/// <summary>
    /// 做直线运动
    /// <para>bullet 敌机子弹</para>
    /// <para>float v 速度</para>
    /// <para>float angle 速度方向</para>
    /// <para>bool isAimToPlayer 是否朝向玩家</para>
    /// </summary>
    /// <param name="luaState"></param>
    /// <returns></returns>
    public static int EnemyBulletDoStraightMove(ILuaState luaState)
    {
        EnemyBulletBase bullet        = luaState.ToUserData(-4) as EnemyBulletBase;
        float           v             = (float)luaState.ToNumber(-3);
        float           angle         = (float)luaState.ToNumber(-2);
        bool            isAimToPlayer = luaState.ToBoolean(-1);

        luaState.Pop(4);
        if (isAimToPlayer)
        {
            Vector2 playerPos = PlayerInterface.GetInstance().GetCharacter().GetPosition();
            angle += MathUtil.GetAngleBetweenXAxis(playerPos - bullet.GetPosition());
        }
        bullet.DoStraightMove(v, angle);
        return(0);
    }