public Vector3f add(Vector3f vec, Vector3f result) {
        result.x = x + vec.x;
        result.y = y + vec.y;
        result.z = z + vec.z;
        return result;
    }
Adds a specified vector and returns the sum in a 3rd vector. The current
instance is unaffected unless it's {@code result}.

@param vec the vector to add (not null, unaffected unless it's
    {@code result})
@param result storage for the sum (not null)
@return {@code result} (for chaining)
jme3-core/src/main/java/com/jme3/math/Vector3f.java