From 2b3c4a48c74c0508c6f75a7d287401a9db00a41a Mon Sep 17 00:00:00 2001
From: tobspr <tobias.springer1@googlemail.com>
Date: Fri, 6 Nov 2015 16:41:51 +0100
Subject: [PATCH] Restore lighting models

---
 Shader/Includes/LightingModels.include | 82 ++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 Shader/Includes/LightingModels.include

diff --git a/Shader/Includes/LightingModels.include b/Shader/Includes/LightingModels.include
new file mode 100644
index 000000000..a2aa892ce
--- /dev/null
+++ b/Shader/Includes/LightingModels.include
@@ -0,0 +1,82 @@
+#pragma once
+
+// GGX
+float DistributionBRDF(float roughness, float NxH)
+{
+
+    // float m = roughness * roughness;
+    // float m2 = m * m;
+    // float d = ( NxH * m2 - NxH ) * NxH + 1;
+    // return m2 / ( d*d );
+
+    float m = roughness * roughness;
+    float m2 = m * m;
+    float NoH2 = NxH * NxH;
+    return exp( (NoH2 - 1) / (m2 * NoH2) ) / ( M_PI * m2 * NoH2 * NoH2 );
+
+    // float m = roughness * roughness;
+    // float m2 = m * m;
+    // float n = 2 / m2 - 2;
+    // return (n+2) / (2*M_PI) * pow( NxH, n );      // 1 mad, 1 exp, 1 mul, 1 log
+
+}
+
+// Schlick
+float GeometricBRDF(float roughness, float NxV, float NxL)
+{   
+    // Fixed-value:
+    // return 0.25;
+
+    float a = roughness * roughness;
+    float a2 = a * a;
+
+    float v = NxV + sqrt( NxV * (NxV - NxV * a2) + a2 );
+    float l = NxL + sqrt( NxL * (NxL - NxL * a2) + a2 );
+    return saturate(1.0 / ( v * l ));
+
+    // float a = roughness * roughness;
+    // float Vis_SmithV = NxL * ( NxV * ( 1 - a ) + a );
+    // float Vis_SmithL = NxV * ( NxL * ( 1 - a ) + a );
+    // return 0.5 / ( Vis_SmithV + Vis_SmithL );
+}
+
+// Schlick
+vec3 FresnelBRDF(vec3 specularColor, float LxH)
+{
+    return specularColor + (1.0 - specularColor) * pow(1.0 - LxH, 5.0); 
+}
+
+
+vec3 DiffuseBRDF(vec3 diffuseColor, float roughness, float NxV, float NxL, float VxH) {
+    float VxL = 2 * VxH - 1;
+    float m = roughness * roughness;
+    float m2 = m * m;
+    float C1 = 1 - 0.5 * m2 / (m2 + 0.33);
+    float Cosri = VxL - NxV * NxL;
+    float C2 = 0.45 * m2 / (m2 + 0.09) * Cosri * ( Cosri >= 0 ? min( 1, NxL / NxV ) : NxL );
+    return diffuseColor / M_PI * ( NxL * C1 + C2 );
+}
+
+float safeDot(vec3 a, vec3 b) {
+    return max(0.0, dot(a, b));
+}
+
+
+float Vis_Smith( float Roughness, float NoV, float NoL )
+{
+    float a = Roughness * Roughness;
+    float a2 = a*a;
+
+    float Vis_SmithV = NoV + sqrt( NoV * (NoV - NoV * a2) + a2 );
+    float Vis_SmithL = NoL + sqrt( NoL * (NoL - NoL * a2) + a2 );
+    return 1.0 / ( Vis_SmithV * Vis_SmithL );
+}
+
+
+
+vec3 computeSpecular(vec3 specularColor, float roughness, float NxL, float LxH, float NxV, float NxH) {
+    float specularD = DistributionBRDF(roughness, NxH);
+    float specularG = GeometricBRDF(roughness, NxV, NxL);
+    vec3  specularF = FresnelBRDF(specularColor, LxH);
+    return (specularD * specularG) * specularF;
+}
\ No newline at end of file