1 files changed, 58 insertions, 0 deletions
diff --git a/brdf.cginc b/brdf.cginc
new file mode 100644
index 0000000..d36d82b
--- /dev/null
+++ b/brdf.cginc
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+#ifndef __BRDF_INC
+#define __BRDF_INC
+
+#include "pbr.cginc"
+#include "lighting.cginc"
+#include "lysenko.cginc"
+#include "math.cginc"
+
+float fresnel(float LoH) {
+  // Schlick's approximation
+  float n1 = 1.0;
+  float n2 = 1.33;
+  float r0 = (n1 - n2) / (n1 + n2);
+  r0 = r0 * r0;
+
+  float term = 1.0 - LoH;
+  float term2 = term * term;
+  float term5 = term2 * term2 * term;
+  return r0 + (1.0 - r0) * term5;
+}
+
+float4 brdf(Pbr pbr, LightData data) {
+  float3 specular = 0;
+  float3 diffuse = 0;
+
+  // Direct
+  if (true) {
+    float F = fresnel(data.direct.LoH);
+    float D = D_GGX(pbr.roughness, data.direct.NoH, data.direct.H);
+    float V = V_SmithGGXCorrelated_Fast(pbr.roughness, data.common.NoV, data.direct.NoL);
+
+    float denom = 4.0f * data.common.NoV * data.direct.NoL;
+    float FDV = denom > _BRDF_Specular_Min_Denom ? F * D * V / denom : 0.0f;
+    specular += FDV * data.direct.color * data.direct.NoL;
+
+    float Fd = Fd_OrenNayar(pbr.roughness, data.common.NoV, data.direct.NoL, data.direct.LoV);
+    float3 remainder = (1.0f - F);
+    diffuse  += (Fd / PI) * remainder * pbr.albedo.xyz * data.direct.color;
+    remainder *= (1.0f - (Fd / PI) * pbr.albedo);
+  }
+
+  // Indirect
+  if (true) {
+    float F = fresnel(data.indirect.LoH);
+
+    specular += F * data.indirect.specular;
+
+    float Fd = 1.0 / PI;
+    float3 remainder = (1.0f - F);
+    diffuse  += Fd * remainder * pbr.albedo.xyz * data.indirect.diffuse;
+    remainder *= (1.0f - Fd * pbr.albedo);
+  }
+
+  return float4(diffuse + specular, 1);
+}
+
+#endif  // __BRDF_INC
+