Level format

The level format is entirely compressed with GZip, so you must first decompress the file.

Note: As the uncompressed data can be very large, it is recommended you decompress via a streaming approach instead of entirely at once.

Note: This format is an extension of the MCSharp/MCZall/MCLawl/MCForge level format, and is forwards compatible with reader software for these formats.

Main data

Header

2   | Identifier (must be 1874)
2   | Width of the map
2   | Length of the map
2   | Height of the map (vertical)
2   | Spawn X coordinate
2   | Spawn Z coordinate
2   | Spawn Y coordinate (vertical)
1   | Spawn horizontal orientation (yaw)
1   | Spawn vertical orientation (pitch)
1   | Min access permission, internally ignored (do not read if identifier is not 1874)
1   | Min build permission,  internally ignored (do not read if identifier is not 1874)

Blocks

var | raw blocks of the map, 1 byte each (number of blocks is width x height x length)

Note: The block id 163 has a special meaning.
It means that the block is a custom block, and that its actual/real id can be found by looking up the custom blocks sparse array at the given coordinates.

Custom blocks

Custom block ids are represented as a sparse array, consisting of groups of 16x16x16 sections. This is done to minimise memory usage.

1   | 0xBD, means data follows (if not 0xBD, or already end of stream, stop reading)
    for (y = 0; y < ceil(height / 16); y += 1)
         for (z = 0; z < ceil(length / 16); z += 1)
              for (x = 0; x < ceil(width / 16); x += 1)
    {
1   | 1 if this section has data, any other value means it is empty and is skipped
4096| Custom block ids for this section
    }

Metadata

There are a variable number of sections which can be read up to the end of stream.

Each section is identified by a unique byte.

Physics data

This section contains persistent data for physics (e.g. time until revert, drop chance, etc), that allows for physics to be properly resumed when a level is loaded again.

1   | 0xFC, means the section is a physics data section
4   | number of entries
var | Each entry is two four-byte integers. (first is position index, second is raw data)

position index may be unpacked as follows:

x = (index % width);
y = (index / width) / length;
z = (index / width) % length;

raw data for an entry is laid out according to this structure