Loading tiles for a 2D game

Question

Hi

Im trying to make an 2D online game (with Z positions), and currently im working with loading a map from a txt file. I have three different map files. One contains an int for each tile saying what kind of floor there is, one saying what kind of decoration there is, and one saying what might be covering the tile. The problem is that the current map (20, 20, 30) takes 200 ms to load, and I want it to be much much bigger. I have tried to find a good solution for this and have so far come up with some ideas.

Recently I'v thought about storing all tiles in separate files, one file per tile. I'm not sure if this is a good idea (it feels wrong somehow), but it would mean that I wouldn't have to store any unneccessary tiles as "-1" in a text file and I would be able to just pick the right tile from the folder easily during run time (read the file named mapXYZ). If the tile is empty I would just be able to catch the FileNotFoundException. Could anyone tell me a reason for this being a bad solution? Other solutions I'v thought about would be to split the map into smaller parts or reading the map during startup in a BackgroundWorker.

Answer 1

Try making a much larger map in the same format as your current one first - it may be that the 200ms is mostly just overhead of opening and initial processing of the file.

If I'm understanding your proposed solution (opening one file per X,Y or X,Y,Z coordinate of a single map), this is a bad idea for two reasons:

• There will be significant overhead to opening so many files.
• Catching a FileNotFoundException and eating it will be significantly slower - there is actually a lot of overhead with catching exceptions, so you shouldn't rely on them to perform application logic.

Answer 2

Are you loading the file from a remote server? If so, that's why it's taking so long. Instead you should embed the file into the game. I'm saying this because you probably take 2-3 bytes per tile, so the file's about 30kb and 200ms sounds like a reasonable download time for that size of file (including overhead etc, and depending on your internet connection).

Regarding how to lower the filesize - there are two easy techniques I can think of that will decrease the filesize a bit:

1) If you have mostly empty squares and only some significant ones, your map is what is often referred to as 'sparse'. When storing a sparse array of data you can use a simple compression technique (formally known as 'run-length encoding') where each time you come accross empty squares, you specify how many of them there are. So for example instead of {0,0,0,0,0,0,0,0,0,0,1,1,2,3,0,0,0,0,0,0,0,0,0,0,0,0,1} you could store {10 0's, 1, 1, 2, 3, 12 0's, 1}

2) To save space, I recommend that you store everything as binary data. The exact setup of the file mainly depends on how many possible tile types there are, but this is a better solution than storing the ascii characters corresponding to the base-10 representation of the numers, separated by delimiters.

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Example Binary Format

• File is organized into segments which are 3 or 4 bytes long, as explained below.

• First segment indicates the version of the game for which the map was created. 3 bytes long.

• Segments 2, 3, and 4 indicate the dimensions of the map (x, y, z). 3 bytes long each.

• The remaining segments all indicate either a tile number and is 3 bytes long with an MSB of 0. The exception to this follows.

• If one of the tile segments is an empty tile, it is 4 bytes long with an MSB of 1, and indicates the number of empty tiles including that tile that follow.

The reason I suggest the MSB flag is so that you can distinguish between segments which are for tiles, and segments which indicate the number of empty tiles which follow that segment. For those segments I increase the length to 4 bytes (you might want to make it 5) so that you can store larger numbers of empty tiles per segment.