From 883e50070aca6017c9d71945c2c6e685938d12c4 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Tue, 11 Nov 2025 21:03:58 -0800
Subject: switch to lambertian diffuse

---
 brdf.cginc    | 8 ++++++++
 lysenko.cginc | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/brdf.cginc b/brdf.cginc
index a12c256..8714181 100644
--- a/brdf.cginc
+++ b/brdf.cginc
@@ -12,6 +12,10 @@ float pow5(float x) {
   return x2 * x2 * x;
 }
 
+float Fd_Lambertian(float NoL) {
+  return NoL;
+}
+
 // Schlick "An Inexpensive BRDF Model for Physically-based Rendering".
 // Equation 24.
 // f0: Reflectance at normal incidence. Typically around 0.04.
@@ -209,7 +213,11 @@ float4 brdf(Pbr pbr, LightData data) {
     direct_specular = max(0, direct_specular);
     specular += direct_specular;
 
+#if defined(F_OREN_NAYAR)
     float Fd = Fd_OrenNayar(pbr.roughness, data.common.NoV, data.direct.NoL, data.direct.LoV);
+#else
+    float Fd = Fd_Lambertian(data.direct.NoL);
+#endif
     float3 direct_diffuse = Fd * (1.0f - pbr.metallic) * pbr.albedo.xyz * data.direct.color;
     direct_diffuse *= layer_attenuation;
     direct_diffuse = max(0, direct_diffuse);
diff --git a/lysenko.cginc b/lysenko.cginc
index 3026caf..d3c51f0 100644
--- a/lysenko.cginc
+++ b/lysenko.cginc
@@ -28,7 +28,7 @@ float Fd_OrenNayar(float roughness, float NoV, float NoL, float LoV) {
   float s = LoV - NoL * NoV;
   float t = lerp(1.0f, max(NoL, NoV), step(0.0f, s));
   float sigma2 = roughness * roughness;
-  float A = 1.0f + sigma2 * rcp(sigma2 + 0.13f) + 0.5f / (sigma2 + 0.33f);
+  float A = 1.0f - 0.5f * sigma2 / (sigma2 + 0.33f);
   float B = 0.45f * sigma2 / (sigma2 + 0.09f);
 
   return max(0.0f, NoL * (A + B * s / t));
-- 
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