Nodes: Add Refract and Faceforward functions to Vector Maths nodes

Cycles, Eevee, OSL, Geo, Attribute

Based on outdated refract patch D6619 by @cubic_sloth

`refract` and `faceforward` are standard functions in GLSL, OSL and Godot shader languages.
Adding these functions provides Blender shader artists access to these standard functions.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D10622

1 files changed, 16 insertions, 0 deletions

diff --git a/intern/cycles/util/util_math_float3.h b/intern/cycles/util/util_math_float3.h
index 67c5c61e4c0..9673c043189 100644
--- a/intern/cycles/util/util_math_float3.h
+++ b/intern/cycles/util/util_math_float3.h
@@ -388,6 +388,22 @@ ccl_device_inline float3 reflect(const float3 incident, const float3 normal)
   return incident - 2.0f * unit_normal * dot(incident, unit_normal);
 }
 
+ccl_device_inline float3 refract(const float3 incident, const float3 normal, const float eta)
+{
+  float k = 1.0f - eta * eta * (1.0f - dot(normal, incident) * dot(normal, incident));
+  if (k < 0.0f)
+    return zero_float3();
+  else
+    return eta * incident - (eta * dot(normal, incident) + sqrt(k)) * normal;
+}
+
+ccl_device_inline float3 faceforward(const float3 vector,
+                                     const float3 incident,
+                                     const float3 reference)
+{
+  return (dot(reference, incident) < 0.0f) ? vector : -vector;
+}
+
 ccl_device_inline float3 project(const float3 v, const float3 v_proj)
 {
   float len_squared = dot(v_proj, v_proj);