XNA 矩形交叉口

Question

我最近开始进行 XNA 开发，过去有一些（非常有限的）经验，我决定尝试制作一个 Pong 克隆，看看我能记住多少。我知道的大部分内容都回到了我的脑海中，但我在球拍和球之间的碰撞检测方面遇到了问题。我设置了 3 个矩形来更新位置以及我正在使用的精灵，当球矩形与蝙蝠矩形相交时，我将球的 X 速度乘以 -1。然而，这会产生一种不寻常的效果，即球在球棒周围反弹，如this video 所示。我在这里做错了什么？

这是这个项目的代码（可怜，我知道）：

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Audio;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.GamerServices;
using Microsoft.Xna.Framework.Graphics;
using Microsoft.Xna.Framework.Input;
using Microsoft.Xna.Framework.Media;

namespace Pong
{

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

    System.Random generator = new Random();

    Texture2D ball;
    Texture2D bat1;
    Texture2D bat2;
    Texture2D middle;

    Vector2 midPos;
    Vector2 bat1Pos;
    Vector2 bat2Pos;
    Vector2 ballPos;
    Vector2 ballVelo;

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

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

    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        //Load sprites
        ball = Content.Load<Texture2D>(@"sprites/pongball");
        bat1 = Content.Load<Texture2D>(@"sprites/pongbat");
        bat2 = Content.Load<Texture2D>(@"sprites/pongbat");
        middle = Content.Load<Texture2D>(@"sprites/pongmiddle");

        //Set default sprite positions
        midPos.X = (Window.ClientBounds.Width / 2) - 5;
        midPos.Y = 0;

        bat1Pos.X = 10;
        bat1Pos.Y = (Window.ClientBounds.Height/2) - 50;

        bat2Pos.X = Window.ClientBounds.Width - 20;
        bat2Pos.Y = (Window.ClientBounds.Height/2) - 50;

        ballPos.X = (Window.ClientBounds.Width / 2) - 5;
        ballPos.Y = (Window.ClientBounds.Height / 2) - 5;

        //Generate random ball velocity
        ballVelo.X = generator.Next(5,10);
        ballVelo.Y = generator.Next(4, 7);
    }

    protected override void UnloadContent()
    {

    }

    protected override void Update(GameTime gameTime)
    {


        //Update rectangle values
        Rectangle bat1Rect = new Rectangle((int)bat1Pos.X, (int)bat1Pos.Y, 10, 100);
        Rectangle bat2Rect = new Rectangle((int)bat2Pos.X, (int)bat2Pos.Y, 10, 100);
        Rectangle ballRect = new Rectangle((int)ballPos.X, (int)ballPos.Y, 10, 100);

        //Move ball
        ballPos += ballVelo;

        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();
        if (Keyboard.GetState().IsKeyDown(Keys.Escape))
            this.Exit();

        //Bat 1 movement and restriction
        if (Keyboard.GetState().IsKeyDown(Keys.Up))
            bat1Pos.Y -= 4;

        if (Keyboard.GetState().IsKeyDown(Keys.Down))
            bat1Pos.Y += 4;

        if (bat1Pos.Y <= 0)
            bat1Pos.Y = 0;

        if (bat1Pos.Y >= Window.ClientBounds.Height - 100)
            bat1Pos.Y = Window.ClientBounds.Height - 100;


        //Bat 2 movement and restriction
        if (Keyboard.GetState().IsKeyDown(Keys.W))
            bat2Pos.Y -= 4;

        if (Keyboard.GetState().IsKeyDown(Keys.S))
            bat2Pos.Y += 4;

        if (bat2Pos.Y <= 0)
            bat2Pos.Y = 0;

        if (bat2Pos.Y >= Window.ClientBounds.Height - 100)
            bat2Pos.Y = Window.ClientBounds.Height - 100;

        //Ball movement restrictions
        if (ballPos.X <= 0)
            ballVelo.X *= -1;

        if (ballPos.Y <= 0)
            ballVelo.Y *= -1;

        if (ballPos.X >= Window.ClientBounds.Width - 5)
            ballVelo.X *= -1;

        if (ballPos.Y >= Window.ClientBounds.Height - 5)
            ballVelo.Y *= -1;


        //Collision detection between bats and ball
        if (ballRect.Intersects(bat1Rect))
        {
            ballVelo.X *= -1;
        }

        if (ballRect.Intersects(bat2Rect))
        {
            ballVelo.X *= -1;
        }

        base.Update(gameTime);
    }

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

        spriteBatch.Begin();
        spriteBatch.Draw(middle, midPos, Color.White);
        spriteBatch.Draw(bat1, bat1Pos, Color.White);
        spriteBatch.Draw(bat2, bat2Pos, Color.White);
        spriteBatch.Draw(ball, ballPos, Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}
}

Answer 1

解决此问题的一种方法是对您的 ballRect.Intersect(barXRect)) if 语句进行以下更改：

    if (ballRect.Intersects(bat1Rect))
    {
        ballVelo.X = Math.Abs(ballVelo.X) * -1;
    }

    if (ballRect.Intersects(bat2Rect))
    {
        ballVelo.X = Math.Abs(ballVelo.X);
    }

这样左栏只会将球向右发送，而右栏只会将球向左发送。我可能有错误的方向，所以最好仔细检查，但这只是意味着将* -1移动到另一个蝙蝠。

Answer 2

Lyise 的解决方案会起作用，但它不会攻击问题的实际根源。在大型游戏中，您将需要更强大的解决方案，因此我将解释高级修复。

问题是您在球仍在球棒内时更改 X 速度。在下一帧中，最可能的结果是球会离开，但不足以退出球棒，因此检测到新的碰撞。速度再次改变，循环重复，直到球通过低于或高于球棒离开球棒。

精确的解决方案需要将球移出球棒，然后反转速度。
选项：

• 将球返回到它在帧开始时的位置。球永远不会碰到球棒。如果球速足够高或帧速率足够低，这将是显而易见的。
• 计算球进入球棒的距离，然后从球的位置中减去该数值。
  // Colliding from the right
impactCorrection = bat.Right - ball.Left;
// Colliding from the left
impactCorrection = bat.Left - ball.Right;
  为了获得额外积分，您可以将球移开 2 * impactCorrection 在 X 中，这样球在每一帧中始终移动相同的距离。