Fix T65298 Eevee: Principled BSDF doesn't use specular with metals

This does add some more register pressure as it passes a new vec3 down
the shading function. But for now we care more about accuracy than
efficiency.

3 files changed, 12 insertions, 9 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
index 0f3e7ba7efb..c332f68728f 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
@@ -644,19 +644,19 @@ vec3 F_schlick(vec3 f0, float cos_theta)
 }
 
 /* Fresnel approximation for LTC area lights (not MRP) */
-vec3 F_area(vec3 f0, vec2 lut)
+vec3 F_area(vec3 f0, vec3 f90, vec2 lut)
 {
   /* Unreal specular matching : if specular color is below 2% intensity,
    * treat as shadowning */
-  return saturate(50.0 * dot(f0, vec3(0.3, 0.6, 0.1))) * lut.y + lut.x * f0;
+  return saturate(50.0 * dot(f0, vec3(0.3, 0.6, 0.1))) * lut.y * f90 + lut.x * f0;
 }
 
 /* Fresnel approximation for IBL */
-vec3 F_ibl(vec3 f0, vec2 lut)
+vec3 F_ibl(vec3 f0, vec3 f90, vec2 lut)
 {
   /* Unreal specular matching : if specular color is below 2% intensity,
    * treat as shadowning */
-  return saturate(50.0 * dot(f0, vec3(0.3, 0.6, 0.1))) * lut.y + lut.x * f0;
+  return saturate(50.0 * dot(f0, vec3(0.3, 0.6, 0.1))) * lut.y * f90 + lut.x * f0;
 }
 
 /* GGX */
diff --git a/source/blender/draw/engines/eevee/shaders/default_frag.glsl b/source/blender/draw/engines/eevee/shaders/default_frag.glsl
index c568b4d94be..64a1c725a6b 100644
--- a/source/blender/draw/engines/eevee/shaders/default_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/default_frag.glsl
@@ -29,8 +29,9 @@ Closure nodetree_exec(void)
   vec3 dielectric = vec3(0.034) * specular * 2.0;
   vec3 albedo = mix(basecol, vec3(0.0), metallic);
   vec3 f0 = mix(dielectric, basecol, metallic);
+  vec3 f90 = mix(vec3(1.0), f0, (1.0 - specular) * metallic);
   vec3 out_diff, out_spec, ssr_spec;
-  eevee_closure_default(N, albedo, f0, 1, roughness, 1.0, out_diff, out_spec, ssr_spec);
+  eevee_closure_default(N, albedo, f0, f90, 1, roughness, 1.0, out_diff, out_spec, ssr_spec);
 
   Closure result = Closure(out_spec + out_diff * albedo,
                            1.0,
diff --git a/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl b/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
index fe3225b1086..e96667c0488 100644
--- a/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
+++ b/source/blender/draw/engines/eevee/shaders/lit_surface_frag.glsl
@@ -119,6 +119,7 @@ void CLOSURE_NAME(vec3 N
 #ifdef CLOSURE_GLOSSY
                   ,
                   vec3 f0,
+                  vec3 f90,
                   int ssr_id
 #endif
 #if defined(CLOSURE_GLOSSY) || defined(CLOSURE_REFRACTION)
@@ -264,12 +265,12 @@ void CLOSURE_NAME(vec3 N
 
 #ifdef CLOSURE_GLOSSY
   vec2 brdf_lut_lights = texture(utilTex, vec3(lut_uv, 1.0)).ba;
-  out_spec *= F_area(f0, brdf_lut_lights.xy);
+  out_spec *= F_area(f0, f90, brdf_lut_lights.xy);
 #endif
 
 #ifdef CLOSURE_CLEARCOAT
   vec2 brdf_lut_lights_clear = texture(utilTex, vec3(lut_uv_clear, 1.0)).ba;
-  out_spec_clear *= F_area(vec3(0.04), brdf_lut_lights_clear.xy);
+  out_spec_clear *= F_area(vec3(0.04), vec3(1.0), brdf_lut_lights_clear.xy);
   out_spec += out_spec_clear * C_intensity;
 #endif
 
@@ -454,7 +455,7 @@ void CLOSURE_NAME(vec3 N
 
   /* This factor is outputted to be used by SSR in order
    * to match the intensity of the regular reflections. */
-  ssr_spec = F_ibl(f0, brdf_lut);
+  ssr_spec = F_ibl(f0, f90, brdf_lut);
   float spec_occlu = specular_occlusion(NV, final_ao, roughness);
 
   /* The SSR pass recompute the occlusion to not apply it to the SSR */
@@ -475,7 +476,8 @@ void CLOSURE_NAME(vec3 N
   NV = dot(C_N, V);
   vec2 C_uv = lut_coords(NV, C_roughness);
   vec2 C_brdf_lut = texture(utilTex, vec3(C_uv, 1.0)).rg;
-  vec3 C_fresnel = F_ibl(vec3(0.04), C_brdf_lut) * specular_occlusion(NV, final_ao, C_roughness);
+  vec3 C_fresnel = F_ibl(vec3(0.04), vec3(1.0), C_brdf_lut) *
+                   specular_occlusion(NV, final_ao, C_roughness);
 
   out_spec += C_spec_accum.rgb * C_fresnel * C_intensity;
 #endif