Vector::angle() now expects normalized vectors.

src/Math/Test/CMakeLists.txt

@@ -1,6 +1,7 @@
 corrade_add_test2(MathMathTypeTraitsTest MathTypeTraitsTest.cpp)
 
 corrade_add_test2(MathVectorTest VectorTest.cpp)
+set_target_properties(MathVectorTest PROPERTIES COMPILE_FLAGS -DCORRADE_GRACEFUL_ASSERT)
 corrade_add_test2(MathVector2Test Vector2Test.cpp)
 corrade_add_test2(MathVector3Test Vector3Test.cpp)
 corrade_add_test2(MathVector4Test Vector4Test.cpp)

src/Math/Test/VectorTest.cpp

@@ -131,7 +131,14 @@ void VectorTest::product() {
 }
 
 void VectorTest::angle() {
-    CORRADE_COMPARE(Vector3::angle({2.0f, 3.0f, 4.0f}, {1.0f, -2.0f, 3.0f}), rad(1.162514f));
+    ostringstream o;
+    Error::setOutput(&o);
+    /* Both vectors must be normalized, otherwise NaN is returned */
+    CORRADE_COMPARE(Vector3::angle(Vector3(2.0f, 3.0f, 4.0f).normalized(), {1.0f, -2.0f, 3.0f}), numeric_limits<Vector3::Type>::quiet_NaN());
+    CORRADE_COMPARE(o.str(), "Math::Vector::angle(): vectors must be normalized!\n");
+    CORRADE_COMPARE(Vector3::angle({2.0f, 3.0f, 4.0f}, Vector3(1.0f, -2.0f, 3.0f).normalized()), numeric_limits<Vector3::Type>::quiet_NaN());
+
+    CORRADE_COMPARE(Vector3::angle(Vector3(2.0f, 3.0f, 4.0f).normalized(), Vector3(1.0f, -2.0f, 3.0f).normalized()), rad(1.162514f));
 }
 
 void VectorTest::negative() {

src/Math/Vector.h

@@ -20,6 +20,7 @@
  */
 
 #include <cmath>
+#include <limits>
 #include <Utility/Debug.h>
 
 #include "MathTypeTraits.h"
@@ -82,16 +83,18 @@ template<size_t size, class T> class Vector {
         }
 
         /**
-         * @brief Angle between vectors
+         * @brief Angle between normalized vectors
          *
          * @f[
          * \phi = \frac{a \cdot b}{|a| \cdot |b|}
          * @f]
-         *
-         * @todo optimize - Assume the vectors are normalized?
+         * @attention If any of the parameters is not normalized (and
+         * assertions are enabled), returns NaN.
          */
         inline static T angle(const Vector<size, T>& a, const Vector<size, T>& b) {
-            return std::acos(dot(a, b)/(a.length()*b.length()));
+            CORRADE_ASSERT(MathTypeTraits<T>::equals(a.dot(), T(1)) && MathTypeTraits<T>::equals(b.dot(), T(1)),
+                           "Math::Vector::angle(): vectors must be normalized!", std::numeric_limits<T>::quiet_NaN());
+            return std::acos(dot(a, b));
         }
 
         /** @brief Default constructor */