雪碧会震动。怎么啦？

Question

我的敌人精灵在到达可变端点后一直在振动。怎么啦？为什么它在震动？此外，变量next_position永远不会为真。但是为什么呢？我想让敌人的精灵在到达当前的终点后移动到一个新的随机终点。

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    Texture2D enemy;
    Vector2 position, endposition;
    bool next_position = false;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        graphics.PreferredBackBufferWidth = 1280;
        graphics.PreferredBackBufferHeight = 720;
    }

    protected override void Initialize()
    {          
        base.Initialize();
    }

    protected override void LoadContent()
    {         
        spriteBatch = new SpriteBatch(GraphicsDevice);
        enemy = Content.Load<Texture2D>("zombie");
        Random randomstart = new Random();
        position = new Vector2(randomstart.Next(100, 200), randomstart.Next(100, 200));
        endposition = new Vector2(randomstart.Next(100, 600), randomstart.Next(100, 400));
    }

    protected override void Update(GameTime gameTime)
    {
        float delta = (float)gameTime.ElapsedGameTime.TotalSeconds;         
        Random random = new Random();
        position.X += 5 * delta;
        position.Y += 3 * delta;

        if (next_position == true)
        {
          endposition = new Vector2(random.Next(100, 600), random.Next(100, 400));
          next_position = false;
        }

        if (Vector2.Dot(endposition - position, endposition - position) > 0 || Vector2.Dot(endposition - position, endposition - position) < 0) 
        {
          Vector2 enemyDirection = Vector2.Normalize(endposition - position) * 100f;
          position += enemyDirection * delta;
        }
        else
        {
            next_position = true;
        }

        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin();
        spriteBatch.Draw(enemy, position, Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}

Answer 1

我对这条线有点困惑

if (Vector2.Dot(endposition - position, endposition - position) > 0 || Vector2.Dot(endposition - position, endposition - position) < 0)

应该做的就是。从代码的其余部分看，你要用它来实现的是检查精灵的位置是否是敌人的位置。这条线实际做的是计算相反方向的向量的点积，它永远不会是零，除非向量是零。因此从理论上讲，这实际上可能是可行的，但前提是位置必须与敌人的位置精确相等。

但是，你是在单位时间内移动精灵一个固定的距离，所以它实际上不会到达敌人，而是超过了敌人。然后发现自己在另一边，它会回到它来自的地方，并再次超过它。这会持续下去，并导致你所描述的振动。

现在，你想要实现的行为通常是计算两个对象(精灵和敌人)之间的距离，使用毕达哥拉斯定理，然后在距离低于某个阈值(容易但容易出错)或小于对象可以通过此特定更新的距离时接受对象的到达(在您的情况下，由于您移动的是归一化向量乘以100f * delta，此距离等于100f * delta)。

我希望我的解释对你有所帮助。当然，请随时要求澄清。

编辑(回复评论)：

您正在创建的limit向量相对没有意义，因为它只是max_distance在x和y方向上的位置偏移。没有必要做这样的事情。但是，另一个if()几乎包含了您想要的代码，请查看以下内容：

// first you calculate the distance we can move this update
float max_distance = 100f * delta;

// now, we compare the actual distance to the end position to that maximum
// if the actual distance is larger, then we are not there yet
// otherwise, (if the actual distance is smaller) we will overshoot the target,
// thus we are in fact there! (=close enough to continue)
// (note: we compare the distances squared to avoid a square root,
//  which makes this check much faster, which is good practice,
//  in case we ever scale this up to more objects)
if ((position - endposition).LengthSquared() > max_distance * max_distance)
{
    /* we are not yet there, continue moving! */
}
else
{
    /* we are there! */
}

它真的很简单，不需要其他的检查。如果这对你有用，请让我知道！

Answer 2

现在好多了，但还不够完美。敌人的精灵不再振动，但当它到达终点位置时，它总是向右移动一些像素。为什么它总是向右移动一些像素？其余的都运行得很好。

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    Texture2D enemy;
    Vector2 position, endposition;
    bool next_position = false;
    int count_nextposition;

    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        graphics.PreferredBackBufferWidth = 1280;
        graphics.PreferredBackBufferHeight = 720;
    }

    protected override void Initialize()
    {
        base.Initialize();
    }

    protected override void LoadContent()
    {
        spriteBatch = new SpriteBatch(GraphicsDevice);
        enemy = Content.Load<Texture2D>("zombie");
        Random randomstart = new Random();
        position = new Vector2(randomstart.Next(100, 200), randomstart.Next(100, 200));
        endposition = new Vector2(randomstart.Next(100, 600), randomstart.Next(100, 400));
        count_nextposition = randomstart.Next(90, 121);
    }

    protected override void Update(GameTime gameTime)
    {
        float delta = (float)gameTime.ElapsedGameTime.TotalSeconds;
        count_nextposition -= 1;
        Random random = new Random();
        position.X += 5 * delta;
        position.Y += 3 * delta;

        if (count_nextposition <= 0)
        {
        if (next_position == true)
        {
            endposition = new Vector2(random.Next(100, 600), random.Next(100, 400));
            next_position = false;
        }
        float max_distance = 100f * delta;
        if ((position - endposition).LengthSquared() > max_distance * max_distance)
        {
           Vector2 enemyDirection = Vector2.Normalize(endposition - position) * 100f;
           position += enemyDirection * delta;
        }
        else
        {

            next_position = true;
            count_nextposition = random.Next(90, 121);
        }
        }

        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin();
        spriteBatch.Draw(enemy, position, Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}