如何检测雪碧在向哪个方向移动？

Question

我正在制作一个2D塔防御游戏，以学习的目的，现在我被困在如何使敌人看到正确的方向时，移动。

以下是我尝试过但没有成功的地方：

    // 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;
    }

下面是更新方法，它是一个5x4雪碧表：

    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;
        }
    }

在绘制方法中，我试图检测精灵所面临的位置，我不确定最好的方法是什么，但它不起作用，敌人被正确而生动地画出来，但有时在地图路径上面对错误的方向，在某一点上他们消失了：

    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);

    }
}
}

Answer 1

我解决了它，我从基类中选择位置并更新基类中的最后一个位置，在敌人类中，update方法将根据位置处理它将使用的帧。

敌人等级更新方法：

            if (lastPosition.Y < position.Y)
            {
                initialFrame = 15;
                lastFrame = 19;
            }

            if (position.Y < lastPosition.Y)
            {
                initialFrame = 10;
                lastFrame = 14;
            }

            if (position.X > lastPosition.X)
            {
                initialFrame = 5;
                lastFrame = 9;
            }

            if (position.X < lastPosition.X)
            {
                initialFrame = 0;
                lastFrame = 4;
            }

            currentFrame = initialFrame;
            totalFrame = lastFrame;

            timeSinceLastFrame += gameTime.ElapsedGameTime.Milliseconds;
            if (timeSinceLastFrame > milisecondsPerFrame)
            {
                timeSinceLastFrame -= milisecondsPerFrame;
                currentFrame++;
                if (currentFrame == totalFrame)
                    currentFrame = 0;
            }       
        }

Answer 2

首先看一看代码的这段：

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;
}

(lastPosition.Y < destinationPosition.Y)和(destinationRectangle.Y > lastPosition.Y)是相同的条件，因此在这两种情况下，您都将拥有south = true。

第二，为什么要使用四个布尔变量？相反，使用一个具有四种可能状态的变量。Enum对此很有好处：

enum Direction
{
    None = 0, // default
    North = 1,
    South = 2,
    East = 3,
    West = 4
}

用单向变量代替四个布尔值。变量越少，麻烦越少。

最后一次。我不太明白你怎么移动你的精灵？我是说，在改变和弦之前，你是如何探测方向的？在我看来，它应该这样做：

1. 在Update()中，检测需要向哪个方向移动和更改方向变量，并在此基础上更改和更新sprite状态。
2. 在当前状态下画精灵。