Chunk Format
This article describes the Chunk Section format used in the Chunk Data packet (Play, 0x20, clientbound).
Concepts
- Chunk Section: a 16×16×16 area, sometimes also called chunk.
- Chunk Column: 16 chunks aligned vertically (totalling 16×256×16).
Format
A Chunk Section is defined in terms of other data types. A Chunk Section consists of the following fields:
| Field Name | Field Type | Notes |
|---|---|---|
| Bits Per Block | Unsigned Byte | How many bits per block in Data Array. If 0, the Palette Length and Palette fields are omitted and the global palette (with 13 bits per block) is used. |
| Palette Length | Optional VarInt | Length of the following array |
| Palette | Optional Array of VarInt | Mapping of block state IDs in the global palette to indices of this array |
| Data Array Length | VarInt | Number of bytes in the following array, divided by 8 (given as such because Notchian implements Data Array as an Array of Long) |
| Data Array | Byte Array | List of 4096 indices pointing to state IDs in the Palette, followed by padding to round the length up to the next multiple of 8 bytes |
| Block Light | Byte Array | Half byte per block |
| Sky Light | Optional Byte Array | Only if in the Overworld; half byte per block |
Data Array, Block Light, and Sky Light are given for each block with increasing x coordinates, within rows of increasing z coordinates, within layers of increasing y coordinates.
The global palette encodes a block as 13 bits. It uses the block ID for the first 9 bits, and the block damage value for the last 4 bits. For example, diorite (block ID 1 for minecraft:stone with damage 3) would be encoded as 000000001 0011.
In half-byte arrays, two values are packed into each byte. Even-indexed items are packed into the high bits, odd-indexed into the low bits.
