Added ZH3 "hallucination" mode for calculating irradiance from L1 SH

BakingLab/AppSettings.cpp

@@ -138,10 +138,11 @@ static const char* SGSpecularModesLabels[3] =
     "ASG Warp",
 };
 
-static const char* SH4DiffuseModesLabels[2] =
+static const char* SH4DiffuseModesLabels[3] =
 {
     "Convolution",
     "Geomerics",
+    "ZH3",
 };
 
 static const char* SHSpecularModesLabels[4] =
@@ -507,7 +508,7 @@ namespace AppSettings
         SGSpecularMode.Initialize(tweakBar, "SGSpecularMode", "SG Settings", "Use ASG Warp", "", SGSpecularModes::ASGWarp, 3, SGSpecularModesLabels);
         Settings.AddSetting(&SGSpecularMode);
 
-        SH4DiffuseMode.Initialize(tweakBar, "SH4DiffuseMode", "SH Settings", "L1 SH Diffuse Mode", "", SH4DiffuseModes::Convolution, 2, SH4DiffuseModesLabels);
+        SH4DiffuseMode.Initialize(tweakBar, "SH4DiffuseMode", "SH Settings", "L1 SH Diffuse Mode", "", SH4DiffuseModes::Convolution, 3, SH4DiffuseModesLabels);
         Settings.AddSetting(&SH4DiffuseMode);
 
         SHSpecularMode.Initialize(tweakBar, "SHSpecularMode", "SH Settings", "SH Specular Mode", "", SHSpecularModes::Convolution, 4, SHSpecularModesLabels);

BakingLab/AppSettings.cs

@@ -327,6 +327,7 @@ enum SH4DiffuseModes
 {
     Convolution = 0,
     Geomerics,
+    ZH3,
 }
 
 enum SHSpecularModes

BakingLab/AppSettings.h

@@ -196,6 +196,7 @@ enum class SH4DiffuseModes
 {
     Convolution = 0,
     Geomerics = 1,
+    ZH3 = 2,
 
     NumValues
 };

BakingLab/AppSettings.hlsl

@@ -168,6 +168,7 @@ static const int SGSpecularModes_ASGWarp = 2;
 
 static const int SH4DiffuseModes_Convolution = 0;
 static const int SH4DiffuseModes_Geomerics = 1;
+static const int SH4DiffuseModes_ZH3 = 2;
 
 static const int SHSpecularModes_Convolution = 0;
 static const int SHSpecularModes_DominantDirection = 1;

BakingLab/Mesh.hlsl

@@ -689,6 +689,8 @@ PSOutput PS(in PSInput input)
 
             if(SH4DiffuseMode == SH4DiffuseModes_Geomerics)
                 indirectIrradiance = EvalSH4IrradianceGeomerics(normalSHSG, shRadiance);
+            else if(SH4DiffuseMode == SH4DiffuseModes_ZH3)
+                indirectIrradiance = EvalSH4IrradianceZH3Hallucinate(normalSHSG, shRadiance);
             else
                 indirectIrradiance = EvalSH4Irradiance(normalSHSG, shRadiance);
 

SampleFramework11/v1.02/Shaders/SH.hlsl

@@ -216,6 +216,27 @@ float3 EvalSH4IrradianceGeomerics(in float3 dir, in SH4Color sh)
                   EvalSH4IrradianceGeomerics(dir, shb));
 }
 
+//-------------------------------------------------------------------------------------------------
+// From "ZH3: Quadratic Zonal Harmonics" - https://torust.me/ZH3.pdf
+//-------------------------------------------------------------------------------------------------
+float3 EvalSH4IrradianceZH3Hallucinate(in float3 dir, in SH4Color sh)
+{
+    const float3 lumCoefficients = float3(0.2126f, 0.7152f, 0.0722f);
+    const float3 zonalAxis = normalize(float3(-dot(sh.c[3], lumCoefficients), -dot(sh.c[1], lumCoefficients), dot(sh.c[2], lumCoefficients)));
+
+    const float3 ratio = float3(abs(dot(float3(-sh.c[3].r, -sh.c[1].r, sh.c[2].r), zonalAxis)),
+                                abs(dot(float3(-sh.c[3].g, -sh.c[1].g, sh.c[2].g), zonalAxis)),
+                                abs(dot(float3(-sh.c[3].b, -sh.c[1].b, sh.c[2].b), zonalAxis))) / sh.c[0];
+    const float3 zonalL2Coeff = sh.c[0] * (0.08f * ratio + 0.6f * ratio * ratio);
+
+    const float fZ = dot(zonalAxis, dir);
+    const float zhDir = sqrt(5.0f / (16.0f * Pi)) * (3.0f * fZ * fZ - 1.0f);
+
+    const float3 baseIrradiance = EvalSH4Irradiance(dir, sh);
+
+    return baseIrradiance + (0.25f * zonalL2Coeff * zhDir);
+}
+
 //-------------------------------------------------------------------------------------------------
 // Converts from 3-band to 2-band SH
 //-------------------------------------------------------------------------------------------------