Merge pull request #22483 from tagcup/fresnel

Restore the Fresnel term in the BRDF.

2 files changed, 94 insertions, 57 deletions

diff --git a/drivers/gles2/shaders/scene.glsl b/drivers/gles2/shaders/scene.glsl
index 958de94485..42b50790b2 100644
--- a/drivers/gles2/shaders/scene.glsl
+++ b/drivers/gles2/shaders/scene.glsl
@@ -898,10 +898,11 @@ varying vec2 uv2_interp;
 
 varying vec3 view_interp;
 
-vec3 metallic_to_specular_color(float metallic, float specular, vec3 albedo) {
-	float dielectric = (0.034 * 2.0) * specular;
-	// energy conservation
-	return mix(vec3(dielectric), albedo, metallic); // TODO: reference?
+vec3 F0(float metallic, float specular, vec3 albedo) {
+	float dielectric = 0.16 * specular * specular;
+	// use albedo * metallic as colored specular reflectance at 0 angle for metallic materials;
+	// see https://google.github.io/filament/Filament.md.html
+	return mix(vec3(dielectric), albedo, vec3(metallic));
 }
 
 /* clang-format off */
@@ -934,6 +935,7 @@ varying highp float dp_clip;
 // E. Heitz, "Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs", J. Comp. Graph. Tech. 3 (2) (2014).
 // Eqns 71-72 and 85-86 (see also Eqns 43 and 80).
 
+/*
 float G_GGX_2cos(float cos_theta_m, float alpha) {
 	// Schlick's approximation
 	// C. Schlick, "An Inexpensive BRDF Model for Physically-based Rendering", Computer Graphics Forum. 13 (3): 233 (1994)
@@ -946,6 +948,15 @@ float G_GGX_2cos(float cos_theta_m, float alpha) {
 	// float sin2 = (1.0 - cos2);
 	// return 1.0 / (cos_theta_m + sqrt(cos2 + alpha * alpha * sin2));
 }
+*/
+
+// This approximates G_GGX_2cos(cos_theta_l, alpha) * G_GGX_2cos(cos_theta_v, alpha)
+// See Filament docs, Specular G section.
+float V_GGX(float cos_theta_l, float cos_theta_v, float alpha) {
+	float v = cos_theta_l * (cos_theta_v * (1.0 - alpha) + alpha);
+	float l = cos_theta_v * (cos_theta_l * (1.0 - alpha) + alpha);
+	return 0.5 / (v + l);
+}
 
 float D_GGX(float cos_theta_m, float alpha) {
 	float alpha2 = alpha * alpha;
@@ -953,6 +964,7 @@ float D_GGX(float cos_theta_m, float alpha) {
 	return alpha2 / (M_PI * d * d);
 }
 
+/*
 float G_GGX_anisotropic_2cos(float cos_theta_m, float alpha_x, float alpha_y, float cos_phi, float sin_phi) {
 	float cos2 = cos_theta_m * cos_theta_m;
 	float sin2 = (1.0 - cos2);
@@ -960,14 +972,30 @@ float G_GGX_anisotropic_2cos(float cos_theta_m, float alpha_x, float alpha_y, fl
 	float s_y = alpha_y * sin_phi;
 	return 1.0 / max(cos_theta_m + sqrt(cos2 + (s_x * s_x + s_y * s_y) * sin2), 0.001);
 }
+*/
 
-float D_GGX_anisotropic(float cos_theta_m, float alpha_x, float alpha_y, float cos_phi, float sin_phi) {
-	float cos2 = cos_theta_m * cos_theta_m;
+// This approximates G_GGX_anisotropic_2cos(cos_theta_l, ...) * G_GGX_anisotropic_2cos(cos_theta_v, ...)
+// See Filament docs, Anisotropic specular BRDF section.
+float V_GGX_anisotropic(float alpha_x, float alpha_y, float TdotV, float TdotL, float BdotV, float BdotL, float NdotV, float NdotL) {
+	float Lambda_V = NdotL * length(vec3(alpha_x * TdotV, alpha_y * BdotV, NdotV));
+	float Lambda_L = NdotV * length(vec3(alpha_x * TdotL, alpha_y * BdotL, NdotL));
+	return 0.5 / (Lambda_V + Lambda_L);
+}
+
+float D_GGX_anisotropic(float cos_theta_m, float alpha_x, float alpha_y, float cos_phi, float sin_phi, float NdotH) {
+	float alpha2 = alpha_x * alpha_y;
+	highp vec3 v = vec3(alpha_y * cos_phi, alpha_x * sin_phi, alpha2 * NdotH);
+	highp float v2 = dot(v, v);
+	float w2 = alpha2 / v2;
+	float D = alpha2 * w2 * w2 * (1.0 / M_PI);
+	return D;
+
+	/* float cos2 = cos_theta_m * cos_theta_m;
 	float sin2 = (1.0 - cos2);
 	float r_x = cos_phi / alpha_x;
 	float r_y = sin_phi / alpha_y;
 	float d = cos2 + sin2 * (r_x * r_x + r_y * r_y);
-	return 1.0 / max(M_PI * alpha_x * alpha_y * d * d, 0.001);
+	return 1.0 / max(M_PI * alpha_x * alpha_y * d * d, 0.001); */
 }
 
 float SchlickFresnel(float u) {
@@ -996,6 +1024,7 @@ void light_compute(
 		float specular_blob_intensity,
 		float roughness,
 		float metallic,
+		float specular,
 		float rim,
 		float rim_tint,
 		float clearcoat,
@@ -1112,9 +1141,11 @@ LIGHT_SHADER_CODE
 
 	if (roughness > 0.0) {
 
-		// D
-
-		float specular_brdf_NL;
+#if defined(SPECULAR_SCHLICK_GGX)
+		vec3 specular_brdf_NL = vec3(0.0);
+#else
+		float specular_brdf_NL = 0.0;
+#endif
 
 #if defined(SPECULAR_BLINN)
 
@@ -1147,7 +1178,6 @@ LIGHT_SHADER_CODE
 
 #elif defined(SPECULAR_DISABLED)
 		// none..
-		specular_brdf_NL = 0.0;
 #elif defined(SPECULAR_SCHLICK_GGX)
 		// shlick+ggx as default
 
@@ -1157,28 +1187,28 @@ LIGHT_SHADER_CODE
 		float cLdotH = max(dot(L, H), 0.0);
 
 #if defined(LIGHT_USE_ANISOTROPY)
-
+		float alpha = roughness * roughness;
 		float aspect = sqrt(1.0 - anisotropy * 0.9);
-		float rx = roughness / aspect;
-		float ry = roughness * aspect;
-		float ax = rx * rx;
-		float ay = ry * ry;
-		float XdotH = dot(T, H);
-		float YdotH = dot(B, H);
-		float D = D_GGX_anisotropic(cNdotH, ax, ay, XdotH, YdotH);
-		float G = G_GGX_anisotropic_2cos(cNdotL, ax, ay, XdotH, YdotH) * G_GGX_anisotropic_2cos(cNdotV, ax, ay, XdotH, YdotH);
+		float ax = alpha / aspect;
+		float ay = alpha * aspect;
+		//float XdotH = dot(T, H);
+		//float YdotH = dot(B, H);
+		float D = D_GGX_anisotropic(cNdotH, ax, ay, XdotH, YdotH, cNdotH);
+		//float G = G_GGX_anisotropic_2cos(cNdotL, ax, ay, XdotH, YdotH) * G_GGX_anisotropic_2cos(cNdotV, ax, ay, XdotH, YdotH);
+		float G = V_GGX_anisotropic(ax, ay, dot(T, V), dot(T, L), dot(B, V), dot(B, L), cNdotV, cNdotL))
 
 #else
 		float alpha = roughness * roughness;
 		float D = D_GGX(cNdotH, alpha);
-		float G = G_GGX_2cos(cNdotL, alpha) * G_GGX_2cos(cNdotV, alpha);
+		//float G = G_GGX_2cos(cNdotL, alpha) * G_GGX_2cos(cNdotV, alpha);
+		float G = V_GGX(cNdotL, cNdotV, alpha);
 #endif
 		// F
-		//float F0 = 1.0;
-		//float cLdotH5 = SchlickFresnel(cLdotH);
-		//float F = mix(cLdotH5, 1.0, F0);
+		vec3 f0 = F0(metallic, specular, diffuse_color);
+		float cLdotH5 = SchlickFresnel(cLdotH);
+		vec3 F = mix(vec3(cLdotH5), vec3(1.0), f0);
 
-		specular_brdf_NL = cNdotL * D /* F */ * G;
+		specular_brdf_NL = cNdotL * D * F * G;
 
 #endif
 
@@ -1197,11 +1227,12 @@ LIGHT_SHADER_CODE
 #endif
 			float Dr = GTR1(cNdotH, mix(.1, .001, clearcoat_gloss));
 			float Fr = mix(.04, 1.0, cLdotH5);
-			float Gr = G_GGX_2cos(cNdotL, .25) * G_GGX_2cos(cNdotV, .25);
+			//float Gr = G_GGX_2cos(cNdotL, .25) * G_GGX_2cos(cNdotV, .25);
+			float Gr = V_GGX(cNdotL, cNdotV, 0.25);
 
-			float specular_brdf_NL = 0.25 * clearcoat * Gr * Fr * Dr * cNdotL;
+			float clearcoat_specular_brdf_NL = 0.25 * clearcoat * Gr * Fr * Dr * cNdotL;
 
-			specular_light += specular_brdf_NL * light_color * specular_blob_intensity * attenuation;
+			specular_light += clearcoat_specular_brdf_NL * light_color * specular_blob_intensity * attenuation;
 		}
 #endif
 	}
@@ -1290,6 +1321,11 @@ void main() {
 	float alpha = 1.0;
 	float side = 1.0;
 
+	float specular_blob_intensity = 1.0;
+#if defined(SPECULAR_TOON)
+	specular_blob_intensity *= specular * 2.0;
+#endif
+
 #if defined(ENABLE_AO)
 	float ao = 1.0;
 	float ao_light_affect = 0.0;
@@ -1808,7 +1844,7 @@ FRAGMENT_SHADER_CODE
 #ifdef USE_VERTEX_LIGHTING
 	//vertex lighting
 
-	specular_light += specular_interp * specular * light_att;
+	specular_light += specular_interp * specular_blob_intensity * light_att;
 	diffuse_light += diffuse_interp * albedo * light_att;
 
 #else
@@ -1823,9 +1859,10 @@ FRAGMENT_SHADER_CODE
 			light_att,
 			albedo,
 			transmission,
-			specular * light_specular,
+			specular_blob_intensity * light_specular,
 			roughness,
 			metallic,
+			specular,
 			rim,
 			rim_tint,
 			clearcoat,
@@ -1872,10 +1909,10 @@ FRAGMENT_SHADER_CODE
 		vec4 r = roughness * c0 + c1;
 		float ndotv = clamp(dot(normal, eye_position), 0.0, 1.0);
 		float a004 = min(r.x * r.x, exp2(-9.28 * ndotv)) * r.x + r.y;
-		vec2 AB = vec2(-1.04, 1.04) * a004 + r.zw;
+		vec2 env = vec2(-1.04, 1.04) * a004 + r.zw;
 
-		vec3 specular_color = metallic_to_specular_color(metallic, specular, albedo);
-		specular_light *= AB.x * specular_color + AB.y;
+		vec3 f0 = F0(metallic, specular, albedo);
+		specular_light *= env.x * f0 + env.y;
 #endif
 	}
 
diff --git a/drivers/gles3/shaders/scene.glsl b/drivers/gles3/shaders/scene.glsl
index bcaf4a57a8..598bd3465e 100644
--- a/drivers/gles3/shaders/scene.glsl
+++ b/drivers/gles3/shaders/scene.glsl
@@ -920,13 +920,14 @@ float GTR1(float NdotH, float a) {
 	return (a2 - 1.0) / (M_PI * log(a2) * t);
 }
 
-vec3 metallic_to_specular_color(float metallic, float specular, vec3 albedo) {
-	float dielectric = (0.034 * 2.0) * specular;
-	// energy conservation
-	return mix(vec3(dielectric), albedo, metallic); // TODO: reference?
+vec3 F0(float metallic, float specular, vec3 albedo) {
+	float dielectric = 0.16 * specular * specular;
+	// use albedo * metallic as colored specular reflectance at 0 angle for metallic materials;
+	// see https://google.github.io/filament/Filament.md.html
+	return mix(vec3(dielectric), albedo, vec3(metallic));
 }
 
-void light_compute(vec3 N, vec3 L, vec3 V, vec3 B, vec3 T, vec3 light_color, vec3 attenuation, vec3 diffuse_color, vec3 transmission, float specular_blob_intensity, float roughness, float metallic, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, inout vec3 diffuse_light, inout vec3 specular_light) {
+void light_compute(vec3 N, vec3 L, vec3 V, vec3 B, vec3 T, vec3 light_color, vec3 attenuation, vec3 diffuse_color, vec3 transmission, float specular_blob_intensity, float roughness, float metallic, float specular, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, inout vec3 diffuse_light, inout vec3 specular_light) {
 
 #if defined(USE_LIGHT_SHADER_CODE)
 	// light is written by the light shader
@@ -1069,11 +1070,10 @@ LIGHT_SHADER_CODE
 
 #if defined(LIGHT_USE_ANISOTROPY)
 
+		float alpha = roughness * roughness;
 		float aspect = sqrt(1.0 - anisotropy * 0.9);
-		float rx = roughness / aspect;
-		float ry = roughness * aspect;
-		float ax = rx * rx;
-		float ay = ry * ry;
+		float ax = alpha / aspect;
+		float ay = alpha * aspect;
 		float XdotH = dot(T, H);
 		float YdotH = dot(B, H);
 		float D = D_GGX_anisotropic(cNdotH, ax, ay, XdotH, YdotH);
@@ -1085,11 +1085,11 @@ LIGHT_SHADER_CODE
 		float G = G_GGX_2cos(cNdotL, alpha) * G_GGX_2cos(cNdotV, alpha);
 #endif
 		// F
-		//float F0 = 1.0;
-		//float cLdotH5 = SchlickFresnel(cLdotH);
-		//float F = mix(cLdotH5, 1.0, F0);
+		vec3 f0 = F0(metallic, specular, diffuse_color);
+		float cLdotH5 = SchlickFresnel(cLdotH);
+		vec3 F = mix(vec3(cLdotH5), vec3(1.0), f0);
 
-		float specular_brdf_NL = cNdotL * D /* F */ * G;
+		vec3 specular_brdf_NL = cNdotL * D * F * G;
 
 		specular_light += specular_brdf_NL * light_color * specular_blob_intensity * attenuation;
 #endif
@@ -1191,7 +1191,7 @@ vec3 light_transmittance(float translucency,vec3 light_vec, vec3 normal, vec3 po
 }
 #endif
 
-void light_process_omni(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 binormal, vec3 tangent, vec3 albedo, vec3 transmission, float roughness, float metallic, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, float p_blob_intensity, inout vec3 diffuse_light, inout vec3 specular_light) {
+void light_process_omni(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 binormal, vec3 tangent, vec3 albedo, vec3 transmission, float roughness, float metallic, float specular, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, float p_blob_intensity, inout vec3 diffuse_light, inout vec3 specular_light) {
 
 	vec3 light_rel_vec = omni_lights[idx].light_pos_inv_radius.xyz - vertex;
 	float light_length = length(light_rel_vec);
@@ -1245,10 +1245,10 @@ void light_process_omni(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 bi
 		light_attenuation *= mix(omni_lights[idx].shadow_color_contact.rgb, vec3(1.0), shadow);
 	}
 #endif //SHADOWS_DISABLED
-	light_compute(normal, normalize(light_rel_vec), eye_vec, binormal, tangent, omni_lights[idx].light_color_energy.rgb, light_attenuation, albedo, transmission, omni_lights[idx].light_params.z * p_blob_intensity, roughness, metallic, rim * omni_attenuation, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
+	light_compute(normal, normalize(light_rel_vec), eye_vec, binormal, tangent, omni_lights[idx].light_color_energy.rgb, light_attenuation, albedo, transmission, omni_lights[idx].light_params.z * p_blob_intensity, roughness, metallic, specular, rim * omni_attenuation, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
 }
 
-void light_process_spot(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 binormal, vec3 tangent, vec3 albedo, vec3 transmission, float roughness, float metallic, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, float p_blob_intensity, inout vec3 diffuse_light, inout vec3 specular_light) {
+void light_process_spot(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 binormal, vec3 tangent, vec3 albedo, vec3 transmission, float roughness, float metallic, float specular, float rim, float rim_tint, float clearcoat, float clearcoat_gloss, float anisotropy, float p_blob_intensity, inout vec3 diffuse_light, inout vec3 specular_light) {
 
 	vec3 light_rel_vec = spot_lights[idx].light_pos_inv_radius.xyz - vertex;
 	float light_length = length(light_rel_vec);
@@ -1280,7 +1280,7 @@ void light_process_spot(int idx, vec3 vertex, vec3 eye_vec, vec3 normal, vec3 bi
 	}
 #endif //SHADOWS_DISABLED
 
-	light_compute(normal, normalize(light_rel_vec), eye_vec, binormal, tangent, spot_lights[idx].light_color_energy.rgb, light_attenuation, albedo, transmission, spot_lights[idx].light_params.z * p_blob_intensity, roughness, metallic, rim * spot_attenuation, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
+	light_compute(normal, normalize(light_rel_vec), eye_vec, binormal, tangent, spot_lights[idx].light_color_energy.rgb, light_attenuation, albedo, transmission, spot_lights[idx].light_params.z * p_blob_intensity, roughness, metallic, specular, rim * spot_attenuation, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
 }
 
 void reflection_process(int idx, vec3 vertex, vec3 normal, vec3 binormal, vec3 tangent, float roughness, float anisotropy, vec3 ambient, vec3 skybox, inout highp vec4 reflection_accum, inout highp vec4 ambient_accum) {
@@ -1895,7 +1895,7 @@ FRAGMENT_SHADER_CODE
 	specular_light *= mix(vec3(1.0), light_attenuation, specular_light_interp.a);
 
 #else
-	light_compute(normal, -light_direction_attenuation.xyz, eye_vec, binormal, tangent, light_color_energy.rgb, light_attenuation, albedo, transmission, light_params.z * specular_blob_intensity, roughness, metallic, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
+	light_compute(normal, -light_direction_attenuation.xyz, eye_vec, binormal, tangent, light_color_energy.rgb, light_attenuation, albedo, transmission, light_params.z * specular_blob_intensity, roughness, metallic, specular, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, diffuse_light, specular_light);
 #endif
 
 #endif //#USE_LIGHT_DIRECTIONAL
@@ -1969,11 +1969,11 @@ FRAGMENT_SHADER_CODE
 #else
 
 	for (int i = 0; i < omni_light_count; i++) {
-		light_process_omni(omni_light_indices[i], vertex, eye_vec, normal, binormal, tangent, albedo, transmission, roughness, metallic, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, specular_blob_intensity, diffuse_light, specular_light);
+		light_process_omni(omni_light_indices[i], vertex, eye_vec, normal, binormal, tangent, albedo, transmission, roughness, metallic, specular, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, specular_blob_intensity, diffuse_light, specular_light);
 	}
 
 	for (int i = 0; i < spot_light_count; i++) {
-		light_process_spot(spot_light_indices[i], vertex, eye_vec, normal, binormal, tangent, albedo, transmission, roughness, metallic, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, specular_blob_intensity, diffuse_light, specular_light);
+		light_process_spot(spot_light_indices[i], vertex, eye_vec, normal, binormal, tangent, albedo, transmission, roughness, metallic, specular, rim, rim_tint, clearcoat, clearcoat_gloss, anisotropy, specular_blob_intensity, diffuse_light, specular_light);
 	}
 
 #endif //USE_VERTEX_LIGHTING
@@ -1994,7 +1994,7 @@ FRAGMENT_SHADER_CODE
 	diffuse_light *= ao_light_affect;
 #endif
 
-	//energy conservation
+	// base color remapping
 	diffuse_light *= 1.0 - metallic; // TODO: avoid all diffuse and ambient light calculations when metallic == 1 up to this point
 	ambient_light *= 1.0 - metallic;
 
@@ -2011,10 +2011,10 @@ FRAGMENT_SHADER_CODE
 		vec4 r = roughness * c0 + c1;
 		float ndotv = clamp(dot(normal, eye_vec), 0.0, 1.0);
 		float a004 = min(r.x * r.x, exp2(-9.28 * ndotv)) * r.x + r.y;
-		vec2 AB = vec2(-1.04, 1.04) * a004 + r.zw;
+		vec2 env = vec2(-1.04, 1.04) * a004 + r.zw;
 
-		vec3 specular_color = metallic_to_specular_color(metallic, specular, albedo);
-		specular_light *= AB.x * specular_color + AB.y;
+		vec3 f0 = F0(metallic, specular, albedo);
+		specular_light *= env.x * f0 + env.y;
 #endif
 	}