C# MonoGame -向后移动

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;

public class Player
{
    public Vector2 Position { get; set; }
    public Vector2 Velocity { get; set; }

    public Player(Vector2 position)
    {
        Position = position;
        Velocity = new Vector2(0, 0);
    }

    public void Update(GameTime gameTime)
    {
        KeyboardState keyboardState = Keyboard.GetState();

        if (keyboardState.IsKeyDown(Keys.W))
        {
            Velocity.Y = -1; // 向上移动
        }
        else if (keyboardState.IsKeyDown(Keys.S))
        {
            Velocity.Y = 1; // 向下移动
        }
        else
        {
            Velocity.Y = 0; // 停止移动
        }

        Position += Velocity * (float)gameTime.ElapsedGameTime.TotalSeconds;
    }

    public void Draw(SpriteBatch spriteBatch, Texture2D texture)
    {
        spriteBatch.Draw(texture, Position, Color.White);
    }
}

public class Game1 : Game
{
    private GraphicsDeviceManager _graphics;
    private SpriteBatch _spriteBatch;
    private Player _player;
    private Texture2D _playerTexture;

    public Game1()
    {
        _graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        IsMouseVisible = true;
    }

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

    protected override void LoadContent()
    {
        _spriteBatch = new SpriteBatch(GraphicsDevice);

        _playerTexture = Content.Load<Texture2D>("player");
        _player = new Player(new Vector2(GraphicsDevice.Viewport.Width / 2, GraphicsDevice.Viewport.Height / 2));
    }

    protected override void Update(GameTime gameTime)
    {
        _player.Update(gameTime);
        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        _spriteBatch.Begin();
        _player.Draw(_spriteBatch, _playerTexture);
        _spriteBatch.End();

        base.Draw(gameTime);
    }
}

public class Camera
{
    public Matrix Transform { get; private set; }

    public Camera(Viewport viewport, Vector2 targetPosition)
    {
        _viewport = viewport;
        TargetPosition = targetPosition;
    }

    public void Update(GameTime gameTime)
    {
        Vector2 position = TargetPosition - _viewport.Size / 2 + new Vector2(20, 20);
        Transform = Matrix.CreateTranslation(-position.X, -position.Y, 0) *
                    Matrix.CreateScale(new Vector3(1, 1, 0)) *
                    Matrix.CreateTranslation(_viewport.Width / 2, _viewport.Height / 2, 0);
    }

    private Viewport _viewport;
    public Vector2 TargetPosition { get; set; }
}

public class Game1 : Game
{
    private Camera _camera;

    protected override void LoadContent()
    {
        // ...

        _camera = new Camera(GraphicsDevice.Viewport, _player.Position);
    }

    protected override void Update(GameTime gameTime)
    {
        _player.Update(gameTime);
        _camera.Update(gameTime);
        base.Update(gameTime);
    }

    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        _spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, null, null, null, null, _camera.Transform);
        _player.Draw(_spriteBatch, _playerTexture);
        _spriteBatch.End();

        base.Draw(gameTime);
    }
}