MREA (Metroid Prime 3)

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

The MREA format, which defines areas/levels, received another large layout overhaul in Metroid Prime 3. The level geometry data received the biggest update, with a new material format, lot of things being moved around, and a few entirely new sections being introduced. This article covers Metroid Prime 3, the MP3 E3 prototype, and Donkey Kong Country Returns.

This file format needs more research There are a few sections we know nothing about.

Format

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

The header is identical between MP3 and DKCR.

Offset	Type	Size	Description
0x0	u32	4	Magic Number; always 0xDEADBEEF
0x4	u32	4	Version; see hub article
0x8	float[12]	48	Transform matrix (transform of the area in world space)
0x38	u32	4	Mesh count
0x3C	u32	4	Layer count
0x40	u32	4	Section count (SC)
0x44	u32	4	Compressed block count
0x48	u32	4	Section number count
0x4C	u32[5]	0x14	Padding
0x60	u32[SC]	-	Section numbers
End of main header data; pad to 32 bytes before compressed section definitions

Compressed Blocks

Compressed blocks are defined in the same manner as Metroid Prime 2. 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 in Metroid Prime 3, and segmented zlib in Donkey Kong Country Returns. 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 section numbers portion of the header starts.

Offset	Type	Size	Description
0x0	u32	4	Buffer size (0x120 bytes larger than uncompressed size - same as uncompressed size for uncompressed blocks)
0x4	u32	4	Uncompressed size
0x8	u32	4	Compressed size (if 0, that indicates an uncompressed block)
0xC	u32	4	Section count (the number of regular sections contained in this block)
0x10	Block definition end

Section Numbers

The section numbers portion of the header indicates the index of each major data chunk. Some of these chunks contain multiple sections; in that case the number will point to the first section of the chunk. Each number is a short 8-byte struct:

Offset	Type	Size	Description
0x0	char[4]	4	Section type
0x4	u32	4	Section number

Here are all the possible section numbers and what they are:

FourCC	Description
AABB	Axis Aligned Bounding Boxes
APTL	PTLA file
COLI	Collision
DEPS	Dependencies
EGMC	EGMC file
GPUD	GPU Data (level geometry)
LITE	Lights
LLTE	Unknown
PFL2	PATH file
PVS!	Probable Visibility Set
ROCT	Area Octree (AROT)
RSOS	RSO file list (Revolution Shared Object)
SOBJ	Script Object layers (SCLY)
SGEN	Script Generator layer (SCGN)
WOBJ	World Object; always 0, points to the materials section

Materials

Materials are identical to those found in CMDL files.

Mesh Headers

The WOBJ sections are unique: they don't have a valid section number, and are always set to 0, however they are always in the sections immediately following the Materials, simply iterate through the mesh count and read the following structs:

Main Header

Type	Description	Notes
long	Unknown	Most likely visor flags in MP3, unknown use and DKCR
CTransform4f	Transformation Matrix	Meshes location in world space
CAABox	Bounding Box	Likely used for Depth sorting as in previous games.

Submesh Offsets

Type	Description	Notes
long (SC)	Submesh count
long	Submesh Offsets[SC]	Relative to the start first submesh, (i.e, the first offset points the the end of the first submesh)

Following the submesh data are two unknown sections, they both seem to be arrays of flags or indices but nothing is known about them.

AROT

Following the WOBJ sections is usually AROT. AROT is a BSP Tree that appears to be used for shot-collision and possibly depth sorting, nothing is known about how to handle this section.

AABB

The AABB section is exactly what it sounds like, it's an array of Axis-Aligned Bounding Boxes, assembling a BVH tree. AABB starts with the number of bounding boxes with each one consisting of the following struct:

Type	Description	Notes
CAABox	Axis Aligned Bounding Box	Used to assist depth sorting, and/or collision
long	Unknown	The first entry in the table always covers the entire, with this value always being -1
short	Self Index	1 indexed position of this particular AABB entry, but ONLY if the previous value is -1.
short	Self Index	1 indexed position of this particular AABB entry, but ONLY if the previous value is -1.

GPU Description Section (GPUD)

The GPUD section is a bit confusing at first glance, however it's really no different from the previous MREA version in terms of ordering. There is also one GPUD per WOBJ section

The section order is as follows:

Vertices

The vertices are always 32bit floats, even in DKCR

Normals

The normals are always 32bit floats.

Colors

Usually 0 filled and completely unused, it's stored in MREA simply for completeness.

Float Texcoords

Metroid Prime 3 uses these exclusively, even for lightmaps, which simplifies UV handling quite a bit.

Short Texcoords

This is only used in DKCR and can be used for anything, not just for lightmaps

Submeshes

The submesh format is exactly the same as the Geometry formats found in Metroid Prime 3 and DKCR.