Hello. I just started an xna rpg game, and needed help with the collision. So, I have a map and a character. I don't want the character to walk onto the water. To do this, I check the block in front of( or whichever direction the player is moving) the character, and see if it is water. If it is, I dont allow the character to walk. Unfortunately, this is not working. I am getting an IndexOutOfRangeException and sometimes no error but it just doesnt work. All help would be appreciated.

Player 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 RPG
{
class Player
{
int X;
int Y;
Texture2D image;
KeyboardState newstate;
KeyboardState oldstate;
Map map;
public Player(int xPos, int yPos, ContentManager content, Map currentmap)
{
map = currentmap;
X = xPos;
Y = yPos;
image = content.Load<Texture2D>("player");
}
public void Move()
{
newstate = Keyboard.GetState();
if (newstate.IsKeyDown(Keys.Down) && oldstate.IsKeyUp(Keys.Down))
{
if (map.grid[X, Y + 1] != 2)
{
Y += 1;
}
}
if (newstate.IsKeyDown(Keys.Up) && oldstate.IsKeyUp(Keys.Up))
{
Y -= 1;
}
if (newstate.IsKeyDown(Keys.Left) && oldstate.IsKeyUp(Keys.Left))
{
X -= 1;
}
if (newstate.IsKeyDown(Keys.Right) && oldstate.IsKeyUp(Keys.Right))
{
X += 1;
}
oldstate = newstate;
}
public void Draw(SpriteBatch spriteBatch)
{

spriteBatch.Draw(image, new Vector2(X * 32, Y * 32), Color.White);
}
}
}



Map 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 RPG
{
class Map
{

public int[,] grid = new int[,] {
{ 1, 1, 1, 1, 1, 1, 2, 0, 0, 0,0,0,0},
{ 2, 2, 2, 2, 2, 2, 2, 0, 0, 0,0,0,0},
{ 1, 1, 1, 1, 1, 1, 2, 0, 0, 0,0,0,0},
{ 1, 1, 1, 1, 1, 1, 2, 0, 0, 0,0,0,0},
{ 1, 1, 1, 1, 1, 1, 2, 0, 0, 0,0,0,0},
{ 1, 1, 1, 1, 1, 1, 2, 2, 2, 2,2,2,2},
{ 1, 1, 1, 1, 1, 1, 1, 1, 2, 1,1,1,1},
{ 1, 1, 1, 1, 1, 1, 1, 1, 2, 1,1,1,1},
{ 1, 1, 1, 1, 1, 1, 1, 1, 2, 1,1,1,1},
{ 1, 1, 1, 1, 1, 1, 1, 1, 2, 1,1,1,1},
{ 1, 1, 1, 1, 1, 1, 1, 1, 2, 1,1,1,1}, };
static int TileWidth = 64;
static int TileHeight = 64;
int mapWidth;
int mapHeight;
public List<Texture2D> tileList = new List<Texture2D>();
public void Draw(SpriteBatch spriteBatch)
{

mapWidth = grid.GetLength(1);
mapHeight = grid.GetLength(0);

for (int x = 0; x < mapWidth; x++)
{
for (int y = 0; y < mapHeight; y++)
{
spriteBatch.Draw(tileList[grid[y, x]],
new Rectangle(x * TileWidth,
y * TileHeight,
TileWidth,
TileHeight),
Color.White);
}
}


}
public Map(ContentManager content)
{
tileList.Add(content.Load<Texture2D>("dirt"));
tileList.Add(content.Load<Texture2D>("grass"));
tileList.Add(content.Load<Texture2D>("water"));
}


}
}


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 RPG
{
/// <summary>
/// This is the main type for your game
/// </summary>
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
Map map;
Player player;

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
map = new Map(this.Content);
player = new Player(0, 0, this.Content, map);
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);

// TODO: use this.Content to load your game content here
}
/// <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();
player.Move();
// TODO: Add your update logic here
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();
map.Draw(spriteBatch);
player.Draw(spriteBatch);
// TODO: Add your drawing code here
spriteBatch.End();
base.Draw(gameTime);
}
}
}


[font=arial,helvetica,sans-serif]

1. Your map tiles are 64x64 but your player is 32x32 so a movement by 1 unit is not going to work. [/font]
[font=arial,helvetica,sans-serif]

2. You do no boundary checks which will result in index out of range errors.[/font]
[font=arial,helvetica,sans-serif]

3. In your player Move method you have the following line but the X and Y is the wrong way round. Plus adding 1 here is not a very good idea due to point 2 above[/font]
[font=arial,helvetica,sans-serif]

if (map.grid[X, Y + 1] != 2)

4. You are only checking for water when the down arrow is pressed.


Try changing your player to 64x64 and use the following code in your player move method[/font].


newstate = Keyboard.GetState();
int TmpX = X;
int TmpY = Y;
if (newstate.IsKeyDown(Keys.Down) && oldstate.IsKeyUp(Keys.Down))
{
TmpY += 1;
}
if (newstate.IsKeyDown(Keys.Up) && oldstate.IsKeyUp(Keys.Up))
{
TmpY -= 1;
}
if (newstate.IsKeyDown(Keys.Left) && oldstate.IsKeyUp(Keys.Left))
{
TmpX -= 1;
}
if (newstate.IsKeyDown(Keys.Right) && oldstate.IsKeyUp(Keys.Right))
{
TmpX += 1;
}

if (TmpX < 0)
TmpX = 0;
if (TmpX > map.mapWidth)
TmpX = map.mapWidth;
if (TmpY < 0)
TmpY = 0;
if (TmpY > map.mapHeight)
TmpY = map.mapHeight;
if (map.grid[TmpY, TmpX] != 2)
{
X = TmpX;
Y = TmpY;
}
oldstate = newstate;


EDIT: didnt realise wannabe got there first but
@ wannabe

[background=rgb(250, 251, 252)].

Your map tiles are 64x64 but your player is 32x32 so a movement by 1 unit is not going to work.[/quote] look at the draw code, thats not a problem for now.[/background]


(map.grid[X, Y + 1] != 2)
//does not check if Y+1 is out of range

(((Y + 1) >= map.grid.GetLength(1) ? 2 : map.grid[X, Y + 1]) != 2)
//I'm sure some of these brackets are unnecessary but I like to be sure while prototyping code.


(Y + 1) >= map.grid.GetLength(1) ?
will check if (Y + 1) is more than or equal to the length of array dimension 1.

2 : map.grid[X, Y + 1]
if true it will return 2 so everything outside of the greed will be treated as if it was water.

if false return map.grid[X, Y+1]
!= 2
check if the returned value is not equal to 2.

do this with the other directions replacing Y + 1 and [X, Y + 1] with whatever is necessary for the direction you intend to move.
if your moving in - directions you need to use something like this (for moving in -X direction in this example)
(X - 1) < 0 ?


always remember when its possible to query outside of the array, make sure you check to see if the desired query is more than the array length or less than the array minimum.
if there's something else wrong I haven't looked through your code to see it, but I noticed this right away and considered it a problem.