xna - A way to store potentially infinite 2D map data?

I have a 2D platformer that currently can handle chunks with 100 by 100 tiles, with the chunk coordinates are stored as longs, so this is the only limit of maps (maxlong*maxlong). All entity positions etc etc are chunk relevant and so there is no limit there.

The problem I'm having is how to store and access these chunks without having thousands of files. Any ideas for a preferably quick & low HD cost archive format that doesn't need to open everything at once?

Answer

Create a custom map format for your game. It's easier than you might think. Just use the BinaryWriter class. First write the header in a few ints or uints. Information to include in the header:

• The magic string / magic number of you file format.


• The start/end/size of the chunks described in this file

and also (and here comes the performance critical part

• ints that describe the starting position inside the file. So you don't have to search for specific chunks.

With the above methode you can (and should) create an index of your files contents, containing some sort of description(a user specified name for the region/chunk, or just the coordinates) and as a second value the position in the file.

Then, when you want to load a specific chunk, you'll just have to search inside the index. When you got the position just set fileStream.Position = PositionOfChunkFromIndex and you can load it.

It's all about the design of the fileformat with the header describing the contents of the file most efficiently.

Just save the files with a custom extension you made up and there you go.

BONUS: Add BZip2 compression to specific regions of the file / the whole contents (not the header!!), so you can unpack specific chunks from the file, for a very small memory footprint.