From 2dfd6322587eb095a5a4f7b22d70e1abcc14d5e3 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Mon, 31 Mar 2025 21:50:39 -0700
Subject: Overhaul wrapped lighting

Now:
* k=0   -> lambertian
* k=0.5 -> half lambertian
* k=1.0 -> flat

All three points should be energy conserving, but I haven't done the
actual analysis yet.
---
 math.cginc | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

(limited to 'math.cginc')

diff --git a/math.cginc b/math.cginc
index 8d404d9..bccb206 100644
--- a/math.cginc
+++ b/math.cginc
@@ -15,9 +15,24 @@ float pow5(float x)
   return (tmp * tmp) * x;
 }
 
-float wrapNoL(float NoL, float factor) {
+float wrapNoL(float NoL, float k) {
+#if 0
 		// https://www.iro.umontreal.ca/~derek/files/jgt_wrap_final.pdf
-    return pow(max(1E-4, (NoL + factor) / (1 + factor)), 1 + factor);
+    return pow(max(1E-4, (NoL + k) / (1 + k)), 1 + k);
+#else 
+    float k_sq = k * k;
+    float b = max(0, lerp(NoL, 1.0, k));
+    float p = -6.0 * k_sq + 5.0 * k + 1.0;
+    // Using the formula
+    float F = pow(b, p);
+
+    // Approximate integral of NoL with respect to theta
+    float I = 0.7856 * k_sq - 0.2148 * k + 1.0;
+
+    float G = F / max(I, 1E-6);
+
+    return G;
+#endif
 }
 
 float halfLambertianNoL(float NoL) {
-- 
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