在 XNA 中画一条永无止境的线

Question

我在 XNA 中画了一条线，我希望它永远不会结束。我还有一个在 X 方向上向前移动的工具和一个以该工具为中心的相机。但是，当我到达视口的尽头时，不再绘制线条。下面是一些图片来说明我的问题：

一开始，这条线穿过整个屏幕，但随着我的工具向前移动，我们到达了这条线的尽头。

以下是绘制线条的方法：

        private void DrawEvenlySpacedSprites (Texture2D texture, Vector2 point1, Vector2 point2, float increment)
    {
        var distance = Vector2.Distance (point1, point2);    // the distance between two points
        var iterations = (int)(distance / increment);       // how many sprites with be drawn
        var normalizedIncrement = 1.0f / iterations;        // the Lerp method needs values between 0.0 and 1.0
        var amount = 0.0f;

        if (iterations == 0)
            iterations = 1;

        for (int i = 0; i < iterations; i++) {
            var drawPoint = Vector2.Lerp (point1, point2, amount);
            spriteBatch.Draw (texture, drawPoint, Color.White);
            amount += normalizedIncrement;
        }
    }

这里是Game中的draw方法。点是我的线：

protected override void Draw (GameTime gameTime)
    {
        graphics.GraphicsDevice.Clear(Color.Black);
        nyVector = nextVector (gammelVector);
        GraphicsDevice.SetRenderTarget (renderTarget);
        spriteBatch.Begin ();
        DrawEvenlySpacedSprites (dot, gammelVector, nyVector, 0.9F);
        spriteBatch.End ();

        GraphicsDevice.SetRenderTarget (null);
        spriteBatch.Begin (SpriteSortMode.Deferred, BlendState.AlphaBlend, null, null, null, null, camera.transform);
        spriteBatch.Draw (renderTarget, new Vector2 (), Color.White);
        spriteBatch.Draw (tool, new Vector2(toolPos.X - (tool.Width/2), toolPos.Y - (tool.Height/2)), Color.White);
        spriteBatch.End ();

        gammelVector = new Vector2 (nyVector.X, nyVector.Y);
        base.Draw (gameTime);
    }

任何人都可以在这里指出正确的方向吗？我猜它与viewport.width有关，但我不太确定如何解决它。感谢您的阅读！

Answer 1

我读了这篇文章，并认为今天早上这将是一个有趣的练习，所以我决定写这篇文章是为了好玩。

实现非常简单，在彼此的末尾不断添加行，直到最后一行超出可视区域。

下面的代码将画一条无限向右的线。作为一项额外的优化，屏幕左侧的线条会在您通过它们时被删除。您可以轻松地使其保留以前存在的线条，或者也可以创建向左的线条。我会把这些练习留给你。

看看下面的Line类，它将在屏幕上定义一条线：

public class Line
{
    Texture2D Texture;
    Color Color;
    public Vector2 PointA;
    public Vector2 PointB;
    float Width;

    public Line(Vector2 pointA, Vector2 pointB, float width, Color color, Texture2D texture)
    {
        Texture = texture;
        PointA = pointA;
        PointB = pointB;
        Width = width;
        Color = color;
    }

    public void Draw(SpriteBatch spritebatch)
    {
        float angle = (float)Math.Atan2(PointB.Y - PointA.Y, PointB.X - PointA.X);
        float length = Vector2.Distance(PointA, PointB);
        spritebatch.Draw(Texture, PointA, null, Color, angle, Vector2.Zero, new Vector2(length, Width), SpriteEffects.None, 0);
    }

}

我在游戏类中编写了实现，因为我是快速编码。您可以在下面看到游戏类：

public class Game1 : Microsoft.Xna.Framework.Game
{
    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;
    Camera Camera;

    Texture2D LineTexture;
    List<Line> Lines;
    Random Random;

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

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

    protected override void LoadContent()
    {
        spriteBatch = new SpriteBatch(GraphicsDevice);
        Camera = new Camera(GraphicsDevice.Viewport, 1f);

        LineTexture = new Texture2D(GraphicsDevice, 1, 1);
        LineTexture.SetData<Color>(new Color[] { Color.White });

        Random = new Random();
        Lines = new List<Line>();
    }

    protected override void UnloadContent()
    {
    }


    protected override void Update(GameTime gameTime)
    {
        //handle input
        KeyboardState kbState = Keyboard.GetState();

        if (kbState.IsKeyDown(Keys.Escape))
            this.Exit();

        if (kbState.IsKeyDown(Keys.OemMinus))
            Camera.Zoom -= 0.015f;
        else if (kbState.IsKeyDown(Keys.OemPlus))
            Camera.Zoom += 0.015f;

        if (kbState.IsKeyDown(Keys.Up))
            Camera.Move(new Vector2(0, -30));
        else if (kbState.IsKeyDown(Keys.Down))
            Camera.Move(new Vector2(0, 30));
        if (kbState.IsKeyDown(Keys.Left))
            Camera.Move(new Vector2(-30, 0));
        else if (kbState.IsKeyDown(Keys.Right))
            Camera.Move(new Vector2(30, 0));


        //check if line is still in viewport - if not remove it
        for (int i = 0; i < Lines.Count; i++)
        {
            if (Lines[i].PointB.X < Camera.Viewport.X)
            {
                Lines.RemoveAt(i);
                i--;
            }
        }

        //if there are no lines, create one to get started
        if (Lines.Count == 0)
        {
            Vector2 p1 = new Vector2(Camera.Viewport.X, Random.Next(Camera.Viewport.Y + 50, Camera.Viewport.Height - 100));
            Vector2 p2 = new Vector2(p1.X + Random.Next(5, 20), p1.Y + Random.Next(-5, 5));
            Line line = new Line(p1, p2, 1, Color.Black, LineTexture);
            Lines.Add(line);
        }

        //Check if we need to add some lines to the right of our last list item
        while (Lines[Lines.Count - 1].PointB.X < Camera.Viewport.X + Camera.Viewport.Width)
        {
            Vector2 p1 = new Vector2(Lines[Lines.Count - 1].PointB.X, Lines[Lines.Count - 1].PointB.Y); ;
            Vector2 p2 = new Vector2(p1.X + Random.Next(5, 20), p1.Y + Random.Next(-5, 5));
            Line line = new Line(p1, p2, 1, Color.Black, LineTexture);
            Lines.Add(line);
        }

        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(new Color(30, 90, 150));

        spriteBatch.Begin(SpriteSortMode.Deferred, null, null, null, null, null, Camera.View);

        foreach (Line line in Lines)
            line.Draw(spriteBatch);

        spriteBatch.End();

        base.Draw(gameTime);
    }
}

为了您的方便，我还添加了 Camera 类：

public class Camera
{
    private const float zoomUpperLimit = 1.5f;
    private const float zoomLowerLimit = 0.1f;

    private float _zoom;
    private Vector2 _pos;

    private int ViewportWidth, ViewportHeight;

    #region Properties

    public float Zoom
    {
        get { return _zoom; }
        set
        {
            _zoom = value;
            if (_zoom < zoomLowerLimit)
                _zoom = zoomLowerLimit;
            if (_zoom > zoomUpperLimit)
                _zoom = zoomUpperLimit;
        }
    }

    public Rectangle Viewport 
    {
        get
        {
            int width = (int)((ViewportWidth / _zoom));
            int height = (int)((ViewportHeight / _zoom));
            return new Rectangle((int)(_pos.X - width / 2), (int)(_pos.Y - height / 2), width, height);
        }
    }

    public void Move(Vector2 amount)
    {
        _pos += amount;
    }

    public Vector2 Position
    {
        get { return _pos; }
        set { _pos = value; }
    }

    public Matrix View
    {
        get
        {
            return Matrix.CreateTranslation(new Vector3(-_pos.X, -_pos.Y, 0)) *
                    Matrix.CreateScale(new Vector3(Zoom, Zoom, 1)) *
                    Matrix.CreateTranslation(new Vector3(ViewportWidth * 0.5f, ViewportHeight * 0.5f, 0));
        }
    }

    #endregion

    public Camera(Viewport viewport, float initialZoom)
    {
        _zoom = initialZoom;
        _pos = Vector2.Zero;
        ViewportWidth = viewport.Width;
        ViewportHeight = viewport.Height;
    }

}