Merge pull request #523 from EvgeniiG/Unity-2017.3

Improve the quality of the FDG texture

ScriptableRenderPipeline/Core/ShaderLibrary/ImageBasedLighting.hlsl

 // ----------------------------------------------------------------------------
 
 // Ref: Listing 18 in "Moving Frostbite to PBR" + https://knarkowicz.wordpress.com/2014/12/27/analytical-dfg-term-for-ibl/
-float4 IntegrateGGXAndDisneyFGD(float3 V, float3 N, float roughness, uint sampleCount = 4096)
+float4 IntegrateGGXAndDisneyFGD(float3 V, float3 N, float roughness, uint sampleCount = 8192)
 {
     float NdotV     = saturate(dot(N, V));
     float4 acc      = float4(0.0, 0.0, 0.0, 0.0);
 
         if (NdotL > 0.0)
         {
-            float3 H = normalize(L + V);
-            float LdotH = dot(L, H);
-            float disneyDiffuse = DisneyDiffuseNoPI(NdotV, NdotL, LdotH, RoughnessToPerceptualRoughness(roughness));
+            float LdotV = dot(L, V);
+            float disneyDiffuse = DisneyDiffuseNoPI(NdotV, NdotL, LdotV, RoughnessToPerceptualRoughness(roughness));
+
+    // Remap from [0, 1.5] to [0, 1] range.
+    acc.z /= 1.5;
 
     return acc / sampleCount;
 }

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.cs

             m_InitPreFGD = CoreUtils.CreateEngineMaterial("Hidden/HDRenderPipeline/PreIntegratedFGD");
 
             // For DisneyDiffuse integration values goes from (0.5 to 1.53125). GGX need 0 to 1. Use float format.
-            m_PreIntegratedFGD = new RenderTexture(128, 128, 0, RenderTextureFormat.RGB111110Float, RenderTextureReadWrite.Linear);
+            m_PreIntegratedFGD = new RenderTexture(128, 128, 0, RenderTextureFormat.ARGB2101010, RenderTextureReadWrite.Linear);
             m_PreIntegratedFGD.filterMode = FilterMode.Bilinear;
             m_PreIntegratedFGD.wrapMode = TextureWrapMode.Clamp;
             m_PreIntegratedFGD.hideFlags = HideFlags.DontSave;

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

 #ifdef LIT_DIFFUSE_LAMBERT_BRDF
     diffuseFGD = 1.0;
 #else
-    diffuseFGD = preFGD.z;
+    // Remap from [0, 1] to [0, 1.5] range.
+    diffuseFGD = 1.5 * preFGD.z;
 #endif
 
     reflectivity = preFGD.y;