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	Type	Count	Name	Description
0x0	u32	1	Magic	Always `0xDEADBEEF`.
0x4	u32	1	Version	See hub article for a list of possible version numbers.
0x8	float	12	Area Transform	Matrix that represents the area's transform from the origin. Most area data is pre-transformed, so this matrix is only used occasionally.
0x38	u32	1	World Model Count	Number of world models in this area.
0x3C	u32	1	Script Layer Count	Number of script layers in this area.
0x40	u32	1	Data Section Count	Number of data sections in the file.
0x44	u32	1	Geometry Section	Section index for world geometry data. Always 0; starts on materials.
0x48	u32	1	Script Layers Section	Section index for script layer data.
0x4C	u32	1	Generated Script Objects Section	Section index for generated script object data.
0x50	u32	1	Collision Section	Section index for collision data.
0x54	u32	1	Unknown Section 1	Section index for first unknown section.
0x58	u32	1	Lights Section	Section index for light data.
0x5C	u32	1	Visibility Tree Section	Section index for visibility tree data.
0x60	u32	1	Path Section	Section index for path data.
0x64	u32	1	Unknown Section 2	Section index for second unknown section.
0x68	u32	1	Portal Area Section	Section index for portal area data.
0x6C	u32	1	Object-To-Static-Geometry Mapping Section	Section index for object-to-static-geometry mapping data.
0x70	u32	1	Compressed Block Count	Number of compressed data blocks in the file.
0x74	u32	3	Padding	Padding bytes that align the file with the next multiple-of-32 offset.
0x80	u32	Data Section Count	Data Section Sizes	Array containing the size of each data section in the file. Every size is always a multiple of 32.
Pad to 32 bytes before compressed block 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	Type	Count	Name	Notes
0x0	u32	1	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	u32	1	Uncompressed Size
0x8	u32	1	Compressed Size	This is 0 on uncompressed blocks.
0xC	u32	1	Data Section Count	The number of regular data 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).

Data Sections

Identifier	Name
	World Geometry
	Unknown Section 1
`SCLY`	Script Layers
`SCGN`	Generated Script Objects
`0xDEAFBABE`	Collision
	Unknown Section 2
`0xBABEDEAD`	Lights
`VISI`	Visibility Tree
	Path
	Portal Area
	Static Geometry Map

World Geometry

See MREA (Metroid Prime)#World Geometry, Materials (Metroid Prime) and Geometry (Metroid Prime)

Largely the same as Prime 1. There are two new sections to watch out for on each world model (described on the Geometry (Metroid Prime) page). There's two sections that are now grouped under the same section number as world geometry.

The first is the area octree section, which is back from Prime 1 but no longer has its own section number.

The second section is an array of a structure that provides the bounding box for every surface group. The first entry in the array has the combined bounding box for all of the world geometry in the entire area, then each surface group is listed in order.

Type	Count	Name	Notes
u32	1	Group Bounds Entry Count	Count of elements in the following array.
Group Bounds Entry	Group Bounds Entry Count	Group Bounds Entry Array	Array of a struct that provides the bounding box for each surface group in the area.

Group Bounds Entry

Offset	Type	Count	Name	Notes
0x0	float	6	Group Bounding Box	Axis-aligned bounding box of all surfaces contained in the group.
0x18	u16	1	World Model Index	Index of the world model that contains this group.
0x1A	u16	1	Surface Group Index	Model-relative index of the surface group.
0x1C	u16	1	Unknown	On the first entry, always 1. On other entries, always -1.
0x1E	u16	1	Unknown	On the first entry, always -1. On other entries, always the entry's index position + 1.
0x20	End of bounds entry

Unknown Section 1

This section appears to be related to world geometry.

Type	Count	Name	Notes
u32	1	Unknown	Always 0?
u32	1	Element Count	Count of elements in the next array. Matches the area's surface group count.
u8	Element Count	Unknown	Every entry is always 0xFF?
End of section

Path

This section only contains a single PATH asset ID.

Type	Count	Name
Asset ID	1	Area PATH Resource
End of section

Portal Area