Eevee: Use "constant folding" for the principle shader

This is more like a static optimisation when some parameters are set to 1.0
or 0.0. In theses case we use a more optimized version of the node.

This also revisit the transmission parameter behaviour to make it closer to
cycles.

1 files changed, 8 insertions, 0 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 8b232bf14a4..286f00783d9 100644
--- a/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/bsdf_common_lib.glsl
@@ -548,6 +548,14 @@ float F_eta(float eta, float cos_theta)
 	return result;
 }
 
+/* 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 fac = saturate((fresnel - f0) / max(1e-8, 1.0 - f0));
+	return mix(f0_color, vec3(1.0), fac);
+}
+
 /* Fresnel */
 vec3 F_schlick(vec3 f0, float cos_theta)
 {