MREA (Metroid Prime 2): Difference between revisions

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''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.
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.


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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.
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.
These are the sections in each MREA file, in the order they appear in the file:
{| class="wikitable"
! Identifier
! Name
|-
| {{none}}
| [[#World Geometry|World Geometry]]
|-
| {{none}}
| [[#Unknown Section 1|Unknown Section 1]]
|-
| <code>SCLY</code>
| [[Scriptable_Layers_(Metroid_Prime_2)|Script Layers]]
|-
| <code>SCGN</code>
| Generated Script Objects
|-
| <code>0xDEAFBABE</code>
| [[#Collision|Collision]]
|-
| {{none}}
| [[#MREA (Metroid Prime)#Unknown Section|Unknown Section 2]]
|-
| <code>0xBABEDEAD</code>
| Lights
|-
| <code>VISI</code>
| Visibility Tree
|-
| {{none}}
| [[#Path|Path]]
|-
| {{none}}
| [[#Portal Area|Portal Area]]
|-
| {{none}}
| [[#Static Geometry Map|Static Geometry Map]]
|}


=== Header ===
=== Header ===
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{| class="wikitable"
{| class="wikitable"
! Offset
! Offset
! Size
! Type
! Count
! Name
! Description
! Description
|-
|-
| 0x0
| 0x0
| 4
| u32
| '''Magic'''; always 0xDEADBEEF
| 1
| '''Magic'''
| Always <code>0xDEADBEEF</code>.
|-
|-
| 0x4
| 0x4
| 4
| u32
| '''Version'''; see [[MREA (File Format)|hub article]]
| 1
| '''Version'''
| See [[MREA (File Format)|hub article]] for a list of possible version numbers.
|-
|-
| 0x8
| 0x8
| 4 &times; 12
| float
| '''Transform matrix'''
| 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
| 0x38
| 4
| u32
| '''Mesh count'''
| 1
| '''World Model Count'''
| Number of world models in this area.
|-
|-
| 0x3C
| 0x3C
| 4
| u32
| '''SCLY layer count'''
| 1
| '''Script Layer Count'''
| Number of script layers in this area.
|-
|-
| 0x40
| 0x40
| 4
| u32
| '''Section count''' (SC)
| 1
| '''Data Section Count'''
| Number of data sections in the file.
|-
|-
| 0x44
| 0x44
| 4
| u32
| '''Geometry section number''' (starts on materials)
| 1
| '''Geometry Section'''
| Section index for world geometry data. Always 0; starts on materials.
|-
|-
| 0x48
| 0x48
| 4
| u32
| '''SCLY section number'''
| 1
| '''Script Layers Section'''
| Section index for script layer data.
|-
|-
| 0x4C
| 0x4C
| 4
| u32
| '''SCGN section number'''
| 1
| '''Generated Script Objects Section'''
| Section index for generated script object data.
|-
|-
| 0x50
| 0x50
| 4
| u32
| '''Collision section number'''
| 1
| '''Collision Section'''
| Section index for collision data.
|-
|-
| 0x54
| 0x54
| 4
| u32
| '''Unknown section number'''
| 1
| '''Unknown Section 1'''
| Section index for first unknown section.
|-
|-
| 0x58
| 0x58
| 4
| u32
| '''Lights section number'''
| 1
| '''Lights Section'''
| Section index for light data.
|-
|-
| 0x5C
| 0x5C
| 4
| u32
| '''Empty section number'''
| 1
| '''Visibility Tree Section'''
| Section index for visibility tree data.
|-
|-
| 0x60
| 0x60
| 4
| u32
| '''PATH section number'''
| 1
| '''Path Section'''
| Section index for path data.
|-
|-
| 0x64
| 0x64
| 4
| u32
| '''FFFFFFFF section number'''
| 1
| '''Unknown Section 2'''
| Section index for second unknown section.
|-
|-
| 0x68
| 0x68
| 4
| u32
| '''Unknown section 2 number'''
| 1
| '''Portal Area Section'''
| Section index for portal area data.
|-
|-
| 0x6C
| 0x6C
| 4
| u32
| '''EGMC section number'''
| 1
| '''Static Geometry Map Section'''
| Section index for static geometry map data.
|-
|-
| 0x70
| 0x70
| 4
| u32
| '''Compressed cluster count'''
| 1
| '''Compressed Block Count'''
| Number of compressed data blocks in the file.
|-
|-
| 0x74
| 0x74
| 0xC
| u32
| 3
| '''Padding'''
| '''Padding'''
| Padding bytes that align the file with the next multiple-of-32 offset.
|-
|-
| 0x80
| 0x80
| 4 &times; SC
| u32
| '''Section sizes'''
| ''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.
|-
|-
| colspan=3 {{unknown|Pad to 32 bytes before compressed cluster definitions begins}}
| colspan=5 {{unknown|Pad to 32 bytes before compressed block definitions begins}}
|}
|}


Following the section sizes comes an array defining the file's compressed cluster. Each definition is 0x10 bytes and is formatted like this:
==== 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:


{| class="wikitable"
{| class="wikitable"
! Offset
! Offset
! Size
! Type
! Description
! Count
! Name
! Notes
|-
|-
| 0x0
| 0x0
| 4
| u32
| '''Buffer size''' (usually 0x120 bytes bigger than uncompressed size)
| 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
| 0x4
| 4
| u32
| '''Uncompressed size'''
| 1
| '''Uncompressed Size'''
|
|-
|-
| 0x8
| 0x8
| 4
| u32
| '''Compressed size''' (if 0, that indicates an uncompressed cluster)
| 1
| '''Compressed Size'''
| This is 0 on uncompressed blocks.
|-
|-
| 0xC
| 0xC
| 4
| u32
| '''Section count''' (the number of regular sections contained in this cluster)
| 1
| '''Data Section Count'''
| The number of regular data sections contained in this block.
|-
|-
| 0x10
| 0x10
| colspan=2 | Cluster definition end
| colspan=5 {{unknown|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).
 
=== World Geometry ===
''See [[MREA (Metroid Prime)#World Geometry]], [[Materials (Metroid Prime)]] and [[Geometry (Metroid Prime)]]''
 
Largely [[MREA (Metroid Prime)#World Geometry|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.
 
==== Area Octree ====
 
The [[MREA (Metroid Prime)#Area Octree|area octree]] section is back from Prime 1, but no longer has its own section number - it's now grouped under the same section number as world geometry.
 
==== Surface Group Bounding Boxes ====
 
This is a new section introduced in Metroid Prime 2, which is grouped under the world geometry section number and appears after the area octree. It contains 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.
 
{| class="wikitable"
! Type
! Count
! Name
! Notes
|-
| u32
| 1
| '''Group Bounds Entry Count'''
| Count of elements in the following array.
|-
| [[#Group Bounds|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 =====
 
{| class="wikitable"
! 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|Unknown}}
| On the first entry, always 1. On other entries, always -1.
|-
| 0x1E
| u16
| 1
| {{unknown|Unknown}}
| On the first entry, always -1. On other entries, always the entry's index position + 1.
|-
| 0x20
| colspan=4 {{unknown|End of bounds entry}}
|}
 
=== Unknown Section 1 ===
 
This section appears to be related to world geometry.
 
{| class="wikitable"
! Type
! Count
! Name
! Notes
|-
| u32
| 1
| {{unknown|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|Unknown}}
| Every entry is always 0xFF?
|-
| colspan=4 {{unknown|End of section}}
|}
|}
=== Collision ===
''Main article: [[Area Collision (File Format)]]''
=== Path ===
This section only contains a single [[PATH (File Format)|PATH]] asset ID.
{| class="wikitable"
! Type
! Count
! Name
|-
| Asset ID
| 1
| '''Area PATH Resource'''
|-
| colspan=3 {{unknown|End of section}}
|}
=== Portal Area ===
This section only contains a single [[PTLA (File Format)|PTLA]] asset ID.
{| class="wikitable"
! Type
! Count
! Name
|-
| Asset ID
| 1
| '''Area PTLA Resource'''
|-
| colspan=3 {{unknown|End of section}}
|}
=== Static Geometry Map ===
This section only contains a single [[EGMC (File Format)|EGMC]] asset ID.
{| class="wikitable"
! Type
! Count
! Name
|-
| Asset ID
| 1
| '''Area EGMC Resource'''
|-
| colspan=3 {{unknown|End of section}}
|}
[[Category:File Formats]]
[[Category:Metroid Prime 2: Echoes]]
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