Treat specular less than 0.02 as occlusion

This is a very common hack used in almost all PBR renderers to allow removing specular contribution in dielectric materials

2 files changed, 5 insertions, 2 deletions

diff --git a/servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl b/servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl
index 5947fc5351..b64d33996a 100644
--- a/servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl
+++ b/servers/rendering/renderer_rd/shaders/scene_forward_clustered.glsl
@@ -1381,7 +1381,7 @@ void fragment_shader(in SceneData scene_data) {
 		float a004 = min(r.x * r.x, exp2(-9.28 * ndotv)) * r.x + r.y;
 		vec2 env = vec2(-1.04, 1.04) * a004 + r.zw;
 
-		specular_light *= env.x * f0 + env.y;
+		specular_light *= env.x * f0 + env.y * clamp(50.0 * f0.g, 0.0, 1.0);
 #endif
 	}
 
diff --git a/servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl b/servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl
index c92b29b14a..e27c81eaea 100644
--- a/servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl
+++ b/servers/rendering/renderer_rd/shaders/scene_forward_lights_inc.glsl
@@ -199,7 +199,10 @@ void light_compute(vec3 N, vec3 L, vec3 V, float A, vec3 light_color, float atte
 #endif // LIGHT_ANISOTROPY_USED
 	   // F
 		float cLdotH5 = SchlickFresnel(cLdotH);
-		vec3 F = mix(vec3(cLdotH5), vec3(1.0), f0);
+		// Calculate Fresnel using specular occlusion term from Filament:
+		// https://google.github.io/filament/Filament.html#lighting/occlusion/specularocclusion
+		float f90 = clamp(dot(f0, vec3(50.0 * 0.33)), 0.0, 1.0);
+		vec3 F = f0 + (f90 - f0) * cLdotH5;
 
 		vec3 specular_brdf_NL = cNdotL * D * F * G;