SkyTexture");
 
         public static readonly int _UseDisneySSS = Shader.PropertyToID("_UseDisneySSS");

ScriptableRenderPipeline/HDRenderPipeline/Lighting/TilePass/TilePass.cs

                             Vector4 cosTime = Shader.GetGlobalVector(HDShaderIDs._CosTime);
                             Vector4 unity_DeltaTime = Shader.GetGlobalVector(HDShaderIDs.unity_DeltaTime);
                             int envLightSkyEnabled = Shader.GetGlobalInt(HDShaderIDs._EnvLightSkyEnabled);
-                            float ambientOcclusionDirectLightStrenght = Shader.GetGlobalFloat(HDShaderIDs._AmbientOcclusionDirectLightStrenght);
+                            Vector4 ambientOcclusionParam = Shader.GetGlobalVector(HDShaderIDs._AmbientOcclusionParam);
 
                             int enableSSSAndTransmission = Shader.GetGlobalInt(HDShaderIDs._EnableSSSAndTransmission);
                             int texturingModeFlags = Shader.GetGlobalInt(HDShaderIDs._TexturingModeFlags);
                                 cmd.SetComputeVectorParam(deferredComputeShader, HDShaderIDs._CosTime, cosTime);
                                 cmd.SetComputeVectorParam(deferredComputeShader, HDShaderIDs.unity_DeltaTime, unity_DeltaTime);
                                 cmd.SetComputeIntParam(deferredComputeShader, HDShaderIDs._EnvLightSkyEnabled, envLightSkyEnabled);
-                                cmd.SetComputeFloatParam(deferredComputeShader, HDShaderIDs._AmbientOcclusionDirectLightStrenght, ambientOcclusionDirectLightStrenght);
+                                cmd.SetComputeVectorParam(deferredComputeShader, HDShaderIDs._AmbientOcclusionParam, ambientOcclusionParam);
 
                                 cmd.SetComputeTextureParam(deferredComputeShader, kernel, HDShaderIDs._SkyTexture, skyTexture ? skyTexture : m_DefaultTexture2DArray);
 

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

 
 // Ambient occlusion texture
 TEXTURE2D(_AmbientOcclusionTexture);
-float _AmbientOcclusionDirectLightStrenght;
+float4 _AmbientOcclusionParam; // xyz occlusion color, w directLightStrenght
 
 // Area light textures
 // TODO: This one should be set into a constant Buffer at pass frequency (with _Screensize)
     // Ambient occlusion use for indirect lighting (reflection probe, baked diffuse lighting)
     float indirectAmbientOcclusion = 1.0 - LOAD_TEXTURE2D(_AmbientOcclusionTexture, posInput.unPositionSS).x;
     // Ambient occlusion use for direct lighting (directional, punctual, area)
-    float directAmbientOcclusion = lerp(1.0, indirectAmbientOcclusion, _AmbientOcclusionDirectLightStrenght);
+    float directAmbientOcclusion = lerp(1.0, indirectAmbientOcclusion, _AmbientOcclusionParam.w);
-    bakeDiffuseLighting *= indirectAmbientOcclusion;
+    bakeDiffuseLighting *= lerp(_AmbientOcclusionParam.rgb, float3(1.0, 1.0, 1.0), indirectAmbientOcclusion);
 #endif
 
     float specularOcclusion = GetSpecularOcclusionFromAmbientOcclusion(preLightData.NdotV, indirectAmbientOcclusion, bsdfData.roughness);
     accLighting.envSpecularLighting *= GTAOMultiBounce(min(bsdfData.specularOcclusion, specularOcclusion), bsdfData.fresnel0);
 #else
-    accLighting.envSpecularLighting *= min(bsdfData.specularOcclusion, specularOcclusion);
+    accLighting.envSpecularLighting *= lerp(_AmbientOcclusionParam.rgb, float3(1.0, 1.0, 1.0), min(bsdfData.specularOcclusion, specularOcclusion));
-    float3 directDiffuseLighting = (accLighting.dirDiffuseLighting + accLighting.punctualDiffuseLighting + accLighting.areaDiffuseLighting) * GTAOMultiBounce(directAmbientOcclusion, bsdfData.diffuseColor);
+    float3 directDiffuseLighting = (accLighting.dirDiffuseLighting + accLighting.punctualDiffuseLighting + accLighting.areaDiffuseLighting)
+#if GTAO_MULTIBOUNCE_APPROX
+                                    * GTAOMultiBounce(directAmbientOcclusion, bsdfData.diffuseColor);
+#else
+                                    * lerp(_AmbientOcclusionParam.rgb, float3(1.0, 1.0, 1.0), directAmbientOcclusion);
+#endif
     // envDiffuseLighting is used for refraction in this Lit material. Use the weight to balance between transmission and reflection
     diffuseLighting = lerp(directDiffuseLighting + bakeDiffuseLighting, accLighting.envDiffuseLighting, accLighting.envDiffuseLightingWeight);
     specularLighting = accLighting.dirSpecularLighting + accLighting.punctualSpecularLighting + accLighting.areaSpecularLighting + accLighting.envSpecularLighting;