Fixed the broken GLSL shader and implemented the Disney BRDF in the

real-time view port.

source/blender/gpu/shaders/gpu_shader_material.glsl

@@ -2378,11 +2378,19 @@ void shade_alpha_obcolor(vec4 col, vec4 obcol, out vec4 outcol)
 
 /*********** NEW SHADER UTILITIES **************/
 
-float fresnel_dielectric(vec3 Incoming, vec3 Normal, float eta)
+float fresnel_dielectric_0(float eta)
+{
+	/* compute fresnel reflactance at normal incidence => cosi = 1.0 */
+	float A = (eta - 1.0) / (eta + 1.0);
+
+	return A * A;
+}
+
+float fresnel_dielectric_cos(float cosi, float eta)
 {
 	/* compute fresnel reflectance without explicitly computing
 	 * the refracted direction */
-	float c = abs(dot(Incoming, Normal));
+	float c = abs(cosi);
 	float g = eta * eta - 1.0 + c * c;
 	float result;
 
@@ -2399,6 +2407,13 @@ float fresnel_dielectric(vec3 Incoming, vec3 Normal, float eta)
 	return result;
 }
 
+float fresnel_dielectric(vec3 Incoming, vec3 Normal, float eta)
+{
+	/* compute fresnel reflectance without explicitly computing
+	 * the refracted direction */
+	return fresnel_dielectric_cos(dot(Incoming, Normal), eta);
+}
+
 float hypot(float x, float y)
 {
 	return sqrt(x * x + y * y);
@@ -2492,6 +2507,57 @@ float floorfrac(float x, out int i)
 	return x - i;
 }
 
+
+/* Principled BSDF operations */
+
+float sqr(float a)
+{
+	return a*a;
+}
+
+float schlick_fresnel(float u)
+{
+	float m = clamp(1.0 - u, 0.0, 1.0);
+	float m2 = m * m;
+	return m2 * m2 * m; // pow(m,5)
+}
+
+float GTR1(float NdotH, float a)
+{
+	if (a >= 1.0) return M_1_PI;
+	float a2 = a*a;
+	float t = 1.0 + (a2 - 1.0) * NdotH*NdotH;
+	return (a2 - 1.0) / (M_PI * log(a2) * t);
+}
+
+float GTR2(float NdotH, float a)
+{
+	float a2 = a*a;
+	float t = 1.0 + (a2 - 1.0) * NdotH*NdotH;
+	return a2 / (M_PI * t*t);
+}
+
+float GTR2_aniso(float NdotH, float HdotX, float HdotY, float ax, float ay)
+{
+	return 1.0 / (M_PI * ax*ay * sqr(sqr(HdotX / ax) + sqr(HdotY / ay) + NdotH*NdotH));
+}
+
+float smithG_GGX(float NdotV, float alphaG)
+{
+	float a = alphaG*alphaG;
+	float b = NdotV*NdotV;
+	return 1.0 / (NdotV + sqrt(a + b - a * b));
+}
+
+vec3 rotate_vector(vec3 p, vec3 n, float theta) {
+	return (
+	           p * cos(theta) + cross(n, p) *
+	           sin(theta) + n * dot(p, n) *
+	           (1.0 - cos(theta))
+	       );
+}
+
+
 /*********** NEW SHADER NODES ***************/
 
 #define NUM_LIGHTS 3
@@ -2555,9 +2621,122 @@ void node_bsdf_toon(vec4 color, float size, float tsmooth, vec3 N, out vec4 resu
 
 void node_bsdf_principled(vec4 base_color, float subsurface, vec3 subsurface_radius, vec4 subsurface_color, float metallic, float specular,
 	float specular_tint, float roughness, float anisotropic, float anisotropic_rotation, float sheen, float sheen_tint, float clearcoat,
-	float clearcoat_gloss, float ior, float transparency, float refraction_roughness, vec3 N, vec3 CN, vec3 T, out vec4 result)
+	float clearcoat_gloss, float ior, float transparency, float refraction_roughness, vec3 N, vec3 CN, vec3 T, vec3 I, out vec4 result)
 {
-	node_bsdf_diffuse(base_color, roughness, N, result);
+	/* ambient light */
+	// TODO: set ambient light to an appropriate value
+	vec3 L = vec3(mix(0.1, 0.03, metallic)) * base_color.rgb;
+
+	float eta = (2.0 / (1.0 - sqrt(0.08 * specular))) - 1.0;
+
+	/* set the viewing vector */
+	vec3 V = -normalize(I);
+
+	/* get the tangent */
+	vec3 Tangent = T;
+	if (T == vec3(0.0)) {
+		// if no tangent is set, use a default tangent
+		Tangent = vec3(1.0, 0.0, 0.0);
+		if (N.x != 0.0 || N.y != 0.0) {
+			vec3 N_xz = normalize(vec3(N.x, 0.0, N.z));
+
+			vec3 axis = normalize(cross(vec3(0.0, 0.0, 1.0), N_xz));
+			float angle = acos(dot(vec3(0.0, 0.0, 1.0), N_xz));
+
+			Tangent = normalize(rotate_vector(vec3(1.0, 0.0, 0.0), axis, angle));
+		}
+	}
+
+	/* rotate tangent */
+	if (anisotropic_rotation != 0.0) {
+		Tangent = rotate_vector(Tangent, N, anisotropic_rotation * 2.0 * M_PI);
+	}
+
+	/* calculate the tangent and bitangent */
+	vec3 Y = normalize(cross(N, Tangent));
+	vec3 X = cross(Y, N);
+
+	/* fresnel normalization parameters */
+	float F0 = fresnel_dielectric_0(eta);
+	float F0_norm = 1.0 / (1.0 - F0);
+
+	/* directional lights */
+	for (int i = 0; i < NUM_LIGHTS; i++) {
+		vec3 light_position_world = gl_LightSource[i].position.xyz;
+		vec3 light_position = normalize(gl_NormalMatrix * light_position_world);
+
+		vec3 H = normalize(light_position + V);
+
+		vec3 light_specular = gl_LightSource[i].specular.rgb;
+
+		float NdotL = dot(N, light_position);
+		float NdotV = dot(N, V);
+		float LdotH = dot(light_position, H);
+
+		vec3 diffuse_and_specular_bsdf = vec3(0.0);
+		if (NdotL >= 0.0 && NdotV >= 0.0) {
+			float NdotH = dot(N, H);
+
+			float Cdlum = 0.3 * base_color.r + 0.6 * base_color.g + 0.1 * base_color.b; // luminance approx.
+
+			vec3 Ctint = Cdlum > 0 ? base_color.rgb / Cdlum : vec3(1.0); // normalize lum. to isolate hue+sat
+			vec3 Cspec0 = mix(specular * 0.08 * mix(vec3(1.0), Ctint, specular_tint), base_color.rgb, metallic);
+			vec3 Csheen = mix(vec3(1.0), Ctint, sheen_tint);
+
+			// Diffuse fresnel - go from 1 at normal incidence to .5 at grazing
+			// and mix in diffuse retro-reflection based on roughness
+
+			float FL = schlick_fresnel(NdotL), FV = schlick_fresnel(NdotV);
+			float Fd90 = 0.5 + 2.0 * LdotH*LdotH * roughness;
+			float Fd = mix(1.0, Fd90, FL) * mix(1.0, Fd90, FV);
+
+			// Based on Hanrahan-Krueger brdf approximation of isotropic bssrdf
+			// 1.25 scale is used to (roughly) preserve albedo
+			// Fss90 used to "flatten" retroreflection based on roughness
+			float Fss90 = LdotH*LdotH * roughness;
+			float Fss = mix(1.0, Fss90, FL) * mix(1.0, Fss90, FV);
+			float ss = 1.25 * (Fss * (1.0 / (NdotL + NdotV) - 0.5) + 0.5);
+
+			// specular
+			float aspect = sqrt(1.0 - anisotropic * 0.9);
+			float a = sqr(roughness);
+			float ax = max(0.001, a / aspect);
+			float ay = max(0.001, a * aspect);
+			float Ds = GTR2_aniso(NdotH, dot(H, X), dot(H, Y), ax, ay); //GTR2(NdotH, a);
+			float FH = (fresnel_dielectric_cos(LdotH, eta) - F0) * F0_norm;
+			vec3 Fs = mix(Cspec0, vec3(1.0), FH);
+			float roughg = sqr(roughness * 0.5 + 0.5);
+			float Gs = smithG_GGX(NdotL, roughg) * smithG_GGX(NdotV, roughg);
+
+			// sheen
+			vec3 Fsheen = schlick_fresnel(LdotH) * sheen * Csheen;
+
+			diffuse_and_specular_bsdf = (M_1_PI * mix(Fd, ss, subsurface) * base_color.rgb + Fsheen)
+			                            * (1.0 - metallic) + Gs * Fs * Ds;
+		}
+		diffuse_and_specular_bsdf *= max(NdotL, 0.0);
+
+		float CNdotL = dot(CN, light_position);
+		float CNdotV = dot(CN, V);
+
+		vec3 clearcoat_bsdf = vec3(0.0);
+		if (CNdotL >= 0.0 && CNdotV >= 0.0 && clearcoat > 0.0) {
+			float CNdotH = dot(CN, H);
+			//float FH = schlick_fresnel(LdotH);
+
+			// clearcoat (ior = 1.5 -> F0 = 0.04)
+			float Dr = GTR1(CNdotH, mix(0.1, 0.001, clearcoat_gloss));
+			float Fr = fresnel_dielectric_cos(LdotH, 1.5); //mix(0.04, 1.0, FH);
+			float Gr = smithG_GGX(CNdotL, 0.25) * smithG_GGX(CNdotV, 0.25);
+
+			clearcoat_bsdf = clearcoat * Gr * Fr * Dr * vec3(0.25);
+		}
+		clearcoat_bsdf *= max(CNdotL, 0.0);
+
+		L += light_specular * (diffuse_and_specular_bsdf + clearcoat_bsdf);
+	}
+
+	result = vec4(L, 1.0);
 }
 
 void node_bsdf_translucent(vec4 color, vec3 N, out vec4 result)

source/blender/nodes/shader/nodes/node_shader_bsdf_principled.c

@@ -65,12 +65,19 @@ static void node_shader_init_principled(bNodeTree *UNUSED(ntree), bNode *node)
 
 static int node_shader_gpu_bsdf_principled(GPUMaterial *mat, bNode *UNUSED(node), bNodeExecData *UNUSED(execdata), GPUNodeStack *in, GPUNodeStack *out)
 {
-	if (!in[16].link)
+	// normal
-		in[16].link = GPU_builtin(GPU_VIEW_NORMAL);
+	if (!in[17].link)
+		in[17].link = GPU_builtin(GPU_VIEW_NORMAL);
 	else
-		GPU_link(mat, "direction_transform_m4v3", in[16].link, GPU_builtin(GPU_VIEW_MATRIX), &in[16].link);
+		GPU_link(mat, "direction_transform_m4v3", in[17].link, GPU_builtin(GPU_VIEW_MATRIX), &in[17].link);
 
-	return GPU_stack_link(mat, "node_bsdf_principled", in, out);
+	// clearcoat normal
+	if (!in[18].link)
+		in[18].link = GPU_builtin(GPU_VIEW_NORMAL);
+	else
+		GPU_link(mat, "direction_transform_m4v3", in[18].link, GPU_builtin(GPU_VIEW_MATRIX), &in[18].link);
+
+	return GPU_stack_link(mat, "node_bsdf_principled", in, out, GPU_builtin(GPU_VIEW_POSITION));
 }
 
 static void node_shader_update_principled(bNodeTree *UNUSED(ntree), bNode *node)