From 0c9cbd834b3169001d38ff47fd2b91ac5b8454ee Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Fri, 6 Mar 2026 14:53:42 -0800
Subject: Begin work on glitter

---
 3ner.shader   | 10 +++++++-
 brdf.cginc    |  2 +-
 glitter.slang | 74 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 2 deletions(-)
 create mode 100644 glitter.slang

diff --git a/3ner.shader b/3ner.shader
index eee9d2b..83872c6 100755
--- a/3ner.shader
+++ b/3ner.shader
@@ -215,7 +215,7 @@ Shader "yum_food/3ner"
           //endex
         [HideInInspector] m_end_Clearcoat("Clearcoat", Float) = 0
         //endex
-      
+
         //ifex _Brightness_Clamp_Enabled==0
         [HideInInspector] m_start_Brightness_Clamp("Brightness Clamp", Float) = 0
           [ThryToggle(_BRIGHTNESS_CLAMP)] _Brightness_Clamp_Enabled("Enable", Float) = 0
@@ -248,6 +248,14 @@ Shader "yum_food/3ner"
         [HideInInspector] m_end_Bent_Normals("Bent Normals", Float) = 0
         //endex
 
+        //ifex _Glitter_Enabled==0
+        [HideInInspector] m_start_Glitter("Glitter", Float) = 0
+          [ThryToggle(_GLITTER)] _Glitter_Enabled("Enable", Float) = 0
+          _Glitter_Amount("Amount", Range(0, 1)) = 0.5
+          _Glitter_Roughness("Roughness", Range(0.001, 0.1)) = 0.01
+        [HideInInspector] m_end_Glitter("Glitter", Float) = 0
+        //endex
+
       [HideInInspector] m_end_Main("Main", Float) = 0
 
       [HideInInspector] m_start_Gimmicks("Gimmicks", Float) = 0
diff --git a/brdf.cginc b/brdf.cginc
index 9e08325..da3fcd6 100755
--- a/brdf.cginc
+++ b/brdf.cginc
@@ -181,7 +181,7 @@ float4 brdf(Pbr pbr, LightData data) {
 #else
   float3 emission = 0;
 #endif
-  return float4(diffuse + specular + emission, 1);
+  return float4(diffuse + specular + emission, pbr.albedo.a);
 }
 
 #endif  // __BRDF_INC
diff --git a/glitter.slang b/glitter.slang
new file mode 100644
index 0000000..5442a0f
--- /dev/null
+++ b/glitter.slang
@@ -0,0 +1,74 @@
+#ifndef __GLITTER_INC
+#define __GLITTER_INC
+
+#define PI 3.1415926535897932384626433832795028841971
+
+float gaussian(float3 x, float3 mu, float sigma) {
+  float3 x_minus_mu = x - mu;
+  return exp(-dot(x_minus_mu, x_minus_mu) / (2 * sigma * sigma)) / (sigma * sqrt(2 * PI));
+}
+
+float det(float2x2 m) {
+  return m[0][0] * m[1][1] - m[0][1] * m[1][0];
+}
+
+float dirac(float3 x) {
+  // Ternary operator short-circuits in slang >:(
+  return any(abs(x) < 1e-4) ? 1e4 : 0;
+}
+
+// Maps a point on the unit hemisphere to an inscribed circle.
+float2 hemisphere_to_inscribed_circle(float3 p) {
+  // TODO
+  return 0;
+}
+
+float3 rand3_hash(float3 p)
+{
+    // Improved Murmurhash3 by Squirrel Eiserloh (GDC 2017)
+    p = float3(dot(p, float3(127.1, 311.7, 74.7)),
+               dot(p, float3(269.5, 183.3, 246.1)),
+               dot(p, float3(113.5, 271.9, 124.6)));
+    return -1.0 + 2.0 * frac(sin(p) * 43758.5453123);
+}
+
+public float D_Kemppinen(
+  float3 worldPos,
+  float3 H_tan,  // halfway vector in tangent space
+  float amount,
+  float roughness)
+{
+  float2x2 J_T__omega_h = 0;  // TODO
+  float det_J_T__omega_h = det(J_T__omega_h);
+  
+  float sum = 0;
+  // x is the current world space position.
+  float3 x = worldPos;
+  // omega_h is the halfway vector *in TBN coordinates.*
+  float3 omega_h = H_tan;
+  float3 T_omega_h = float3(
+      hemisphere_to_inscribed_circle(omega_h),
+      0);
+  uint K_p = 1;  // TODO
+  for (uint i = 0; i < K_p; ++i) {
+    // x_i is the position of the facet.
+    float3 x_i = worldPos;  // TODO randomize position
+    // mu_i is the orientation of the facet.
+    float3 mu_i = abs(rand3_hash(x_i));
+
+    float a_star = roughness;
+
+    float cur_gauss = gaussian(
+        T_omega_h,
+        mu_i,
+        a_star * sqrt(det_J_T__omega_h));
+
+    sum += cur_gauss * dirac(x_i - x);
+  }
+
+  float scale = det_J_T__omega_h / K_p;
+  return sum * scale;
+}
+
+#endif  // __GLITTER_INC
+
-- 
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