1 files changed, 65 insertions, 5 deletions
diff --git a/lighting.cginc b/lighting.cginc
index 66b7220..5055798 100644
--- a/lighting.cginc
+++ b/lighting.cginc
@@ -98,11 +98,71 @@ float3 getIndirectSpecular(v2f i, float roughness, float3 view_dir, float3 refle
 }
 
 float3 yumSH9(float4 n, float3 worldPos, inout LightIndirect light) {
-  LightVolumeSH(worldPos, light.L00, light.L01r, light.L01g, light.L01b);
-  return light.L00 + float3(
-    dot(light.L01r, n.xyz),
-    dot(light.L01g, n.xyz),
-    dot(light.L01b, n.xyz));
+  [branch]
+    if (_UdonLightVolumeEnabled) {
+      LightVolumeSH(worldPos, light.L00, light.L01r, light.L01g, light.L01b);
+      return light.L00 + float3(
+          dot(light.L01r, n.xyz),
+          dot(light.L01g, n.xyz),
+          dot(light.L01b, n.xyz));
+    }
+
+  // No light volumes - use SH9
+  // Unity gives us the first three bands (L0-L2) of SH coefficients as follows:
+  //   unity_SHA*.w:   L0 coefficients
+  //   unity_SHA*.xyz: L1 coefficients
+  //   unity_SHB*:     first four of the L2 coefficients
+  //   unity_SHC:      last L2 coefficient
+
+  // Parse out coefficients into a simpler but less efficient format.
+  float3 L00  = float3(unity_SHAr.w, unity_SHAg.w, unity_SHAb.w);
+  float3 L1_1 = float3(unity_SHAr.x, unity_SHAg.x, unity_SHAb.x);
+  float3 L10  = float3(unity_SHAr.y, unity_SHAg.y, unity_SHAb.y);
+  float3 L11  = float3(unity_SHAr.z, unity_SHAg.z, unity_SHAb.z);
+  float3 L2_2 = float3(unity_SHBr.x, unity_SHBg.x, unity_SHBb.x);
+  float3 L2_1 = float3(unity_SHBr.y, unity_SHBg.y, unity_SHBb.y);
+  float3 L20  = float3(unity_SHBr.z, unity_SHBg.z, unity_SHBb.z);
+  float3 L21  = float3(unity_SHBr.w, unity_SHBg.w, unity_SHBb.w);
+  float3 L22  = unity_SHC;
+
+  // Equation 13 from "An Efficient Representation for Irradiance Environment
+  // Maps" by Ramamoorthi and Hanrahan. Note that the order of some
+  // coefficients is different, and normalization constants have been
+  // premultiplied by Unity.
+  float3 L0 = L00;
+  float3 L1 = L1_1 * n.x + L10 * n.y + L11 * n.z;
+  float3 L2 =
+    L2_2 * n.x * n.y +
+    L2_1 * n.y * n.z +
+    L20  * n.z * n.z +
+    L21 * n.x * n.z +
+    L22 * (n.x * n.x - n.y * n.y);
+
+  // TODO expose this as a parameter
+  float wrap_term = 0.0f;
+  // Original coefficients: 1, 2/3, 1/4.
+  // Wrapped coefficients: 1, (2-w)/3, ((1-w)^2)/4.
+
+  // Setting w=0, the l1 band is:
+  //   (2-w)/3 = 2/3
+  //   2-w = 2
+  //   1-w/2 = 1
+  float l1_wrap = 1.0f - wrap_term * 0.75f;
+  L1 *= l1_wrap;
+
+  // The l2 band is:
+  //   ((1-w)^2)/4 = 1/4
+  //   (1-w)^2 = 1
+  float l2_wrap = (1.0f-wrap_term);
+  l2_wrap *= l2_wrap;
+  L2 *= l2_wrap;
+
+  light.L00 = L00;
+  light.L01r = unity_SHAr.xyz * l1_wrap;
+  light.L01g = unity_SHAg.xyz * l1_wrap;
+  light.L01b = unity_SHAb.xyz * l1_wrap;
+
+  return L0 + L1 + L2;
 }
 
 float4 getIndirectDiffuse(v2f i, Pbr pbr, inout LightIndirect light) {