Matrix3x3(const Quaternion& q)
    {
        float yy = q.y * q.y;
        float zz = q.z * q.z;
        float xy = q.x * q.y;
        float zw = q.z * q.w;
        float xz = q.x * q.z;
        float yw = q.y * q.w;
        float xx = q.x * q.x;
        float yz = q.y * q.z;
        float xw = q.x * q.w;

        m_mat[0][0] = 1 - 2 * yy - 2 * zz;
        m_mat[0][1] = 2 * xy + 2 * zw;
        m_mat[0][2] = 2 * xz - 2 * yw;

        m_mat[1][0] = 2 * xy - 2 * zw;
        m_mat[1][1] = 1 - 2 * xx - 2 * zz;
        m_mat[1][2] = 2 * yz + 2 * xw;

        m_mat[2][0] = 2 * xz + 2 * yw;
        m_mat[2][1] = 2 * yz - 2 * xw;
        m_mat[2][2] = 1 - 2 * xx - 2 * yy;
    }