MREA (Metroid Prime)

The MREA format defines areas (rooms) in Metroid Prime. It's a massive format that contains tons of different data, including terrain geometry, collision, objects, lights, and more.

To do: There's a LOT of sections that are mostly known, but need some documentation written up. SCLY and collision need separate articles (although the unique parts of the collision format, like the octree, could maybe be documented here). The rest should probably stay on this page.

This file format needs more research The AROT section is largely unknown, there's a lot of unknowns in the lights section, and we don't know what the unknown/empty sections are for. That's not even touching on how much is unknown in SCLY.

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 below
0x8	4 × 12	Transform matrix
0x38	4	Mesh count
0x3C	4	Section count (SC)
0x40	4	Geometry section number (starts on materials)
0x44	4	SCLY section number
0x48	4	Collision section number
0x4C	4	Unknown section number
0x50	4	Lights section number
0x54	4	Empty section number
0x58	4	PATH section number
0x5C	4	AROT section number
0x60	4 × SC	Section sizes
End of header; pad to 32 bytes before first section begins

Geometry

See Geometry (Metroid Prime)

MREA files have one material section, followed by a number of meshes, each of which has its own set of geometry sections. Each mesh starts with an extra header section which is formatted like this:

Offset	Size	Description
0x0	4	Unknown (flags?)
0x4	4 × 12	Transform matrix
0x34	4 × 6	Axis-aligned bounding box
0x4C	End of mesh header section

There's couple small differences you'll usually see on MREA meshes compared to CMDL ones:

• Vertices are always normals, so vertex format 0 is never used.
• Most MREA meshes use lightmaps, so normally the first UV coordinate on each texture will read from the short UV array. This isn't always the case, though; you need to make sure you check the material so you know where to read from.
• Submeshes will usually have a bounding box in the extra data in the submesh header. This bounding box is used for depth sorting.

AROT

The AROT section operates on terrain geometry; it's used to implement things like projectile collision with terrain. It's mostly unknown.

SCLY

To do: SCLY is definitely complicated enough to need its own article.

The SCLY section contains data for objects.

Collision

To do: Collision needs a separate article because it shares so many similarities with DCLN. How should we document the parts where the format diverges, though?

You have three guesses what the collision section is for, and the first two don't count.

Unknown Section

This one is sandwiched between collision and lights, and usually just contains a single 32-bit "1". Purpose is unknown.

Lights

To do: Antidote, would you mind writing the structure of this section?

This section is for dynamic lights.

Empty Section

This is usually listed with a size of 0. Currently unknown what this actually is.

Path

This is the final section in the file; it's always 0x20 bytes, and its only value is a single PATH file ID.