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Based on outdated refract patch D6619 by @cubic_sloth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

2 files changed, 13 insertions, 0 deletions

diff --git a/intern/cycles/kernel/shaders/node_math.h b/intern/cycles/kernel/shaders/node_math.h
index 3a008721d5e..2da73b94212 100644
--- a/intern/cycles/kernel/shaders/node_math.h
+++ b/intern/cycles/kernel/shaders/node_math.h
@@ -88,6 +88,13 @@ point wrap(point value, point max, point min)
                wrap(value[2], max[2], min[2]));
 }
 
+/* Built in OSL faceforward is `(dot(I, Nref) > 0) ? -N : N;` which is different to
+ * GLSL `dot(Nref, I) < 0 ? N : -N` for zero values. */
+point compatible_faceforward(point vec, point incident, point reference)
+{
+  return dot(reference, incident) < 0.0 ? vec : -vec;
+}
+
 matrix euler_to_mat(point euler)
 {
   float cx = cos(euler[0]);
diff --git a/intern/cycles/kernel/shaders/node_vector_math.osl b/intern/cycles/kernel/shaders/node_vector_math.osl
index 30f0b1daf4c..3963c23ea9c 100644
--- a/intern/cycles/kernel/shaders/node_vector_math.osl
+++ b/intern/cycles/kernel/shaders/node_vector_math.osl
@@ -46,6 +46,12 @@ shader node_vector_math(string math_type = "add",
   else if (math_type == "reflect") {
     Vector = reflect(Vector1, normalize(Vector2));
   }
+  else if (math_type == "refract") {
+    Vector = refract(Vector1, normalize(Vector2), Scale);
+  }
+  else if (math_type == "faceforward") {
+    Vector = compatible_faceforward(Vector1, Vector2, Vector3);
+  }
   else if (math_type == "dot_product") {
     Value = dot(Vector1, Vector2);
   }