public Vector2f subtract(Vector2f vec, Vector2f store) {
        if (store == null) {
            store = new Vector2f();
        }
        store.x = x - vec.x;
        store.y = y - vec.y;
        return store;
    }
Subtracts the specified vector and returns the difference in a 3rd
vector. The current instance is unaffected unless it's {@code store}.

<p>It is safe for {@code vec} and {@code store} to be the same object.

@param vec the vector to subtract (not null, unaffected unless it's
    {@code store})
@param store storage for the difference, or null for a new Vector2f
@return either {@code store} or a new Vector2f
jme3-core/src/main/java/com/jme3/math/Vector2f.java