//my listener for gravity physics
    class GravityListener : public VEEventListener {
        VESceneNode* m_pObject = nullptr;
        VESceneNode* m_pPlane = nullptr;

        glm::vec3 f = glm::vec3(0, 0, 0);
        glm::vec3 v = glm::vec3(0, 0, 0);
        glm::vec3 w = glm::vec3(0, 0, 0);
        glm::vec3 l = glm::vec3(0, 0, 0);

        float m = 1;
        float width = 1;
        float height = 1;
        float depth = 1;

        glm::mat3 i = glm::mat3(
            glm::vec3(1.0f / 12.0f * m * (height * height + depth * depth), 0, 0),
            glm::vec3(0, 1.0f / 12.0f * m * (width * width + depth * depth), 0),
            glm::vec3(0, 0, 1.0f / 12.f * m * (width * width + height * height))
        );

        glm::vec3 m_pVertices[8] = {
            glm::vec3(0.500000, -0.500000, 0.500000),
            glm::vec3(0.500000, -0.500000, 0.500000),
            glm::vec3(-0.500000, 0.500000, 0.500000),
            glm::vec3(0.500000, 0.500000, 0.500000),
            glm::vec3(-0.500000, 0.500000, -0.500000),
            glm::vec3(0.500000, 0.500000, -0.500000),
            glm::vec3(-0.500000, -0.500000, -0.500000),
            glm::vec3(0.500000, -0.500000, -0.500000)
        };


    public:
        ///Constructor
        GravityListener(std::string name, VESceneNode* pObject, VESceneNode* pPlane) :
            VEEventListener(name), m_pObject(pObject), m_pPlane(pPlane) {

            glm::vec3 ax = glm::vec3(0, 0, 1);
            float angle = (float)rand();

            glm::mat3 rotation_matrix = glm::rotate(angle, ax);

            glm::vec3 origin = m_pObject->getPosition();
            m_pObject->setPosition(glm::vec3());
            m_pObject->multiplyTransform(rotation_matrix);
            m_pObject->setPosition(origin);

            for (glm::vec3& vertex : m_pVertices) {

                vertex = vertex * rotation_matrix;

            }
        };

        void onFrameStarted(veEvent event) {

            glm::vec3 a = f / m;

            v = v + event.dt * a;

            m_pObject->setPosition(glm::vec3(
                m_pObject->getPosition().x + event.dt * v.x,
                m_pObject->getPosition().y + event.dt * v.y,
                m_pObject->getPosition().z + event.dt * v.z)
            );

            glm::vec3 t = glm::cross(f, l);

            glm::vec3 angular_acceleration = glm::vec3();

            if (t.x != 0 || t.y != 0 || t.z != 0) {
                angular_acceleration = glm::inverse(i) * t;
            }

            w = w + event.dt * angular_acceleration;

            if (glm::length(w) != 0) {

                glm::mat3 rotation_matrix = glm::rotate(glm::length(w), glm::normalize(w));

                glm::vec3 origin = m_pObject->getPosition();
                m_pObject->setPosition(glm::vec3());
                m_pObject->multiplyTransform(rotation_matrix);
                m_pObject->setPosition(origin);

                for (glm::vec3& vertex : m_pVertices) {

                    vertex = vertex * rotation_matrix;

                }
            }

            //collision detection and response
            for (glm::vec3& vertex : m_pVertices) {

                if (m_pObject->getPosition().y + vertex.y < 0) {

                    m_pObject->setPosition(glm::vec3(
                        m_pObject->getPosition().x,
                        -vertex.y,
                        m_pObject->getPosition().z
                    ));

                    glm::vec3 n = glm::vec3(0, 1, 0);
                    float rest_coeff = 0.5;

                    //velocity at collision
                    glm::vec3 vc = v + glm::cross(w, vertex);

                    //this works for velocity
                    glm::vec3 j = -(1 + rest_coeff) * vc  * n /  (1 / m);

                    //this should work for both theoretically
                    //glm::vec3 j = (-(1 + rest_coeff) * va * n) / (1 / m + n * glm::cross(glm::inverse(i) * glm::cross(vertex, n), vertex));

                    v = v + (j * n) / m;

                    //w = w + glm::inverse(i) * glm::cross(vertex, j * n);
                }
            }
        }

        virtual bool onKeyboard(veEvent event) {

            if (event.idata3 == GLFW_RELEASE) {
                return false;
            }

            if (event.idata1 == GLFW_KEY_SPACE) {
                // 'activates' gravity
                f = glm::vec3(0, -9.81 * m, 0);

                return false;
            }
            return false;
        }

    };