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Based on outdated refract patch D6619 by @cubic_sloth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, 18 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_float3.hh b/source/blender/blenlib/BLI_float3.hh
index 7e49cc89b52..cbc4d4ed366 100644
--- a/source/blender/blenlib/BLI_float3.hh
+++ b/source/blender/blenlib/BLI_float3.hh
@@ -191,6 +191,24 @@ struct float3 {
     return result;
   }
 
+  static float3 refract(const float3 &incident, const float3 &normal, const float eta)
+  {
+    float3 result;
+    float k = 1.0f - eta * eta * (1.0f - dot(normal, incident) * dot(normal, incident));
+    if (k < 0.0f) {
+      result = float3(0.0f);
+    }
+    else {
+      result = eta * incident - (eta * dot(normal, incident) + sqrt(k)) * normal;
+    }
+    return result;
+  }
+
+  static float3 faceforward(const float3 &vector, const float3 &incident, const float3 &reference)
+  {
+    return dot(reference, incident) < 0.0f ? vector : -vector;
+  }
+
   static float3 safe_divide(const float3 &a, const float3 &b)
   {
     float3 result;