Merge pull request #78 from EvgeniiG/master

PBS Fixes and Improvements

Assets/ScriptableRenderLoop/HDRenderPipeline/Lighting/TilePass/TilePass.hlsl

 // EnvIndex can also be use to fetch in another array of struct (to  atlas information etc...).
 float4 SampleEnv(LightLoopContext lightLoopContext, int index, float3 texCoord, float lod)
 {
-    lod = min(lod, UNITY_SPECCUBE_LOD_STEPS);
-
     // This code will be inlined as lightLoopContext is hardcoded in the light loop
     if (lightLoopContext.sampleReflection == SINGLE_PASS_CONTEXT_SAMPLE_REFLECTION_PROBES)
     {

Assets/ScriptableRenderLoop/HDRenderPipeline/Material/Lit/Lit.cs

             public void Build()
             {
                 m_InitPreFGD = CreateEngineMaterial("Hidden/HDRenderPipeline/PreIntegratedFGD");
+                // TODO: switch to RGBA64 when it becomes available.
                 m_PreIntegratedFGD = new RenderTexture(128, 128, 0, RenderTextureFormat.ARGBHalf);
 
                 m_LtcGGXMatrix                    = LoadLUT(TextureFormat.RGBAHalf, s_LtcGGXMatrixData);

Assets/ScriptableRenderLoop/HDRenderPipeline/Material/Lit/Lit.hlsl

     // Maybe always using aniso maybe a win ?
     if (bsdfData.materialId == MATERIALID_LIT_ANISO)
     {
-        float TdotL = saturate(dot(bsdfData.tangentWS, L));
-        float BdotL = saturate(dot(bsdfData.bitangentWS, L));
+        // For anisotropy we must not saturate these values
+        float TdotH = dot(bsdfData.tangentWS, H);
+        float TdotL = dot(bsdfData.tangentWS, L);
+        float BdotH = dot(bsdfData.bitangentWS, H);
+        float BdotL = dot(bsdfData.bitangentWS, L);
 
         #ifdef LIT_USE_BSDF_PRE_LAMBDAV
         Vis = V_SmithJointGGXAnisoLambdaV(  preLightData.TdotV, preLightData.BdotV, preLightData.NdotV, TdotL, BdotL, NdotL,
                                     bsdfData.roughnessT, bsdfData.roughnessB);
         #endif
 
-        // For anisotropy we must not saturate these values
-        float TdotH = dot(bsdfData.tangentWS, H);
-        float BdotH = dot(bsdfData.bitangentWS, H);
         D = D_GGXAniso(TdotH, BdotH, NdotH, bsdfData.roughnessT, bsdfData.roughnessB);
     }
     else
         float lightPdf = 0.0;               // Pdf of the light sample
 
         float2 u = Hammersley2d(i, sampleCount);
-        u = frac(u + randNum + 0.5);
+        u = frac(u + randNum);
 
         float4x4 localToWorld = float4x4(float4(lightData.right, 0.0), float4(lightData.up, 0.0), float4(lightData.forward, 0.0), float4(lightData.positionWS, 1.0));
 
     for (uint i = 0; i < sampleCount; ++i)
     {
         float2 u    = Hammersley2d(i, sampleCount);
-        u           = frac(u + randNum + 0.5);
+        u           = frac(u + randNum);
 
         float3 L;
         float NdotL;
     for (uint i = 0; i < sampleCount; ++i)
     {
         float2 u    = Hammersley2d(i, sampleCount);
-        u           = frac(u + randNum + 0.5);
+        u           = frac(u + randNum);
 
         float3 L;
         float NdotL;
     float3x3 localToWorld = GetLocalFrame(N, tangentX);
     float    NdotV        = GetShiftedNdotV(N, V, false);
     float3   acc          = float3(0.0, 0.0, 0.0);
+
 
     // Add some jittering on Hammersley2d
     float2 randNum  = InitRandom(V.xy * 0.5 + 0.5);
         float2 u    = Hammersley2d(i, sampleCount);
-        u           = frac(u + randNum + 0.5);
+        u           = frac(u + randNum);
 
         float VdotH;
         float NdotL;
         // GGX BRDF
-        if (bsdfData.materialId = MATERIALID_LIT_ANISO)
+        if (bsdfData.materialId == MATERIALID_LIT_ANISO)
         {
             ImportanceSampleAnisoGGX(u, V, N, tangentX, tangentY, bsdfData.roughnessT, bsdfData.roughnessB, NdotV, L, VdotH, NdotL, weightOverPdf);
         }

Assets/ScriptableRenderLoop/ShaderLibrary/BSDF.hlsl

     return PI * g;
 }
 
+// Ref: Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, p. 19, 29.
+float G_MaskingSmithGGX(float NdotV, float VdotH, float roughness)
+{
+    roughness = max(roughness, UNITY_MIN_ROUGHNESS);
+
+    // G1(V, H)    = HeavisideStep(VdotH) / (1 + Λ(V)).
+    // Λ(V)        = -0.5 + 0.5 * sqrt(1 + 1 / a²).
+    // a           = 1 / (roughness * tan(theta)).
+    // 1 + Λ(V)    = 0.5 + 0.5 * sqrt(1 + roughness² * tan²(theta)).
+    // tan²(theta) = (1 - cos²(theta)) / cos²(theta) = 1 / cos²(theta) - 1.
+
+    float hs = VdotH > 0.0 ? 1.0 : 0.0;
+    float a2 = roughness * roughness;
+    float z2 = NdotV * NdotV;
+
+    return hs / (0.5 + 0.5 * sqrt(1.0 + a2 * (1.0 / z2 - 1.0)));
+}
+
+// Ref: Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs, p. 12.
+float D_GGX_Visible(float NdotH, float NdotV, float VdotH, float roughness)
+{
+    // Note that we pass 1.0 instead of 'VdotH' since the multiplication will already clamp.
+    return D_GGX(NdotH, roughness) * G_MaskingSmithGGX(NdotV, 1.0, roughness) * VdotH / NdotV;
+}
+
 // Ref: http://jcgt.org/published/0003/02/03/paper.pdf
 float V_SmithJointGGX(float NdotL, float NdotV, float roughness)
 {

Assets/ScriptableRenderLoop/ShaderLibrary/ImageBasedLighting.hlsl

 
 void ImportanceSampleCosDir(float2   u,
                             float3x3 localToWorld,
-                        out float3   L)
+                        out float3   L,
+                        out float    NdotL)
-    float cosTheta = sqrt(saturate(1.0 - u.x));
+    float cosTheta = sqrt(1.0 - u.x);
-    L = SphericalToCartesian(phi, sinTheta, cosTheta);
-    L = mul(L, localToWorld);
+    float3 localL = SphericalToCartesian(phi, sinTheta, cosTheta);
+
+    NdotL = localL.z;
+
+    L = mul(localL, localToWorld);
 }
 
 void ImportanceSampleGGXDir(float2   u,
                         out float3   L,
+                        out float    NdotL,
                         out float    NdotH,
                         out float    VdotH,
                             bool     VeqN = false)
         VdotH  = saturate(dot(localV, localH));
     }
 
-    // Compute { L = reflect(-localV, localH) }
-    L = -localV + 2.0 * VdotH * localH;
+    // Compute { localL = reflect(-localV, localH) }
+    float3 localL = -localV + 2.0 * VdotH * localH;
+
+    NdotL = localL.z;
-    L = mul(L, localToWorld);
+    L = mul(localL, localToWorld);
 }
 
 // ref: http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_notes_v3.pdf p26
                          out float    NdotL,
                          out float    weightOverPdf)
 {
-    ImportanceSampleCosDir(u, localToWorld, L);
-
-    NdotL = saturate(dot(localToWorld[2], L));
+    ImportanceSampleCosDir(u, localToWorld, L, NdotL);
 
     // Importance sampling weight for each sample
     // pdf = N.L / PI
                      out float    NdotL,
                      out float    weightOverPdf)
 {
-    float3 H;
-    float  NdotH;
-    ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotH, VdotH);
-
-    NdotL = saturate(dot(localToWorld[2], L));
+    float NdotH;
+    ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotL, NdotH, VdotH);
 
     // Importance sampling weight for each sample
     // pdf = D(H) * (N.H) / (4 * (L.H))
     // weightOverPdf = F(H) * 4 * (N.L) * V(V, L) * (L.H) / (N.H) with V(V, L) = G(V, L) / (4 * (N.L) * (N.V))
     // Remind (L.H) == (V.H)
     // F is apply outside the function
+
+    // For anisotropy we must not saturate these values
-    float TdotL = saturate(dot(tangentX, L));
-    float BdotL = saturate(dot(tangentY, L));
+    float TdotL = dot(tangentX, L);
+    float BdotL = dot(tangentY, L);
 
     float Vis = V_SmithJointGGXAniso(TdotV, BdotV, NdotV, TdotL, BdotL, NdotL, roughnessT, roughnessB);
     weightOverPdf = 4.0 * Vis * NdotL * VdotH / NdotH;
 // 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)
 {
-    float NdotV     = GetShiftedNdotV(N, V, false); // This fix some rare artifact at edge.
+    float NdotV     = saturate(dot(N, V));
     float4 acc      = float4(0.0, 0.0, 0.0, 0.0);
     // Add some jittering on Hammersley2d
     float2 randNum  = InitRandom(V.xy * 0.5 + 0.5);
         u.x = lerp(u.x, 0.0, bias);
 
         float3 L;
-        float  NdotH, VdotH;
-        ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotH, VdotH, true);
-
-        float NdotL = saturate(dot(N, L));
+        float  NdotL, NdotH, VdotH;
+        ImportanceSampleGGXDir(u, V, localToWorld, roughness, L, NdotL, NdotH, VdotH, true);
 
         float mipLevel;