MREA (Metroid Prime 2)

See MREA (File Format) for the other revisions of this format.

The MREA format defines areas (rooms) in Metroid Prime 2. It serves the same purpose as the MREA files from Prime 1, but in Echoes it was updated with new features, including some new data sections and the ability to compress most of the data in the file.

To do: Rest of the article needs to be written. There's a lot known about this format that should be documented.

Format

Like CMDL, MREA files are split up into a number of 32-byte aligned sections. Every section both starts and ends on a 32-byte boundary. These are used to separate different parts of the file; different types of sections typically indicate different sets of data. The header declares the section count and the size of each one; using these is the only way to navigate the file.

Header

Offset	Size	Description
0x0	4	Magic; always 0xDEADBEEF
0x4	4	Version; see hub article
0x8	4 × 12	Transform matrix
0x38	4	Mesh count
0x3C	4	SCLY layer count
0x40	4	Section count (SC)
0x44	4	Geometry section number (starts on materials)
0x48	4	SCLY section number
0x4C	4	SCGN section number
0x50	4	Collision section number
0x54	4	Unknown section number
0x58	4	Lights section number
0x5C	4	VISI section number
0x60	4	PATH section number
0x64	4	FFFFFFFF section number
0x68	4	PTLA section number
0x6C	4	EGMC section number
0x70	4	Compressed block count
0x74	0xC	Padding
0x80	4 × SC	Section sizes
Pad to 32 bytes before compressed cluster definitions begins

Compressed Blocks

The MREA format contains compressed blocks that can each contain a number of regular file sections within them. The data defining these blocks is at the end of the MREA header; the beginning and end of the compressed block list is padded to 32 bytes. The decompressed size of a block is capped at 0x20000 bytes; each section contains as many MREA sections as it can fit under that size limit. There are two exceptions:

• If a single section's uncompressed size is larger than 0x20000, then its corresponding compressed block can exceed the size limit.
• Each SCLY and SCGN layer is always in its own block, regardless of how close to the limit it is.

This is the structure of each block definition:

Offset	Size	Description	Notes
0x0	4	Buffer size	This is always 0x120 bytes larger than the uncompressed size on compressed bytes, and the same value as the uncompressed size on uncompressed blocks
0x4	4	Uncompressed size
0x8	4	Compressed size	This is 0 on uncompressed blocks.
0xC	4	Section count	The number of regular sections contained in this block.
0x10	Block definition end

The actual data contained in these blocks is padded to 32 bytes, but their padding is located at the beginning of the block rather than the end, so it's required to account for the padding before you start decompressing. Thee data is compressed using segmented LZO1X-999; the "segmented" part means there's multiple segments of data that are compressed/decompressed separately. Each segment starts with a 16-bit size value. The size value is signed; a negative value indicates the segment is not compressed (this is done when compressing a segment doesn't reduce its size). Each segment is 0x4000 bytes large when decompressed (except the last one).