Math: function for negating Quaternion, improved tests.

src/Math/Quaternion.h

@@ -112,6 +112,17 @@ template<class T> class Quaternion {
             };
         }
 
+        /**
+         * @brief Negated quaternion
+         *
+         * @f[
+         *      -q = [-\boldsymbol q_V, -q_S]
+         * @f]
+         */
+        inline Quaternion<T> operator-() const {
+            return {-_vector, -_scalar};
+        }
+
         /**
          * @brief Multiply with scalar and assign
          *

src/Math/RectangularMatrix.h

@@ -221,7 +221,7 @@ template<std::size_t cols, std::size_t rows, class T> class RectangularMatrix {
             return *this;
         }
 
-        /** @brief Negative matrix */
+        /** @brief Negated matrix */
         RectangularMatrix<cols, rows, T> operator-() const {
             RectangularMatrix<cols, rows, T> out;
 

src/Math/Test/MathQuaternionTest.cpp

@@ -27,6 +27,7 @@ class QuaternionTest: public Corrade::TestSuite::Tester {
         explicit QuaternionTest();
 
         void construct();
+        void negated();
         void multiplyDivideScalar();
         void multiply();
         void length();
@@ -45,6 +46,7 @@ typedef Math::Vector3<float> Vector3;
 
 QuaternionTest::QuaternionTest() {
     addTests(&QuaternionTest::construct,
+             &QuaternionTest::negated,
              &QuaternionTest::multiplyDivideScalar,
              &QuaternionTest::multiply,
              &QuaternionTest::length,
@@ -65,6 +67,10 @@ void QuaternionTest::construct() {
     CORRADE_COMPARE(Quaternion(), Quaternion({0.0f, 0.0f, 0.0f}, {1.0f}));
 }
 
+void QuaternionTest::negated() {
+    CORRADE_COMPARE(-Quaternion({1.0f, 2.0f, -3.0f}, -4.0f), Quaternion({-1.0f, -2.0f, 3.0f}, 4.0f));
+}
+
 void QuaternionTest::multiplyDivideScalar() {
     Quaternion a({1.0f, 3.0f, -2.0f}, -4.0f);
     Quaternion b({-1.5f, -4.5f, 3.0f}, 6.0f);
@@ -141,6 +147,9 @@ void QuaternionTest::matrix() {
     Quaternion q = Quaternion::fromRotation(angle, axis);
     Matrix<3, float> expected = Matrix4<float>::rotation(angle, axis).rotationScaling();
     CORRADE_COMPARE(q.matrix(), expected);
+
+    /* Verify that negated quaternion gives the same rotation */
+    CORRADE_COMPARE((-q).matrix(), expected);
 }
 
 void QuaternionTest::debug() {