Add ambient occlusion & normal filtering

1 files changed, 32 insertions, 10 deletions

diff --git a/pbr.cginc b/pbr.cginc
index d7d51b9..8ec69cb 100755
--- a/pbr.cginc
+++ b/pbr.cginc
@@ -26,8 +26,11 @@ struct Pbr {
 #endif
 };
 
-#define MIN_PERCEPTUAL_ROUGHNESS 5e-2f
-#define MIN_ROUGHNESS 5e-3f
+// From filament: min roughness s.t. MIN_PERCEPTUAL_ROUGHNESS^4 > 0 in target
+// precision. We use fp32. The smallest non-subnormal is 2^(-126). The 4th
+// root of that is ~3.29 * 10^-10.
+#define MIN_PERCEPTUAL_ROUGHNESS (3.3E-10)
+#define MIN_ROUGHNESS            (1.09E-19)
 
 #if defined(_PARALLAX_HEIGHTMAP)
 float2 parallax_offset(float2 uv, float3 view_dir_world, float3x3 tbn) {
@@ -115,10 +118,29 @@ float2 parallax_offset(float2 uv, float3 view_dir_world, float3x3 tbn) {
 }
 #endif  // _PARALLAX_HEIGHTMAP
 
-// TODO consider normal filtering like filamented
+// Tokuyashi and Kaplanyan 2019 "Improved Geometric Specular Antialiasing"
+float normalFiltering(float3 normal, float perceptual_roughness) {
+  float3 du = ddx(normal);
+  float3 dv = ddy(normal);
+
+  // Boxed equation in section 3.2 "Proposed Error Reduction."
+  float variance = dot(du, du) + dot(dv, dv);
+  float sigma = 0.5f;  // standard deviation of pixel filter kernel in image space
+  float Sigma = sigma * sigma * variance;
+
+  // Equation 1 in section 4.2 "Constraint for Conservative Isotropic Filtering"
+  float roughness = perceptual_roughness * perceptual_roughness;
+  float kappa = 0.18;
+  roughness = roughness + min(2 * Sigma, kappa);
+
+  return sqrt(roughness);
+}
+
 void propagateSmoothness(inout Pbr pbr) {
-  pbr.roughness_perceptual = max(MIN_PERCEPTUAL_ROUGHNESS, 1.0f - pbr.smoothness);
-  pbr.roughness = max(MIN_ROUGHNESS, pbr.roughness_perceptual * pbr.roughness_perceptual);
+  pbr.smoothness = 1.0f - normalFiltering(pbr.normal, 1.0f - pbr.smoothness);
+
+  pbr.roughness_perceptual = clamp(1.0f - pbr.smoothness, MIN_PERCEPTUAL_ROUGHNESS, 1);
+  pbr.roughness = clamp(pbr.roughness_perceptual * pbr.roughness_perceptual, MIN_ROUGHNESS, 1);
 #if defined(_CLEARCOAT)
   pbr.cc_roughness = max(MIN_ROUGHNESS, pbr.cc_roughness * pbr.cc_roughness);
 #endif
@@ -168,25 +190,25 @@ Pbr getPbr(v2f i) {
   pbr.objPos = imp.objPos;
 #endif
 #else
-  pbr.albedo = _MainTex.Sample(aniso16_trilinear_repeat_s, uv_parallax * _MainTex_ST.xy + _MainTex_ST.zw);
+  pbr.albedo = _MainTex.Sample(aniso4_trilinear_repeat_s, uv_parallax * _MainTex_ST.xy + _MainTex_ST.zw);
   pbr.albedo *= _Color;
   apply_marble(i.worldPos, pbr.albedo.xyz);
 
-  float3 normal_tangent = UnpackNormal(_BumpMap.Sample(aniso16_trilinear_repeat_s, uv_parallax * _BumpMap_ST.xy));
+  float3 normal_tangent = UnpackNormal(_BumpMap.Sample(aniso4_trilinear_repeat_s, uv_parallax * _BumpMap_ST.xy));
   normal_tangent.xy *= _BumpScale;
 
 #if defined(_DETAILS)
   float2 detail_uv = get_uv_by_channel(i, _Details_UV_Channel);
-  float3 detail_normal = UnpackNormal(_DetailNormalMap.Sample(aniso16_trilinear_repeat_s, detail_uv * _DetailNormalMap_ST.xy));
+  float3 detail_normal = UnpackNormal(_DetailNormalMap.Sample(aniso4_trilinear_repeat_s, detail_uv * _DetailNormalMap_ST.xy));
   detail_normal.xy *= _DetailNormalMapScale;
-  float detail_mask = _DetailMask.Sample(aniso16_trilinear_repeat_s, detail_uv * _DetailMask_ST.xy).r;
+  float detail_mask = _DetailMask.Sample(aniso4_trilinear_repeat_s, detail_uv * _DetailMask_ST.xy).r;
   detail_normal.xy *= detail_mask;
   normal_tangent = blendNormalsHill12(normal_tangent, detail_normal);
 #endif
 
   pbr.normal = normalize(mul(normal_tangent, pbr.tbn));
 
-  float4 metallic_gloss = _MetallicGlossMap.Sample(aniso16_trilinear_repeat_s, uv_parallax * _MetallicGlossMap_ST.xy);
+  float4 metallic_gloss = _MetallicGlossMap.Sample(aniso4_trilinear_repeat_s, uv_parallax * _MetallicGlossMap_ST.xy);
   pbr.smoothness = metallic_gloss.a * _Glossiness;
   pbr.metallic = metallic_gloss.r * _Metallic;
 #endif  // _IMPOSTORS