Alpha Map Format

Alpha worlds consist of several files, all held together in one folder under a very rigid directory structure.

Level

The level is a file called "level.dat" in the root of the world.

Name	Type	Description
Data	Compound	General level data Name Type Description RandomSeed Long The seed of the world, which is used to generate new geometry. SpawnX Int The X coordinate of the default spawn point SpawnY Int The Y coordinate of the default spawn point SpawnZ Int The Z coordinate of the default spawn point

Chunks

Chunks are stored in folders inside the world corresponding to their coordinates in base-36. The path is "<base-36-x-63>/<base-36-z-63>/c.<base-36-x>.<base-36-z>.dat", where <base-36-x-63> is the base-36 representation of the X coordinate of the chunk AND'd bitwise with 63.

For example, if we have the chunk coordinate (39, -13), we end up with the path 13/1f/c.13.-d.dat

The main world is stored in the root directory of the world. The Nether is stored in the "DIM-1" folder in the root and uses the same chunk folder system.

The Base-36 Algorithm

To retrieve the base-36 representation of a number, use the digits "0123456789abcdefghijklmnopqrstuvwxyz", and prefix the result with a hyphen ("-") if the number is negative.

Example code in Python, from Beta:

def base36(i):
    """
    Return the string representation of i in base 36, using lowercase letters.
    """
    letters = "0123456789abcdefghijklmnopqrstuvwxyz"
    if i < 0:
        i = -i
        signed = True
    elif i == 0:
        return "0"
    else:
        signed = False
    s = ""
    while i:
        i, digit = divmod(i, 36)
        s = letters[digit] + s
    if signed:
        s = "-" + s
    return s

Example code in C#:

<source lang=csharp> public static string Base36Encode(long input) { if (input == 0){ return "0"; } string chars = "0123456789abcdefghijklmnopqrstuvwxyz"; bool negative = (input < 0);

StringBuilder sb = new StringBuilder();

if (negative) { input = -input; sb.Append("-"); } while (input > 0) { sb.Insert((negative ? 1 : 0), chars[(int)(input % 36)]); input /= 36; } return sb.ToString(); } </source>

Players

Persistent data for players is stored in a folder called "players". Each player has a file called "<username>.dat".

Beta player files

Player files are NBT encoded.

The file starts with a nameless TAG_Compound which contains all other data.

Tag Name	Type	Description
SleepTimer	TAG_Short
Motion	TAG_List(3 TAG_Double)
OnGround	TAG_Byte
HurtTime	TAG_Short
Health	TAG_Short
Dimension	TAG_Int
Air	TAG_Short
Inventory	TAG_List or TAG_Byte(when empty)	See Inventory table below
Pos	TAG_List(3 TAG_Double)
AttackTime	TAG_Short
Sleeping	TAG_Byte
Fire	TAG_Short
FallDistance	TAG_Float
Rotation	TAG_List(2 TAG_Float)
DeathTime	TAG_Short
SpawnX	TAG_Int	Only present when spawn is set elsewhere
SpawnY	TAG_Int	Only present when spawn is set elsewhere
SpawnZ	TAG_Int	Only present when spawn is set elsewhere

Inventory items are in the TAG_Compound format with the following tags:

Tag Name	Type	Description
Slot	TAG_byte
id	TAG_Short
Damage	TAG_Short
Count	TAG_Byte

Other formats

The following format is not used in Beta. May be the Alpha format.

Name	Type	Description
Pos	List of 3 doubles	X, Y, and Z coordinates of the player position, in pixel coordinates
Rotation	List of 2 doubles	Yaw and pitch of the player, in degrees

Map Generation

There are several approaches to map generation.

Noise

Two-dimensional noise functions can be used to provide a terrain height at certain coordinates.