From 4c1608378a79d62d239cb9c6270832720bde57c3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20Vondru=C5=A1?= <mosra@centrum.cz>
Date: Sat, 16 Feb 2013 20:12:35 +0100
Subject: [PATCH] Math: document that Quaternion::rotationAxis() might return
 NaN vector.

---
 src/Math/Quaternion.h            | 4 +++-
 src/Math/Test/QuaternionTest.cpp | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Math/Quaternion.h b/src/Math/Quaternion.h
index 47c4f3991..be49ec335 100644
--- a/src/Math/Quaternion.h
+++ b/src/Math/Quaternion.h
@@ -170,7 +170,9 @@ template<class T> class Quaternion {
         /**
          * @brief Rotation axis of unit quaternion
          *
-         * Expects that the quaternion is normalized. @f[
+         * Expects that the quaternion is normalized. Returns either unit-length
+         * vector for valid rotation quaternion or NaN vector for
+         * default-constructed quaternion. @f[
          *      \boldsymbol a = \frac{\boldsymbol q_V}{\sqrt{1 - q_S^2}}
          * @f]
          * @see rotationAngle(), rotation()
diff --git a/src/Math/Test/QuaternionTest.cpp b/src/Math/Test/QuaternionTest.cpp
index cfd6686eb..079c0b755 100644
--- a/src/Math/Test/QuaternionTest.cpp
+++ b/src/Math/Test/QuaternionTest.cpp
@@ -213,6 +213,10 @@ void QuaternionTest::rotation() {
     CORRADE_COMPARE(q2, Quaternion(Vector3(-0.5f, -0.5f, -0.5f), 0.5f));
     CORRADE_COMPARE(q2.rotationAngle(), deg(120.0f));
     CORRADE_COMPARE(q2.rotationAxis(), -axis);
+
+    /* Default-constructed quaternion has zero angle and NaN axis */
+    CORRADE_COMPARE(Quaternion().rotationAngle(), deg(0.0f));
+    CORRADE_VERIFY(Quaternion().rotationAxis() != Quaternion().rotationAxis());
 }
 
 void QuaternionTest::angle() {