Glitter: move back to dominant direction for IBL

1 files changed, 7 insertions, 14 deletions

diff --git a/glitter.cginc b/glitter.cginc
index 676b902..022b176 100644
--- a/glitter.cginc
+++ b/glitter.cginc
@@ -14,9 +14,7 @@
  *   1. Syntax changes required to translate GLSL to HLSL.
  *   2. Stylistic preferences, like using "1" or "1.0" instead of "1.".
  *   3. The `GetGlitterLighting` function, which populates data required for
- *      IBL. The original paper only discusses analytic lighting. For IBL, you
- *      also need the micro-normal to figure out which part of the cubemap to
- *      sample.
+ *      indirect glitter. The original paper only discusses analytic lighting.
  *
  * @article{KPT:2025:Glinty,
  *   title = {Evaluating and Sampling Glinty NDFs in Constant Time},
@@ -171,6 +169,7 @@ float3 disk_to_ndf_ggx(float2 v_disk, float alpha) {
   return float3(alpha * hemi.xy, hemi.z) / denom;
 }
 
+// Algorithm 1 from Kemppinen et. al.
 float D_Kemppinen(float3 h, float alpha, float glint_alpha, float2 uv,
     float2x2 uv_J, float N, float filter_size, out float3 micro_normal) {
   float res = sqrt(N);
@@ -235,9 +234,6 @@ struct LightGlitter {
   float direct_D;
 
   float indirect_D;
-  float3 indirect_specular;
-  float3 indirect_dir;
-  float3 indirect_H;
   float indirect_NoL;
   float indirect_LoH;
 };
@@ -246,7 +242,7 @@ struct LightGlitter {
 LightGlitter GetGlitterLighting(
     float glitter_amount, float glitter_roughness,
     float2 uv, float3x3 tbn, float roughness,
-    float3 normal, float3 V, float3 direct_H, float3 indirect_H) {
+    float3 normal, float3 V, float3 direct_H, float3 indirect_dir) {
   LightGlitter g;
   const float glitter_filter_size = 0.7f;
   float2x2 uv_J = uv_ellipsoid(transpose(float2x2(ddx(uv), ddy(uv))));
@@ -259,19 +255,16 @@ LightGlitter GetGlitterLighting(
       uv, uv_J, N, glitter_filter_size, direct_micro_normal);
 
   // Indirect
+  float3 indirect_H = normalize(V + indirect_dir);
   float3 indirect_H_tangent = mul(indirect_H, transpose(tbn));
-  float3 indirect_micro_normal;  // used to sample cubemap
+  float3 indirect_micro_normal;  // unused, but required by D_Kemppinen
   g.indirect_D = D_Kemppinen(indirect_H_tangent, roughness, glitter_roughness,
       uv, uv_J, N, glitter_filter_size, indirect_micro_normal);
-  // Normal vector is the halfway vector in IBL.
-  g.indirect_H = normalize(mul(indirect_micro_normal, tbn));
-  g.indirect_dir = reflect(-V, g.indirect_H);
-  g.indirect_NoL = max(1e-4, dot(normal, g.indirect_dir));
-  g.indirect_LoH = max(1e-4, dot(g.indirect_dir, g.indirect_H));
+  g.indirect_NoL = max(1e-4, dot(normal, indirect_dir));
+  g.indirect_LoH = max(1e-4, dot(indirect_dir, indirect_H));
 
   return g;
 }
 #endif
 
 #endif  // __GLITTER_INC
-