XNA 2D Rectangular Sprite Bonding Box

Question

So I'm trying to figure out bounding boxes in XNA, and I'm having a little trouble. Below is my code. The program is just composed of a rectangular object that you can move in an UDLR manner (I just used a Thwomp sprite from the super Mario games) and a list of randomly generated boxes that are bouncing around the screen (I used question mark box sprites, also from Mario). I've got the code to where the boxes bounce off of the sides of the Thwomp, but not the top and bottom (it just passes through the sprite). So the bounding box is less of a box and more of a left and right wall right now. What can I do to my code to make the boxes bounce off the top and bottom of the Thwomp as well?

Thanks

Game class:

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 BoundingBoxCollision
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{


    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    Sprite playerOne;

    static public int height;
    static public int width;

    static Random rand = new Random();

    KeyboardState keyboardState;

    List<Sprite> ballList = new List<Sprite>();
    int ballCount = 10;

    private void CheckPaddleWallCollision()
    {

    }


    private void CheckBallCollision(Sprite ball)
    {

        int MaxX =
            graphics.GraphicsDevice.Viewport.Width - ball.BoundingBox.Width;
        int MinX = 0;
        int MaxY =
            graphics.GraphicsDevice.Viewport.Height - ball.BoundingBox.Height;
        int MinY = 0;



        if (ball.BoundingBox.Intersects(playerOne.BoundingBox))
        {
            ball.Velocity.X *= -1;
            ball.Position += ball.Velocity;
        }

        if (ball.BoundingBox.Y > MaxY)
        {
            ball.Velocity.Y *= -1;
            ball.Position += ball.Velocity;
        }

        if (ball.BoundingBox.Y < MinY)
        {
            ball.Velocity.Y *= -1;
            ball.Position += ball.Velocity;
        }

        if (ball.BoundingBox.X < MinX)
        {
            ball.Velocity.X *= -1;
            ball.Position += ball.Velocity;
        }

        if (ball.BoundingBox.X > MaxX)
        {
            ball.Velocity.X *= -1;
            ball.Position += ball.Velocity;
        }
        /*if ((ball.Position.X < -ball.BoundingBox.Width)
            || (ball.Position.X > Window.ClientBounds.Width))
            SetInStartPostion(); */
    }

    /*private void SetInStartPostion()
    {
        playerOne.Position.Y = (
            Window.ClientBounds.Height -
            playerOne.BoundingBox.Height) / 2;


        ball.Position.X = playerOne.BoundingBox.Right + 1;

        ball.Position.Y = (
            Window.ClientBounds.Height -
            ball.BoundingBox.Height) / 2;

        ball.Velocity = new Vector2(8f, -8f);
    } */

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

    /// <summary>
    /// Allows the game to perform any initialization it needs to before starting to run.
    /// This is where it can query for any required services and load any non-graphic
    /// related content.  Calling base.Initialize will enumerate through any components
    /// and initialize them as well.
    /// </summary>
    protected override void Initialize()
    {
        // TODO: Add your initialization logic here

        base.Initialize();
    }

    /// <summary>
    /// LoadContent will be called once per game and is the place to load
    /// all of your content.
    /// </summary>
    protected override void LoadContent()
    {
        // Create a new SpriteBatch, which can be used to draw textures.
        spriteBatch = new SpriteBatch(GraphicsDevice);

        height = GraphicsDevice.Viewport.Height;
        width = GraphicsDevice.Viewport.Width;

        Texture2D paddleTexture = Content.Load<Texture2D>("Thwomp");
        Vector2 position;

        position = new Vector2(
            100,
            (Window.ClientBounds.Height - paddleTexture.Height) / 2);
        playerOne = new Sprite(paddleTexture, position);

        position = new Vector2(
            (Window.ClientBounds.Width - paddleTexture.Width),
            (Window.ClientBounds.Height - paddleTexture.Height) / 2);

        Texture2D ballTexture = Content.Load<Texture2D>("QuestionMarkBlock");

        position = new Vector2(
                 playerOne.BoundingBox.Right + 1,
                 (Window.ClientBounds.Height - ballTexture.Height) / 2);

        for (int i = 0; i < ballCount; i++)
        {
            position = new Vector2(rand.Next(Game1.width), rand.Next(Game1.height));
            Sprite ball = new Sprite(
                     ballTexture,
                    position,
                     new Vector2(4f, -4f));
            ballList.Add(ball);
        }
    }


    /// <summary>
    /// UnloadContent will be called once per game and is the place to unload
    /// all content.
    /// </summary>
    protected override void UnloadContent()
    {
        // TODO: Unload any non ContentManager content here
    }

    /// <summary>
    /// Allows the game to run logic such as updating the world,
    /// checking for collisions, gathering input, and playing audio.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Update(GameTime gameTime)
    {
        // Allows the game to exit
        if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
            this.Exit();



        keyboardState = Keyboard.GetState();

        if (keyboardState.IsKeyDown(Keys.Up))
            playerOne.Position.Y -= 4f;

        if (keyboardState.IsKeyDown(Keys.Down))
            playerOne.Position.Y += 4f;

        if (keyboardState.IsKeyDown(Keys.Left))
            playerOne.Position.X -= 4f;

        if (keyboardState.IsKeyDown(Keys.Right))
            playerOne.Position.X += 4f;



        foreach (Sprite block in ballList)
        {
            block.Position += block.Velocity;
            CheckBallCollision(block);

        }

        CheckPaddleWallCollision();



        base.Update(gameTime);
    }


    /// <summary>
    /// This is called when the game should draw itself.
    /// </summary>
    /// <param name="gameTime">Provides a snapshot of timing values.</param>
    protected override void Draw(GameTime gameTime)
    {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        spriteBatch.Begin();

        playerOne.Draw(spriteBatch);

        foreach (Sprite block in ballList)
        {
            block.Draw(spriteBatch);
        }

        spriteBatch.End();

        base.Draw(gameTime);
    }


    public static int vGameWidth { get; set; }
}
}

Sprite class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

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

namespace BoundingBoxCollision
{
public class Sprite
{



    Texture2D texture;
    public Vector2 Position;
    public Vector2 Velocity;


    public Rectangle BoundingBox
    {
        get
        {
            return new Rectangle(
                (int)Position.X,
                (int)Position.Y,
                texture.Width,
                texture.Height);
        }
    }

    public Sprite(Texture2D texture, Vector2 position)
    {
        this.texture = texture;
        this.Position = position;
    }

    public Sprite(Texture2D texture, Vector2 position, Vector2 velocity)
    {
        this.texture = texture;
        this.Position = position;
        this.Velocity = velocity;
    }



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

}
}

Answer 1

For number 2 (top/bottom) you could you do a position check using

playerOne.BoundingBox.Top

and

playerOne.BoundingBox.Bottom ?

.Top and .Bottom should return the Y coordinate of Top of the rectangle or the bottom of the rectangle.

Answer 2

The simplest way would be :

if (ball.BoundingBox.Intersects(playerOne.BoundingBox))
        {
            ball.Velocity.X *= -1;
            ball.Velocity.Y *= -1;
            ball.Position += ball.Velocity;
        }

This would be a complete reflection. If you are going for a more realistic way you would like to do something like this (Pseudocode):

1. Check if ball and player collide
2. Determine if it is colliding on top/bottom, left/right, or exact corner
   1. left/right : ball.Velocity.X*= -1;
   2. top/bottom : ball.Velocity.Y *= -1;
   3. corner : ball.Velocity.X *= -1; && ball.Velocity.Y *= -1;

I hope this helps a bit!

Regards

floAr