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# 2D tilemaps "Chunk Theory".

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Hello!

I'm looking to get as much theory as possible on this subject, I have a hobby project i'm working on: a 2D orthographic game which i have used the standard tile grid array technique to render in XNA. But would like to implement dynamic loading of groups of tiles (chunks) so i can implement larger worlds then a standard grid.

The part of the theory i most understand is when the camera, or object gets close to the edge of a chunk the new one is loaded in the direction the camera is traveling and the chunk behind is unloaded. I guess the theory is to have an array that tracks chunks, then another array inside the chunk to track tiles?

Things I don't understand:

• Best way to "signal" a new chunk should be loaded.
• General Implementation details

I would like to heavy research this topic as i want it to be a center point of any other 2d games i make in the future.

So i welcome any and all recommended:

• Books
• Tutorials
• Videos

And of course code snippets and comments would be very valuable to me. (most proficient with XNA)

Thanks.

Edit: (Also had another question on general tile maps, should i ask here or start a new thread)?

Edited by Mellkor

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This is my very simple attempt at drawing a single chunk, Its probably horribly inefficient and "incorrect" lol

public class Game1 : Game
{
//Chunksize
int width = 10;
int height = 10;

//tilesize
int tSize = 64;

GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;

public static Texture2D texture;

//Chunks
chunk[] ChunkArray = new chunk[5];

//Tile
public class tile
{
public Texture2D texture;
}

//chunk
public class chunk
{
public tile[,] tiles;

public chunk()
{
this.tiles = new tile[5, 5];
BuildChunk();
}

public void BuildChunk()
{
for (int x = 0; x < 5; x++)
{
for (int y = 0; y < 5; y++)
{
this.tiles[x, y] = new tile();
this.tiles[x, y].texture = Game1.texture;
}
}

}

}
{
ChunkArray[0] = new chunk();
}

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

protected override void Initialize()
{

base.Initialize();
}

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

{
// TODO: Unload any non ContentManager content here
}

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

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

spriteBatch.Begin();

//foreach (var chunk in ChunkArray)
for (int ci = 0; ci < ChunkArray.Length; ci++)
{
{
if (ChunkArray[ci] != null)
{
foreach (var tile in ChunkArray[ci].tiles)
{
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
spriteBatch.Draw(tile.texture, new Rectangle(x * 64, y * 64, tSize, tSize), Color.White);
}
}
}
}
}
spriteBatch.End();
base.Draw(gameTime);
}
}
}
}


My next goal was to set up another chunk to the right of that one using the array, but it seems from your post that i should pretty much reevaluate the whole theory?

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Assuming the map can expand in four directions, you might have a grid of 9 chunks, much like a Tic-Tac-Toe board, loaded into memory at once (if you are only moving in one direction, vertically or horizontally, then 3 or 5 would be a better  number). The chunk in which the player currently resides is always at the center. When the player crosses the boundary into another chunk, then you would unload one column or row and load a new one depending on the direction the player moved.

For example, say the player moves north into the chunk directly above the center one. Now, you unload the entire bottom row (three chunks). The center row now becomes the bottom row, the top row now becomes the center row, and you load three new chunks to fill in the top row. If diagonal movement is disallowed, you could simplify it to 5 chunks - the middle, N, S, E and W. You're still loading and unloading the same number of chunks, just in a different pattern. But I'd still go with 9 myself.

You'll want a decent chunk size for this, though. If the chunks are too small, you'll be loading more frequently unless you adapt the algorithm a bit.

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Assuming the map can expand in four directions, you might have a grid of 9 chunks, much like a Tic-Tac-Toe board, loaded into memory at once (if you are only moving in one direction, vertically or horizontally, then 3 or 5 would be a better  number). The chunk in which the player currently resides is always at the center. When the player crosses the boundary into another chunk, then you would unload one column or row and load a new one depending on the direction the player moved.

For example, say the player moves north into the chunk directly above the center one. Now, you unload the entire bottom row (three chunks). The center row now becomes the bottom row, the top row now becomes the center row, and you load three new chunks to fill in the top row. If diagonal movement is disallowed, you could simplify it to 5 chunks - the middle, N, S, E and W. You're still loading and unloading the same number of chunks, just in a different pattern. But I'd still go with 9 myself.

You'll want a decent chunk size for this, though. If the chunks are too small, you'll be loading more frequently unless you adapt the algorithm a bit.

Yes, I understand that in theory, and that's what i'm trying to accomplish but its the implementation theory that's my problem.

If I have a chunk that is 50x50 tiles big, The player/camera gets to local tile 30,0 and wants to load the next chunk(next set of 50x50 tiles), How do i know where to start drawing the next chunk?

Edited by Mellkor

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If I have a chunk that is 50x50 tiles big, The player/camera gets to local tile 30,0 and wants to load the next chunk(next set of 50x50 tiles), How do i know where to start drawing the next chunk?

How is your camera set up? How big are your tiles in pixels (or what is your camera scale) ? You should be able to trivially map the camera position to a visual (pixel?) position within the chunk, which you then just subtract from the chunk's visual width to find out the dimensions of the screen bounding box of the chunk. That is then easily used to find the draw location of each adjacent chunk.

If your camera is set up sensibly than you're really going to be working in units of tiles, e.g. each tile is 1x1 in-game units, and the camera scales those units when rendering to get the actual on-screen size you want. All the math for determining bounding boxes becomes super simple then. You can find out if the chunk is within the screen or goes past the screen by putting it through the camera pipeline/matrix (taking you from world space or units of 1 tile to camera space or normalized [-1,+1] coordinates mapping to the screen bounds) and then checking if the bounds exceed [-1,+1].

Sorry, I don't feel I'm explaining this super well. Hopefully someone else with a better ability to illustrate math will step in and help. Edited by SeanMiddleditch

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Hi Mellkor

A similar question popped up on the Microsoft XNA forums a while back, and I posted some graphics to visualize the theory and a code sample with class diagram.

(scroll down to "I found some time yesterday, and coded a framework for making infinite worlds.")

I hope it will prove useful to you

Kind regards - Jakob

Edited by xnafan

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Hi Mellkor

A similar question popped up on the Microsoft XNA forums a while back, and I posted some graphics to visualize the theory and a code sample with class diagram.

(scroll down to "I found some time yesterday, and coded a framework for making infinite worlds.")

I hope it will prove useful to you

Kind regards - Jakob

Thanks mate! ill have take a look over the drawings and code.

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( I am working on a similar problem in Java )

From what I am reading - small "chunk" groups need to be saved as a separate map files, and loaded into memory off screen to reduce "lag".

However the more I think about it - wouldn't constantly opining and closing files cause system strain ?

How the hay does MineCraft do it ?

Edited by Shippou

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Hi Shippou You could fiddle a bit with the chunk sizes, to ensure that you would only read/dump files from and to disk every so often. If your maps are pretty simple, the amount of data in memory shouldn't be a problem. To my knowledge this is the same way Minecraft does it. You could also cache a bigger amount of chunks, say two concentric circles worth around the one the player is currently in. I can't see this becoming a problem on modern computers. Try the sample that's for download on my Blog - I haven't experienced any problems, and the chunks there are very small, to illustrate the concept. If you make 255x255 chunks you would load a lot less and the files would still be fast to read and not too much of a strain on memory. Kind regards - Jakob

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