Math: ability to explicitly create Quaternion for given vector.

src/Math/Quaternion.h

@@ -124,6 +124,13 @@ template<class T> class Quaternion {
         /** @brief Create quaternion from vector and scalar */
         inline constexpr /*implicit*/ Quaternion(const Vector3<T>& vector, T scalar): _vector(vector), _scalar(scalar) {}
 
+        /**
+         * @brief Create quaternion from vector
+         *
+         * Scalar is set to `0`.
+         */
+        inline constexpr explicit Quaternion(const Vector3<T>& vector): _vector(vector), _scalar(T(0)) {}
+
         /** @brief Equality comparison */
         inline bool operator==(const Quaternion<T>& other) const {
             return _vector == other._vector && MathTypeTraits<T>::equals(_scalar, other._scalar);

src/Math/Test/QuaternionTest.cpp

@@ -28,6 +28,7 @@ class QuaternionTest: public Corrade::TestSuite::Tester {
 
         void construct();
         void constructDefault();
+        void constructFromVector();
         void addSubtract();
         void negated();
         void multiplyDivideScalar();
@@ -54,6 +55,7 @@ typedef Math::Vector3<float> Vector3;
 QuaternionTest::QuaternionTest() {
     addTests(&QuaternionTest::construct,
              &QuaternionTest::constructDefault,
+             &QuaternionTest::constructFromVector,
              &QuaternionTest::addSubtract,
              &QuaternionTest::negated,
              &QuaternionTest::multiplyDivideScalar,
@@ -83,6 +85,10 @@ void QuaternionTest::constructDefault() {
     CORRADE_COMPARE(Quaternion(), Quaternion({0.0f, 0.0f, 0.0f}, {1.0f}));
 }
 
+void QuaternionTest::constructFromVector() {
+    CORRADE_COMPARE(Quaternion({1.0f, 2.0f, 3.0f}), Quaternion({1.0f, 2.0f, 3.0f}, 0.0f));
+}
+
 void QuaternionTest::addSubtract() {
     Quaternion a({1.0f, 3.0f, -2.0f}, -4.0f);
     Quaternion b({-0.5f, 1.4f, 3.0f}, 12.0f);