如何检测精灵的移动方向

我正在制作一款用于学习目的的 2D 塔防游戏，现在我被困在如何让敌人在移动时看向正确的方向。

这是我尝试过的没有成功：

    // Class constructor
    public AnimatedSprite(Texture2D texture, int lines, int columns, Vector2 position)
        : base ( texture, position)
    {
        this.texture = texture;
        this.position = position;
        Lines = lines; // How many lines the sprite-sheet have
        Columns = columns; How many columns the sprite-sheet have
        totalFrames = Lines * Columns;
    }

这是更新方法，它是一个 5x4 的精灵表：

    public override void Update(GameTime gameTime)
    {
        // Depending on the direction the sprite is moving
        // it will use different parts of the sprite-sheet
        if (west == true)
        {
            initialFrame = 0;
            finalFrame = 4;
        }
        if (east == true)
        {
            initialFrame = 5;
            finalFrame = 9;
        }
        if (north == true)
        {
            initialFrame = 10;
            finalFrame = 14;
        }
        if (south == true)
        {
            initialFrame = 15;
            finalFrame = 19;
        }
        // When to update the current frame
        timeSinseLastFrame += gameTime.ElapsedGameTime.Milliseconds;
        if (timeSinceLastFrame > milisecondsPerFrame)
        {
            timeSinceLastFrame -= milisecondsPerFrame;
            currentFrame++;
         // Reset the frame to complete the loop
            if (currentFrame == finalFrame)
                currentFrame = initialFrame;
        }
    }

尝试检测精灵面对的位置，我不确定最好的方法，但它不起作用，敌人被正确绘制并动画化，但有时沿着地图路径面向错误的方向，在某个点它们消失：

    public override void Draw(SpriteBatch spriteBatch)
    {
        int width = texture.Width / Columns;
        int height = texture.Height / Lines;
        int line = (int)((float)currentFrame / (float)Columns);
        int column = currentFrame % Columns;
        Rectangle originRectangle = new Rectangle(width * column, height * line, width, height);
        Rectangle destinationRectangle = new Rectangle((int)position.X, (int)position.Y, width, height);

        // Heres what i think it's not correct, how to detect the direction
        // I tried to calculate it by the last X and Y position
        // So if the current Y value is smaller the last Y value
        // The sprite moved south
        Rectangle lastPosition = originRectangle;
        Rectangle destinationPosition = destinationRectangle;
        if (lastPosition.Y < destinationPosition.Y)
        {
            north = true;
            south = false;
            east = false;
            west = false;
        }
        if (destinationRectangle.Y > lastPosition.Y)
        {
            north = false;
            south = true;
            east = false;
            west = false;
        }
        if (destinationRectangle.X > lastPosition.X)
        {
            north = false;
            south = false;
            east = true;
            west = false;
        }
        if (destinationRectangle.X < lastPosition.X)
        {
            north = false;
            south = false;
            east = false;
            west = true;
        }
        spriteBatch.Draw(texture, destinationRectangle, originRectangle, Color.White);
    }
}
}