[QQuaternion] Add operator* that rotates a vector with a quaternion

Same as quaternion.rotatedVector(vec).
Expression like `vec = quat * vec` quite common in the 3D world.

Change-Id: I0edd5a5f80537bd149f03f682b3de15c54463e23
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

src/gui/math3d/qquaternion.cpp

@@ -748,6 +748,18 @@ QQuaternion QQuaternion::fromRotationMatrix(const QMatrix3x3 &rot3x3)
     \sa QQuaternion::operator/=()
 */
 
+#ifndef QT_NO_VECTOR3D
+
+/*!
+    \fn QVector3D operator*(const QQuaternion &quaternion, const QVector3D &vec)
+    \since 5.5
+    \relates QQuaternion
+
+    Rotates a vector \a vec with a quaternion \a quaternion to produce a new vector in 3D space.
+*/
+
+#endif
+
 /*!
     \fn bool qFuzzyCompare(const QQuaternion& q1, const QQuaternion& q2)
     \relates QQuaternion

src/gui/math3d/qquaternion.h

@@ -308,6 +308,11 @@ inline QVector3D QQuaternion::vector() const
     return QVector3D(xp, yp, zp);
 }
 
+inline QVector3D operator*(const QQuaternion &quaternion, const QVector3D &vec)
+{
+    return quaternion.rotatedVector(vec);
+}
+
 inline void QQuaternion::getAxisAndAngle(QVector3D *axis, float *angle) const
 {
     float aX, aY, aZ;