MREA (Metroid Prime 3)

The .MREA file format is used to define areas in Metroid Prime 3 and Donkey Kong Country Returns. MREA files are broken up into many sections, and each section serves a specific purpose.

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

Universal Header

This header is shared between Metroid Prime and Donkey Kong Country, and is fairly straight forward.

Offset	Size	Description
0x0	4	Magic Number 0xDEADBEEF
0x4	4	Version; see hub article
0x8	48	Transformation Matrix The position of the area in world-space
0x38	4	Mesh Count
0x3C	4	Layer Count
0x40	4	Section Count
0x0	4	Compressed Block Count
0x4	4	Section Number Count

Compressed Blocks

Compressed blocks are handled in the exact same manner as Metroid Prime 2, however with DKCR simply replace LZO with zlib.

Section Numbers

Section Numbers are preceded by the compressed blocks, each section is designated in the following:

let N=Section Number Count

Type	Description
FourCC	Section type
Long	Section Number

Repeat N times, one for each section, and the sections sections are associated with the following FourCC values:

FourCC	Description
AABB	Axis Aligned Bounding Boxes
APTL	PTLA file
COLI	Collision
DEPS	Dependencies
EGMC	EGMC file
GPUD	Submesh data, e.g, vertices, normals, etc.
LITE	Lights
LLTE	Unknown
PFL2	PATH file
PVS!	Probable Visibility Set
ROCT	Unknown
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

Sections

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.