Extend BRDF

leenkx/Shaders/std/brdf.glsl

@@ -138,4 +138,137 @@ float D_Approx(const float Roughness, const float RoL) {
 	return rcp_a2 * exp2( c * RoL - c );
 }
 
+#ifdef _ClearCoat
+vec3 clearcoatBRDF(const float clearcoat, const float clearcoat_rough,
+	const float coat_ior,
+	const float dotNL, const float dotNH, const float dotNV, const float dotVH) {
+	if (clearcoat <= 0.0) return vec3(0.0);
+	float a = clearcoat_rough * clearcoat_rough;
+	// F0 from Fresnel equation for dielectric
+	float ccF0 = (coat_ior - 1.0) / (coat_ior + 1.0);
+	ccF0 = ccF0 * ccF0;
+	float F = ccF0 + (1.0 - ccF0) * pow(1.0 - dotVH, 5.0);
+	float D = d_ggx(dotNH, a);
+	float G = g2_approx(dotNL, dotNV, a);
+	return vec3(clearcoat * D * G * F / max(4.0 * dotNV, 1e-5));
+}
+
+float coatAttenuation(const float clearcoat,
+	const float coat_ior, const float dotNV) {
+	if (clearcoat <= 0.0) return 1.0;
+	float ccF0 = (coat_ior - 1.0) / (coat_ior + 1.0);
+	ccF0 = ccF0 * ccF0;
+	// Schlick with pow(.,5) - cheaper than exp2
+	float F = ccF0 + (1.0 - ccF0) * pow(1.0 - dotNV, 5.0);
+	return max(1.0 - F * clearcoat, 0.0);
+}
+
+vec3 coatTintAttenuation(const float clearcoat, const vec3 coat_tint, const float dotNV) {
+	if (clearcoat <= 0.0) return vec3(1.0);
+	float absorption = 1.0 / max(dotNV, 0.3);
+	return mix(vec3(1.0), coat_tint, clamp(absorption * 0.2, 0.0, 1.0));
+}
+#endif
+
+#ifdef _Sheen
+// based on Blender sheen model/Frostbite PBR
+vec3 sheenBRDF(const float sheen, const float sheen_rough,
+	const vec3 sheen_tint, const float dotNL, const float dotNH, const float dotNV) {
+	if (sheen <= 0.0) return vec3(0.0);
+	float rough = clamp(sheen_rough, 1e-3, 1.0);
+	float a = rough * rough;
+	float sinNH2 = 1.0 - dotNH * dotNH;
+	float a2 = a * a;
+	float D = (2.0 + a2) * sinNH2 / (2.0 * 3.1415926535 * pow(1.0 + a2 * sinNH2, 2.0));
+	float V = 1.0 / (4.0 * dotNL * dotNV + 1e-5);
+	float sheenAlbedo = (1.0 - 0.5 * rough) * mix(1.0, dotNV, 0.5);
+	return sheen_tint * sheen * D * V * dotNL * sheenAlbedo;
+}
+
+float sheenAttenuation(const float sheen, const float sheen_rough,
+	const vec3 sheen_tint, const float dotNV) {
+	if (sheen <= 0.0) return 1.0;
+	float rough = clamp(sheen_rough, 1e-3, 1.0);
+	float sheenAlbedo = (1.0 - 0.5 * rough) * mix(1.0, dotNV, 0.5);
+	float maxComp = sheen * max(max(sheen_tint.r, sheen_tint.g), sheen_tint.b) * sheenAlbedo;
+	return max(1.0 - maxComp, 0.0);
+}
+#endif
+
+#ifdef _Anisotropy
+// anisotropic GGX Burley 2012
+vec3 anisotropicBRDF(const vec3 f0, const float roughness, const float anisotropy,
+	const float aniso_rot, const vec3 tangent, const vec3 bitangent,
+	const vec3 n, const vec3 l, const vec3 v,
+	const float dotNL, const float dotNV) {
+	if (abs(anisotropy) <= 0.001) return vec3(0.0);
+	float rot = aniso_rot * 3.1415926535 * 2.0;
+	float cr = cos(rot);
+	float sr = sin(rot);
+	vec3 t = normalize(tangent * cr + bitangent * sr);
+	vec3 b = normalize(bitangent * cr - tangent * sr);
+	float aniso_abs = abs(anisotropy);
+	float at = max(roughness * (1.0 + aniso_abs), 1e-5);
+	float ab = max(roughness * (1.0 - aniso_abs), 1e-5);
+	if (anisotropy < 0.0) { vec3 tmp = t; t = b; b = tmp; }
+	float at2 = at * at;
+	float ab2 = ab * ab;
+	vec3 h = normalize(l + v);
+	float dotTH = dot(t, h);
+	float dotBH = dot(b, h);
+	float dotTV = dot(t, v);
+	float dotBV = dot(b, v);
+	float dotTL = dot(t, l);
+	float dotBL = dot(b, l);
+	float denom = max(dotTH * dotTH / at2 + dotBH * dotBH / ab2, 1e-7);
+	float D = 1.0 / (3.1415926535 * at * ab * denom * denom);
+	float V = 1.0 / max(dotNL * (dotTL / at + dotBL / ab) * (dotTV / at + dotBV / ab), 1e-5);
+	float dotVH = max(dot(v, h), 0.0);
+	vec3 F = f_schlick(f0, dotVH);
+	return D * V * F / max(4.0 * dotNV, 1e-5);
+}
+#endif
+
+#ifdef _Subsurface
+// Blenders bssrdf_burley implementation
+vec3 subsurfaceBRDF(const vec3 albedo, const vec3 sss_color,
+	const vec3 sss_radius, const float subsurface, const float sss_anisotropy,
+	const float dotNL) {
+	if (subsurface <= 0.0) return vec3(0.0);
+	vec3 mfp = sss_radius * (0.25 / 3.1415926535);
+	vec3 A = clamp(albedo, 0.0, 1.0);
+	vec3 d = 1.9 - A + 3.5 * (A - 0.8) * (A - 0.8);
+	d = mfp / max(d, 1e-5);
+	float aniso = clamp(sss_anisotropy, 0.0, 0.9);
+	float scatter = subsurface * (1.0 / 3.1415926535);
+	vec3 sssDiffuse = sss_color * scatter * dotNL;
+	float backScatter = max(0.0, 1.0 - dotNL) * (1.0 - aniso) * 0.5;
+	vec3 sssBack = sss_color * subsurface * backScatter;
+	float dist = max(0.0, 1.0 - dotNL);
+	vec3 rcp_d = 1.0 / max(d, vec3(1e-5));
+	vec3 x = vec3(dist) * rcp_d;
+	vec3 extinction = 1.0 / (1.0 + x + 0.5 * x * x);
+	return sssDiffuse * extinction + sssBack * (vec3(1.0) - extinction);
+}
+#endif
+
+#ifdef _Transmission
+// Blenders microfacet glass/refraction model
+vec3 transmissionBRDF(const vec3 albedo, const float transmission,
+	const float trans_rough, const float ior, const float thin_wall,
+	const float dotNL, const float dotNV, const float dotVH) {
+	if (transmission <= 0.0) return vec3(0.0);
+	float F0 = (ior - 1.0) / (ior + 1.0);
+	F0 = F0 * F0;
+	float F = F0 + (1.0 - F0) * pow(1.0 - dotVH, 5.0);
+	float transmittance = 1.0 - F;
+	if (thin_wall > 0.5) {
+		return albedo * transmission * transmittance * dotNL;
+	}
+	float a = trans_rough * trans_rough;
+	float rough_atten = mix(1.0, 1.0 / max(dotNV, 0.1), a);
+	return albedo * transmission * transmittance * rough_atten * dotNL;
+}
+#endif
+
 #endif