public Vector3f subtract(Vector3f vec, Vector3f result) {
        if (result == null) {
            result = new Vector3f();
        }
        result.x = x - vec.x;
        result.y = y - vec.y;
        result.z = z - vec.z;
        return result;
    }
Subtracts the specified vector and returns the difference in a 3rd
vector. The current instance is unaffected unless it's
{@code result}.

@param vec the vector to subtract (not null, unaffected unless it's
    {@code result})
@param result storage for the difference, or null for a new Vector3f
@return either {@code result} or a new Vector3f
jme3-core/src/main/java/com/jme3/math/Vector3f.java