section_data_table.md

Section Data Table

The section data table is a sequence of zero or more section data entries back to back in memory.

See metadata's section index table for how to know where each section is.

Section Data Entry

A section data entry includes the data contained within a specified volume.

Each volume must fit within a single sub-chunk where a sub-chunk is a 16x16x16 region of blocks with the first alligned with 0,0,0. This means that a section can be at most 16x16x16 blocks however it can be smaller by modifying the minimum coordinates and/or the section shape.

There can be multiple sections per sub-chunk.

Each section data entry is a gzip'd binary TAG_Compound with the following structure:

TAG_Compound({
    "entities": TAG_List([
        TAG_Compound({
            "namespace": TAG_String(),
            "base_name": TAG_String(),
            "x": TAG_Double(),
            "y": TAG_Double(),
            "z": TAG_Double(),
            "nbt": TAG_Compound()
        })
        ...
    ]),
    "block_entities": TAG_List([
        TAG_Compound({
            "namespace": TAG_String(),
            "base_name": TAG_String(),
            "x": TAG_Int(),
            "y": TAG_Int(),
            "z": TAG_Int(),
            "nbt": TAG_Compound()
        })
        ...
    ]),
    "blocks_array_type": TAG_Byte(),
    "blocks": <See below>
})

Blocks

In order to reduce size of the construction format, the blocks array can be stored as any of the NBT Array types. The value of the blocks_array_type describes which of the tag types is used.

There is also a special case where blocks and block_entities do not exist. This is useful for storing sections that contain entities but are not populated with block data.

blocks_array_type value	blocks tag type
-1	blocks and block_entities keys do not exist
7	TAG_Byte_Array
11	TAG_Int_Array
12	TAG_Long_Array

Blocks Array

The block array for each chunk is a flattened array of size specified in the metadata section index table with each element being an index into the block palette.

Entities and BlockEntities

Entities and BlockEntities are contained in a TAG_List with each element being a TAG_Compound in the format as shown above. They are converted into the format for the version specified in the metadata before they are serialised.