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.

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.

Compressed Blocks
The MREA format contains compressed blocks that can each contain a number of regular file sections within them. These blocks are compressed using segmented LZO1X-999. Compressed blocks are 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. The compressed data is segmented, which 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).

Compressed blocks are defined after the main header. After reading them, pad to 32 bytes before the main file data starts.