Math: added Quaternion addition and subtraction.

src/Math/Quaternion.h

@@ -120,6 +120,28 @@ template<class T> class Quaternion {
             };
         }
 
+        /**
+         * @brief Add and assign quaternion
+         *
+         * The computation is done in-place. @f[
+         *      p + q = [\boldsymbol p_V + \boldsymbol q_V, p_S + q_S]
+         * @f]
+         */
+        inline Quaternion<T>& operator+=(const Quaternion<T>& other) {
+            _vector += other._vector;
+            _scalar += other._scalar;
+            return *this;
+        }
+
+        /**
+         * @brief Add quaternion
+         *
+         * @see operator+=()
+         */
+        inline Quaternion<T> operator+(const Quaternion<T>& other) const {
+            return Quaternion<T>(*this)+=other;
+        }
+
         /**
          * @brief Negated quaternion
          *
@@ -131,6 +153,28 @@ template<class T> class Quaternion {
             return {-_vector, -_scalar};
         }
 
+        /**
+         * @brief Subtract and assign quaternion
+         *
+         * The computation is done in-place. @f[
+         *      p - q = [\boldsymbol p_V - \boldsymbol q_V, p_S - q_S]
+         * @f]
+         */
+        inline Quaternion<T>& operator-=(const Quaternion<T>& other) {
+            _vector -= other._vector;
+            _scalar -= other._scalar;
+            return *this;
+        }
+
+        /**
+         * @brief Subtract quaternion
+         *
+         * @see operator-=()
+         */
+        inline Quaternion<T> operator-(const Quaternion<T>& other) const {
+            return Quaternion<T>(*this)-=other;
+        }
+
         /**
          * @brief Multiply with scalar and assign
          *

src/Math/Test/MathQuaternionTest.cpp

@@ -27,6 +27,7 @@ class QuaternionTest: public Corrade::TestSuite::Tester {
         explicit QuaternionTest();
 
         void construct();
+        void addSubtract();
         void negated();
         void multiplyDivideScalar();
         void multiply();
@@ -46,6 +47,7 @@ typedef Math::Vector3<float> Vector3;
 
 QuaternionTest::QuaternionTest() {
     addTests(&QuaternionTest::construct,
+             &QuaternionTest::addSubtract,
              &QuaternionTest::negated,
              &QuaternionTest::multiplyDivideScalar,
              &QuaternionTest::multiply,
@@ -67,6 +69,15 @@ void QuaternionTest::construct() {
     CORRADE_COMPARE(Quaternion(), Quaternion({0.0f, 0.0f, 0.0f}, {1.0f}));
 }
 
+void QuaternionTest::addSubtract() {
+    Quaternion a({1.0f, 3.0f, -2.0f}, -4.0f);
+    Quaternion b({-0.5f, 1.4f, 3.0f}, 12.0f);
+    Quaternion c({0.5f, 4.4f, 1.0f}, 8.0f);
+
+    CORRADE_COMPARE(a+b, c);
+    CORRADE_COMPARE(c-b, a);
+}
+
 void QuaternionTest::negated() {
     CORRADE_COMPARE(-Quaternion({1.0f, 2.0f, -3.0f}, -4.0f), Quaternion({-1.0f, -2.0f, 3.0f}, 4.0f));
 }