EEVEE: Better fit of BTDF LUTeevee-ggx-lut-fix

This simplify the BTDF retreival removing the manual clean cut at
low roughness.

This maximize the precision of the LUT by scalling the sides by the
critical angle.

Also touched the ior > 1.0 approximation to be smoother.

1 files changed, 2 insertions, 1 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 1ac965d24ca..cb4d8931af0 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
@@ -24,6 +24,7 @@ float ior_from_f0(float f0)
   return (-f - 1.0) / (f - 1.0);
 }
 
+/* Simplified form of F_eta(eta, 1.0). */
 float f0_from_ior(float eta)
 {
   float A = (eta - 1.0) / (eta + 1.0);
@@ -69,7 +70,7 @@ float F_eta(float eta, float cos_theta)
 /* Fresnel color blend base on fresnel factor */
 vec3 F_color_blend(float eta, float fresnel, vec3 f0_color)
 {
-  float f0 = F_eta(eta, 1.0);
+  float f0 = f0_from_ior(eta);
   float fac = saturate((fresnel - f0) / (1.0 - f0));
   return mix(f0_color, vec3(1.0), fac);
 }