2 files changed, 20 insertions, 0 deletions
diff --git a/src/math/axis.cc b/src/math/axis.cc
index 4d752bf..aa35d92 100644
--- a/src/math/axis.cc
+++ b/src/math/axis.cc
@@ -74,6 +74,23 @@ void Axis::change_roll(const float angle) {
 	axis_vector[1].assign(up);
 }
 
+// perform a rotation about an arbitrary axis
+/* notes:
+	http://mathworld.wolfram.com/RotationFormula.html
+*/
+void Axis::rotate(Vector3f const &normal, float angle)
+{
+	float cosa = cosf(angle);
+	float sina = sinf(angle);
+
+	for (size_t i =0; i < 3; i++) {
+		axis_vector[i] = 
+			axis_vector[i]*cosa + 
+			normal * dotproduct(normal, axis_vector[i]) * (1 - cosa) + 
+			crossproduct(axis_vector[i], normal)*sina;
+	}
+}
+
 /*
 Axis const Axis::transpose()
 {
diff --git a/src/math/axis.h b/src/math/axis.h
index d011675..1422564 100644
--- a/src/math/axis.h
+++ b/src/math/axis.h
@@ -48,6 +48,9 @@ public:
 	/// change roll, rotate around forward vector (positive is left)
 	void change_roll(const float angle);
 
+	/// rotation about an arbitrary axis
+	void rotate(Vector3f const &normal, float angle);
+
 private:
 	Vector3f		axis_vector[3];
 };