1 files changed, 32 insertions, 0 deletions
diff --git a/res/effectlib/calculateRoughness.glsllib b/res/effectlib/calculateRoughness.glsllib
new file mode 100644
index 0000000..13ca823
--- /dev/null
+++ b/res/effectlib/calculateRoughness.glsllib
@@ -0,0 +1,32 @@
+float calculateRoughness( in vec3 N, in float roughnessU, in float roughnessV, in vec3 tangentU )
+{
+  float roughness = roughnessU;
+  if ( abs(roughnessU - roughnessV) > 0.00001)
+  {
+    // determine major and minor radii a and b, and the vector along the major axis
+    float a = roughnessU;
+    float b = roughnessV;
+
+    // we need the angle between the major axis and the projection of viewDir on the tangential plane
+    // the major axis is the orthonormalization of tangentU with respect to N
+    // the projection of viewDir is the orthonormalization of viewDir with respect to N
+    // as both vectors would be calculated by orthonormalize, we can as well leave the second cross
+    // product in those calculations away, as they don't change the angular relation.
+    vec3 minorAxis = normalize( cross( tangentU, N ) );   // crossing this with N would give the major axis
+                                                          // which is equivalent to orthonormalizing tangentU with respect to N
+    if ( roughnessU < roughnessV )
+    {
+      a = roughnessV;
+      b = roughnessU;
+      minorAxis = cross( N, minorAxis );
+    }
+
+    vec3 po = normalize( cross( viewDir, N ) );
+    float cosPhi = dot( po, minorAxis );
+
+    // determine the polar coordinate of viewDir, take that radius as the roughness
+    float excentricitySquare = 1.0f - square( b / a );
+    roughness = b / sqrt( 1.0f - excentricitySquare * square( cosPhi ) );
+  }
+  return( roughness );
+}